The Effect of Topical Nerve Growth Factor (NGF) on Corneal Nerve Morphology after LASIK in Rabbits

Abstract

Abstract: : Purpose: Prior animal models have demonstrated corneal nerve regeneration after Laser Assisted In Situ Keratomileusis (LASIK). Existing data suggests that Nerve Growth Factor (NGF) may modulate healing properties of the cornea. We evaluated the effect of topical NGF on corneal nerve regeneration after LASIK in rabbits. Methods: Animal Care and Use Committee (ACUC) approval at Northwestern University was obtained. Eight New Zealand white rabbits underwent bilateral LASIK. NGF ointment (5 µg/ml) and vehicle were prepared. One randomly selected eye of each rabbit was treated with 100µl of NGF ointment twice daily for either 5 weeks or 10 weeks. The fellow eye was similarly treated with ointment vehicle as a control. Corneas were harvested at the 5 week and 10 week time points. Monoclonal antibody for tubulin protein and counterstaining with a fluorescent probe (Alexa 488) were used to identify corneal nerve axons. Confocal microscopy at 10X magnification was employed to visualize stained corneas in 1 µm tangential sections. Corneal nerves were analyzed by taking 3 different digital images of a cornea section. Nerve surface area in the anterior 50 µm of the cornea in each image was calculated by digital imaging software (Carl Zeiss, Inc.) that detected the intensity of corneal nerve fluorescence. Results:The average total nerve surface area measured in treatment groups was 1.14 mm² versus 0.68 mm² in control groups. The average difference of corneal nerve surface area between the treated and the untreated group was 0.46 mm². This difference was found to be statistically significant (P=0.004). Conclusions: This pilot study demonstrates that topical NGF treatment after LASIK in rabbits is associated with increased corneal nerve surface area compared to vehicle control.

Keywords: cornea: basic science • refractive surgery • immunohistochemistry