Rasterstereography-based classification of normal corneas.

PURPOSE: To attempt to classify the topographic patterns identified by rasterstereography in a population with normal corneas. SETTING: Tulane Medical Center Clinic, New Orleans, Louisiana. METHODS: Corneal elevation pictures of 100 eyes of 50 volunteers were taken using the PAR Corneal Topography System. The volunteers had no history of eye injury, disease, or surgery, and none wore contact lenses. Three observers independently assigned the images to one of five subgroups. RESULTS: Five categories were identified: unclassified, regular ridge, irregular ridge, incomplete ridge, and island. There were significant statistical differences in the degree of astigmatism between the irregular ridge and incomplete ridge groups (P = .0419) and between the irregular ridge and island groups (P = .017). CONCLUSION: The topographic patterns identified by rasterstereography in normal corneas can be classified into five distinct groups.

New technique for studying incision depth in experimental radial keratotomy.

Older techniques of analyzing incision depth in incisional keratotomy consist of serial transverse sections taken at various points along the incision. Information as to shape and depth of the incision are reconstructed from these sections. We describe a new method for studying the incision depth and profile along the entire incision length.

Videokeratographic evaluation of peripheral redeepening in the cadaver eye.

Radial incisions must be deep enough to correct myopia. As currently performed, most surgeons set their diamond blades at a constant depth and do not alter the blade length throughout the procedure. The cornea is not uniformly thick; the central cornea is the thinnest and it thickens toward the periphery. Therefore, an incision of constant depth would be deeper centrally and thinner peripherally. Peripheral redeepening of the cornea would in theory make the incision depth deeper throughout and should increase the effect of radial incisions. We reviewed the literature on this technique and performed radial incisional studies on the human cadaver eye using videokeratography to measure incision depth indirectly. Based on our studies, we believe that peripheral redeepening has no effect on central cornea flattening.

Compensating for thermally caused dimensional changes in the cryolathe.

Dimensional changes in the Barraquer cryolathe , resulting from contraction due to refrigeration, can exert a considerable effect on the dimensions of the lathed lenticule . We have devised a simple technique for re- zeroing the cryolathe after freezing. This procedure negates the effects of the dimensional changes and thereby improves the accuracy of shaping the lenticules .

A prospective study of the use of hyperopic epikeratophakia grafts for the correction of aphakia in adults.

The results of a prospective clinical study of hyperopic epikeratophakia grafts for the visual rehabilitation of aphakic patients are presented. Visual acuity data are given for 21 aphakic patients who have been followed for up to six months postoperatively. With spectacle overrefraction, on the average, patients were within three lines of their preoperative potential vision at three months postoperative and within two lines at six months postoperative. Three months postoperatively, two patients achieved visual acuities of 20/20, and 57% had 20/40 or better with spectacle overcorrection. Six months postoperatively, three patients achieved best-corrected visual acuities of 20/20, and 80% had best-corrected visual acuities of 20/40 or better.

Clinical results of keratophakia and keratomileusis.

Thirteen keratophakia patients were followed for 13 to 35 months. Eighteen cases of hyperopic keratomileusis or hyperopic keratomileusis using preserved corneal tissue were followed for 2 to 30 months. All 13 patients who underwent keratophakia achieved 20/50 or better acuity. All seven patients having hyperopic keratomileusis achieved 20/60 or better acuity. Eight of the 11 patients who had hyperopic keratomileusis using donor corneal tissue achieved 20/60 or better acuity. The preservation of lenticules after lathing did not adversely affect the correlation between predicted and observed dioptric corrections. There was a statistically significant correlation between predicted and observed dioptric corrections. There was a statistically significant correlation between predicted and observed dioptric correction measured at the corneal surface when the lenticule was lathed from fresh tissue (hyperopic keratomileusis) or from relatively fresh tissue (keratophakia). However, we found that there was poor correlation between the predicted and observed corrections when the lenticule was lathed from donor tissue that had been cryopreserved for long periods of time (hyperopic keratomileusis with preserved corneal tissue).