Pentacam topographic changes after collagen cross-linking in patients with keratoconus

Abstract

Keratoconus is a bilateral, progressive, non inflammatory corneal degeneration. Corneal deformation and thinning causes irregular astigmatism and leads to visual impairment. Treatment modalities were based on refractive correction with spectacles, contact lenses, and intrastromal corneal rings to correct astigmatism and restore visual acuity. Such modalities do not stop ectatic progression and further visual deterioration. Corneal collagen cross linking (CXL) is the only therapeutic approach for progressive keratoconus (KC) combining the use of riboflavin and ultraviolet-A radiation by creating new covalent bonds between the stromal collagen fibrils. CXL increases the resistance to deformation, thereby strengthening the cornea against its natural ectatic process.

Scheimpflug imaging (by pentacam) is considered among the most prevalent modalities in the diagnosis, staging, and follow-up of KC patients. It is based on a rotating camera and a monochromatic slit-light source, which rotate together. In addition to pachymetry and topographic imaging, Scheimpflug devices provide elevation maps of the anterior and the posterior corneal surfaces.

Our study included 31 eyes of 24 patients. All underwent CXL between September 2015 and March 2016. Preoperative a

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Summary

detailed medical and ophthalmic history were taken from all patients, followed by complete ophthalmic examination; including UCVA and BCVA, anterior segment examination by slit lamp biomicroscopy, posterior segment examination using a +20 diopters lens for indirect ophthalmoscopy , or a +90 diopters lens for slit lamp fundus biomicroscopy, and IOP measurement by the Goldmann applanation tonometer. Also pentacam image was taken to evaluate K readings, degree of corneal astigmatism, pachymetry at thinnest corneal point, anterior elevations and posterior elevations.

The operation was done in the operating room by first applying the eyelid speculum for better exposure. Then the conjunctival sac was rinsed with 10% povidone iodine solution. The corneal epithelium was removed in the central 8-9 mm by mechanical scrapping with a blunt metal spatula to allow for better diffusion of the riboflavin.

Step of De-epithelialization was followed by instillation of 0.1 % isotonic riboflavin (VibeX Rapid, Avedro, Inc, Ma, USA) every 2 minutes for 10 minutes until the stroma was completely saturated and a yellow flare is noted in the anterior chamber.

Then UVA irradiation was performed using KXL system (Avedro, Inc, MA, USA) with wavelength 365 nm. The UVA-irradiation was 30 mW/cm2 for 4 minutes and total dose intensity of 7.2 J/cm2.

Follow up was done twice at 1 to 2 months and up to 3 months postoperatively, where UCVA, BCVA were recorded and