Analysis of Retinal Function using chromatic Pupillography in advanced Retinitis pigmentosa

Abstract

 

Purpose

 

The pupil light reflex is beneath rods and cones also influenced by intrinsically photosensitive retinal ganglion cells (ipRGC). This small subpopulation of retinal ganglion cells is considered to determine the sustained post-illumination pupil response (PIPR) following a visual stimulation with bright blue light. In Retinitis Pigmentosa (RP) rods and cones continuously diminish whereas retinal ganglion cells - including the ipRGC - stay largely untouched for a long time. The purpose of this study is to analyze pupil responses using specific chromatic stimuli in blind RP-patients to find out whether color pupillography could be a useful tool for an objective analysis of retinal function and helpful as a predictor for individual benefit from retinal implants.

 

Methods

 

Pupillography is an objective method recording the pupil light reflex by means of infrared-pupillometry (CiP by AMTech Germany). Pupil baseline diameter, latency, constriction amplitude and the PIPR are calculated. One eye is stimulated under mesopic conditions with 28 lx bright light of either red (605nm) or blue (420nm) color and a stimulus duration of either 1s or 4s. The consensual pupil light reaction of the fellow eye is recorded over an entire period of 16 seconds including a pre-stimulus time of five seconds. Furthermore the individual threshold of perception for electrically evoked phosphenes is tested by transcorneal electrostimulation (OKUSTIM by Okuvision, Germany). Patients being blind by an advanced RP (visual acuity < 0,02 or visual field ≤ 5°) and having defunct answers in the scotopic ERG shall be compared to age-matched healthy subjects.

 

Results

 

Hitherto 31 eyes of 16 RP-patients have been examined. Currently we see a trend towards reduced pupil responses to red stimuli but well-preserved responses to blue stimuli with a distinct PIPR (see figure relative amplitude vs. time, 4s stimuli).

 

Conclusions

 

The interim results hitherto correspond to our hypothesis of a reduced pupil light reflex to red stimuli due to a loss of the outer photoreceptors in RP-patients but an increasing PIPR after blue stimuli according to a persisting ipRGC-function and a reduced interaction (inhibition) by rods and cones. Both phenomena may be useful for either selection of suitable patients for a retinal implant as well as objective marker for the efficacy of any retinal intervention.

 

 

Pupillograms using 4 second stimuli of blue and red color

 

Keywords: 668 pupillary reflex • 531 ganglion cells • 648 photoreceptors