Corneal Biomechanics and Optic Nerve Head Compliance: Corneal Hysteresis But Not Corneal Thickness Correlates with Optic Nerve Surface Deformation in Glaucoma Patients
Anthony Philip Wells 1*,
David (Ted) Garway-Heath 2,
Ali Poostchi 3,
Tracey Wong 3,
Kenneth C.Y. Chan 3,
and
Nisha Sachdev 3
1 Capital Eye Specialists, L2 / 148 Cuba St, Wellington, 6001, New Zealand; Ophthalmology, Wellington Hospital, Wellington, New Zealand
2 Moorfields Eye Hospital - Glaucoma Research Unit, London, United Kingdom
3 Ophthalmology, Wellington Hospital, Wellington, New Zealand
* To whom correspondence should be addressed. E-mail: twells{at}eyetext.net.
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Abstract |
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Purpose: To investigate relationships between acute intraocular pressure induced optic nerve head deformation and corneal hysteresis and thickness in glaucomatous and non-glaucomatous human eyes.
Methods: Prospective study of 100 subjects: 38 with glaucoma, 62 without. Data collected included spherical equivalent (SE), central corneal thickness (CCT), axial length (AL), cylinder, Goldmann intraocular pressure (IOP), Pascal IOP, and corneal hysteresis (CH). IOP elevation was induced with a modified LASIK suction ring to an average of 64mmHg for less than 30s. Heidelberg Retina Tomography II (HRT) was performed before and during IOP elevation. Mean cup depth (MCD) was calculated using HRT data analysis software. Change in optic disc depth was calculated and tests for correlation with the parameters listed above were performed.
Results: CH and CCT were lower in the glaucoma group (8.8mmHg, 532µ) than in the control group (9.6mmHg, p=0.012 and 551µ, p=0.011 respectively). There were no statistically significant differences in SE, cylinder, AL, or optic disc size. There was no difference in amount of IOP elevation between the two groups (p=0.41); the average difference in mean cup depth between baseline (247µ) and IOP elevation was 33µ (29.8µ glaucoma, 36.1µ control, p=0.5). Multiple variable analysis, controlling for age and gender, showed that CH correlated with MCD increase (p=0.032). This relationship persisted (p=0.032) after controlling for glaucoma status, age and gender. Other factors including CCT (p=0.3), AL (p=0.9), and SE (p=0.38) were not significant in this model.
Conclusions: In the glaucoma patients but not controls, CH was associated with increased deformation of the optic nerve surface during transient elevations of IOP.
Key Words:
glaucoma, optic nerve head, corneal biomechanics
