Oscillatory potentials, flash and pattern-reversal electroretinograms in amblyopia

Evaluation of amblyopic eyes with optical coherence tomography angiography and electrophysiological tests

Purpose

To investigate the structural and functional changes of the retina and optic nerve in amblyopia.

Methods

Eighteen patients with unilateral anisometropic amblyopia and 27 age-matched healthy controls were involved in this study. All patients underwent optical coherence tomography angiography (OCTA), pattern visual evoked potential (pVEP), and flash electroretinogram (fERG).

Results

There was no statistically significant difference in terms of the foveal avascular zone (FAZ), perifoveal superficial density, whole superficial density, parafoveal deep density, perifoveal deep density among the eyes (P > 0 0.05). Significant differences were found only in superficial capillary plexus (SCP) vessel density in whole (P = 0.029) and parafoveal (P = 0.008) image. In electrophysiological tests, while VEP latencies of the amblyopic eyes increased compared to nonamblyopic eyes and controls (P = 0.027), VEP amplitudes decreased in amblyopic and nonamblyopic eyes compared to controls (P = 0.01), amplitudes of the rod (P = 0.027) and cones (P < 0.001) also decreased in amblyopic eyes compared to nonamblyopic and healthy eyes. When we assessed the correlation between the parameters of OCTA and electrophysiological test, only a significant correlation was found between parafoveal SCP vessel density and VEP amplitudes (r = 0.341).

Conclusion

We found a significant decrease only in SCP vessel density of the OCTA parameters in amblyopic eyes compared to healthy eyes. We detected a significant relationship between parafoveal SCP vessel density and VEP parameters, which might be associated with the underlying pathophysiology of the amblyopia.

Organic visual loss measured by kinetic perimetry and retinal electrophysiology in children with functional amblyopia

PURPOSE

To demonstrate an organic (retinal) amblyogenic defect in functional amblyopes not responding to treatment.

METHODS

Twenty-four children (Mean age: 5.9 ± 1.8 years; range: 4-10 years) with functional amblyopia were recruited for this study. All these children underwent complete ophthalmic and orthoptic evaluation. In addition, Kinetic Goldman Visual Fields (KGVF), Spectral Domain Optical Coherence Tomography (SD-OCT), full field flash electroretinograms (ffERG) and multifocal electroretinograms (mfERG) were also performed. Ratios were subsequently derived by comparing the amplitudes obtained from the amblyopic eye (AE) to the good eye (GE) for the a- and b-waves of the ffERG, as well as for the ring analysis of the mfERG.

RESULTS

KGVF showed a central scotoma of varying size (3°-7°) and density (absolute to relative), with increasing target size in 14/24 patients whose best post-treatment vision in the AE ranged from 20/100 to 20/40. The scotoma decreased in size and density with improving vision until a plateau of recovery was reached. The remaining 10/24 patients with a vision ≥ 20/30 showed no scotoma. SD-OCT showed no significant difference between the AE and GE. ffERG and mfERG were obtained in 18/24 patients. The ffERG AE/GE ratio was abnormal in 7 patients, 5 of which had large scotomas on KGVF. The mfERG ring 1 AE/GE ratio was significantly (p < .05) attenuated in 9/18 patients out of which 3 were no longer amblyopic. However, there was no significant difference (p > .05) in ring 1 AE/GE amplitude ratio between those who achieved 20/50-20/40 (.81 ± .26) and those with ≥ 20/25(.86 ± .25).

CONCLUSIONS

The combined findings of central scotoma on KGVF and mfERG anomalies in patients who did not achieve optimal vision with treatment suggest an underlying organic defect impairing macular function.

Multifocal electroretinography in amblyopia

PURPOSE

To identify whether there are functional abnormalities in the retina of amblyopic eyes using multifocal electroretinography (mfERG).

METHODS

This is a prospective study of patients ≥ 7 years of age identified with unilateral amblyopia (strabismic or anisometropic). Multifocal ERG and flash ERG were performed to compare parameters between the amblyopic and non-amblyopic fellow eyes. A complete analysis of the five ring averages was done including the central ring.

RESULTS

Thirty-eight patients were included: mean age was 14.3 ± 7.3 years; 18 patients were strabismic and 20 were anisometropic. Amblyopic eye responses across the rings in multifocal ERG were diminished compared with fellow non-amblyopic eyes with significant differences detected in the central rings (p = 0.001). On the other hand, flash ERG did not show any consistently significant differences. When divided by severity, amplitudes of central rings were significantly lower in severely amblyopic eyes compared with non-amblyopic eyes (p = 0.001), while in mild amblyopia, no significant differences were observed. No significant difference was observed between anisometropic and strabismic amblyopic eyes.

CONCLUSIONS

Using multifocal ERG, significantly decreased amplitudes were observed in amblyopic eyes compared with normal fellow eyes in the central ring. This correlated with the severity of amblyopia. No difference was observed when comparing the two groups of amblyopia (strabismic and anisometropic). Those findings may help clarify the pathophysiology of amblyopia better and open the door for new objective ways to monitor the response to amblyopia treatment but this needs to be further studied.

Evaluation of Amblyopic Scotoma by Electrophysiological Examinations and Computerized Perimetry

To evaluate amblyopic scotoma and the most affected neural cells in suppressive phenomena, eight patients with deep amblyopia from strabismus (visual acuity of the amblyopic eye between 4/50 and 2/10) underwent a pattern electroretinogram (PERG), pattern visual evoked potential (VEP), and event-related potential (ERP) from visual stimuli, and computerized perimetry. The results of stimulation of the amblyopic eye, the leading eye and the leading eye penalized by Ryser filters were compared statistically. Computerized perimetry was used to quantify the depth and amplitude of the amblyopic scotoma. All electrophysiological potentials were reduced in amplitude and the implicit times of VEP and ERP were longer when stimulating the amblyopic eye compared to the leading eye. Only in PERG the penalization induced major changes. Our data suggest that the important suppressive phenomena present in the squint amblyopic eye involve not only the occipital cortex, but also the cognitive areas.

Prognostic Value of Visual Evoked Responses in Childhood Amblyopia

We assessed the possible clinical utility of pattern reversal visual evoked potentials in predicting the success of pleoptic treatment. Thirty amblyopic children –- 16 strabismic, 11 anisometropic and three of refractive type (in all cases the amblyopia was monocular) –- and ten children without amblyopia (control group) were examined by conventional psychometric methods. Visual evoked potentials (VEP) to pattern reversal stimulation were also recorded. The amblyopic group was treated with occlusion of the preferred eye for three to six months. Psychometric and VEP tests were repeated in 15 amblyopic children after the treatment. The pre-treatment VEP amplitude side-differences (between amblyopic and better fellow eye) were significant, with first positive wave, P1, being invariably lower on the amblyopic side. We correlated the side-differences in visual acuity with the corresponding side-differences in amplitude and latency of the P1 wave. In the former the correlation coefficient was r = 0.47 (p<0.01), and in the latter r = 0.65 (p<0.01). Latency was prolonged in the eyes with significantly reduced visual acuity in which the wave form was also typical for amblyopia. We then correlated the difference between pre- and post- treatment visual acuity of the amblyopic eye with the pre- and post-treatment difference in amplitude (correlation coeff. r-0.51 (p=0.05)) and latency of the P1 wave (correlation coeff. r=0.40 (p>0.05)). Finally, by correlating the pre- and post-treatment difference in visual acuity with the pretreatment P1 amplitude and latency (for the former, there was no regular interdependence, and for the latter r=-0.64 (p=0.01)), we tried to test our assumption that an alteration of VEP indicates poor visual rehabilitation of the amblyopic eye. Although the correlation was not unanimous, this study showed that VEP recording may still serve as an extra aid in predicting the therapeutic outcome in amblyopic children.

Decreased severity of age-related macular degeneration in amblyopic eyes

AIM

To evaluate whether people with age-related macular degeneration (AMD) and a history of amblyopia have equal severity of AMD in both eyes.

METHODS

Billing records were used to locate all people with a history of amblyopia and AMD evaluated between 1 January 2003 and 1 June 2015 at a single ophthalmology institute. Two ophthalmic graders blinded to amblyopia status determined the severity of AMD in each eye using fundus photos and a validated grading scale.

RESULTS

A total of 14 people were found to have AMD and a documented history of amblyopia. Average patient age was 77.0 years and average best corrected visual acuity was 20/160 in eyes with a history of amblyopia and 20/40 in fellow eyes without amblyopia. Eyes with a history of amblyopia were found to have a lower AMD severity score (mean lower score: -1.38; paired t-test P=0.019). Of the 11 people with asymmetric disease severity, 10 individuals had worse AMD in the non-amblyopic eye while one person had worse AMD in the amblyopic eye (P=0.0067).

CONCLUSIONS

Our pilot study suggests that eyes with a history of amblyopia may manifest decreased severity of AMD compared with non-ambylopic eyes in the same patient. Further research is warranted to investigate this clinical observation.

Structural and functional comparison of the persistent and resolved amblyopia

PURPOSE

To assess structural or functional differences of the retina among subjects with persistent and resolved amblyopia.

METHODS

Fourteen eyes with persistent amblyopia that did not reach normal visual acuity (VA) levels (≤0.1 LogMAR) despite amblyopia treatment, 18 eyes with resolved amblyopia, and 16 eyes of 16 normal subjects were included. All subjects underwent optical coherence tomography (OCT), pattern visual evoked potential (PVEP), and pattern electroretinography (PERG) evaluation.

RESULTS

There was no significant difference in foveal thickness, foveal volume, macular volume, ganglion cell layer thickness, and total and sectorial retinal nerve fiber layer measurements among three groups (p > 0.05). Foveolar thickness was significantly increased in both resolved and persistent amblyopia groups compared with the control group (p = 0.031). However, there was no difference between amblyopic groups (p = 0.98). Although, in the PVEP study, N75 implicit time was found significantly prolonged in both amblyopia groups (p = 0.046), there were no significant differences in P100 implicit time and amplitude among the groups (p > 0.05). PERG amplitude of the persistent group was significantly lower than that of the control group (p = 0.003). There were no significant differences in P50, N95 implicit times among groups (p > 0.05).

CONCLUSIONS

In our study, the only significant difference between persistent and resolved amblyopia groups was the initial VA. Neither OCT nor electrophysiological examinations were found to be useful in order to explain why some cases were resistant to the treatment for amblyopia.

The morpho-functional evaluation of retina in amblyopia

PURPOSE

To investigate the morphological or functional differences of retina in amblyopia.

MATERIALS AND METHODS

Forty-one patients with unilateral strabismic, anisometropic or combined amblyopia were included in the study. A control group was composed of 16 normal children. All participants were tested with optical coherence tomography (OCT) and pattern electroretinography (PERG). The findings from amblyopic and nonamblyopic eyes were compared among the amblyopic groups. Also, amblyopic and nonamblyopic eyes were compared with the healthy control eyes.

RESULTS

No significant difference was found in OCT parameters for amblyopic and nonamblyopic eyes among the amblyopic groups (p > 0.05). In the combined and anisometropic groups, ganglion cell complex (GCC) was found to be significantly increased in both amblyopic and nonamblyopic eyes compared to the control group (p < 0.05). In strabismic amblyopia, significant reduction in GCC thickness and increase in foveal thickness were found, compared to nonamblyopic eyes (p = 0.019, p = 0.08). There were no significant differences in PERG amplitude and latency between the amblyopic and the nonamblyopic eyes in amblyopic groups (p > 0.05). PERG amplitude in amblyopic eyes was found to be significantly decreased compared with that in normal eyes (p < 0.05). When the nonamblyopic eyes were compared with the control group, only the anisometropic amblyopia group demonstrated significant reduction in amplitude and prolongation in latency (p = 0.002, p = 0.026).

CONCLUSION

We found no significant differences in morphological and functional measures among amblyopic groups. However, we detected significant differences in the retinal function and morphology of both amblyopic and nonamblyopic eyes compared with healthy control eyes.

Macular and nerve fiber layer thickness in amblyopia: the Sydney Childhood Eye Study

PURPOSE

To examine macular and peripapillary retinal nerve fiber layer (RNFL) thickness in amblyopia.

DESIGN

Population-based cross-sectional study.

PARTICIPANTS

Of 4118 children examined in the Sydney Childhood Eye Study (incorporating the Sydney Myopia Study) from 34 randomly selected primary schools and 21 secondary schools from 2003 to 2005, 3529 (85.7%) were included in this analysis. The median age of the 2 samples was 6 years (n = 1395) and 12 years (n = 2134), respectively.

METHODS

A detailed eye examination was conducted on all children, including determination of best-corrected visual acuity (logarithm of the minimum angle of resolution [logMAR]), autorefraction (RK-F1 autorefractor, Canon, Tokyo, Japan) after cyclopentolate (1%), cover testing to identify strabismus, and optical coherence tomography (StratusOCT, Carl Zeiss Meditec, Dublin, CA) through dilated pupils to obtain macula and peripapillary RNFL thickness. Amblyopia was defined as best visual acuity <0.3 logMAR units not explained by any obvious underlying eye or visual pathway abnormalities. Anisometropia was defined as an interocular difference of at least 1.0 diopter of the spherical equivalent refraction.

MAIN OUTCOME MEASURES

Macular and peripapillary RNFL thickness.

RESULTS

Amblyopic eyes had slightly greater foveal minimum thickness than the normal fellow eye (by 5.0 microm; 95% confidence interval 0.1-9.9) and right eyes of non-amblyopic children (by approximately 10 microm), both P<0.05. This was more pronounced in 6-year-old children (6.9 microm) than 12-year-old children (4.2 microm). Amblyopic eyes also had slightly thicker central macula (1 mm diameter region) in both comparisons, although these differences were not statistically significant. The inner macular ring (outer radius 1.5 mm) was thinner in amblyopic than normal fellow eyes. Peripapillary RNFL thickness was not significantly different between amblyopic and normal fellow eyes or normal eyes of non-amblyopic children.

CONCLUSIONS

In children aged predominantly 6 and 12 years, central macular thickness may be increased in eyes with amblyopia, although it is uncertain if this precedes or follows the development of amblyopia. No differences in peripapillary RNFL thickness were found when compared with normal eyes.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Receptor and neural visual readaptation after exposure to colored flash

The time needed to recover optokinetic nystagmus or electroretinography complexes after a glare inducing flash was measured to study the receptor and neural visual readaptation. Electroretinographs and optokinetic nystagmus were evoked with low intensity stimuli. The light from a flash tube was filtered with an interference filter (Tmax = 536 or 622 nm) and evenly distributed into a Goldmann hemisphere observed by the subject. The Recovery of the amplitude of the a-wave of the electroretinography is quicker than the recovery of optokinetic nystagmus after a low intensity glare inducing flash. The recovery time was shorter for a red than for a green flash of equivalent dose for both recovery modalities. The time difference between electroretinography a-wave and optokinetic nystagmus recovery was the same and independent of glare inducing flash wavelength. The recovery of the amplitude of the a-wave of the electroretinography was quicker than the recovery of optokinetic nystagmus after a low intensity glare inducing flash. This time difference between the recovery modalities may in part be due to the difference between the physiological stimuli used, but it is believed that most of the time difference is because the recovery of optokinetic nystagmus monitors more of the afferent visual pathway with complex post receptor neural mechanisms than the recovery of the a-wave.

Pupillary responses in amblyopia

Relative afferent pupillary defects (RAPD) were detected in 32.3% of patients with amblyopia by a modification of the swinging flashlight test and the synoptophore. After consideration of various clinical investigations the significant factors identified in patients showing a RAPD were: anisometropia, early age of onset where strabismus was present, level of visual acuity following treatment, longer period of occlusion therapy. These points bear similarities to the results of pattern electroretinograms (PERG) in amblyopes, and the possibility of the causative defect being at ganglion cell level is discussed. The effect of occlusion treatment cannot be predicted from the presence or absence of a RAPD.

A review of the clinical applications of the pattern electroretinogram

The pattern electroretinogram (PERG) has recently been introduced as a clinical procedure. It has been thought by many to represent activity of the retinal ganglion cells, although this is still a matter of contention. The exciting prospect of a selective test of ganglion cell function led to the application of the PERG in a variety of ophthalmological conditions. In the course of these investigations the PERG was found to be diminished in cases of maculopathy, optic atrophy, optic neuritis, toxic optic neuropathy, neurotransmitter disorders, glaucoma and ocular hypertension and in retinal vascular disorders such as diabetes. It was also affected in some cases of amblyopia. This paper briefly describes the techniques used to record the PERG and reviews current literature pertaining to its clinical application.

Short latency visual evoked potentials in functional amblyopia shown using moving topography

The conduction from the eye to the visual cortex through the brainstem was investigated in 43 cases of functional amblyopia by means of moving topography of short latency visual evoked potential (SVEP). Anomaly of the SVEP such as a defect of the main component and remarkable reduction of amplitude was found in cases with severe amblyopia whose visual acuity was less than 0.5. The incidence of abnormal SVEP was recognized in 44% of anisometropic amblyopia (18 cases), 52% of strabismic amblyopia (15 cases), and 50% of deprivation amblyopia (10 cases). The results suggested a reduction of electric activity in the subcortical visual pathway including transmitting nuclei.

The pattern electroretinogram

Physiological experiments and the exploitation of clinical conditions have provided compelling evidence that retinal ganglion cells and other inner retinal structures generate the pattern ERG (PERG). As an increasing number of clinical reports have been published some contradictory findings have been reported. These may be ascribed to variation in recording and measuring techniques. The PERG consists of two major portions, the early positive and the following negative component which can be investigated separately if the stimulus conditions allow isolated (or "transient") responses to be recorded. Care has to be taken in positioning the reference electrode, maintaining accurate refraction, and the influence of pupil size must be considered. Furthermore the PERG is contaminated by a luminance component which may be generated in the outer retina. The size of this increases with low spatial frequency (large check-sizes) and high mean luminance. The PERG permits the examination of an additional level of the retina and helps the understanding of pathophysiology of various eye diseases, and is of clinical importance in routine diagnosis and assessment. In glaucoma the PERG amplitude is often reduced before it is possible to detect a scotoma and it is therefore an important prognostic indicator in patients with ocular hypertension. In diabetic retinopathy, retinal ischaemia sufficient to lead to the pre-proliferative state can be demonstrated. The PERG also has a major clinical role in examining localised retinal pathology. If combined with VECP recording, it greatly extends the interpretations possible, since not only can damage to the optic nerve be detected by both tests, but the normal PERG in the presence of an abnormal PVECP implies that the losses are confined to the central pathway.