Flap hinge position no effect on corneal sensitivity

By Stefanie Petrou-Binder MD

Heidelberg - The hinge position of corneal flaps appears not to affect central corneal sensitivity or influence the rate of dry eye problems post-LASIK, according to a study performed at the Storm Eye Institute in Charleston, South
Carolina.

Mike P. Holzer MD presented study results at the annual Congress of the DGII (German-Speaking Organisation of Intraocular Lens Implantation and Refractive Surgery). The prospective, randomised, double-blind study included 47 patients who underwent bilateral LASIK.

Surgeons used the Hansatome Microkeratome on one eye, which produced superiorly-hinged flaps. They employed the Amadeus microkeratome on the other eye, producing nasally-hinged flaps.

Corneal sensitivity was assessed preoperatively, revealing no difference in the various corneal areas measured. The corneal surface was divided into five regions: superior, inferior, temporal, nasal and central.

Patients were monitored at one day, one week, and at one, three and six months following LASIK. Postoperative assessments included corneal sensitivity, Schirmer Test, VA, contrast sensitivity, tear film break-up time and the patients' subjective input.
The investigators found no difference in visual acuity or contrast sensitivity between the two groups. The Schirmer Test revealed only a slight increase at three months, compared to preoperative values, and showed no difference between the two groups.

The tear film break-up-time was significantly decreased at three months compared to preoperative values, and revealed no difference between the superior and nasal groups.
Both groups demonstrated a significant decrease in the sensitivity of the central corneal region at the one week, one month and three month follow-up dates. Both groups also revealed decreased sensitivity of the temporal and superior corneal regions, but to a lesser extent.

The inferior corneal region showed only slight changes in sensitivity and there were no differences between the nasally-hinged and the superiorly-hinged groups.
Dr Holzer reported, however, that nasal corneal sensitivity was less decreased at one week and one month post-LASIK in the nasally-hinged group. Sensitivity here was higher than in the eyes with a superiorly-positioned hinge. This effect was no longer significant at three months.

Complaints regarding dry-eye did not vary between the two groups. There were no other subjective differences, he reported.
Some recent studies which compared nasal and central corneal sensitivity corroborate these results, showing that the nasal cornea is more sensitive with a nasally-hinged flap following LASIK.

As dry eye syndrome occurred with equal frequency in both groups, showing no preference for either hinge-position, it follows that neither the nasal nor the superior hinge position has any specific influence regarding the development of dry-eye following LASIK.

The study, however, demonstrated that dry eye syndrome and decreased corneal
sensitivity affect many LASIK patients postoperatively and that even three months following LASIK, corneal sensitivity is significantly decreased compared to preoperative measurements.

Although these study results matched those of related trials quite well, Dr Holzer said it would be necessary to wait out the six month follow-up period for more certainty.
Ease in performing a flap with a particular hinge position is of interest to the eye surgeon. It is also important to note the different effects that hinge positions may have during the postoperative observation period, particularly on the cornea, he stressed.

Top