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A. Bayoumi, D. Descovich, A. S. Hafez, M. R. Lesk; The Relationship Between Corneal Biomechanics and Optic Nerve Head Biomechanics in Glaucoma and Ocular Hypertension. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2132.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the relationship between corneal hysteresis and optic nerve head topographical changes induced by IOP reduction i.e. the relationship between biomechanical properties of the cornea and the optic nerve head in open angle glaucoma and ocular hypertension patients.
34 patients with open angle glaucoma and 16 patients with ocular hypertension all with a clinical indication for therapeutic IOP reduction were recruited prospectively from our glaucoma clinics. Optic nerve head topography & corneal hysteresis were assessed in one eye on one visit before and at least 8 weeks after sustained IOP reduction by at least 20%. The IOP was reduced by medical, laser or surgical therapy. The optic nerve head topography was measured using the Heidelberg Retina Tomograph-3. The optic nerve head stereometric parameters for each imaging session were derived from one high quality triplicate mean topography image centered on the optic nerve head. The corneal hysteresis was measured using the Ocular Response Analyzer (Reichert). The hysteresis value for each session was derived from the mean of 4 measurements. The patients were divided into two groups (with low or high hysteresis) based on the median value of the corneal hysteresis.
In the OAG group, the mean IOP fell from (mean± SD) 21.3 ± 6.7 to 12.5 ± 4.5 mmHg, a reduction of 40%. Compared with the 17 patients with high CH (CH: 10.9 ± 1.0 mmHg; mean IOP fell from 23.6±7.5 to 13.4±4.4 mmHg, a reduction of 41%), the 17 patients with low CH (CH: 8.2 ± 0.7 mmHg, mean IOP fell from 19.1±5.1 to 11.6±4.4 mmHg, a reduction of 39.8%) had a greater reduction in the mean cup depth (13 ± 10 µm vs. 0 ± 11 µm, P < .01). In OHT patients, the mean IOP fell from 29.5 ± 5.1 to 18.8 ± 2.5 mmHg, a reduction of 35%. The changes in the mean cup depth between the 8 patients with high CH (CH: 10.9±1.8 mmHg; mean IOP fell from 31.1±6.7 to 18.4±1.8, a reduction of 41%) and the 8 patients with low corneal hysteresis (CH: 8.7 ± 0.9 mmHg; mean IOP fell from 28.9±3.1 to 19.1±3.1, a reduction of 33%) was not statistically significant (-5 ± 11 µm vs.5 ±14 µm, P = 0.13).
In glaucoma patients, but not significantly in ocular hypertension patients, low corneal hysteresis (a more viscoelastic cornea) was associated with greater shallowing of the optic cup i.e. possibly a more mobile lamina cribrosa, after sustained reduction of IOP.
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