Abstract
Purpose:
To investigate visual function and retinal structure in suspected carriers of choroideremia using clinical methods, and high-resolution imaging techniques.
Methods:
Three symptomatic suspected carriers of choroideremia from one family aged 24, 59 and 62 yo and nine healthy age-matched controls with normal logMAR letter acuity and no observed ocular abnormalities, were included in the study. The youngest carrier was examined two-years ago and re-examined this year. Visual field and dark adaptation were examined with standard Humphrey VFA. Images of retinal layers and the cone mosaic of the fovea, para- and perifoveal regions were obtained with the Heidelberg Spectralis OCT and the Kongsberg Adaptive Optics Ophthalmoscope II, respectively. The subject’s eye was dilated and accommodation suspended with Cyclopentolate 1% prior to imaging.
Results:
All the carriers had normal logMAR letter acuity. A ring-shaped visual field loss and poorer rod dark adaptation was observed in all three carriers (mean deviation >12.02 dB difference and >0.4 log units difference, respectively, as compared with age-matched controls). OCT showed intact retinal layers in the central 5 deg of the 24 yo and the central 2-3 deg of the 59 yo and 62 yo carrier. Beyond this point the layers of outer and inner segments, external limiting membrane and outer nuclear layer merged in to one. Foveal retinal thinning was observed in the 24 yo and 59 yo as compared with age-matched controls, but not in the 62 yo. All three have patches of pigmentary abnormalities in the periphery. The 24 yo showed a marked change over a two-year periode. The region of intact retinal layers was 1 deg smaller and foveal and parafoveal retinal layers were nearly 20 um thinner than two years ago. Her patches of pigmentary abnormalities seemed unchanged. Visual sensitivity (mean deviation) was reduced by 2 dB. AO images revealed reduced cone density as compared with normal controls and loss of reflective cones beyond the central parts corresponding with findings on OCT images.
Conclusions:
Changes in retinal structure in female carriers of choroideremia progress over time and are clearly visible both in OCT and AO images. Loss of sensitivity is seen both with standard visual field testing and dark adaptation. The latter indicates a greater loss of rods in peripheral parts.