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Fixed diameter scan protocol preferable for retinal nerve fiber layer measurement by Optical Coherence Tomography in all sizes of optic discs
  1. Sushmita Kaushik (sushmita_kaushik{at}yahoo.com),
  2. Surinder Singh Pandav (sspandav{at}yahoo.com),
  3. Parul Ichhpujani (parul777{at}rediffmail.com),
  4. Amod Gupta (eyepg{at}sif.com)
  1. Advanced Eye Centre, Postgraduate Institute of medical Education and Research, Chandigarh, India
  2. Advanced Eye Centre, Postgraduate Institute of medical Education and Research, Chandigarh, India
  3. Advanced Eye Centre, Postgraduate Institute of medical Education and Research, Chandigarh, India
  4. Advanced Eye Centre, Postgraduate Institute of medical Education and Research, Chandigarh, India

    Abstract

    Background: Retinal nerve fiber layer(RNFL) measurements using a fixed-diameter versus a user-defined scan-protocol of optical coherence tomography(Stratus OCT©) were compared in 32 normal, 62 glaucoma suspects and 36 glaucomatous eyes.

    Methods: Peripapillary RNFL thickness was measured using the standard “Fast”RNFL scan-protocol and Proportional 2.27xdisc scan-protocol. Disc size was measured using “Fast” Optic Disc protocol. Correlation between RNFL thickness by each scan-protocol and disc size was analyzed.

    Results: In normal eyes, RNFL thickness was independent of optic-disc area using the fixed-diameter protocol(p=0.92), but was inversely proportional to disc size using proportional protocol(p<0.001). In glaucoma suspects, optic disc area correlated with RNFL thickness using the fixed-diameter protocol(p<0.001). On multivariate analysis in glaucomatous eyes, RNFL thickness using the fixed-diameter protocol was significantly affected by mean deviation on visual fields but not by disc area(p<0.001and p= 0.64 respectively)

    Conclusion: In normal subjects, disc size does not appear to affect RNFL measurements by OCT using the fixed-diameter protocol, indicating that RNFL thickness may be related to distance from the centre of the optic disc rather than the margin. The thicker RNFL observed in large-sized glaucomatous discs in this study may be related to the earlier stage of glaucoma, though it may not apply to the general population.

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