CORNEAL CROSS-LINKING

Corneal collagen crosslinking (CXL) procedures have an unpredictable but generally beneficial effect on the refraction and visual acuity of patients with keratoconus, said Mohammed Iqbal Hafez Ahmed MD, lecturer of ophthalmology, Sohag University Hospital, Egypt. “Crosslinking can both preserve and improve vision. The greatest improvements in the cornea appear to be in the myopic component, astigmatism did not change dramatically,” Dr Ahmed told a Cornea Day Session at the 18th ESCRS Winter Meeting in Ljubljana.

He presented a retrospective study involving 58 eyes of 40 keratoconus patients who had at least 24 months of follow-up after undergoing conventional epi-off CXL. The patients in the study ranged in age from 12 to 39 years and had a mean age of 17 years. Dr Ahmed carried out the crosslinking procedures using riboflavin 0.1per cent (Ricrolin®, SOOFT Italia) and the Opto XLink Corneal Cross-Linking System (Opto). After a follow-up of 24 to 30 months, the best-corrected visual acuity had improved from postoperative values by one line in 54 per cent of eyes, remained unchanged in 36 per cent and decreased by one line in 10 per cent.

Astigmatism remained within half a dioptre of preoperative values in 86.2 per cent of eyes, and decreased by a mean of 1.2 D in 13.8 per cent eyes. The K value of the apex decreased by a mean of -2.73 D in 65.5 per cent of eyes, a statistically significant change. This value remained stable in 25.9 per cent of eyes and increased by 1.0 D in the remainder. The maximum K value decreased by a mean of 2.47 D in 55 per cent of eyes, remained unchanged in 38 per cent and increased by 1.0 D in the remainder. Spherical and higher-order aberration showed no significant variations, but there was a very significant reduction in the coma component from six months onward.

To illustrate the kind of results that can be achieved with collagen cross-linking, Dr Ahmed presented a case-study of a patient who had undergone the procedure. He noted that postoperative pachymetry showed that at two years’ follow-up, the eye’s central corneal thickness had decreased markedly from a preoperative 389 microns to 308 microns, whereas the peripheral corneal thickness increased from 623 microns to 668 microns. In addition, the average K decreased from 51.66 D to 49.2 D, but the astigmatism remained unchanged. In this case the uncorrected visual acuity improved from 3/60 to 5/60 and the best corrected visual acuity improved from 6/30 to 6/20.

Figure 1 shows pre-and postoperative corneal topographies in this case with marked postoperative central corneal thinning and remarkable central corneal flattening. Dr Ahmed attributed the decrease in myopia that occurred in many patients to a synergistic interaction between the increased radius of curvature of the flattened cross-linked corneal surface and a reduction in the cornea’s refractive index resulting from the thinning of central cornea.

Figure 2 shows the postoperative forces affecting the cornea explaining the good results obtained post CXL. He added that an analysis of findings obtained from 23 cases with more than three years of follow-up showed that for every seven microns decrease in the average central corneal thickness, the average K decreased by one dioptre.