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Aditi Mohla, Ranjana Mathur, Monisha Esther Nongpiur, Carol Yim-lui Cheung, Nia Milastuti, Valencia Foo, Shamira Perera; The effects of panretinal photocoagulation on retinal nerve fiber layer at the optic nerve head. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3902. doi: https://doi.org/.
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To investigate the effects of Pascal (Topcon Medical Laser Systems, Inc. Oakland, NJ) pan-retinal photocoagulation (PRP) on the optic nerve head (ONH).
This was a prospective case control study comparing 3 groups of patients seen in the diabetic retinopathy (DR) clinics, all devoid of any coexistent optic nerve pathology. Group A patients had proliferative or severe non proliferative DR necessitating PRP. Group B patients had mild or moderate DR and did not require PRP. Group C patients had PRP at least 2 years ago. Group A had retinal oxygenation measurements and retinal vessel caliber readings by Oxymap T1(Oxymap, Reykjavik, Iceland), optic disc stereophotographs, HD OCT (high Definition Optical Coherence Tomography) scans of the ONH by both Cirrus (Carl Zeiss Meditec Inc, Dublin, CA) and Spectralis (Heidelberg Engineering, Heidelberg Germany). These were performed prior to PRP at baseline, then at 3 and 6 months post PRP. Group B and C had the same at baseline, 3 and 6 months. An analysis of variance (ANOVA) with Bonferroni method for multiple comparisons was used. Paired t-test was used to assess the mean changes in parameters from baseline.
A total of 96 patients were included for analysis, 33 in Group A, 31 in Group B and 32 in Group C. At baseline, the average RNFL was thicker in group A compared to group B (101.5 ± 16.3 Vs 90.7 ± 12.3 μm, p=0.007) and C (88.9 ± 11.4 μm, p=0.001). There was no significant difference between group B and C. At 3 months, group A exhibited a significant increase in the Cirrus average RNFL thickness (5.5 ± 8.1% increase, p=0.002), but no change was observed in groups B and C. The increase was in the superior (p=0.008) and temporal (p=0.02) quadrants. The Spectralis did not show any significant change. Oxygen saturation dropped in all 3 groups, being significant only in group B (-1.9 ± 3.9%, p=0.03). At 6 months, the mean Cirrus RNFL in Group A had thinned back to baseline values. Baseline thickness minus that at 6 months was -2.61μm ± 16.3 (p=0.57). In contrast, the Spectralis revealed RNFL thickening (7.01 ± 8.9%, p=0.001).
We observed Cirrus RNFL thickening at 3 months post PRP, followed by a progressive thinning at 6 months, unrelated to changes in retinal oxygenation.
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