Ординатура / Офтальмология / Английские материалы / Electrodiagnosis of Retinal Disease_Miyake_2005

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 pigmentation and some atrophy of the RPE [12].

Because the retina and choroid are unaffected, 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.

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).

References

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Recent advances in vitreoretinal surgery are such that patients with many acquired macular diseases can now undergo surgery and regain normal macular configuration. Despite the normal configuration after surgery, however, some patients still do not obtain good visual function. It is particularly important and interesting to investigate how the pathophysiology of the macula changes following the recovery of macular configuration.

Our focal macular electroretinography (ERG) system allows us to assess macular function objectively, layer by layer, via examining the a-wave, b-wave, oscillating potentials (OPs), and off (d)-wave [1, 2]. With the advent of

References

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2.Miyake Y, Shiroyama N, Ota I, Horiguchi M (1988) Oscillatory potentials in electroretinograms of the

optical coherence tomography (OCT) [3], an objective layer-by-layer assessment of the macular morphology can be obtained with a high degree of precision. We are now at a time when the relations between the psychophysical visual function, objective macular function (focal macular ERGs), and macular morphology (OCT) can be compared before and during recovery from macular surgery.

This chapter is devoted to a review and summary of our results on focal macular ERGs, correlating them with the OCT findings and other examinations that assess the pathophysiology of the macula before and after treatment for various macular diseases.

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Idiopathic central serous chorioretinopathy typically affects young and middle-aged adults. Ophthalmoscopically, the sensory retina appears to be elevated because of the accumulation of serous fluid between the photoreceptors and the retinal pigment epithelium (RPE) cells (Fig. 4.1). Typically, the patient experiences metamorphopsia, relative scotoma, and micropsia. Visual acuity is often only slightly reduced and may be improved to near normal by a weak hyperopic correction.

The focal macular ERGs of five representative patients with central serous chorioretinopathy [1] are shown in Fig. 4.2A. The a-wave and b-wave amplitudes of all of the affected eyes are reduced,and the implicit times are delayed. Our study of a large series of

patients with relatively recent-onset unilateral central serous chorioretinopathy and bestcorrected visual acuity ranging from 0.4 to 1.5 (mean 1.0) showed that the amplitudes of the a-waves, b-waves, and OPs in the affected eyes were significantly smaller and the implicit times significantly longer than those in the normal fellow eyes [1].

The relative amplitudes of the b-wave (affected eye/normal fellow eye) are significantly smaller than the relative amplitudes of the a- wave, and the relative amplitudes of the OPs are significantly smaller than those of the a-waves and b-waves. Because the OPs and b-waves are significantly more depressed than the a-waves in the presence of macular detachment, central serous chorioretinopathy may involve functional

disturbances in the inner retinal layer as well as the photoreceptors [1].

In many of our cases, focal macular ERGs were recorded again 2–5 months after the macular detachment had resolved spontaneously or by photocoagulation. The results of five representative patients at the convalescent stage are shown in Fig. 4.2B. Our analysis of a large series of patients at the convalescent stage with the macula attached showed that the amplitudes and implicit times of the a-waves and b-waves in the affected eyes were not significant different from that in the normal fellow eyes. However, the OPs were still significantly smaller in the affected eyes, indi-

cating that only recovery of the OPs was significantly delayed [1].

With central serous chorioretinopathy, it is conceivable that the macular photoreceptors are damaged because of the sensory retinal detachment. Therefore, this disease may be considered a model of macular photoreceptor damage. Indeed, it has been shown that all the components of focal macular ERGs have reduced amplitude and delayed implicit time, indicating photoreceptor damage. However, it is interesting that the data indicate that the inner retinal layers were also damaged, and their recovery was delayed after the subretinal fluid was resorbed.

The mechanism by which central serous chorioretinopathy affects the inner retina is unknown. However, as shown in Fig. 4.3, OCT reveals thickening of the sensory retina in the macula area when subretinal fluid is present; interestingly, this thickening of the macula remains even after the subretinal fluid is absorbed during the convalescent stage and the macular OPs are selectively abnormal [2]. The

thickened macula may indicate that macular edema, which is known to depress inner retinal function,is still present during the convalescent stage and is the cause of the decreased OPs. Therefore, functional changes in eyes with central serous chorioretinopathy probably result from both the sensory detachment and edema of the macula.

References

1.Miyake Y, Shiroyama N, Ota I, Horiguchi MC (1988) Local electroretinographic responses in idiopathic central serous chorioretinopathy. Am J Ophthalmol 106:546–550

2.Miyake Y (2002) What can we know from focal macular ERG? Jpn Clin Ophthalmol 56:680–688

Cystoid macular edema (CME), a common complication of cataract surgery, manifests as leakage of plasma from the perifoveal capillaries, formation of macular cystoid spaces, and marked visual impairment [1, 2]. The disease may or may not resolve spontaneously, and vitrectomy leads to successful resolution of the edema in some patients with CME. Fluorescein angiograms and OCT images of a patient with typical CME before and after vitrectomy are shown in Fig. 4.4. The fluorescein angiogram (Fig. 4.4A) shows extensive fluorescein leakage from the macular capillaries, and OCT reveals multiple cystic spaces in the macula before surgery. After vitrectomy, fluorescein leakage

is not present (Fig. 4.4B), and the macular configuration evaluated by OCT returns to normal.

Although CME may be associated with several retinal diseases, aphakic and pseudophakic CMEs are good models for studying the principle of the pathophysiology of CME. This is because, unlike the CME in diabetic retinopathy or central retinal vein occlusion, there are few background abnormalities such as ischemia or damaged RPE. Thus, the pathophysiology may be relatively simple to analyze. The interpretations may then be extended to analysis of more complex CME, such as that seen with diabetic retinopathy.

The focal macular ERGs in the affected eyes of patients with aphakic or pseudophakic CME without systemic disease may be classified into three types (Fig. 4.5) [3]. In type 1, the amplitudes of the OPs are reduced compared to that of the normal fellow eye, but the amplitudes of the a-waves and b-waves are nearly normal. In type 2, the amplitude of the OPs and b-waves are reduced, but the a-wave is normal; and in type 3 the amplitude of the OPs, a-waves, and b-waves are reduced.

The distribution of the best-corrected visual acuity for each type of CME is shown in Fig. 4.6. The difference in visual acuity between types 1 and 3 is statistically significant.

Fluorescein angiograms and focal macular ERGs in eyes with CME and after the resolution of CME are illustrated for three representative cases in Figs. 4.7 to 4.9. Case 1 (Fig. 4.7) was a 51-year-old man who had had cataract surgery on his right eye with implantation of a posterior chamber lens. His preoperative visual acuity of 0.1 improved to 0.9 postoperatively but then gradually decreased to 0.6 five months later. Fluorescein angiography disclosed CME in the right eye. The OPs of the focal macular ERGs were selectively reduced (type 1) compared with that of the normal fellow eye. Six months later the CME resolved spontaneously, and fluorescein angiography disclosed a

Fig. 4.5. Focal macular ERGs recorded from representative patients with types 1, 2, and 3 pseudophakic CME.The stimulus spot was 10° in diameter. (From Miyake et al. [3], with permission)

Fig. 4.6. Distribution of best-corrected visual acuity in patients with types 1, 2, and 3 aphakic or pseudophakic CME. The difference between types 1 and 3 is statistically significant (P = 0.0072). (From Miyake et al. [3], with permission)