LITHUANIAN UNIVERSITY OF HEALTH SCIENCES
FACULTY OF MEDICINE
Comparison of the results between binocular lateral rectus muscle
recession (BLR) and unilateral lateral rectus recession–medial
rectus resection(RR) for the exotropia surgical treatment.
MASTER'S THESIS OF INTEGRATED MEDICAL STUDIES
AUTHOR: Syed Amaan Tariq
SUPERVISOR: Arvydas Gelžinis
Kaunas 2021
Table of contents
SUMMARY
4
ACKNOWLEDGEMENT
5
CONFLICT OF INTEREST:
5
ABBREVIATION’S LIST:
6
KEY TERMS:
7
1.INTRODUCTION
8
1.1 Eye structure 81.2 The external structure of an eye: 8
1.3 The internal structure of an eye: 8
1.4 Eye muscles 9
2.AIMS AND OBJECTIVES: 10
3.LITERATURE REVIEW
11
3.1 Eye disorders 11
3.1.1 Age-related macular degeneration 11
3.1.2 Cataracts 11 3.1.3 Diabetic retinopathy 11 3.1.4 Glaucoma 12 3.1.5 Amblyopia 12 3.2 Strabismus 12
3.2.1 Introduction to strabismus
12
3.2.2 Etiology 133.2.3 Eye deviation causes 14
3.2.4 Exotropia or divergent eyes (Exotropia) 14
3.2.5 Tests and diagnosis 15
3.2.6 Risk factors 15
3.2.7 Epidemiology 15
3.2.8 Strabismus in children 15
3.2.9 Treatment and Management 16
3.2.10 Complications of strabismus 18
3.3 Eye deviation and diplopia in adults and children 19
3.3.1 Diplopia in children 19
3.3.2 Treatment of diplopia in children 19
3.4 Surgical treatment (60) 20
3.4.3 Lateral rectus recession 23 3.4.4 Surgical Outcome 23
4.METHODOLOGY
25
5.Results
26
6. Discussion
29
7. Conclusion
33
8.References
34
SUMMARY
Exotropia, also known as divergent strabismus, is a type of eye misalignment in which one or alternately both eyes turn outward. Exotropia may be constant or it may occur from time to
time(intermittent exotropia), and is found in every age group. Exotropia usually is treated surgically. Two most common surgical methods used are binocular lateral rectus muscle recession (BLR) and monolateral lateral rectus muscle recession - medial rectus muscle resection (RR).
Recommendations which type of surgery to use treating distinct types of exotropia remains controversial.
Aim: To Analyse and compare the results between binocular lateral rectus muscle recession (BLR) and lateral rectus muscle recession-medial rectus muscle resection (RR) for the exotropia surgical treatment in selected scientific literature in period between 2015 – 2020.
Objectives:
1. To estimate preoperative factors associated with the choice of the type of surgery.
2. To evaluate and compare the risks of both types of surgeries for the consecutive exotropia. 3. To compare the residual or recurrent strabismus considering each type of surgery.
Method:
Literature search and review was performed using Medline database for publications between 2012-2021 using MESH terms “exotropia”, “strabismus”, “surgical treatment”, “binocular lateral rectus muscle recession” and “unilateral lateral rectus recession–medial rectus resection”. English language papers describing either surgery method for exotropia and its outcomes were included and analyzed. Results: A total of 24 studies on this topic were reviewed and 14 were selected for this literature review
Conclusion: The result of this literature review showed that there are varying opinions and results on comparison of the two surgical methods so one can not conclusively give superiority of one method over the other
Based on the above mentioned aims and objectives we may conclude that strabismus surgeries should only be considered after the conservative treatments have failed
1-Preoperative factor in choosing the the type of surgery should be distance/near differences and PD angle deviations.
Patients whose distance deviation equals to the near deviation are basic type of exotropia and those who have a large angle high PD should be recommended for unilateral rectus recess/resect surgery (RR).
Patients in whom distance deviation exceeded the near deviation are divergence excess exotropia , for such patients BLR should be considered along patients with small angle PD.
2-More patients from the RR group showed likelihood of esodeviation than the BLR group, so the BLR group should be the choice to avoid consecutive esotropia.
3- Literature review showed that exodrift and undercorrection was more common in BLR, RR is better , as exotropic recurrence was more in BLR.
ACKNOWLEDGEMENT
I would like to thank the Almighty God , my dear parents especially my mother Dr.Arshi Aziz who inspired me for this study and lastly my friends who supported me and helped me finalize the project.
I especially appreciate my dear professor and supervisor Dr. Arvydas Gelžinis
His help and guidance lead me to most efficient data, deeply understand the topic and study about it.
CONFLICT OF INTEREST:
ABBREVIATION’S LIST:
RR- lateral rectus muscle recession-medial rectus muscle resection BLR - binocular lateral rectus muscle recession
AMD- Age Related Macular Degeneration DR – Diabetic Retinopathy
IPD- interpupillary distance
Δ ,PD- Prism Diopter
IXT – Intermittent Exotropia CI- Convergence insufficiency
ADHD - Attention-deficit/hyperactivity disorder FDT- Forced duction test
MR- Medial rectus LR- Lateral rectus XT- Exotropia
KEY TERMS:
Exotropia; Exotropia treatment; Exotropia treatment options; Surgical treatment of exotropia;BLR surgery, Strabismus;BLR patient group;diplopia;RR exotropia surgery, RR patient group; divergent eyes; eye disease; esotropia
1.INTRODUCTION
Exotropia, it is known as divergent strabismus and is misalignment of the eye when one or two eyes are turn outward. It is may be constant or intermittent when it occurs from time to time. Exotropia may occur at every age. It is usually treated by surgical method. In most cases there are used two surgical methods as binocular lateral rectus muscle recession (BLR) and monolateral lateral rectus muscle recession - medial rectus muscle resection (RR). But the question which operation to use for exotropia surgical treatment it is controversial.
1.1 Eye structure
The eye has the anterior and the posterior segments, it has spherical structure. There are several muscles and there is external and internal structures of the human eye (1).
1.2 The external structure of an eye:
The Sclera is made of connective tissue, it is visible part of the eye, it protects the inner parts of it. Conjunctiva lines the sclera and it is made of classified squamous epithelium. It lubricates the eye by mucus and tears secretion. The Cornea is anterior part of the eye and covers the pupil and iris. The main function of the cornea is refraction of the light to the lens. The Iris is visible from the outside. The main function of it is the control of the pupil diameter according to the light. The Pupil is at the center of the iris and it allows entering the light to focus it to the retina (2, 3).
1.3 The internal structure of an eye:
The Lens is connected to the celestial body by the ligaments. It refracts the light and focuses on the retina. The Retina is most inner layer of the eyeball. It is very sensitive to the light and it acts as camera film. There are nerve cells layers, as ganglion and bipolar cells, and light receptors. The retina converts the image into electrical nerve impulses, they are taken to the brain for perception. The Optic nerve is at the back of the eye and it carries nerve impulses from the retina to the human brain in order to perceive vision. The Aqueous humor is watery liquid supplies the eye with fluid and nourishes it. The main function of the vitreous humor it is to protect the eye ball and to maintain the spherical shape of it (4, 5):
1.4 Eye muscles
There are six muscles, they move and rotate the eyeball in specific direction. The eyes cannot move properly when is disorder of binocular vision, they don’t work together in a balanced way.
The lateral rectus muscle moves eye outward and rotates the eye. The medial rectus muscle that moves the eye inside. The upper rectus muscle moves the eye upward and slightly inward. The lower rectus muscle moves the eye downward and slightly inward. The inferior oblique muscle elevates and laterally moves the eyeball. The superior oblique muscle rotates the eye down and internally and
inferolaterally by abducting the eye.
For both eyes to be able to look at the same object, we need the eye muscles on one side to fully align with the eye muscles on the other side. For example, to look to the left, the lateral rectus muscle in the left eye pulls the left eye out, and the middle rectus muscle in the right eye pulls the right eye toward the nose.
If this does not happen, either because the eye muscles on one side do not receive exactly the same signals from the brain, or because the eye muscles respond unevenly to these signals, then the eyes In one direction they do not completely coincide.
2.AIMS AND OBJECTIVES:
Aim: To analyse and compare the results between binocular lateral rectus muscle recession (BLR) and lateral rectus muscle recession-medial rectus muscle resection (RR) for the exotropia surgical treatment in selected scientific literature in the period between 2012 – 2021.
Objectives:
1. To estimate preoperative factors in exotropia associated with the types of squint surgery. 2. To evaluate and compare the risks of both types of surgeries for the consecutive exotropia. 3. To compare the residual or recurrent strabismus considering each type of surgery
3.LITERATURE REVIEW
3.1 Eye disorders
Refractive Errors
Refractive errors are the most common eye problem in the United States. Refractive errors may be myopia, hyperopia, astigmatism, and presbyopia that occurs between the ages of 40-50 (loss of ability to concentrate closely, inability to read. The National Eye Institute states that corrective failure correction can improve vision among 150 million Americans (6).
3.1.1 Age-related macular degeneration
Age-related macular degeneration (AMD), is an age-related ocular disorder which results in damage of the central vision. This disease affects the central part of the retina - macula, which allows the eyeball to see small objects and details (7,8).
There are 1.8 million Americans 40 and older who are suffered by AMD, and 7.3 million large drones are at the significant risk for the development of AMD. In 2020 year the number of people with AMD is about 2.95 million in USA. The reading and good or near vision may be impaired in age-related
macular degeneration between 65 year and older (9).
3.1.2 Cataracts
Although in cataract the treatment is widely available, but there are some barriers to access good results as lens costs, selection of patients, or awareness of the lack to prevent many people from receiving appropriate operation (10).
About 20.5 million (17.2%) of Americans 40 years and older have cataract, and 6.1 million (5.1%) had cataract operations. In 2020 year the total amount of people with cataracts is increased to 30.1 million (11).
3.1.3 Diabetic retinopathy
Diabetic retinopathy often is the leading cause of blindness in adults. In this disease may be the progressive disorder of the retinal blood vessels, bleeding, vitreous hemorrhages and blur visual
acuity. Diabetic retinopathy often damages both eyes (12). In early detection of DR changes and early treatment the risk of vision loss may be reduced. About 50% of patients taking their eyes are not examined or other patients are diagnosed very late and the treatment is not effective. The by diabetic retinopathy is the most cause of the blindness in the United States in adults between 20 and 74 years. About 12 % people are affected each year by diabetic retinopathy in the United States and the longer patient has diabetes the higher chances of development vision-threatening diabetic retinopathy (13-15).
3.1.4 Glaucoma
Glaucoma can occur in patients with normal eye pressure. When early treatment is started, it can be protected eyes from severe vision loss (16, 17).
3.1.5 Amblyopia
The most common cause of visual impairment in children is Amblyopia. It is also known as "lazy eye". The medical term amblyopia is used when the visual acuity in one eye is low, the eyebal and the brain do not work properly together. The eyeball looks normal itself, but is not normally used because the brain is interested in the other eye. The causes which lead to amblyopia are: strabismus, the imbalance in the position of the two eyes, more myopic, hyperopic, or astigmatic one eye than the another, rarely other cause may be cataract of one eye. Amblyopia is the most common cause of the constant vision disorder in children and young and middle-aged adults (18, 19).Unless successfully treated early in children, juvenile and adult patients.
3.2 Strabismus
3.2.1 Introduction to strabismus
There are six muscles in the eye that control its movements Two of these muscles moves the eye to the right and the other to the left. The other four muscles move the eye up, down, or at a certain angle. To focus on a single image, all six muscles need to work together (20).
To align and focus on a single goal, all the muscles in both eyes must work together and balance. The brain controls these muscles. People with ocular deviations usually have a problem that affects their eye muscles. Some of these problems are as follows (20, 21):
1. Health problems such as diabetes, thyroid disease (Graves' disease), myasthenia gravis, brain tumors or a stroke
2. Accidents or brain injuries
3. Damage to the eye muscles during eye surgery.
Many adults with childhood visual problems develop this disorder. But in some other cases, the disease starts at an older age (22, 23)
In a normal function, the brain's ability to see three-dimensional objects requires proper coordination of the eyes. When two eyes are aligned and looking at the same target. The visual part of the brain combines shapes received from two eyes into an image. When a person has strabismus, different images are sent to the brain because the eyes are looking in opposite directions. Therefore, after combining the images, binoculars are created(7, 51).
3.2.2 Etiology
Strabismus means eyes looking oblique in Greek or also can mean crossed eyes ,In normal eyes, while looking at an object both eyes are focused and fixate equally however in strabismus eyes cannot fixate equal one or both can diverge inward or outward. This can be due to many reasons such as neuromuscular disorder which effects eye muscles and as result eye movements.
General classifications and their causes 1. Pseudo-strabismus:
• Pseudoesotropia can occur from negative angle kappa • Pseudoexotropia occurs due to positive angle kappa
2. Heterotopia(Manifest squint) : Concomitant squint and incomitant squint • Refractive error
• obstruction of pupillary area and optic nerve disease.
• intraocular or extraocular muscle accommodation abnormalities. 3. Heterophoria
• Orbital asymmetry.
• Psychiatric disorders and old age.
3.2.3 Eye deviation causes
The exact cause of eye deviations is still unknown. There are six muscles in the eye that are responsible for controlling and moving the eye. There are four muscles for moving up and down the eye and two muscles for moving left and right. Muscles must work in unison to get a single image of the brain. Some types of strabismus may occur when one or more muscles do not work properly (56).
Eye deviations are more common in children with brain disorders such as cerebral palsy, Down syndrome, hydrocephalus, and brain tumors. Recent studies show that children with exotropia are three times more likely to develop psychiatric disorders.
Exotropia begins in children with poor vision in one eye or genetic disorders that affect eye function.
However, there is no known cause. Ophthalmologists should be consulted immediately when such signs are noticed. (57).
3.2.4 Exotropia or divergent eyes (Exotropia)
It is a type of deviation in which the eyes are deflected outwards. Children who suffer from exotropia ocular deviations will develop diplopia in the future. Cross- sectional exotropia is a relatively common condition. Congenital extrusion occurs in the first years of life and is less common than primary extrusion, which occurs several years after birth (52, 53).
Divergent eye symptoms:
1. Deviation of the eyes outwards. This condition is manifested when the child is tired or when he does not feel well.
2. The image closes one of the eyes.
3. Sensitivity (closing the eyes) to bright light 4. Decreased ability to see in three dimensions
5. Weakness in recognizing the distance of objects from the eye
In children with deviated eyes from the beginning, the brain notices the inconsistency of the eyes in sending the image and sends the best of the two images sent to the output. This condition is called amblyopia, which results in binocular vision and reduced vision in three dimensions. If a person catches eye deviations in adulthood, the images combine to form diplopia, as the brain is trained to receive images from both eyes (6, 54, 55).
3.2.5 Tests and diagnosis
1. Vision test in each eye both separately and both eyes simultaneously (age appropriate)
2. Cycloplegic refraction (a process for determining the refractive error of the eye. To perform this test, it is paralyzed by muscle drops that help the eye focus.)
3. Retinal examination
4. Complete eye exams (suitable for age) (59).
3.2.6 Risk factors
1. Having a positive family history of eye deviations, eye laziness 2. Childhood cataracts or glaucoma (58).
Strabismus may be in syndromes, as Down, Apert-Crouzon syndromes, cerebral palsy, premature infants with small birth weight, in siblings, in neonatal whose parents were affected. These patients must be screened at an early age for early detection of strabismus.
3.2.7 Epidemiology
Overall, 2-3 % of population is affected with strabismus, exotropia is more common than esotropia since it older age range of 55 to 75 years. (25) In a population-based studies among children showed African Americans are more affected than other races. Exotropia was more common than esotropia. (26) Esotropia in children is more common as fully or partially accommodative. (27) 8.1 % of all esotropia is included as infantile esotropia (28) Exotropia is more common is Asian and African also more in female than male (29,32)
1. Congenital or childhood esotropia
This is a type of diplopia that causes the eye to rotate inward and usually occurs in the first six months of a baby's life. There is no known underlying cause for this condition (also called idiopathic condition) .56
2. Adaptive esotropia
This type of esotropia occurs as a result of hyperopia, which causes the eye to rotate inward. This type of diplopia can be corrected or eliminated by wearing glasses.
3. Maladaptive esotropia
This esotropia causes the eye to rotate inward, which usually occurs in children between the ages of 2 and 5, and this type of diplopia does not improve with glasses.
4. Exotropia from alternating distance
This is a type of intermittent strabismus that causes the eye to rotate outward, and is usually more visible when the child is looking at objects at a distance, and is usually noticed by parents when the child is tired, or while Is daydreaming or being in the sun. The child may also close or rub one eye when going out and in the sun.
Amblyopia occurs when the visual pathway does not grow properly in one eye because the eye is unable to send a clear image to the brain, which causes vision to blur in that eye even when the child is wearing glasses. An eye that has amblyopia is called amblyopic or lazy.
A child with diplopia can also develop amblyopia of the eye because vision in this eye is not used by the brain. Other children may be amblyopic, but they may not have complaints of double vision. This may be because one or both eyes may be particularly myopic, farsighted, or have high astigmatism. Amblyopia can permanently reduce how well an eye can see. There are several treatments for an amblyopic eye, the treatment is more effective at the age of seven or eight when visual acuity is still developing. It is very important to treat quickly the causes of amblyopia in order to improve diplopia and amblyopia (111, 112).
3.2.9 Treatment and Management
Method to treat strabismus Observation:
Strabismus which has been caused due to myasthenia gravis, diabetic mononeuropathy, and post-traumatic restrictive strabismus mostly improve with time and with the treatment of the prim-ary cause. (33).
Correction of Refractive Errors:
It must be done full correction of hypermetropia in order to correct all forms of esotropia. Executive bifocals, hyperopic correction should be prescribed in convergence strabismus and hypermetropia (34). In patients with intermittent exotropia, should be prescribed myopic correction which controls divergent deviation (35).
Treat Amblyopia:
In this case visual acuity is affected due to visual pathway abnormality, the most effective treatment can be done by refractive correction (36) In children is recommended to patch the healthy eye to force brain use the weaker eye, 2-6 hours is gold standard. Atropine eye drops can be effective too (37,38). Alone refractive correction is effective in one-third of the patients in order to improve amblyopia (36).
Orthoptics: Commonly prescribed in intermittent exotropia such as pencil push-ups, this helps accommodation strengthening convergences in exotropia.
Prismatic Correction: Performed in case of deviation of less than 20 PD although are Contraindications for prism therapy are amblyopia, anomalous retinal correspondence and suppression (39).
Pharmacological Therapy: To treat accommodative esotropia, patients can use ecothiopate iodide eyedrop once a day, mainly used for children who are too young or intolerant for spectacles. (40) Botulinum type A is used to cause temporarily paralysis of selected muscles to improve strabismus usually is used for patient's postoperative diplopia. (41) .
Extraocular Muscle Surgery: only if conservative treatment is not effective for correction of the deviation strabismus operation should be done. The surgery may be done in patients with more than 15 PD esotropia and more than 20 PD exotropia after refraction correction. In accommodative esotropias as it induces consecutive esotropias the effectiveness of surgical treatment is not sufficient (42, 43). Children strabismus surgery is best performed before the age of two. The residual deviation should be 4 PD or less after surgical treatment in order to achieve binocular vision (44). The reduction
of the overall deviation in 60 percent of patients or a deviation of less than10 PD 6 week post operatively should be sufficient outcome of surgery in patients with horizontal strabismus (45). There are three types of strabismus surgical procedures:
Weakening procedure: this method is used to reduce muscle strength, Faden procedure or disinsertion are types of this method.
• Strengthening procedure: most common methods are double breasting, Teno plication and cinching. • Vector adjustment method: in this method trans positioning is used to change the direction of muscle movements. E.g., Helveston.
3.2.10 Complications of strabismus
● Amblyopia ● Reduced stereopsis ● Asthenopia ● Diplopia ● Nystagmus● Abnormal head and neck posture ● Impaired social and mental growth
● In patients with strabismus after surgical treatment may be: ● Diplopia
● Under/over-correction
● Scars of conjunctiva, granulomas, chronic inflammations ● Corneal Dellen
● Scleral perforation ● Lost muscle ● Endophthalmitis
3.3 Eye deviation and diplopia in adults and children
In natural vision, both eyes are focused on a single point. The brain transforms the images received from our two eyes into a single, three-dimensional image. In this way we can tell how close or distant an object is to us (called depth perception) (46).
When one of the eyes goes out of alignment, two different images are sent to the brain. In a young child, the brain learns to ignore an out-of-regulation eye image. Instead, the brain receives and sees only the image of the healthy eye or the eye that has better vision. As a result, the child loses perception of depth.
Adults who develop strabismus after childhood develop double vision or diplopia. This is because the brain learns to receive images from both eyes in previous periods. Their brains are unable to remove the image created by the distorted eye (46, 47)
Strabismus in children lead to diplopia (108,110)
3.3.1
Diplopia in children
1- Mono Ocular Diplopia – This occurs when transmission of light to retina is distorted and two images may form, one being of normal quality (e.g. brightness, contrast, clarity); the rest are of inferior quality
● Problems of corneal shape, such as keratoconus ● Uncorrected refractive error, usually astigmatism
● Other causes include corneal scarring and dislocated lens. Complaints also may represent malingering.
● Cataract (129)
2- Bino-Ocular diplopia – This is mostly caused due to misalignment of eyes as in the case of strabismus, they’re two images of equal quality that are formed.
Etiology:
● Cranial nerve (3rd, 4th, or 6th) palsy
● Orbital infiltration (e.g, thyroid infiltrative ophthalmopathy, orbital pseudotumor) ● Myasthenia Gravis (129)
Therapeutic goals for ocular diplopia in childhood are to make sure that vision develops naturally in both eyes (for example, to prevent amblyopia) and to help both eyes work together so that vision Binoculars and 3D also grow as much as possible. For this treatment to be successful, it is necessary to perform the treatment before the end of the development of the visual pathway, ie before the age of 7-8 years. Most ocular diplopia treatments are ongoing, usually involving regular visits and examinations to the hospital's eye clinic for several years. How often the child needs an eye clinic examination depends on factors such as their age, type of diplopia and how they work. How a child develops diplopia depends on what type of diplopia they have. Often more than one treatment or combination of treatments may be needed to achieve the best outcome for a child (113, 114).
Some children may need surgery on their eye muscles to correct their binoculars. This is usually needed if the binoculars are too large and cannot be corrected with glasses. In a small number of children who develop ocular diplopia from a very young age, surgery may be suggested to adjust the eyes so that the eyes work together in pairs to create a three-dimensional vision.
This is usually planned when the child is about one year old. In older children, surgery may be used to straighten the eyes. Surgery cannot raise the level of vision in a lazy eye, so it may be necessary to wear glasses or glue to cover the eye after surgery. Surgery usually weakens or strengthens the eye muscles, so that the eyes are better aligned.
In general, the risk of ocular diplopia after surgical treatment is very low and no more than one surgery is needed. This does not mean that something went wrong, but repeated operation should be needed to get good results. Binocular strabismus surgery in patients with strabismus usually is performed under general anesthesia, which means that the child is anesthetized and does not feel any pain. This type of surgery is usually done during the day, so children do not have to be admitted at hospitals at night (115).
3.4 Surgical treatment (60)
IXT (Intermittent exotropia) is effectively treated with method of Surgery(61). Stereoacuity loss(at near or distance) is considered a popular criteria for intervention along with deteriorating fusional control, large angle of deviation, or a combination; but potential thresholds are still not defined properly (62). Restoration of the eye alignment and preservation of the binocular function are the goals of the surgery for intermittent exotropia but the time when operation must be performed remains unclear. The most important point is the stereo visual acuity establishment postoperatively. In order to measure the clinical severity of exotropia, the Newcastle Control Score is a useful to follow the
The single lateral rectus recession for small angle exotropia is used, but when and how it has to be done remains unclear (62). There are data in medical literature, that the presence of the mono fixation syndrome after surgical treatment in presumed intermittent exotropia most likely that it was present before the operation, and the term mono fixational exotropia is more often in these cases (64).
3.4.1 Time of Intervention and Goals of Surgery
Most surgeons are of the opinion that early surgical intervention for children is indicated to prevent progress to constant exotropia and restoration of bifixation, while in case of surgery of adult patients can only be helpful in achieving orthotropia, but not bifoveal fixation (65).
Patients may achieve a superior sensory outcome with motor realignment before the age of 7 years or less than 5 years of the duration of strabismus (66, 67). Other authors have argued that the surgery should be delayed for several years because patients have intermittent exotropia. In intermittent exotropia therefore bifoveol fixation can be achieved, not effective surgery results are in progressive intermittent exotropias, or when operation is done later and it was incomplete (68). Deviation of the eye remains stable in some cases whereas it has also been noticed to improve in few other cases. Nevertheless, other researchers held a strong opinion that patients will achieve binocular function if operated after age 7 and over 5 years of strabismus duration (69, 70). Surgical intervention before 2 years of age have also shown positive and successful results being reported by many authors (71). A critical indication in intermittent exotropia for intervening surgically is when the tropia phase is seen to increase because detoriation of the fusional control is what this is indicating. This increase in frequency of the tropia phase will potentially lead to binocular functional loss along with loss of fusion control. (72). The progression of deviation should be followed by documenting the angle of strabismus, fusion function, the duration of manifest strabismus (73). The authors proposed that distance stereo visual acuity is objective measurement and is needed when the surgical treatment is indicated (74)., Patients with intermittent exotropia may develop anomalous retinal correspondence and/or suppression. The surgery should be done in order to avoid diplopia. There are administered positive correcting exercises in order to restore normal bifoveal vision, and exercises with synoptophore in order to achieve binocular visual acuity.
3.4.2 Classification and Choice of Procedure
Intermittent exotropia was classified by Burian(75,76) on the basis of distance/near differences and different surgical approaches were recommended by him based on this classification. It was defined that patients whose distance deviation is equal to the deviation when they see objects near to them are
to be classified as basic type of exotropia and they were recommended to be operated with RR . A study by Kushner also suggested the same (77). In the Cochrane review, a study that was conducted by a single surgeon in the United States was published , it compared the results of surgery conducted on one eye or both eyes on 36 children that have basic type of exotropia. A successful result was defined as no recurrence of exotropia( or any other form of stabismus) after 1 year of surgery. The study concluded that operating on both eyes(52%) was less effective than operating on single eye(82% success) (62).
Divergence excess type exotropia was the classification of those patients whose distance deviation was more than the near deviation; the recommendation for such patients by Burian was bilateral lateral rectus recessions(BLR). These recommendations were based on the assumption that BLR would affect distance deviation better than near deviations while RR would affect near and distance deviations equally.
Scobee(78) states an observation that patients who exhibited divergence excess type of exotropia manifested an increased near deviation following 24 hours of monocular occlusion. It was determined later on that approx. 1 hour monocular occlusion it is enough in order to elicit this increase (75,76) Surgery procedures should be performed for the largest angle measured (79). "Simulated Divergence Excess” type of exotropia was the definition given by Burian to such patients (75,76). Kushner subdivided Burian's classification and concerned the simulated divergence excess which was caused by excessive accommodative convergence or an excess of divergence (80). Authors believed that patients with this disorder really have near deviation which equaled the distance deviation, it was masked by fusional vergence at near distance. Researchers recommended that patients must be treated as they had a basic type of exotropia and underwent recess/resect surgical operation. Other authors suggested that patients with basic type intermittent exotropia should be treated with recess/resect surgery. Patients with simulated divergence excess are needed lateral rectus recession operations (81). Other authors described better results in treating patients with three of these patterns of intermittent exotropia with surgery by symmetric lateral rectus recession (81, 82).
Scobee reported that patients with a simulated divergence excess exotropia (according to Burian's classification) (75, 76) showed similar results to those who had divergence excess pattern and were operated by bilateral lateral rectus recession. When bilateral lateral rectus recessions are performed, patients with a basic type of exotropia do not show as good results compared with the patients with simulated divergence excess exotropia or divergence excess. About two years survival analysis after bilateral rectus recession and unilateral recess/resect surgery in intermittent exotropia showed that
in the bilateral rectus recession group as compared to recess/resect patients group. Recurrence rate was low after six months after bilateral lateral rectus recession operation (83).
Bilateral lateral rectus recession was done in patients with bilateral dissociated horizontal deviation or with unilateral dissociated horizontal deviation combined with exotropia (84).
Weakening operations on all four oblique muscles are overacting in high angle exotropia should be done, later it was showed that overaction of all obliques may appear and disappear after horizontal recuts muscles surgery (85).
3.4.3 Lateral rectus recession
Many investigators (97-100) acknowledge that unilateral rectus recession to be effective in exotropia of 15–20 PD, reporting surgical success rate of 72– 90% in these angles (97-103). Others (104) suggest one muscle surgery in exotropia of 30 PD and lower. A recent study comparing between lateral rectus surgical treatment of one eye and lateral rectus recession operation which combined with medial rectus resection surgical treatment for intermittent exotropia, authors showed similar data for both surgical operations. Other authors showed that two types of operations (unilateral lateral rectus surgery and lateral rectus recession/resection) for exotropia have a similar effect. There was lower recurrence after two or three years after the lateral rectus recession combined with medial rectus resection than unilateral lateral rectus operation (103). Kim et al (105) showed that contralateral rectus recession was safe and effective surgical treatment in recurrent exotropia after muscle resection operation in intermittent exotropia.
In unimuscle ocular operation instead of the time of anesthesia is shorter comparing with two muscles surgery. It is lower risk of complications as endophthalmitis, scleral perforation and retinal detachment. For future intervention if needed there may be operated more muscles. It is the lower rate of overcorrection and consecutive esotropia in the unimuscle ocular operation (97-107).
In the unilateral lateral rectus recession may be postoperative lateral rectus function disorder but it was ruled out in (97, 99, 100), but other authors showed that it may be when there was recession of the lateral rectus muscles more than 9 mm (99,104)
3.4.4 Surgical Outcome
According to some studies the successful outcome of IXT surgery is 60-70% which is dependent on the patients follow up after surgery which is reported to be more effective if it is of longer duration of time (86). Some studies suggested post bilateral lateral rectus recession surgery undercorrection is
seen which lead to a quarter of patients to be in need of a second surgery. (87, 88). The overcorrection in different studies reported as such: 6% in (81), 8%in (89),11% in (90),17%in (91), and 20% in (92). Showing small degree of esotropia , which should be observed for six months time , second surgical intervention is only advised when there is significant limitations of ductions causing the disorder in lateral gaze.
Second surgery is recommended only after 6 months. Age of patients is also a crucial factor affecting the surgical outcome, a recent study (93) showed pediatrics patients below 7 years old age had a success rate of 77 % reported by reducing dose of surgery and in patients age over 12 years rate of 80% increasing dose of surgery .according to this study dose adjustment for IXT surgery is significant in surgery outcome.
4.METHODOLOGY
Literature search and review was performed using Medline database for publications between 2012-2021 using MESH terms “exotropia”, “strabismus”, “surgical treatment”, “unilateral lateral rectus recession, unilateral medial rectus resection”, “binocular lateral rectus muscle recession” and binocular lateral rectus muscle resection” English language papers describing either surgery method for exotropia and its outcomes were included and analyzed
5.RESULTS
The studies studied in this research are summarized in the following table Table 1: Brief of studies
The studies studied in this research are summarized in the following table Table 1: Brief of studies
Authors (year) Number of patient age Follow u p time Brief of result Haeng-Jin Lee & Seong-Joon Kim 2020(116) 236 BLR 100 RR
6.2 ± 2.1 2 years There were 28 patients (8.3%) with consecutive esotropia. 6 in the recession - resection group and 22 in the bilateral rectus recession group
RR superior to BLR At postoperative two years, Haeng-Jin Lee
2019(117)
144 - 2.2 years
Surgical outcomes were better in th e bilateral rectus
recession group than in the RP group
Hwan Heo, Mi Sun Sung (118)
319 - 3 year
the overcorrection resolved faster and recurrence rates were lower in bilateral rectus recession group than in the recession - resection group. Yugo Kimura &
Tohru Kimura 2017(119)
88 21± 7.6 - Bilateral rectus recession and recession - resection
achieved comparable distance devia tion and success rates at 12
months. PR had a better short-term success
rate, and might prevent postoperativ e diplopia
caused by overcorrection
Ko Eun Kim, Hee Kyun Yang,Jeon g Min Hwang 2015(120) 86 - More than 2 years
Recession - resection group showed better results than bilateral rectus recession in large angle exotropia over a long time albeit over short time results were similar
Eun Kyoung Lee 2015(121)
392 - 37.0±11.
5 months
Prismatic correction achieves good motor outcome while maintaining a favourable sensory status in most patients with
consecutive esotropia after bilateral rectus recession
27
Bang SP, Cho Y,
Lee SY 2017(130)
99 - 2 years At short period bilateral rectus recession success rate was more after and 5 years years 41% in recession - resection group 54 % in BLR group Authors (year) Numb er of pat ient ag e Follo w up time Brief of result Yuan Sun 2018(122) _ _ 1.5 ye ars
The overall findings from this meta- analysis indicated that the conventional Recession - resection procedure is associated with
higher success rates and lower recurrence rates in patients with basic intermittent exotropia
Sean P Donahue 2019(123)
197 - 3 year s
unable to recommend one
surgical approach over the other for childhood Intermittent exotropia Oscar Oliva 2018
(124)
5 Unilateral recess/resection might achieve greater surgical success and probably decrease the rate
of undercorrection/recurrence when compared to bilateral lateral rectus
recession Seonghwan Kim 2018(125) 129 4.4±2. 3 years
There was used forced duction test in order to reduce the risk of recurrence at 2 years after surgery when recession - resection was performed with more passive tension of the lateral rectus. Intraoperative FDT
may be considered to choose which eye to operate on when
planning Recession - resection in intermittent exotropia Burton
J. Kushner 2018( 126)
- - - Recession - resection superior to bilateral rectus recession for basic Intermittent
exotropia and speculated the better results were because of a stabilizing effect that Recession - resection has for limiting an exotropic drift
Seok Hyun Bae,
Dong Gyu Choi 2018 (131)
121 - - Lateral rectus recession surgeries induced changes in HoAs and corneal topography while recession - resection only did so in HoA
Xian Yang , Teng-Teng Man ,
Qiao-Xia Tian(132)
213 2 year Surgical outcomes were better for recession - resection after six months but after three years bilateral rectus recession showed better results , this may be due to less recurrence rate in bilateral rectus recession group
29
6. DISCUSSION
Whether BLR surgery gives comparable results to R&Rs is an important question, because many surgeons have an intrinsic bias toward one or the other approach. Some prefer BLR because it does not create horizontal income deviation, is less apt to narrow the palpebral fissure, and is aesthetically more appealing. Some prefer R&R because it involves operating on only 1 eye, is more acceptable to patients if only 1 eye is seen to deviate, and allows for a more predictable secondary procedure if there is an under correction (116). An R&R in the other eye is probably more predictable than bilateral MR resections(127).
In this literature review I aim to answer this question by reviewing literature comparing the two surgical methodologies.
Some studies, like majority of research in our time included patients with a variety of ages: kids, young people, and grown-ups, the rate of success for unilateral rectus recession for intermittent exotropia showed varying results based on differing studies. Patients who underwent unilateral lateral rectus recession and patients who underwent lateral rectus recession and medial rectus resection for exotropia of 20–25 PD the surgical outcomes were reported. Suh et al. observed the results and found that the rate of effectiveness did not differ about 45.9% in patients with the lateral rectus group and 39.4% in patients with the recession-resection group. There was found a surgical effectiveness rate about 60.9% when the angle of deviation was 25 PD (103).
In patients when there was operated one ocular rectus muscle the time of general anesthesia was shorter and lower ocular risks than in those who had operations of two muscles. The rate of residual and recurrent exotropia after the first operation is not low, it should be needed to spare other horizontal ocular muscle for future operations. In unilateral lateral rectus recession the great advantage is the lower rate of overcorrection. After the operation for intermittent exotropia when overcorrection occurs, it may be a constant esotropia with double vision and loss of stereoscopic visual acuity, and it is need another operation of lateral ocular rectus or medial rectus recession. Suh and colleagues (123) showed that overcorrection the operation is less common in one eye lateral rectus operation. In the recession-resection patients group, in 9% of the patients was overcorrection, and in the unilateral lateral rectus group no patient showed an overcorrection after the operation (103).
Burian recommended that basic XT be treated with unilateral recession of a lateral rectus (LR) muscle combined with resection of its antagonist medial rectus (MR) muscle (R&R), on the mistaken and unproven assumption that weakening the LR would affect the distance deviation more than the near and resecting the MR would affect the near more than the distance. With the subsequent popularity of
symmetric surgery, many ophthalmologists shifted to treating basic intermittent XT (IXT) with bilateral LR recessions (BLRc) (123).
Donuhue SP and his Pediatric Eye Disease Investigator Group (PEDIG) group did a study to present the benefit of R&R over BLRc for treating basic IXT(123). The study presented the likelihood of a suboptimal post operative results by 3 years of 46% in the BLRc group versus 37% for R&R, for a difference of 9%. This difference was not deemed big enough and hence they concluded that this study to be inconclusive. Although in my opinion what is to be of importance is the more likelihood of exodrift occuring in the BLRc patients as compared to the RR group in this study because of which re operation occurred in 10 % of the BLR group as compared to only 5 % of the RR group
In the study conducted by Haeng-Jin Lee et al , there were compared long-term surgical results in patients with intermittent exotropia treated with bilateral rectus recession and recession - resection. The recession - resection group showed a higher rate of overcorrection in the early postoperative period, but recurrence rates gradually increased over time. In contrast, the bilateral rectus recession group showed an earlier exodrift followed by a stable course during up. After a mean follow-up period of 2 years, the Bilateral rectus recession grofollow-up showed a higher success rate compared with the recession - resection group. (116)
Haeng Jin Lee in 2019 found similar effectiveness in exotropia correction with resection or plication of the medial rectus muscle, but 37% less effectiveness with plication of the lateral rectus muscle on long- term follow-up compared to resection(117). After Alkharashi and Hunter(128) reported lower success rates post intermediate and long term for operation of medial rectus . Therefore, Lee et al(117) augmented the surgical dosage by 1.0–1.5 mm over the original surgical formula of resection. Lee et al used this approach in the current study and found that both the angle of esodeviation at 1 postoperative week and overcorrection were larger in RP group compared to the BLR group. Although Lee et al augmented the surgical dosage of RP, which resulted a higher and sufficient overcorrection rate in the early phase, exodrift progressively occurred over time in the RP group. So one may conclude that if the RP surgery even achieves similar success rate as BLR , its esodeviation will be larger , albeit it the result showed that success rate of RP was much less compared to BLR over long term exodrift occurred in the RP . Such could be prevented by wearing appropriately prescribed prism glasses after surgery. deviation at near became larger than deviation at distance in both groups after surgery, especially in the BLR group. However, distance-near differences did not significantly increase in this study, and even slightly decreased after surgery. We found that BLR could maintain or reduce the distance-near disparity effectively in the basic type of intermittent exotropia
31
Lee and Kim in 2017 also showed Results Of the 186 patients, 114 underwent RR and 72 underwent Bilateral rectus recession. The angle of exodeviation steadily increased over time in both groups after surgery. The durations of exodrift were longer in the Bilateral rectus recession group than in the recession - resection group. The surgical success at postoperative year 2 was 55.3% in the recession - resection group and 27.8% in the Bilateral rectus recession group (p<0.001). The amount of overcorrection was associated with successful outcomes in both groups (116) on the other hand the study conducted Hwan Heo et al. On 336 patients over 3 year time showed greater correction of esodeviation that had happened post strabismus surgery in the Bilateral rectus recession group as compared to the recession - resection group, moreover the recurrence rate was also lesser in the former.(118)
According to Yugo Kimura & Tohru Kimura’s study, Bilateral rectus recession and recession - resection achieved comparable result over an year although over short period of time Bilateral rectus recession showed better result , Bilateral rectus recession group could be preferred to avoid post operative diplopia that occurs due to overcorrection . The study showed 45 patients underwent Bilateral rectus recession and 43 underwent recession - resection. The mean preoperative distance deviation was 40.1 ± 12.9 PD in the Bilateral rectus recession group and 40.0 ± 14.9 PD in the RR group (P = 0.96). Mean follow-up was 21.0 ± 7.6 months for bilateral rectus recession and 24.0 ± 8.6 months for RR (P = 0.08). The mean postoperative distance deviation at 12 months was 8.3 ± 7.4 PD for BLR and 9.9 ± 9.6 PD for recession - resection (P = 0.38). Bilateral rectus recession had a significantly better outcome than RR at 1 week (BLR 89%; RR 72%; P = 0.04), but there was no difference between recession - resection at 12 months BLR 67%; RR 60%; P = 0.50). (119). Ko Eun Kim et al. Conducted a study that could be conclusive for us and meaningfully help us decide which surgery to prescribe , the result of this study concluded that in large angle exotropias , it would be prefrable to select unilateral lateral rectus recess/resect over the bilateral lateral rectus recession the results of this showed over long period of time , as bilateral rectus recession had recurrence of exotropia. (120).
Sun et al reported as generated from the pooled estimates, suggested that success rates for the R&R procedure were significantly greater than that of BLR (OR, 0.50; 95% CI, 0.31–0.79; P = 0.003) and patients subjected to the Bilateral rectus recession procedure were more likely to be recurrent (OR, 2.44; 95% CI, 1.17–5.10; P = 0.02). No statistically significant differences in the combined results for overcorrection rates were present between the BLR and R&R procedures (OR, 0.85; 95% CI, 0.32– 2.28; P = 0.75)(122).
In a study conducted by Seok Hyun Bae(132) which was on corneal topographic changes and ocular aberrations after exotropic surgery on a pool of 121 patients , the data for RR and Bilateral rectus recession was analyzed , the result showed that Lateral rectus recession induced changes in both corneal topographic measurements and HOAs, whereas recession - resection did so only in HOAs, in this study hence we can come to a conclusion that in order to avoid occular aberrations recession - resection is a better choice , the main reason for such an event to occur could be because symmetry of the cornea is maintained when surgery is conducted on both the muscles as is the case of recess--resect when compared to one sided lateral recess surgery
In a study by Xiang Yang et al. (132) showed that after 12,24 months after surgery the motor outcomes of both recession - resection and Bilateral rectus recession showed no considerable difference however when followed at 36 months were signally different in each group, indicating the success rate in recession - resection group at 6mo was higher than that in Bilateral rectus recession group (83.02% vs 82.24%, P<0.05) but the result was contrary at the 3y examination (60.75% vs 43.40%, P<0.05) . It was concluded that results of recession - resection group were better than in BLR group at 6mo after surgery, while the 3y outcomes were better in Bilateral rectus recession group, (132).
After reviewing 24 studies and selecting 14 for this literature review, the supremacy of one surgical method or the other can not be conclusively stated Albeit in my opinion Bilateral rectus recession showed slightly better reviews than recession - resection mainly owing to it not wasting any muscle , operating on one muscle , and less over correction , it is also more aesthetically pleasing.
33
7. CONCLUSION
The result of this literature review showed that there are varying opinions and results after comparison of the two surgical methods so one can not conclusively give superiority of one method over the other Based on the above mentioned aims and objectives we may conclude that strabismus surgeries should only be considered after the conservative treatments have failed
1-Preoperative factor in choosing the the type of surgery should be distance/near differences and PD angle deviations
Patients whose distance deviation equals to the near deviation are basic type of exotropia or those who have a large angle 45 PD or more and should be recommended for unilateral rectus recess/resect surgery (RR)
Patients in whom distance deviation exceeded the near deviation are divergence excess exotropia , for such patients BLR should be considered also patients with small angle deviation
2-More patients from the RR group showed likelihood of esodeviation than the BLR group, so the BLR group should be the choice to avoid over correction
3- Literature review showed that exodrift and undercorrection was more common in BLR, RR is better , as exotropic recurrence was more in BLR
4- Practical recomendations:-
In some cases, low angle strabismus may improve without surgery
CI, convergance insufficiency can be improved by eye adaptation and vision therapy without the need of surgery. Later on, it is preferred to perform surgical correction using BLR unless the patient has a large exodeviation in that scenario RR should be given priority. Following the surgery , a short term vision therapy program, Orthoptics should be recommended to improve blurred vision and brief binocular vision problem that may persist after the strabismus surgery
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