A new noncontact tonometer using corneal photoelasticity: porcine eye study.
OBJECTIVE
To propose a new noncontact tonometer based on corneal photoelasticity.


METHODS
In this study, we experimented with 18 enucleated porcine eyes. The anterior chamber was infused with a physiological solution. A circular polarizing filter was attached to an ophthalmic surgical microscope. Color fringe changes at the peripheral cornea related to its photoelasticity were recorded using an ophthalmic surgical microscope equipped with a charge-coupled device camera while intraocular pressure (IOP) changes were determined by the height of the physiological solution bottle. A peak intensity of the color fringes was determined by Image J software.


RESULTS
Circular, rainbow-like color fringes, a phenomenon that is the basis of photoelasticity, were detected in the peripheral cornea. When IOP increased from 7 to 29 mm Hg, the color fringes moved more peripherally becoming narrower with their peak intensity increasing. At an IOP of 7, 15, 22 and 29 mm Hg, the mean peak intensity of the color fringes had a gray value of 113.6, 114.2, 114.7 and 115.5, respectively. Correlation analysis between IOP and peak intensity of the color fringes in these porcine eyes showed a significant positive correlation with a Pearson correlation coefficient of 0.993 (p < 0.01).


CONCLUSIONS
The proposed noncontact tonometer based on photoelasticity of the cornea could become a true noncontact device that could be used for the screening of glaucoma or as an IOP follow-up for glaucoma patients.
Department of Ophthalmology and Visual Science, College of Medicine, Catholic University of Korea, Seoul, Republic of Korea.
Hosik
H
Hwang
Mansoo
M
Kim
Chankee
C
Park
D000818:Animals; D001718:Birefringence; D003315:Cornea / Q000502:physiology*; D004547:Elastic Tissue / Q000502:physiology*; D004548:Elasticity / Q000502:physiology / Q000528:radiation effects*; D007429:Intraocular Pressure / Q000502:physiology*; D008027:Light; D013552:Swine; D014065:Tonometry, Ocular / Q000295:instrumentation*