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Randy H Kardon, Pieter Poolman, John N Pienta, Jan M Full, Susan C Anderson; A New Automated 20 Second Pupillographic Test to Quantify the Log Unit Relative Afferent Pupillary Defect and its Relationship to Retinal Ganglion Cell Thickness. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3539.
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© ARVO (1962-2015); The Authors (2016-present)
This study was designed to automate the measurement of the relative afferent pupillary defect (RAPD) with a compact computerized pupillometer utilizing a novel stimulus and analysis paradigm designed for high volume clinical use. The structure-function relationship of the RAPD to the inter-ocular asymmetry of the inner retinal layer thickness was also studied.
A 20 second protocol spanning seven intensities for each eye (0.0 to 2.6 log lux) was implemented using a commercial binocular pupillometer (Neuroptics DP2000, Irvine, CA). The protocol was administered and analyzed in 37 consecutive patients tested prospectively in the setting of a neuro-ophthalmology clinic. Clinical RAPDs were obtained independently by neuro-ophthalmologists evaluating patients during their clinic visit and were quantified with neutral density filters. A software program was created to compare the recorded pupillographic responses across the intensity spectrum and to match the waveform pupil responses elicited from the right eye stimuli with those elicited from the left eye stimuli from the array of waveform pupil light reflexes derived as a function of light intensity. The inter-ocular difference in the OCT measured retinal ganglion cell-inner plexiform layer (RGC-IPL) thickness was also correlated with the computerized RAPD in a subset of patients.
There was a highly significant correlation between the automated and clinical RAPD (r = 0.86 p < 0.01). Additionally, the relationship between RAPD as a function of light intensity revealed novel effects of damage. The automated RAPD also correlated significantly with the inter-ocular asymmetry of RCG-IPL thickness (r=0.71, p<0.01).
The use of a short, automated protocol to assess the log unit RAPD is feasible, returns results similar to clinical measurements, and correlates with structural loss. This allows for fast, objective screening. There may be diagnostic utility in introducing an intensity range over which the RAPD is measured as a new method of further characterizing damage.
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