Pupillometry in Patients with Leber Congenital Amaurosis: Feasibility, Residual Retinal Cell Function, and Paradoxical Response

Abstract

Purpose: This is a feasibility study of pupillometry in blind children with LCA due to various genotypes. We are investigating the extent of the remaining rod, cone and ganglion cell function and the origin of the paradoxical pupil. Testing remaining rod, cone and ganglion cell function by pupilllometry in diverse LCA genotypes may allow for new insights into LCA disease mechanisms.

Methods: We genotyped 30 LCA children and young adults by a variety of molecular genetic techniques, including Whole Exome Sequencing. The spectral bands for this study were 640 ±10 nm (red light) to test cone function, 467±17 nm (blue light) to test rod function, and sustained blue light to test ganglion cell function. The light stimulus paradigm (Kardon et al) consisted of the first light stimulus at 1 cd/m2 for 13 secs, followed by a second light stimulus at 10 cd/m2 for 13 secs, followed by a third light stimulus at 100 cd/m2 for 13 secs, followed by darkness (light termination) using red-light stimulus first. After a minimum interval of 60 seconds without light stimulus, the paradigm was repeated using the blue-light stimulus, and then the white light after another 60 seconds without light stimulus.

Results: We identified LCA mutations in NMNAT1, CRB1, GUCY2D, AIPL1, CEP290, RPE65 and LRAT, reflecting a diverse underlying disease severity and disease mechanisms. Most patients showed significant pupillary responses, despite non recordable ERGs. We identified rod, cone and ganglion cell responses. Stimulating the intrinsically photosensitive melanopsin ganglion cells using blue light in the highest intensity was found to generate the most prominent response when present ( > 75% pupillary constriction sometimes, p-value <0.001). We are currently correlating the pupillometry results with the LCA genotypes.

Conclusions: Pupillometry testing is feasible in children with LCA with a wide variety of disease severities and genotypes. It is a promising method for testing different retinal cell types objectively in a noninvasive way using preferential light stimulation while bypassing cortical processing. Our data also describes the retinal cells and layers mostly affected in the different genotypes, as well as providing evidence of residual viable cells previously thought to be lost.

Keywords: 696 retinal degenerations: hereditary • 688 retina • 539 genetics