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Ashutosh Richhariya, Yogesh Verma, Divakar K. Rao, Cynthia J. Roberts, Ashraf M. Mahmoud, Virender S. Sangwan, Sunil K. Punjabi, Pradeep K. Gupta; Effect of Intraocular Pressure and Anisotropy on the Optical Properties of the Cornea: An Experimental Study. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4203.
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Corneal geometry and optical performance are very important parameters for visual rehabilitation after corneal surgery, including refractive surgery, lamellar keratoplasty, and penetrating keratoplasty. We hypothesize that due to the anisotropic material and optical properties of the cornea, there should be a change in birefringence with an increase in intraocular pressure (IOP). In the present in-vitro study, anisotropic properties, stress distribution within the cornea, and effect of IOP on changes in stress level is investigated.
Inflation tests were performed on eight human donor corneo-scleral rims, mounted on a specially designed test cell. The test cell was then mounted on a turntable so that it could be rotated. Each corneo-scleral rim was subjected to a hydrostatic pressure by means of rising column method. Readings for six corneas were taken at pressures of 0,10,15,20 mm of Hg and remaining two had leakages. At each pressure step, four scans at 0, 45, 90 and 135 degrees were taken by a Polarization Sensitive Optical Coherence Tomography (OCT) system and the birefringence changes as well as normal OCT images were recorded. The images were later compiled for analysis and plots were generated for each image.
The retardation changed significantly (P(T<=t) one-tail 0.025) with the axis of orientation and IOP (P(T<=t) one-tail 0.019).The optical thickness of the cornea also decreased with increasing IOP.
The optical properties of the cornea are modified with change in Intra Ocular Pressure. This is not uniform due to distinct anisotropic properties. It is proposed that the direction of incision or ablation on the cornea may cause an unexpected change in optical properties, which may be a significant contributor to post-operative astigmatism in penetrating keratoplasty or other visual aberrations.
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