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Mine Baris, Lama Al-Aswad, Dana Blumberg, George Cioffi, Jeffrey M Liebmann, Tongalp H Tezel, Gulgun Tezel; Functional correlation of retinal inner plexiform layer (IPL) alterations in glaucoma. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6137.
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© ARVO (1962-2015); The Authors (2016-present)
Our recent retrospective cohort study detected some IPL alterations in the absence of detectable alterations in RNFL/RGCL in glaucoma patients who were examined one-year apart. This continuation study aimed to determine functional relationship of glaucoma-related IPL alterations.
The studied pilot cohort included 24 eyes of 16 patients with primary open-angle glaucoma, who did not have other retina or optic nerve pathologies. In addition to automated thickness measurements of RNFL, RGCL, and IPL by SD-OCT, the images collected in the macular area were analyzed in segmented layers for the same parameters on nasal and temporal sides at a distance of 1, 1.5, and 2 mm from the center of the macula. The parameters analyzed over the one-year follow-up period also included the IPL density assessed by the reflectance volume of linear densitometry. To analyze functional correlation of these structural paremeters, visual field parameters that were obtained by standard 10-2 automated perimetry on the same day as SD-OCT images were used.
No significant alteration was detectable in RNFL, RGCL, or IPL thickness (p>0.05) of the studied patients (age: 68±12 years; female/male: 7/9) who were on topical IOP-lowering treatment. However, IPL density exhibited a prominent increase (p<0.004). Linear regression analysis found this observation correlated to visual sensitivity in corresponding points on 10-2 visual fields (R=0.35, p=0.001). Some eyes that were followed for a period longer than one-year also presented a trend towards decreasing density and thickness of IPL in correlation to progressing visual field loss.
Early alterations of IPL prior to manifest RGCL/RNFL loss in glaucoma patients were correlated to developing visual field defects. The glaucoma-related increase in IPL density might be due to dendritic remodeling, mitochondrial redistribution, and glial responses for synapse maintenance and tissue cleaning, although decreased IPL thickness could reflect dendrite atrophy. These observations provide clinical validation for early synapse loss in experimental glaucoma; however, synaptic pruning and function loss may likely develop through a longer process in human glaucoma than animal models because glaucoma patients are typically treated to lower IOP. Further studies should determine whether IPL alterations may serve as an imaging-based biomarker to improve clinical testing of glaucoma.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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