ORIGIN OF TAPETAL-LIKE REFLEXES IN CARRIERS OF X-LINKED RETINITIS-PIGMENTOSA

Purpose. To determine the origin of the tapetal-like reflex (TLR) in c arriers of X-linked retinitis pigmentosa. Methods, Spectral fundus ref lectance of carriers of X-linked retinitis pigmentosa was measured and compared with that of normal subjects. The influence of visual pigmen t was determined by measuring the density difference, that is, the dif ference between the logarithmically scaled spectra of a bleached and a dark-adapted retina. In addition, fundus reflectance maps at 514 nm w ere made with a scanning laser ophthalmoscope in a bleached and a dark -adapted condition. Finally, the optical Stiles-Crawford effect was me asured to determine the angular sensitivity of the TLR, Results, The t apetal-like reflex showed its spectral fingerprint in a high reflectan ce for wavelengths smaller than 600 nm. The density difference measure d at retinal sites of TLR was significantly larger than in normals, bu t the shape of the spectrum was similar. The optical Stiles-Crawford e ffect showed a similar peakedness for all retinal positions. However, in the TLR region, the amplitude of the directionally dependent part w as increased dramatically. For the foveal region, no differences were observed. Conclusions. An increase in reflectance of the outer segment s of the photoreceptors in heterozygotes compared to normals can expla in both the high-density difference and the large amplitude of the Sti les-Crawford effect. An earlier suggestion that only cones contribute to the TLR is unlikely.