Abstract
Purpose: :
To evaluate the correlations of structural retinal damage (cystic space) with the electrical (ERG) and psychophysical function (visual field) and to search for trends with age.
Methods: :
Retrospective analysis of 14 genetically confirmed XLRS patients aged 7 to 23 years with Goldmann visual fields, Stratus OCT 3 and Ganzfeld-ERG (DTL-electrodes, Nicolet Spirit, ISCEV standard). Retinal structure approx. 1 mm peripheral from the fovea was analysed quantitatively using OCT 3 and image processing. Structural damage was evaluated by the mean ratio of cystic to normal retinal area as obtained from 6 OCT scans in star pattern centered on the fovea and disregarding the central third. Visual field area was calculated from the coordinates of detection of I/4e targets. Electrical function was obtained by measuring b-wave and a-wave amplitude elicited by scotopic standard flashes.
Results: :
Cysts occupied 10% to 40% of the retinal area in OCT without an obvious age-trend. Visual field area ranged from ~15% to normal , typically showing smaller fields for younger patients. Scotopic ERG b-waves measured between about 15% and normal values, scotopic a-waves 25% to 200% of normal and the b/a-ratio ranged from 0.7 to 1.9. Whereas absolute ERG amplitudes showed no clear trend, the b/a-ratio decreased with subject’s age. The ratio of cysts to retina showed a weak inverse correlation with visual field area but neither with b-wave nor b/a-ratio. No correlation was found between visual field and the above ERG parameters.
Conclusions: :
Although using a simplified approach, we were able to show some link of the amount of cystic retinal changes in XLRS with light sensitivity as measured by visual field with I/4e. It was difficult however, to link either of the two parameters with ERG b-wave or b/a-ratio possibly due to the large distribution of the latter. With age, a-waves appeared to deteriorate less than b-waves. The pathophysiological effects of the cysts still remain to be investigated.
Keywords: electroretinography: clinical • visual fields • retinal degenerations: hereditary