Ординатура / Офтальмология / Английские материалы / Electrodiagnosis of Retinal Disease_Miyake_2005

normal pattern with no leakage; the visual acuity improved to 1.2. The focal macular ERGs returned to normal levels, with the amplitudes of the OPs comparable to those recorded from the fellow eye.

Case 2 (Fig. 4.8) was a 70-year-old woman who visited our hospital 14 months after cataract surgery with implantation of a posterior chamber lens in her right eye. Her visual acuity was 0.2, and CME was detected with fluorescein angiography. The focal macular ERG had a type 2 pattern, with normal a-waves and reduced b-waves and OPs. Because vitreous was incarcerated by the iris, pars plana vitrectomy was performed to separate the vitreous from the iris. Five months after vitrectomy her visual acuity had improved to 0.7, and the CME was no longer present (seen by fluorescein angiography). The focal macular ERG recovered to the type 1 pattern in which only the OPs were reduced. Thus, the focal macular ERGs changed from type 2 to type 1 after resolution of the CME by vitrectomy.

Case 3 (Fig. 4.9) was a 60-year-old man who was examined after bilateral intracapsular cataract extraction 16 and 20 months earlier. Fluorescein angiography disclosed CME in the right eye. The focal macular ERGs had a type 3 pattern with reduced a-wave, b-wave, and OP amplitudes. Careful examination showed that vitreous was incarcerated in the corneoscleral wound, and the pupil was distorted. Pars plana vitrectomy was performed to detach the vitreous from the wound to restore the shape of the pupil. Four months after vitrectomy, his visual acuity was 0.3, and fluorescein angiography disclosed less severe CME. The focal macular ERGs recorded 4 months after vitrectomy had a type 2 pattern; that is, the a-wave amplitude recovered almost to the level seen in the fellow eye, but the b-wave and OP amplitude remained smaller than that in the normal eye.

With aphakic or pseudophakic CME, the amplitudes of the OPs are reduced and the implicit times are delayed regardless of the

visual acuity. These findings suggest that OPs are the most sensitive indicator of CME. The progressive increase in the severity of CME is manifested by a decrease in the b-wave

followed by a reduction of the a-wave. Therefore, analysis of each component of the focal macular ERG can be used to quantify the severity of CME [3].

Fig. 4.8. Case 2. Focal macular ERGs (left) and fluorescein angiograms (right) before vitrectomy (top) and 5 months after vitrectomy (bottom). After resolution of the CME by vitrectomy, the focal macular ERG recovered from type 2 to type 1. (From Miyake et al. [3], with permission)

Fig. 4.9. Case 3. Focal macular ERGs (left) and fluorescein angiogram (right) recorded before vitrectomy (top) and 4 months after vitrectomy (bottom). After resolution of the CME, the focal macular ERG changed from type 3 to type 2. (From Miyake et al. [3], with permission)

It is conceivable that the full-field ERGs may be within the normal limits in cases of simple aphakic or pseudophakic CME without an associated systemic disease such as diabetes. This is true because the abnormal fundus and fluorescein angiographic findings are limited to the macula or within the posterior pole. The full-field ERGs should be normal because the peripheral retina contributes more significantly than the macula to the full-field ERGs. However, our study of full-field ERGs showed that, although there were no significant differences in the amplitudes and implicit times of the a- waves and b-waves between the affected eyes and the fellow eyes without CME, the amplitudes of OPs were significantly reduced in the affected eyes [4] (Figs. 4.10, 4.11). The degree of reduction of the OPs was strongly correlated with visual acuity (Fig. 4.12), and the mean implicit time of the first OP was significantly

delayed in the affected eyes. The abnormal OPs of the full-field ERGs indicated that the abnormality was not limited to the macula but had spread over the entire retina.

What do these findings mean? Chemical mediators are biosynthesized at the site of the primary lesion in various diseases, and it has been postulated that they diffuse into the vitreous and cause macular edema postoperatively [5]. Why do the chemical mediators act only on the macula and not on other parts of the retina or eye? The results of full-field ERG suggest that, even without a visible vasculopathy, as in diabetic retinopathy, the inflammatory chemical mediators do affect the retinal vessels over a large area of the retina in the presence of aphakic or pseudoaphakic CME. This suggests that CME is only one manifestation of a more diffuse intraocular pathological alteration.

References

1.Irvine SR (1953) A new defined vitreous syndrome following cataract surgery: interpreted according to recent concepts of the structure of the vitreous. Am J Ophthalmol 36:599–619

2.Gass JDM, Norton EWD (1966) Cystoid macular edema and papilledema following catarct extraction; a fluorescein funduscopic and angiographic study. Arch Ophthalmol 76:646–661

3.Miyake Y, Miyake K, Shiroyama N (1993) Classification of aphakic cystoid macular edema

with focal macular electroretinograms. Am J Ophthalmol 116:576–583

4.Terasaki H, Miyake K, Miyake Y (2003) Reduced oscillatory potentials of the full-field electroretinogram of eyes with aphakic or pseudophakic cystoid macular edema. Am J Ophthalmol 135:477–482

5.Miyake K (1995) Cystoid macular edema as part of diffuse intraocular symptoms. Folia Ophthalmol Jpn 46:219–231

Epimacular membranes (Fig. 4.13) can be caused by trauma, inflammation, retinal vascular disease, and retinal detachment surgery. We have studied the focal macular ERGs of patients with unilateral idiopathic epimacular membrane (IEM) to determine how the altered retinal function correlates with visual acuity and OCT images [1, 2]. We found that the changes in the focal macular ERG while the macula was altered and after recovery of the macula closely resemble those seen in the presence of aphakic (pseudophakic) CME (see Section 4.2).

Focal macular ERGs demonstrating the damaged and recovered stages are shown in

Fig. 4.14.A 56-year-old woman noted decreased vision in her right eye with visual acuity of 1.0; the visual acuity in her left eye was 2.0. She had an IEM in the right eye, and the a-waves and b- waves of her focal macular ERGs for the right eye were not significantly different from those in the normal fellow eye at the initial visit. However, OPs of the right eye were smaller (Fig. 4.14A).

Six months later, the best-corrected visual acuity in her right eye had decreased to 0.1, and the a-waves, b-waves, and OPs of the focal macular ERGs were markedly reduced. There was also a decrease in the b-wave/a-wave (b/a) ratio (Fig. 4.14B). Vitrectomy was then per-

formed to remove the ERM in her right eye, and 10 months after surgery her best-corrected visual acuity improved to 0.8. At this time, the a-wave amplitude had recovered nearly to the level in the fellow eye, but the b-wave and the OPs remained smaller than in the fellow eye, resulting in a lower b/a ratio (Fig. 4.14C). Fifteen months after surgery, the b-wave and OPs improved, and the b/a ratio was almost identical to that in the fellow eye (Fig. 4.14D).

In our analysis of 37 eyes with an IEM [2], the relative amplitudes (affected eye/normal fellow eye) of the a-waves, b-waves, and OPs were 75%, 69%, and 45%, respectively. The lower b/a wave ratio in the affected eyes resulted from a significantly greater reduction of the b-wave amplitude than the a-wave amplitude. The reduced amplitude of OPs was significantly greater than that of the other two components, and the implicit times were significantly prolonged for all components. These findings are similar to those for eyes with aphakic or pseudophakic CME.

There was a significant correlation between the preoperative relative b-wave amplitude and visual acuity and between the preoperative relative a-wave amplitude and postoperative visual acuity (Fig. 4.15).

The OCT examinations showed that the mean thickness of the preoperative foveal and parafoveal retina in the affected eyes was significantly thicker than the mean of the normal fellow eyes. After surgery, the thickness decreased significantly, although it was still thicker than in the normal fellow eyes [2].

The changes in the waveform of the focal macular ERG and the OCT findings before and after vitrectomy in two patients with an IEM are shown in Fig. 4.16. After surgery, the foveal thickness was decreased in both patients. In case 1, all components of the preoperative focal macular ERGs had reduced amplitudes, but the a-wave amplitude was relatively better preserved (decreased b/a ratio). The b-waves and a-waves had recovered to normal levels 3 months after surgery, in conjunction with an

Fig. 4.14. Focal macular ERGs elicited by a 10° spot before (A, B) and after (C, D) vitrectomy in a patient with unilateral IEM. A On the patient’s initial visit, only the OPs were attenuated. B Six months later, the a-wave and b-wave amplitude and the b/a ratio were also reduced. C Ten months after successful removal of the IEM, the a-wave amplitude recovered. OPs were still absent. D Fifteen months after vitrectomy, the ERGs recovered almost to normal. (From Tanikawa et al. [1], with permission)

increase in the b/a ratio. The focal macular ERGs examined 12 months after surgery demonstrated recovery of the OPs.

In case 2, the a-wave amplitude was first detected to have recovered at 5 months after surgery, and recovery was associated with a decrease in the b/a ratio. The b-wave and OP

amplitudes of the focal macular ERGs were increased at 22 months after surgery. There were significant correlations between the preoperative a-wave amplitude and postoperative visual acuity (Fig. 4.15B) and between the postoperative OPs amplitude and postoperative parafoveal thickness (Fig. 4.17).

References

1.Tanikawa A, Horiguchi M, Kondo M, Suzuki S, Terasaki H, Miyake Y (1999) Abnormal focal macular electroretinograms in eyes with idiopathic epimacular membrane. Am J Ophthalmol 127: 559–564

Fig. 4.17. There was a significant correlation between postoperative OP amplitude and postoperative parafoveal thickness (r = -0.460, P = 0.011). OP amplitudes are shown as a percentage of those in the normal fellow eye. (From Niwa et al. [2], with permission)

2.Niwa T, Terasaki H, Konde M, Piao CH, Suzuki T, Miyake Y (2003) Function and morphology of macula before and after removal of idiopathic epiretinal membrane. Invest Ophthalmol Vis Sci 44:1652–1656

The results of focal macular ERGs and OCTs from patients with central serious chorioretinopathy, aphakic or pseudophakic CME, and IEM have some findings in common that contribute to our understanding of the relation between macular morphology and macular ERG. The macula OPs at the early stage of aphakic or pseudophakic CME and IEM are selectively reduced, and this reduction was observed during the convalescent stage of central serous chorioretinopathy even after the submacular fluid had been resorbed. The common change in these patients was the increase in the OCT-determined thickness of the macula, which was due to macular edema. These observations indicate that the macular OPs are the most sensitive indicator among the focal macular ERG components when the macula is edematous with minimal systemic pathology.

It was also determined that macular OPs have the slowest recovery following treatment of macular edema. This relation was confirmed by the significant correlation between the macular thickness measured by OCT and the amplitude of macular OPs in many patients with IEM after vitrectomy (Fig. 4.17).

When macular edema is long-standing or severe,the b-wave and then the a-wave may also become depressed. These findings indicate that the pathological process first affects the OPs, followed by the b-wave, and finally the a-wave as the macula thickness increases. The recovery process follows the reverse course; the a-wave recovers first, followed by the b-wave, and finally the OPs. This rule is important when analyzing complicated cases of macula edema associated with significant background pathology, such as diabetic macular edema (see Section 3.2.3).

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 subretinal fluid, thickening of the retina, and tractional elevation of the retina surrounding the macular hole. Multifocal ERGs may demonstrate the volcano-like depression of the central retina (Fig. 4.18).