Once postoperative endophthalmitis develops, its early recognition and prompt treatment are important for preserving visual function. In animal studies, the ERG b-wave in eyes with endophthalmitis induced by Enterococcus faecalis or Pseudomonas aeruginosa decreases within 2–3 days after inoculation of the microorganisms into rabbit eyes [1, 2]. Clini- cally, the mixed rod–cone ERG is useful for the diagnosis and prognostic evaluation of eyes that develop endophthalmitis after intraocular lens implantation [3]. Eyes with early (within 1 week) endophthalmitis associated with a b/a ratio of <1.0 have a worse postoperative
prognosis than eyes with late-onset end- ophthalmitis and/or a b/a ratio of >1.0.
These observations are quite important when deciding on the appropriate time to perform vitrectomy. For example, a patient with endophthalmitis that was detected within 1 week after intraocular lens implantation and an ERG b/a ratio of <1.0 should undergo vitrec- tomy without delay. On the other hand, when endophthalmitis develops relatively long after surgery and the ERG b/a ratio is >1.0, the timing of the vitrectomy or other treatment is not as critical. Representative examples are shown in Fig. 3.19.
3.4 Inflammatory Diseases of Retina and Choroid
3.4.1 Endophthalmitis
Fig. 3.19. Left: Preoperative mixed rod–cone (bright flash) ERGs recorded from two patients with endophthalmitis after intraocular lens implantation. The negative configuration of the ERG (case 1) suggests poorer visual prognosis after vitrectomy than for the patient with normal-shaped ERGs (case 2). Right: Postoperative fundus. Case 1 showed extensive retinal vascular occlusions (arrows), with poor postoperative visual function as expected. Case 2 showed an essentially normal fundus with good postoperative visual function. (From Horio et al.
[3])
Multiple evanescent white dot syndrome (MEWDS) [4], acute zonal outer retinopathy (AZOOR) [5], and acute idiopathic blind spot enlargement syndrome [6] have several similar ophthalmological and demographic findings:
unilateral, blurred vision, multiple paracentral scotomas usually including a temporal scotoma, photopsia, and blind spot enlarge- ment; and it affects young women. These symp- toms usually develop soon after a flu-like illness. Among these disorders, only MEWDS has ophthalmoscopic abnormalities, which include clusters of tiny white or light-orange dots in the foveola and multiple small, often poorly defined gray-white patches at the level of the RPE and outer retina (Fig. 3.20). The visual function and fundus abnormalities may
return to normal in 7–10 weeks. It is likely that most patients reported as having the acute idio- pathic blind spot enlargement syndrome and AZOOR probably had MEWDS, and the white lesions were either overlooked or had faded by the time of the examination.
The common functional abnormality of these disorders is acute occult visual field loss resulting from receptor cell damage. Because the ophthalmoscopic fundus abnormalities are minimal except in MEWDS, the patients may easily be misdiagnosed as having pathological alterations of the central nervous system.
The ERGs are useful for the diagnosis; the full-field ERGs have different degrees of abnor- malities depending on the extent of the visual field loss. In unilateral cases, the ERG of the
3.4.2 MEWDS, AZOOR, Acute Idiopathic Blind Spot Enlargement Syndrome
Fig. 3.20. Fundus of a patient with multiple evanescent white dot syndrome (MEWDS)
affected eye is always reduced compared to that of the normal fellow eye (Fig. 3.21). Above all, the most convincing diagnostic finding for these disorders is the approximate correspon-
dence of the subjective visual field defect to the low-amplitude zone in the multifocal ERGs (Fig. 3.22). The multifocal ERG findings indi- cate the retinal nature of the visual field loss.
Fig. 3.21. Comparison of full-field ERGs for the eye with MEWDS and the normal fellow eye shown in Fig. 3.19. All ERG components are slightly smaller in the affected eye than in the normal fellow eye
Fig. 3.22. Static visual fields (A) and topographic map of the amplitudes of the multifocal ERG responses (B) recorded from the patient with MEWDS shown in Fig. 3.20
Fig. 3.23. Fundus photograph and fluorescein angiogra- phy of the right eye with acute idiopathic blind spot enlargement syndrome. (From Kondo et al. [4], with permission)
Moreover and importantly, multifocal ERGs may be used to detect subclinical retinal dys- function in these disorders.
The clinical course of acute idiopathic blind spot enlargement is exemplified by the case of a 35-year-old woman. This patient, in previous good health, noted a small purple flickering spot in the upper right field of her right eye. Her visual acuity was 1.0 in both eyes. Fundus examination and fluorescein angiography
were normal, except for slight peripapillary hyperfluorescence (Fig. 3.23). Based on the blind spot enlargement of the static perimetry in her right eye, acute idiopathic blind spot enlargement was diagnosed. As shown in Fig.
3.24, abnormalities of the multifocal ERGs may
remain in such patients even after the subjec-
tive static visual fields have recovered normal
sensitivities at almost all locations [7].
Fig. 3.24. Results of static visual fields (A) and multifocal ERGs obtained from a patient with acute idiopathic blind spot enlargement syndrome shown in Fig. 3.23. These measurements were made 2 weeks (A–D) and 4 months (E–H) after the onset. The left-most panel is the gray scale of the static visual field thresholds. The second panel from the left shows the deviation plot of the static visual field. The third and fourth panels are the 61 response arrays and topo- graphic map of the multifocal ERG responses. Note that the amplitudes of the ERG responses are reduced in a broad area in the temporal field where the visual fields have normal sensitivities at almost all locations. (From Kondo et al.
[4], with permission)
Diffuse unilateral subacute neuroretinitis (DUSN) [8] is caused by an unidentified species of nematodes that may wander in the subreti- nal space for 4 years or longer and cause pro- gressive ocular damage. DUSN is characterized by early visual loss, vitritis, papillitis, retinal vasculitis, and recurrent crops of evanescent, grayish white outer retinal lesions that may develop in one eye of an otherwise healthy indi- vidual. At a late stage, there is severely reduced vision, optic atrophy, retinal vessel narrowing, and diffuse RPE degeneration. The appearance of the fundus can resemble that in several other diseases at different stages, such as optic neuritis, sarcoidosis, MEWDS, unilateral optic atrophy, unilateral retinitis pigmentosa, among others. Ancylostoma caninum, a hookworm of dogs, is a common cause of DUSN.
One of the reasons this syndrome is included here is because diagnosing DUSN is not always easy and the ERG findings can be helpful especially at the early stage. Full-field ERGs from the affected eye are usually reduced at all stages of the disease and are often mod- erately or severely reduced, with the b-wave affected more than the a-wave during the later stages of the disease [8–10].
The pathogenesis of DUSN appears to result from a local toxic reaction of the outer retina to the by-products of the worm, which are left in its wake, as well as a more diffuse toxic reaction affecting both the inner and outer retinal tissues. This latter reaction is manifested ini- tially by rapid loss of visual function and alter- ations of the ERGs, suggesting inner retinal abnormalities. At a more advanced stage, the
loss of ganglion cells (optic atrophy) and nar- rowing of the retinal vessels indicate damage to the inner retina.
There are at least two endemic areas for the nematode in the United States. It is also found in the Caribbean islands and Latin America, and individual cases have been reported from other countries including Japan. The patient to be described [9, 10] was a 30-year-old man who had noticed reduced visual acuity 3 years earlier while living in Sao Paulo, Brazil. He was referred to our clinic for a diagnosis and possi- ble treatment. His visual acuity was 1.5 (OD) and 0.07 (OS), and he had a central scotoma in the left eye with a defect in the nasal field.
The rod and cone components of the full- field ERGs were moderately reduced, and the mixed rod–cone ERG had a negative configura- tion (Fig. 3.25). His multifocal ERG amplitudes in the nasal retina including the macula were reduced, which roughly corresponded with the defect of visual field (Fig. 3.26).As shown in Fig.
3.27, the nematode was not detected initially in our case even with a detailed examination of the fundus (Fig. 3.27A). The blood vessels in the posterior pole of the fundus were attenuated, and mild optic atrophy was present (Fig. 3.27A).
Fluorescein angiography showed diffuse RPE mottling (Fig. 3.27B). Twelve days later, a nema- tode was detected ophthalmoscopically and was photographed by scanning laser ophthal- moscopy (Fig. 3.27C). The nematode was killed by laser photocoagulation (Fig. 3.27D), and examination 2 years later showed no further progression of the visual loss or depression of the ERGs.
3.4.3 Diffuse Unilateral Subacute
Neuroretinitis
Fig. 3.25. Full-field ERGs recorded from a patient with diffuse unilateral subacute neuroretinitis (DUSN) com- paring the affected eye and the normal fellow eye. Note that the mixed rod–cone (bright) ERG shows a nega- tive configuration. (From Tanikawa et al. [3])
Fig. 3.26. Visual fields of the affected left eye and multifocal ERGs for both eyes in a patient with DUSN. (From Ito et al. [2])
Fig. 3.27. A Fundus photograph. B Composite fluorescein angiogram. C Fundus photograph obtained using a scan- ning laser ophthalmoscope (SLO). D Fundus photograph after killing the nematode by laser photocoagulation. At the initial examination, the nematode was not detected in the fundus (A), but thereafter it was photographed clearly by SLO (C, arrow)
Rubella retinitis is the most common ocular manifestation of congenital rubella, with the appearance of the fundus taking several forms [11]. Salt-and-pepper mottling of the RPE may be localized only in the posterior pole, or it may extend farther into the peripheral retina (Fig.
3.28). Both eyes are affected in 80% of the patients. These alterations of the RPE may occur alone or may be associated with other ocular abnormalities (e.g., cataracts and microphthalmos) and systemic abnormalities, including deafness and congenital heart disease. Pathologically, the salt-and-pepper changes in the fundus are caused by altered pig- mentation and some atrophy of the RPE [12].
Because the retina and choroid are unaf- fected, full-field ERGs, focal macular ERGs, EOG, visual acuity, and color vision are normal (Fig. 3.29). It should be noted that the results of electrophysiological tests are all normal despite the ophthalmoscopic appearance of a severely affected retina.
Rubella retinopathy may mimic inherited dystrophies of the RPE, the carrier state of X- linked ocular albinism (see Section 2.9, Fig.
2.53), X-linked choroideremia and its carrier state (see Section 2.5, Fig. 2.23), and some toxic diseases of the RPE.
3.4.4 Rubella Retinitis
Fig. 3.28. Fundus photograph (top) and fluorescein angiogram (bottom) obtained from a 20-year-old man with rubella retinitis. The visual acuity was 1.5 for both eyes
Fig. 3.29. Full-field ERGs and focal macular ERGs recorded from a normal control and the patient shown in Fig. 3.28.
Despite the marked change in the retinal pigment epithelium, the ERGs are normal
Congenital or acquired syphilis can present as pigmentary retinopathy that resembles, in some aspects, advanced retinitis pigmentosa [13]. However, the retinal pigmentary changes are more varied and patchy, and the pigment deposits are in clumps with large patches of black pigment associated with the chorioretinal scars (Fig. 3.30). Interstitial keratitis is often
associated with congenital syphilis (Fig. 3.30).
The prognosis for vision with congenital luetic choroiditis is better than that with retinitis pigmentosa.
Full-field ERGs are usually subnormal, unlike the undetectable ERGs from retinitis pigmentosa (Fig. 3.31).
3.4.5 Luetic Chorioretinitis
Fig. 3.30. Fundus photograph (left) and interstitial keratitis (right) of congenital luetic chori- oretinopathy in a 44-year-old woman with visual acuity of 0.4
Fig. 3.31. Full-field ERGs from a normal subject and the patient with congenital luetic chorioretinopathy shown in Fig. 3.30. The appearance of the fundus is similar to that of retinitis pigmentosa, although relatively good responses were recorded
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