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Tin Aung Tun, Owen Png, Baskaran Mani, Sourabh Sharma, Hla Myint Htoon, Sri Gowtham Thakku, Ching-Yu Cheng, Nicholas G Strouthidis, Tin Aung, Michael J A Girard; Shape Changes of the Anterior Lamina Cribrosa in Healthy and Glaucoma Eyes following Acute Intraocular Pressure Elevations. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3556. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To estimate and compare changes in anterior lamina cribrosa (LC) morphology in normal and glaucoma eyes following acute elevations in intraocular pressure (IOP)
One optic nerve head (ONH) of 18 ocular hypertension (OHT), 21 primary open angle glaucoma (POAG), 33 chronic primary angle closure glaucoma (PACG) and 31 normal subjects was imaged using spectral-domain optical coherence tomography (OCT; Spectralis, Heidelberg Engineering, Germany). IOP was raised twice by gently applying a force (0.64 N then 0.9 N) to the anterior sclera (through the lower eye lid) using an ophthalmo-dynamometer (spring-loaded indenter). After each IOP increment, IOP was held constant, measured with a TonoPen, and each ONH was rescanned with OCT. In each OCT volume, the anterior LC was enhanced with adaptive compensation, manually delineated, and its global shape index (GSI) calculated (Thakku et al., IOVS. 2015 Jun;56(6):3604-14). GSI is a single index that provides a global measure of LC shape and that varies from -1 (posteriorly curved LC) to +1 (anteriorly curved LC). Wilcoxon signed-Rank tests and Linear Mixed Models were used to assess the differences in GSI across groups.
Of the 103 subjects, 51.5% were males with a mean age of 64.5±7.1 years. At baseline, IOP was 17.5±3.4 mmHg and was increased to 37.6±5.9, then 46.2±6.1 mmHg. When considering the first IOP increment, the GSI median was significantly smaller than that at baseline in normal (Z=2.73, P=0.006) and in glaucoma subjects (Z=2.45, P=0.014), but not in OHT subjects (Z=77, P=0.734). For the second IOP increment, the GSI median was significantly smaller than that at baseline in normal (Z=3.2, P=0.001) and in OHT (Z=32, P=0.018). (Figure1) After adjusting for age, gender and baseline IOP, mixed model analysis showed that the LC of PACG eyes was significantly more posteriorly curved than that of normal subjects (Estimated Mean difference -0.15, 95% confidence interval = -0.299, -0.001, P=0.047), but this was not found for other diagnoses.
We demonstrated that acute IOP elevations altered anterior LC shape in living human eyes. The connective tissues of OHT eyes might be stiffer than those from all other groups because the LC of OHT eyes only deformed at high IOP. The LC of PACG eyes was more posteriorly curved following acute elevations in IOP when compared to that of normal eyes.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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