Thermokeratoplasty for the treatment of hyperopia: a clinical follow-up

RESUMO

Corneal curvature can be altered by shrinking stromal collagen with a retractable cautery probe tip that produces controlled thermal burns in a procedure termed hyperopic thermokeratoplasty (HTK). This procedure induces steepening of the central cornea. We performed HTK in 12 sighted eyes from eight patients placing a radical pattern of spots on the peripheral cornea, using the Fyodorov thermal unit. The number of spots and the shape of the optical zone (rounded or ovoid) was determined by a computer software provided by the manufacturer. Follow-up ranged from 24 to 54 weeks (mean of 31.50 weeks). Spherical equivalent changed from a preoperative mean of 4.10 +/- 1.12 diopters to -0.85 +/- 0.86 (P=0.001), 1.05 +/- 1.34 (P=0.001) and 3.84 +/- 1.13 diopters (P+o.16), respectively at 4,12 and 24 weeks after the surgery and at the last follow-up. The induced keratometric steepening at 4 weeks postoperatively (4.50 +/- 1.31, P+0.001), reduced to 1.04 +/- 0.43 diopters of corneal steepening at the last Follow-up (P=0.25). Uncorrected visual acuity improved at least two lines in nine eyes (75.0 percent), remained unchanged in twho eyes (16.7 percent), Eight eyes (66,6 percent) had uncorrected visual acuity equal to or better than 20/40 at the last visit. None of the patients had recurrent erosions, stromal necrosis or vascularizations. Endothelial cell counts performend six mouths after surgery in two patients that underwent unilateral surgery indicated no quantitative effects from HTK. These data support previous studies indicating that central corneal topography can be modified by heating corneal stroma in a controlled fashion. Regression of effect and induction of astigmatism limited the success of our series. Surgical correction of hyperopia includes hyperopic keratomileusis, hyperopic epikeratophakia, hexagonal keratotomy, thermokeratoplasty and more recently photorefractive keratectomy. 1-5 Thermokeratoplasty, a surgical procedure that involves heating of the corneal tissues, was initially attempted in patients with keratoconus. 6 Initial reports of success 6 were followed by reports of profound initial flattening but with subsequsnt return to preoperative topography, 7 and complications such as delayed epithelial healing, recurrent epithelial erosions, aseptic stromal necrosis and melting and vascularization 8...