Modified nerve fiber analyzer compensates for birefringence

MIAMI — A modified nerve fiber analyzer can give surgeons the ability to measure the corneal polarization axis and magnitude so that compensation for corneal birefringence is eye-specific, according to researchers here at Bascom Palmer Eye Institute.

Harmohina Bagga and colleagues noted that macular strategies for neutralization of corneal birefringence using scanning laser polarimetry with variable corneal compensation (SLP-VCC) can fail if Henle’s layer is disrupted by macular disease. To examine this phenomenon they conducted complete ocular exams in 20 normal eyes and 27 eyes with maculopathy.

Macular birefringence patterns were classified as well-defined, weak or indeterminate bow ties. Eyes with macular disease had significantly more indeterminate bow ties than those without the disease. Although no relationship was observed between the corneal polarization axis and 12 retardation parameters obtained with SLP-VCC in normal eyes, eyes with macular disease showed a significant association between corneal polarization axis and average thickness, ellipse average, superior average, inferior average and superior integral, suggesting incomplete corneal compensation.

The investigators reported that a new “screen” method for SLP-VCC is a more robust measure of anterior segment birefringence in some eyes with macular disease.

The study is published in the May issue of Investigative Ophthalmology & Visual Science.