Ординатура / Офтальмология / Английские материалы / Electrodiagnosis of Retinal Disease_Miyake_2005

Because there are only a few reports on electrophysiological changes in eyes with a choroidal detachment, it is important to review the common EOG findings in patients with choroidal detachment [3]. When compared to the normal fellow eye, the EOG base value is not significantly reduced in eyes with rhegmatogenous retinal detachment. However, once choroidal detachment is associated with retinal detachment, the base value decreases significantly (Fig. 3.17). The base value amplitudes are shown in Fig. 3.18 as a function of the rhegmatogenous retinal detachment in 28 eyes without choroidal detachment (group 1) and 11 eyes with it (group 2). Most eyes without choroidal detachment have normal or increased base values, whereas all eyes with choroidal detachment have markedly reduced base values.

There is no significant correlation of the base value amplitude with the intraocular pressure or the extent of the choroidal detachment (Fig. 3.18).

Selective reduction of the EOG base value is also seen with hypotonic retinopathy caused by blunt trauma [4]. In such eyes, the extreme low intraocular pressure may lead to hypotonic maculopathy. The choroidal detachment is often present, although it may not always be detected ophthalmoscopically. The reason the base value does not decrease in eyes with a recent retinal detachment but does so in eyes with choroidal detachment is not known. However, these results indicate that contact between the retinal photoreceptors and RPE is less important than contact between the choroid and the RPE for generating the standing potential.

Fig. 3.17. A Electrooculogram (EOG) of a patient with unilateral rhegmatogenous retinal detachment and a normal fellow eye. B EOG of a patient with unilateral rhegmatogenous retinal detachment associated with choroidal detachment and a normal fellow eye. In each EOG, the black and white circles indicate the normal fellow eye and the affected eye, respectively

References

1.Yonemura D, Kawasaki K (1979) New approaches to ophthalmic electrodiagnosis by retinal oscillatory potential, drug-induced responses from retinal pigment epithelium and cone potential. Doc Ophthalmol 48:163–222

2.Miyake Y (1974) Electro-oculographic changes in retinal arterial occlusion and its analysis. Acta Soc Ophthalmol Jpn 78:311–323

Fig. 3.18. Base value and extent of retinal detachment without (group 1) and with (group 2) choroidal detachment. The base value amplitude is expressed as a percentage of the amplitude in the normal fellow eye. The number expressing the extent of retinal detachment represents the detached quadrant (4 indicating total retinal detachment). Dotted zone indicates the range (± SD) of control baseline values obtained by recording base values for the left versus the right eyes of 30 normal subjects. (From Miyake et al. [3], with permission)

3.Miyake Y, Akiyama K, Sugita S, Horiguchi M (1993) Electrophysiologic detection of choroidal detachment in eyes with rhegmatogenous retinal detachment. Retina 13:234–237

4.Nuno Y, Tanikawa A, Kachi S, Terasaki H, Miyake Y (2001) Recovery of visual function following surgery for persistent hypotony maculopathy secondary to traumatic cyclodialysis. Clin Ophthalmol Jpn 55:1853–1957

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]. Clinically, 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 endophthalmitis 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 vitrectomy 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.

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 enlargement; and it affects young women. These symptoms 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 idiopathic 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 abnormalities depending on the extent of the visual field loss. In unilateral cases, the ERG of the

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 indicate 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

Moreover and importantly, multifocal ERGs may be used to detect subclinical retinal dysfunction 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 subjective static visual fields have recovered normal sensitivities at almost all locations [7].

Diffuse unilateral subacute neuroretinitis (DUSN) [8] is caused by an unidentified species of nematodes that may wander in the subretinal space for 4 years or longer and cause progressive 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 individual. 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 moderately 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 initially by rapid loss of visual function and alterations of the ERGs, suggesting inner retinal abnormalities. At a more advanced stage, the

loss of ganglion cells (optic atrophy) and narrowing 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 possible 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 fullfield ERGs were moderately reduced, and the mixed rod–cone ERG had a negative configuration (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 nematode was detected ophthalmoscopically and was photographed by scanning laser ophthalmoscopy (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.