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J. Cotliar, A. Shrivastava; Is There a Correlation Between Cirrus OCT RNFL and the Frequency of an APD on Clinical Examination. Invest. Ophthalmol. Vis. Sci. 2010;51(13):236.
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© ARVO (1962-2015); The Authors (2016-present)
To determine at what degree of asymmetry in retinal nerve fiber layer thickness (RNFL), by Cirrus OCT, would one expect to detect a relative afferent pupillary defect (RAPD) in glaucoma or glaucoma suspect patients.
This is a retrospective study of 69 patients carrying the diagnosis of glaucoma (both primary and secondary), or glaucoma suspect (glaucomatous cupping or ocular hypertensive), in a tertiary referral glaucoma practice in the Bronx, NY, examined between the dates of 08/2009 to 11/2009. Each patient was examined by standard techniques by one attending physician, including pupil exam in dim light, slit lamp examination, and dilated fundoscopic examination. The presence or absence of an RAPD was noted for each patient. Neutral density filter examination and gradation of RAPDs was not performed. Cirrus OCT RNFL analysis was ordered for all patients included in the study based upon suspicion or confirmation of a glaucomatous process. A chart review was performed on patients meeting the above criterion, and subjects were divided into two groups based upon the presence or absence of an RAPD. Subjects with OCT signal strength less than 6/10 in either eye were excluded from the study. Data recorded included patient demographic information, signal strength, average thickness of RNFL, quadrant and extent of RNFL thinning if any, presence or absence of RAPD. To determine the degree of asymmetry of retinal nerve fiber layer thickness, the "% difference" was calculated by comparing the difference in thickness between the two eyes, divided by the thickness of the larger value. Statistical analysis was performed to determine the degree of asymmetry which would predict the clinical detection of an RAPD.
Of the original 69 patients who met inclusion criteria, 8 patients were excluded based upon poor signal strength. Of the 61 subjects remaining, 4 patients were noted to have an RAPD on initial examination. The mean "% difference" in the group without an RAPD was 5.305 and SD= 4.19. The mean "% difference" in the RAPD group was 30.60% (SD= 0.051). These groups were found to be statistically significant at a level of p< 0.01.The maximum "% difference" within the group without a clinically detectable RAPD was 20%. Within the RAPD group, the minimum "% difference" was noted to be 23.4%.
This preliminary data suggests that an RAPD is generally not clincially apparent until there is a significant retinal nerve fiber layer thickness asymmetry of approximately 20% using our calculation of "% difference" from Cirrus OCT analysis.
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