Electrophysiological assessment of aphakic cystoid macular oedema

Surrogate electroretinographic markers for assessing therapeutic efficacy in the retina

Visual acuity remains the primary surrogate marker for clinical trials in ophthalmology (and the primary outcome for most US Food and Drug Administration applications) due to its long history, ease of measurement and clear relationship to clinically meaningful characteristics of daily life. However, treatment trials are being planned for diseases that are currently untreatable where visual acuity may not be the most appropriate outcome measure. Specialized electroretinographic tests can be powerful surrogate markers in such trials. The selection of outcome measures and surrogate markers depends in part on whether the goal is to preserve remaining vision in a progressive retinal degeneration or to improve vision in an eye that has already undergone extensive degeneration. Among the electroretinographic tests available are those involving the whole retina (full-field electroretinographic), the posterior pole (pattern electroretinographic) or focal areas within the macula (multifocal electroretinographic). The advantages and disadvantages of each will be discussed along with selected applications of each test to a specific category of disease.

Cystoid macular edema

We review the epidemiology, pathophysiology, and etiology of cystoid macular edema (CME). Inflammatory, diabetic, post-cataract, and macular edema due to age-related macular degeneration is described. The role of chronic inflammation and hypoxia and direct macular traction is evaluated in each case according to different views from the literature. The different diagnostic methods for evaluating the edema are described. Special attention is given to fluoroangiography and the most modern methods of macula examination, such as ocular coherence tomography and multifocal electroretinography. Finally, we discuss the treatment of cystoid macular edema in relation to its etiology. In this chapter we briefly refer to the therapeutic value of laser treatment especially in diabetic maculopathy or vitrectomy in some selected cases. Our paper is focused mainly on recent therapeutic treatment with intravitreal injection of triamcinolone acetonide and anti-VEGF factors like bevacizumab (Avastin), ranibizumab (Lucentis), pegaptamid (Macugen), and others. The goal of this paper is to review the current status of this treatment for macular edema due to diabetic maculopathy, central retinal vein occlusion and post-cataract surgery. For this reason the results of recent multicenter clinical trials are quoted, as also our experience on the use of intravitreal injections of anti-VEGF factors and we discuss its value in clinical practice.

Pattern electroretinography and visual evoked potentials in optic nerve diseases

BACKGROUND

To evaluate transient pattern electroretinography (PERG) and pattern visual evoked potential (VEP) for the diagnosis, differential diagnosis and follow-up of optic nerve diseases.

METHODS

Twenty-nine consecutive patients (14 female, 15 male) with the diagnosis of ischaemic optic neuropathy (n=14) and optic neuritis (n=15) were included in this study. Mean age of the patients with ischaemic optic neuropathy was 63.3+/-3.3 (60-78) years and the mean age of the patients with optic neuritis was 28.3+/-8.4 (19-43) years. In each patient ophthalmological examination and systemic evaluation were done and VEP and PERG were recorded. As a control group, VEP recordings of 35 healthy subjects were included.

RESULTS

In the ischaemic optic neuropathy group (group 1), mean VEP amplitude (+/-SD) (1.96+/-0.95 microV) was found to be decreased significantly in the affected eyes in comparison to the control group and the unaffected eyes. The delay in latency (116.3+/-20.14 msec in the affected eyes compared with 101.31+/-6.19 msec in unaffected eyes) was statistically significant when compared with the healthy subjects. In the optic neuritis group (group 2), VEP amplitude was decreased (4.13+/-4.04 microV vs 6.97+/-3.35 microV and 6.97+/-4.43 microV) and latency was increased (122.59+/-20.09 msec vs 101.31+/-6.19 msec and 108.76+/-13.57 msec) in affected eyes significantly in comparison to the unaffected eyes and control group, respectively. Even though there were no significant differences for P50 latency and N95/P50 ratios between affected and unaffected eyes in both groups, N95 amplitude decreased significantly in the affected eyes of the ischaemic optic neuropathy patients and N95 latency was found to be decreased in optic neuritis patients. There was no correlation between VEP and PERG findings in both groups.

CONCLUSION

VEP amplitude decreased significantly in ischaemic optic neuropathies while latency delay was more significant in patients with optic neuritis. PERG findings showed decreased N95 amplitude in ischemic optic neuropathy without associated latency changes.

Pattern visual evoked potentials in eyes with disc swelling due to cat scratch disease-associated neuroretinitis

PURPOSE

To evaluate optic nerve function by pattern visual evoked potentials (VEPs) in eyes with optic disc swelling due to neuroretinitis associated with cat scratch disease (CSD).

METHODS

Four eyes of four patients with marked optic disc swelling resembling optic neuritis but diagnosed serologically as CSD received systemic steroid treatment. VEPs elicited by black and white checkerboard stimuli created on a TV monitor were recorded before the treatment.

RESULTS

The visual acuity (VA) in the affected eyes was decreased to 20/50 in two eyes and finger counting in two eyes at their initial visits. Ophthalmoscopic examination revealed neuroretinitis characterized by severe optic disc swelling, chorioretinal exudates, and macular edema in all eyes. Anti-Bartonella henselae serum antibody was markedly elevated in all patients confirming the diagnosis of CSD. The P100 of the transient VEPs was only mildly reduced without a delay in the implicit times in three eyes and only slightly delayed in the other eye. The steady-state VEPs were mildly reduced in two eyes and phase-reversed in other two eyes. The VA fully recovered after systemic steroid treatment in all patients.

CONCLUSIONS

Although all examined patients showed marked swelling of the optic disc and visual decrease, the pattern VEPs were not affected as severely as in idiopathic optic neuritis. However, the degree of change of the pattern VEPs varied among patients.

Reduced oscillatory potentials of the full-field electroretinogram of eyes with aphakic or pseudophakic cystoid macular edema

PURPOSE

To report reduced oscillatory potentials (OPs) in the full-field electroretinogram (ERG) of eyes with aphakic or pseudophakic cystoid macular edema (CME).

DESIGN

Observational case series.

METHODS

Bright white flash full-field ERGs were recorded from 19 eyes of 19 patients (ages, 53-84 years) with aphakic or pseudophakic CME. Seven of the cases had uncomplicated phacoemulsification (PE) with implantation of a posterior chamber intraocular lens (PC-IOL) and 6 had posterior capsular rupture during phacoemulsification and aspiration with implantation of a PC-IOL. Four additional patients had uncomplicated intracapsular cataract extraction (ICCE), and 2 had secondary anterior chamber intraocular lens after ICCE. Their fellow eyes without CME served as controls. Cystoid macular edema was diagnosed as clinically significant by slit-lamp examination and by fluorescein angiography. The grading for severity of CME was based on the fluorescein angiography. The visual acuity ranged from 20/200 to 20/16.

RESULTS

There were no significant differences in the mean amplitudes and implicit times of the a-waves and b-waves between the affected eyes and the fellow eyes. The mean summed amplitude of the OPs was significantly reduced in the affected eyes (P =.0003, Wilcoxon signed rank test). This decrease was strongly correlated with visual acuity (r =.779, P <.0001). The mean implicit time of the first OP was significantly delayed in the affected eyes (P =.0089, Wilcoxon signed rank test).

CONCLUSIONS

Because the peripheral retina contributes more significantly to full-field ERGs than the macula, the reduced OP amplitudes of the full-field ERGs in eyes with aphakic or pseudophakic CME suggest a functional impairment not only in the macula but also throughout the retina.

Pattern electroretinography (PERG) and an integrated approach to visual pathway diagnosis

The pattern electroretinogram (PERG) provides an objective measure of central retinal function, and has become an important element of the author's clinical visual electrophysiological practice. The PERG contains two main components, a positivity at approximately 50ms (P50) and a larger negativity at approximately 95ms (N95). The P50 component is affected by macular dysfunction with concomitant reduction in N95. The PERG therefore complements the Ganzfeld ERG in the assessment of patients with retinal disease. In contrast, the ganglion cell origins of the N95 component allow electrophysiological evaluation of ganglion cell function both in primary disease and in dysfunction secondary to optic nerve disease, where selective loss of N95 can be observed. Both macular dysfunction and optic nerve disease can give abnormalities in the visual evoked cortical potential (VEP), and the PERG thus facilitates more meaningful VEP interpretation. This review addresses the origins and recording of the PERG, and then draws on extensive clinical data from patients with genetically determined retinal and macular dystrophies, other retinal diseases and a variety of optic nerve disorders, to present an integrated approach to diagnosis.

Infrared scanning laser tomography of macular cysts

OBJECTIVE

To perform three-dimensional, noninvasive, quantitative analysis of cystoid macular edema and macular cysts using infrared scanning laser tomography and to correlate findings with visual acuity (VA) as a basis for interventional studies.

DESIGN

Cross-sectional, nonrandomized study.

PARTICIPANTS

Seventeen patients (29-86 years of age) with macular cysts associated with a broad spectrum of diseases.

INTERVENTION

Confocal infrared imaging with scanning laser tomography with the TopSS (790 nm) (Laser Diagnostic Technologies, San Diego, CA) with digitized images was used to perform three-dimensional, quantitative analysis of cysts in the central 5 degrees of the macula.

MAIN OUTCOME MEASURES

Measurements of macular cyst number, area, volume, depth, slope, height of the surrounding macular elevation, and correlation with VA.

RESULTS

Scanning laser tomography detected macular cysts in all patients. The number per patient ranged from 1 through 15. Cysts were accompanied by surrounding macular elevation in 16 patients (mean macular height, 216 microm). The area covered by cysts in the central 5 degrees was 0.087 to 0.969 mm2, and volume was 0.007 to 0.549 mm3. Visual acuity was significantly poorer in patients with greater cyst area (P = 0.0007), cyst volume (P = 0.0009), macular thickening (P = 0.0002), and cyst depth (P = 0.0013). Cyst number, average slope, and maximum slope, however, did not correlate significantly with VA. Grouping of macular cysts according to macular height and average cyst depth revealed that cysts in a more thickened retina were significantly deeper, had steeper slopes, and corresponded to worse VA. Macular height and average cyst depth were highly associated with each other, suggesting that in eyes with surrounding macular edema, cysts were deeper and may reflect more widespread tissue destruction. Individual confocal tomographic images provided additional information. Neither ophthalmoscopy nor fluorescein angiography delineated features such as retinal folds that suggested vitreous traction or changes in deeper layers that suggested occult choroidal new vessels.

CONCLUSIONS

Infrared scanning laser tomography is a rapid and noninvasive imaging method that provides quantitative analysis of macular cysts in addition to qualitative information not seen clinically. Because poor VA is related to severe involvement of the central retina, scanning laser tomography could provide an objective outcome measure for interventional studies.

Electroretinographic findings in Fuchs' heterochromic cyclitis

PURPOSE

Fuchs' heterochromic cyclitis (FHC) is an inflammatory disease of unknown aetiology. Although anterior segment signs and vitreous changes are well recognised, retinal features are unusual. To assess the extent of retinal involvement, we performed electrophysiological testing in a group of FHC patients.

METHODS

Retinal function was assessed by means of flash electroretinogram (ERG) using a Ganzfeld stimulus, and pattern electroretinogram (PERG) using a checkerboard stimulus of spatial frequency 0.5 and 1.0 cycle per degree reversing at 6 Hz. A total of 21 patients with unilateral, normotensive FHC with visual acuities of 6/5 to 6/9 were studied.

RESULTS

In the flash ERG, selective scotopic b-wave abnormalities occurred in 9 (43%) of 21 FHC eyes. Despite clear media and no history of ocular surgery, 7 patients showed abnormalities of the PERG.

CONCLUSIONS

These electrophysiological findings suggest subclinical damage to the inner retinal layers, but not involving the photoreceptors, in eyes with FHC.

Classification of aphakic cystoid macular edema with focal macular electroretinograms

We compared the amplitude and implicit times of the a-waves, b-waves, and oscillatory potentials of the focal macular electroretinograms of 30 eyes with aphakic cystoid macular edema and the healthy fellow eyes. Ten affected eyes were characterized by reduced amplitudes of the oscillatory potentials with normal a-wave and b-wave responses (type 1). Nine affected eyes had both reduced amplitudes of the oscillatory potentials and the b-waves (type 2). Ten affected eyes were characterized by reduced amplitude of the oscillatory potentials, the a-waves, and the b-waves (type 3). One eye could not be classified. Visual acuities were as follows: type 1, 0.55 (20/36.4); type 2, 0.31 (20/64.5); and type 3, 0.12 (20/166.7). The mean time between cataract surgery and the electroretinographic testing was significantly longer for type 2 and 3 eyes than for type 1 eyes. The differences in the electroretinographic responses between the affected eye and the normal fellow eye suggested either an increased severity or the stage of the cystoid macular edema.

Macular oscillatory potentials in humans. Macular OPs

Studies of the focal macular electroretinogram (ERG) have been made with special reference to oscillatory potentials (OPs) by using a fundus monitoring system in humans. Human macular OPs consist of 3 to 4 wavelets (mean peak interval, approximately 6.5 msec). The distribution of OPs in relation to those in a- and b-waves was studied. The amplitudes of a-waves, b-waves, and OPs of the upper macula were significantly larger than those of the lower macula. The distribution of OPs is relatively sparse in the fovea, becoming more dense than the a- and b-waves from the fovea toward the parafovea, and differing even more toward the perifovea. There was no statistical difference of amplitude in a- and b-waves between nasal and temporal macula. The amplitude of OPs in the temporal macula, however, was significantly larger than in the nasal macula. In some macular diseases, such as diabetic maculopathy, cystoid macular edema, or the convalescent stage of central serous chorioretinopathy, macular OPs were selectively reduced, leaving the a- and b-waves intact. Macular OPs can provide a new aspect of macular function and can be a sensitive indicator to assess that function in macular diseases.

The focal electroretinogram in the clinical assessment of macular disease

Focal electroretinograms (ERGs) were obtained from the fovea in 142 eyes with a variety of macular diseases and 50 age-matched eyes with acuity loss in which macular disease was ruled out. Across all eyes, the accuracy rate of discriminating macular disease from other causes of acuity loss was 87%. Among all eyes with macular disease, the sensitivity rate of the focal ERG to the presence of macular disease was 85%. Log focal ERG amplitude was significantly correlated with log Snellen acuity, except in those eyes with macular holes. The sensitivity rate increased to 94% when eyes with 20/40 or greater acuity and eyes with macular holes were excluded.