PURPOSE To test the hypothesis that eyes with amblyopia may have thicker retina, retinal nerve fiber layer thickness (RNFLT) was investigated in patients with unilateral amblyopia. METHODS Thirty-eight patients with unilateral amblyopia were studied. Among them, 20 patients had amblyopia with strabismus and 18 had refractive amblyopia without strabismus. Nineteen of 38 had anisometropia of 2.0 D or more. In addition, 17 patients with anisometropia of 2.0 D or more but without amblyopia were enrolled as control subjects. RNFLT was measured by optical coherence tomography with scan pattern "Nerve Head 2.0R" (Carl Zeiss Meditec, Dublin, CA). Average RNFLT was multiplied with their corresponding scan circumferences to estimate the integral values of the total RNFL area (RNFLT(estimated integrals)). RESULTS In all 38 patients with unilateral amblyopia, the difference in RNFLT and in RNFLT(estimated integrals) between the amblyopic eyes and the normal fellow eyes were statistically significant. Multivariate regression analysis with adjustment for axial length, spherical equivalence, age, and sex indicated significant differences as well. In the group of strabismic amblyopia, the difference in RNFLT and in RNFLT(estimated integrals) between the amblyopic eyes and the normal fellow eyes did not reach statistical significance. However, in the group of refractive amblyopia, the difference in RNFLT and in RNFLT(estimated integrals) between the amblyopia eyes and the normal fellow eyes both had a statistical significance. In the 19 patients with anisometropic amblyopia, the difference in RNFLT and in RNFLT(estimated integrals) between the amblyopic eyes and the normal fellow eyes were statistically significant. In the control group of 17 patients with nonamblyopic anisometropia, the difference in RNFLT and in RNFLT(estimated integrals) between both eyes did not reach statistical significance. CONCLUSIONS RNFLT may be affected by refractive amblyopia, but further histopathologic confirmation is needed.

Retinal nerve fiber layer thickness in unilateral amblyopia.

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.

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The pattern electroretinogram

Macular and Nerve Fiber Layer Thickness in Amblyopia: The Sydney Childhood Eye Study

Amblyopia

Objective To compare the thickness of the retinal nerve fiber layer (RNFL), the macular volume, and the macular thickness of the amblyopic eye with those of the non-amblyopic eye in patients with unilateral strabismic amblyopia using optical coherence tomography (OCT). Patients and methods OCT was performed for 14 patients with unilateral strabismic amblyopia who had no neurologic disease. Nine male and 5 female patients, whose ages ranged from 5 to 18 years, were enrolled in the study. The RNFL thickness average analysis program was used to evaluate mean superior, inferior, temporal, and nasal thickness. The data for all clock quadrants (12 values averaged) were identified as the overall RNFL. The retinal thickness and volume analysis program was used to evaluate macular scans. Data were compared using the Mann-Whitney U test. Results The mean age (+/- standard deviation) was 10.43 years (+/- 4.09 years). There were 6 right eyes and 8 left eyes with amblyopia; this group had a mean visual acuity (+/- standard error) of 0.3 (+/- 5.70). OCT parameters including the RNFL thickness in all quadrants, overall RNFL thickness, macular thickness, and macular volume showed no significant differences between the two groups (P > .05). Conclusion Assessment of RNFL thickness, macular thickness, and macular volume with OCT revealed no difference between the two eyes of patients with unilateral strabismic amblyopia.

Thickness of the retinal nerve fiber layer, macular thickness, and macular volume in patients with strabismic amblyopia.

The authors have recorded pattern ERGs in 62 amblyopic children. In 12 who were occluded up until the morning of the test, the occluded eye response was reduced, and the ratio ([response amplitude of amblyopic eye]/[response amplitude of fellow eye]) was greater than unity. In the remainder, the ratio was considerably less than unity. Ratios of less than 1.0 were found for anisometropic, esotropic, exotropic, and microtropic amblyopes. The ratio was not related to visual acuity or to squint but was higher in those children whose vision was improved by orthoptic treatment. In a group of older children recalled to the clinic, the ratio was 1.0 in those who had maintained equal visual acuity and was less than unity in those children whose acuity had regressed after treatment, or had not improved during treatment. The reduction of the pattern ERG in amblyopes occurs without a corresponding reduction in the focal ERG. In adult amblyopes, the relationship between loss of acuity, loss of grating contrast sensitivity, and the reduction in the PERG is complex and may differ according to the type of amblyopia.

G B Arden

Papers

Pattern ERG in amblyopia.