4.5 Idiopathic Macular Hole
4.5.1 Pathophysiology and Macular ERGs
Fig. 4.18. Fundus photograph (top left), OCT (bottom left) and topographic maps of multifocal ERGs (top right) obtained from a patient with an idiopathic macular hole. The macular hole is surrounded by the cuff. Multifocal ERG topography shows the volcano-like depression at the central peak
Eyes with an idiopathic full-thickness macular hole usually have reduced visual acuity and an absolute central scotoma caused by the macular hole. Relative scotomas are usually detected in areas surrounding the hole that can be identified by OCT (Fig. 4.18). The loss of retinal function is attributed to the defect in the
central retina, the surrounding cuff of subreti-
nal fluid, thickening of the retina, and trac-
tional elevation of the retina surrounding the
macular hole. Multifocal ERGs may demon-
strate the volcano-like depression of the central
retina (Fig. 4.18).
It is extremely important to monitor the location of the stimulus when recording the focal macular ERGs in patients with an idio- pathic macular hole to determine the relation between the stimulus spot and the macular hole. This relation can be studied precisely with our system because focal macular ERGs are recorded under the fundus monitor. As shown in Fig. 4.19, when the spot is smaller than or equal to the macular hole, a response cannot be recorded (Fig. 4.19A). When the spot is slightly larger than the macular hole, the stimulus light stimulates the parafoveal cuff and a reduced response with delayed implicit time is recorded (Fig. 4.19B). When the spot is much larger than the macular hole, a large response is elicited from the normal perifoveal retina. Although the amplitude is still smaller than that of the
normal fellow eye, the implicit time is not delayed because the implicit time of the b-wave reflects the function of the surrounding normal retina.
Another interesting phenomenon is seen in the focal macular ERGs elicited by a large spot in patients with an idiopathic macular hole.
When the stimulus used to stimulate the affected eye and the normal fellow eye are bal- anced to elicit nearly equal-amplitude a-waves and b-waves, the OPs of the affected eyes are always larger than those of the fellow eyes (Fig.
4.20). This is caused by the unique distribution
of OPs around the macular region, as described
earlier [1]. Namely, the distribution of OPs is
larger in parafovea than fovea and eyes with
macular hole are stimulated more in parafovea
than fovea (see Section 1.2.3, Fig. 1.28).
Fig. 4.19. Relation between the size of the macular hole, the size of the stimulus spot, and focal macular ERG responses. Fundus photographs (top), stimulus spot on the fundus (middle), and focal macular ERGs recorded from the affected eye and the normal fellow eye (bottom). A When the stimulus spot is smaller than or equal to the macular hole, the macular ERG is absent. B When the stimulus spot is slightly larger than the macular hole, the b-wave amplitude is smaller and the implicit time is longer than that in the normal fellow eye. This indicates that the response is elicited from the cuff surrounding the macular hole. C When the stimulus spot is much larger than the macular hole, the amplitude of the b-wave is slightly smaller and the implicit time is normal.
This ERG response is evoked from the normal retina outside the cuff
Fig. 4.20. Focal macular ERGs recorded from four patients with an idiopathic macular hole. The size of the stimulus spots is balanced to elicit approximately equal-amplitude a-waves and b-waves from the affected eye and the normal fellow eye. Two time constants (T.C.) are used simultaneously to evaluate a- waves and b-waves (0.03 s) and OPs (0.003 s)
4.5.2 Surgical Treatment and Focal Macular ERGs
Recent advances of vitreoretinal surgery have made it possible to close the macular hole and recover the normal configuration of the macula, which can be confirmed by OCT (Fig.
4.21). The surgical technique to close the macular hole consists of standard three-port pars plana vitrectomy and separation of the posterior hyaloid from the retina after remov- ing the cortical vitreous. Residual vitreous cortex is removed when it is present around the macular hole. After vitrectomy, fluid-gas exchange is performed [2].
The changes in the focal macular ERGs before and after macular hole surgery [3] are shown in Fig. 4.22. A 65-year-old man had noted decreased vision in his left eye for 6 months. Examination disclosed a stage 3 full- thickness macular hole, and his visual acuity was 0.08 (OD) and 1.0 (OS). Focal macular ERGs were recorded with 2°, 3°, and 4° stimu-
lus spots from both eyes before surgery. The different stimulus spot sizes are photographi- cally superimposed on the fovea to compare the sizes of the stimulus spot and the macular hole.
In the affected eye, responses were not recorded when the stimulus size was equal to or smaller than the size of the macular hole (2° and 3°).
When the stimulus spot was larger than the macular hole (4°), a response suggestive of a focal macular ERG was recorded (A).
The patient underwent surgery, and the macular hole was closed. Six months later his visual acuity improved to 0.4, and focal macular ERGs were successfully recorded even with the smallest 2° spot. These results confirmed that the area of retinal deficit, the macular hole, was closed by the surgery, and function had returned (B).
The focal macular ERGs elicited by 4° and 5°
stimulus spots before and after surgery in four
Fig. 4.21. OCT images obtained from a 56-year-old woman with an idiopathic macular hole before (PRE OP) and after (POST OP) vitrectomy. The macular hole is closed.
The preoperative visual acuity of 0.3 improved to 0.8 postoperatively
patients with a full-thickness macular hole are shown in Fig. 4.23. The amplitudes of the b- wave of the focal macular ERGs were increased in all eyes, and the implicit times were decreased after the surgery. In our study of a large series of patients [3], the preoperative b-wave implicit time measured with a 5°
spot significantly correlated with the post- operative corrected visual acuity (Fig. 4.24). In addition, the postoperative b-wave amplitude and implicit time of the focal macular ERGs elicited by a 5° spot significantly correlated
with the postoperative visual acuity. These results strongly suggest that parafoveal func- tion in the area surrounding the macular hole is closely related to the visual prognosis after surgery in patients with an idiopathic macular hole.
To increase the closure rate of macular holes, removing the internal limiting mem- brane (ILM) in addition to routine vitrectomy has recently been advocated [4]. The exact role of the ILM in retinal physiology has not been determined, although the ILM is the basal
A B
Fig. 4.22. A Preoperative fundus photograph and photographs with 2°, 3°, and 4° stimulus spots superimposed on the fovea as seen on the television monitor (left). Preoperative focal macular ERGs of the eye with the macular hole are compared to those from the fellow eye (right). B Postoperative fundus photograph compares the three spots used to the size of the macular hole (left). Postoperative focal macular ERGs comparing the responses of fellow eye. (From Terasaki et al. [3], with permission)
Fig. 4.23. Focal macular ERGs elicited by a 4° spot (top) and a 5° spot in four patients with a full- thickness macular hole before (Pre-op) and after (Post-op) surgery. All eyes show increased amplitude and decreased implicit time of the b-wave. (From Terasaki et al. [3], with permission)
lamina of Mueller cells and is connected to the end-feet of the Mueller cells [5]; and Mueller cells are involved in generation of the ERG b- wave [6]. In addition, the anionic sites on the ILM may act as a charge barrier between the retina and the vitreous cavity [7].
The changes in the focal macular ERG after conventional vitrectomy without ILM removal (ILM-on) and with ILM removal (ILM-off) are compared [8] in Fig. 4.25. Six weeks after vit- rectomy without ILM peeling, the amplitudes of the b-waves and OPs of the focal macular ERGs were larger, and an additional increase was observed 6 months after surgery. On the other hand, the patient with ILM-off showed a
marked decrease in the amplitudes of the b- waves and OPs 6 weeks after surgery, which then recovered to the preoperative level at 6 months.
Analysis of a large series of patients showed that visual acuity increased significantly after surgery in both groups, and no significant difference was found between the two groups.
However, recovery of the b-wave in focal macular ERGs in the ILM-off group was significantly delayed until 6 months after surgery compared with that of the ILM-on group, suggesting slower recovery of retinal physiology in the macular region in the ILM- off group.
Fig. 4.24. There is a significant correlation between the preoperative b-wave implicit time elicited by a 5° spot and the postoperative best-corrected visual acuity (r= 0.62; P = 0.001). (From Terasaki et al.
[3], with permission)
References
1. Miyake Y, Shiroyama N, Ota I, Horiguchi M (1988) Oscillatory potentials in electroretinograms of the human macular region. Invest Ophthalmol Vis Sci 29:1631–1635
2. Johnson RN, Gass JD (1988) Idiopathic macular holes: observations, stages of formation, and impli- cations for surgical intervention. Ophthalmology 95:917–924
3. Terasaki H, Miyake Y, Tanikawa A, Kondo M, Ito Y, Horiguchi M (1998) Focal macular electroretino- grams before and after successful macular hole surgery. Am J Ophthalmol 125:204–213
4. Park DW, Sipperley JO, Sneed SR, Dugel PU, Jacob- son J (1999) Macular hole surgery with internal- limiting membrane peeling and intra-vitreous air.
Ophthalmology 106:1392–1397
5. Nishihara H (1989) Studies on the ultrastructure of the inner limiting membrane of the retina. I.
Surface replication study on the inner limiting membrane of the retina. Acta Soc Ophthalmol Jpn 93:429–438
6. Terasaki H, Miyake Y, Piao CH, Hori K, Niwa T, Kondo M (2001) Focal macular ERGs in eyes after removal of macular ILM during macular hole surgery. Invest Ophthalmol Vis Sci 42:229–234 Fig. 4.25. Left: Representative focal macular ERGs recorded before and 6 weeks and 6
months after surgery for an idiopathic macular hole without internal limiting membrane (ILM) removal (ILM-on) and the fellow eye. Right: Changes in the focal macular ERG in an eye with the ILM removed (ILM-off) and the fellow eye. The b-wave and OPs were markedly reduced 6 weeks after surgery but had recovered at 6 months to the same level as that before surgery. (From Terasaki et al. [6], with permission)
