Pupillometry has great potential as a patient-friendly clinical measure of retinal function. Recently, protocols have been developed that measure preferentially rod, cone, and melanopsin function. Other studies have identified how underlying biologic variables affect pupillary responses to light. For full clinical use, however, it is necessary to determine how specific types of retinal pathology affect pupillary responses. This need is complicated by the heterogeneous clinical presentation and molecular cause/disease mechanism of many retinal diseases.
The
characterization of pupil responses in autosomal dominant retinitis pigmentosa by
Kawasaki et al.
1 marks a new phase in the development of pupillometry for clinical use.
A recently developed clinical protocol was applied to a group of patients with identical mutations in NR2E3 that cause autosomal dominant retinitis pigmentosa (adRP). The clinically most important finding was a progressive loss of rod sensitivity (dark-adapted responses to blue light), but not of cones (response to red light). They were able to track rod function even at stages of disease progression where electroretinogram responses were unrecordable.
The authors also find a small reduction in the intrinsic photosensitivity of melanopsin retinal ganglion cells (ipRGCs) contributing to the pupil response. This is not explained by our understanding of NR2E3 or adRP pathology, and identifies melanopsin ganglion cells as a means to study NR2E3 gene function and disease mechanism.
The success of this study suggests that pupillometry will fulfill its potential in the clinic, but also in the lab. With further studies in molecularly characterized patient groups, pupillometry will be able to aid diagnosis, track disease, measure therapy efficacy, and direct disease mechanism studies.