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Birgit Lorenz, Elisabeth Strohmayr, Steffen Zahn, Knut Stieger; Chromatic Pupillometry Dissects Function Of The Three Different Light Sensitive Retinal Cell Populations In RPE65 Deficiency. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1311.
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© ARVO (1962-2015); The Authors (2016-present)
Patients with mutations in the RPE65 gene develop early onset severe retinal dystrophy or Leber congenital amaurosis. Objective methods for the characterization of photosensitive cells are highly needed not only for improving the quality of examination results, but also for analysing treatment success with current therapeutic strategies. The pupil light reflex is driven by rod, cone, and intrinsic photosensitive retinal ganglion cell (ipRGC) input. Two protocols (one original and one optimized) of chromatic pupillometry with differing stimulus paradigms are under investigation to gather isolated functional information of the three cell populations. The aim of this study was to evaluate the two protocols in RPE65 patients, and to correlate the data with the clinical phenotype.
The study group comprised 12 patients with RPE65 mutations, and for control purposes 18 healthy probands and 2 achromats. A custom made binocular chromatic pupillometer (Bino I, AMTech) connected to the Colordome Ganzfeld stimulator (Diagnosys LLC) was used to assess changes in pupil diameter in response to red (640nm) and blue (462nm) light stimuli. Light intensities, stimulus duration and background varied depending on the protocol used. In addition, visual field examination (Goldmann perimetry) and Full field stimulus test (FST) were performed.
Chromatic pupil stimulation in the achromats was done to verify specificity of cone-weighted answers and while showing a normal rod response to rod-weighted stimulation, a mixed rod/cone response was observed in the cone-weighted pupil reaction with the original protocol. In contrast, no pupil response to the cone-weighted stimulation was observed with the optimized protocol. Pupil reactions to rod-weighted stimulation were diminished in all RPE65 patients. Pupil reactions to cone weighted stimuli differed among RPE65 patients and did not always correspond to residual visual field and to cone sensitivity loss with FST. Pupil reactions to ipRGC-weighted answers were preserved.
Absence of rod function and unaltered ipRGC function were measured in RPE65 patients with either protocol. However, the optimized protocol was more sensitive to measure cone sensitivity losses. Chromatic pupillometry represents a highly sensitive and objective testing method to quantify the function of rods, cones, and ipRGCs in RPE65 patients.
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