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V. Dave, T. Dada, A. Aggarwal, J. Ashar, S. Bhartiya, A. Panda; Effect of Two Different Macular Birefringence Imaging Protocols Used for Corneal Compensation, on Retinal Nerve Fiber Layer (rnfl) Thickness Parameters Using Scanning Laser Polarimetry With Variable Corneal Compensation (gdxvcc) in Normals and Eyes Having Macular Lesions. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5819.
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To study the effect of two different macular birefringence imaging protocols used for corneal compensation, on retinal nerve fiber layer (RNFL) thickness parameters using scanning laser polarimetry with variable corneal compensation (GdxVCC) in normals and eyes having macular lesions.
50 eyes of 50 normal subjects (no disc or visual field abnormalities, IOP < 21 mm Hg) and 50 eyes of 50 patients with macular pathology (subretinal neovascular membrane, macular scar, diabetic macular edema, and macular hole) were evaluated. Compensation for anterior segment birefringence was done using the standard protocol after imaging the macula (method I: small circle 10 X 10) and then repeated using the irregular pattern protocol (method II: large square 60X60)). The various RNFL parameters evaluated using the two different protocols included TSNIT average, Superior average, Inferior average, & Nerve Fiber Indicator (NFI).
There was no significant difference between the RNFL parameters using both protocols in normal eyes. In patients with macular pathology, 18 out of 50 eyes (36%) had a significant overestimation of all RNFL thickness parameters with method I which normalized when repeated with method II (Table 1). Out of these 18 eyes, 16 had CNVM, one had DME and one eye had macular hole. Thirty two eyes (64%) did not show a significant change on GDx VCC parameters on either of the two scan protocols.
Imaging the RNFL using GDxVCC leads to significant overestimation of RNFL thickness in more than one third of eyes with a macular pathology. It is recommended that the irregular macula protocol be used for imaging in such cases. These findings highlight the need to change the imaging protocol in patients with macular lesions or those glaucoma patients who develop macular lesions during their course of follow up.
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