Corneal Birefringence: A Useful Tool To Assess Corneal Structure Or Just Topography

The generation of corneal birefringence patterns is not disassociated from reflections at the ocular surface. This study was aimed to predict the patterns that would be expected just by reflections at the ocular surface alone when using a simple technique to observe corneal birefringence.

Kyiv City Clinical Ophthalmological Hospital “Eye Microsurgery Center”, Ukraine; Phycics Faculty, Taras Shevchenko Kyiv National University, Kyiv, Ukraine.

Corneal birefringence can be observed using a slit lamp biomicroscope with the eye illuminated by appropriately adjusted linearly polarized light at 20-40° from the temporal side and the subject’s line of sight directed along the observation beam fitted with an orthogonal linear polariser. The intensity distribution of rays reflected off the ocular surface for this, and permutations thereof, arrangement can be estimated using the Fresnel equations and compared with the observed pattern.

The predicted intensity of light distribution is fairly uniform over the temporal region with dark patches in the nasal region above and below the horizontal axis of the cornea. The pattern did not resemble the actual observed pattern. Changing the axes of illumination and observation affect the predictions, but still the predictions did not match the observed pattern.

Reflections off the ocular surface may contribute to the corneal birefringence pattern but, in theory, these do not appear to be the main determinates of the observed pattern.