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Xinbo Zhang, Ou Tan, David Huang; Modeling Thickness Variation Of Ganglion Cell Complex And Nerve Fiber Layer Measured Using Fourier-domain Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2011;52(14):202.
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To model the between-visit variation and with-visit variation and age related thinning in the overall average thickness of ganglion cell complex (GCC) and nerve fiber layer (NFL) measured using Fourier-Domain optical coherence tomography (FD-OCT); and to establish criteria for detection of glaucoma progression by serial measurement of GCC and NFL thickness during follow-up visits.
We analyzed the data from participants enrolled at the Doheny/USC site of the multi-center longitudinal Advanced Imaging for Glaucoma Study (www.AIGStudy.net). An FD-OCT system (RTVue) was used to map GCC and NFL thickness 3 times on each study visit. The overall average thickness was first adjusted based on the OCT signal strength index (0.05 µm per SSI for GCC and 0.11 µm per SSI for NFL). Next, the natural logarithm of thickness measured from each OCT scan on the normal (N) patient was analyzed in a mixed effect model. The model included age as the fixed effect to account for age related thinning and subject, eye, between-visit and with-in visit variation as the random effects. If the GCC or NFL thickness of a patient is confirmed to decrease beyond a threshold set by the normal eyes, the patient is considered progressed. In this study the threshold was set as 1% cut-off from the distribution of the GCC or NFL thickness after ajusting for age related thinning effect.
The analysis included 65 eyes (33 participants) from normal group; 47 eyes (36 participants) from glaucoma suspect or pre-perimetric glaucomatous (GSPPG) group; and 88 eyes (57 participants) from perimetric glaucoma (PG) group. Each eye was measured on 1 to 6 visits (average 2.7). The one percentile level cut-off for glaucoma progression based on GCC thickness loss was given by the formula: 7.6% + 0.31%*TIME, where TIME is the number of the years between the follow-up and baseline tests. (Example: the patient is considered progressed if the GCC thickness decreased by 7.6% + 0.31%*10 = 10.7% over 10 years.) The criterion for NFL was 9.4% + 0.08%*TIME. The progression must be confirmed by 3 consecutive measurements in the GSPPG and PG group. 8 eyes in the GSPPG and PG group had confirmed progression using GCC or NFL loss criteria over average follow-up of 18 months.
The study developed criteria to detect glaucoma progression based on serial FD-OCT measurements of GCC and NFL thickness that takes consideration of normal aging and normal variation. The criteria may be used in combination of visual field test to enhance glaucoma diagnosis. Long term follow-up data will be needed to improve the criteria.
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