Frequency Doubling Technology Visual Field Loss in Fabry Subjects Related to Retinal Ganglion Cell Function as Explored by ERG and OSOME

Abstract

Purpose: This study aims to evaluate potential causes of FDT visual field loss in a selected group of Fabry subjects.

Patients and methods: This is a pilot observational study. Subjects were assessed during 2 visits. The following tests were performed: visual acuity, tonometry, optical coherence tomography (OCT) optic nerve scan, frequency doubling time (FDT) and threshold (SAP) VF, ERG, and Online Spectro-reflectometry Oxygenation Measurement in the Eye (OSOME). Results are compared across visits and, when indicated, interpreted against those collected on non-Fabry population matched for age and sex.

Results: The study population was composed of 3 males (34.3 ± 8.9 y.o.) and 5 females (46.4 ± 6.5 y.o). For all subjects, BCVA remained 6/6 OU throughout the study and OCT optic nerve scans were normal. FDT showed a defect in at least 1 quadrant for all participants, in contrast with SAP. FDT PSD value was found different vs SAP. For ERG, the i-wave (52.1 + 2.7 ms) and B-waves (31.6 ± 2.1 ms) peak times were significantly longer compared to a non-Fabry population (p < 0.05). Overall blood oxygenation varied from 61.3% ± 4% to 68.1% ± 4% at the second visit, suggesting a loss of capillary perfusion. Blood volume varied based on location (superior/inferior), eye tested (OD/OS) and time (visit 1/2). The range of values exceeds normal subjects findings (p < 0.05). Blood volume was correlated to FDT PSD value for the superior area of the optic nerve.

Conclusion: The results suggest that Fabry subjects present FDT deficits and abnormal ERG patterns that may be explained by a retinal dysfunction affecting retinal ganglion cells (RGCs), second to vascular alterations.

Keywords: Fabry disease; OSOME; electroretinography; retinal ganglion cells.

Figure 1

Typical corneal verticillata showing pigments and haze.

Figure 2

Bulbar conjunctival vessels tortuosities and micro-aneurysms.

Figure 3

The same blood vessel tortuosities may be seen on the external upper lid.

Figure 4

Arterioles and venules showing tortuosities.

Figure 5

Typical Fabry posterior sub-capsular cataract.

Figure 6

(A–D) Evolution of the visual field defects. (A) Patient A OD year 1- no defect; (B) patient A OD year 2- defect in 3 quadrants; (C) patient B OS year 1 - defect in 4 quadrants; (D) patient B OS year 2 – defect in 3/4 quadrants but more severe.

Figure 7

Example of a typical graph showing the relationship between PSD and blood volume.

Figure 8

Example of a typical graph showing the relationship between MD and blood volume.