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

Termoceratoplastia para a correção de hipermetropia: Um estudo clínico

SUMMARY

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 radial pattern of spots on the peripheral cornea, using the Fyodorov thermal unit. The number of spots and the shape ofthe 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), 0.74±1.26 (P=0.001), 1.05±1.34 (P=0.001) and 3.84±1.13 diopters (P=0.16), 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%), remained unchanged in one eye (8.3%) and decreased in two eyes (16.7%). Eight eyes (66.6%) 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 vascularization. Endothelial cell counts performed six months after surgery in two patients that underwent unilateral surgery indicated no quantitative or qualitative 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 ofhyperopia 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 subsequent return to preoperative topography,⁷ and complications such as delayed epithelial healing, recurrent epithelial erosions, aseptic stromal necrosis and melting and vascularization⁸. The Los Alamos probe, an instrument designed to heat the stromal collagen using radiofrequency waves, was reported to procedure short-lived topographic changes. ^9,10 Alternative methods of heating the corneal stroma to steepen the central cornea or using a hot copper wire, such as the one introduced by Fyodorov, or others using different types of thermalasers, have been reported. ^4,11-16

Clinical experience reported in the literature with heating of the corneal tissues to produce topographic changes is limited. We report here our results in a prospective study using the Fyodorov thermal unit to treat hyperopia and hyperopia associated with astigmatism in sighted eyes.

Key Words:
Hyperopia; Thermokeratoplasty; Cornea, Stromal shrinkage

RESUMO

A curvatura corneana pode ser alterada através da concentração das fibras colágenas com a utilização de um cautério sob a forma de sonda, em um procedimento denominado termoceratoplastia para hipermetropia. Este processo induz aumento da curvatura corneana e acentuação de seu poder dióptrico. Doze olhos hipermétropes de oito pacientes foram tratados por esta técnica aplicando-se a unidade térmica de Fyodorov de forma radial. A programação cirúrgica foi determinada pelo "software” que acompanha a unidade. O acompanhamento variou de 24 a 54 semanas (média de 31,5). O equivalente esférico variou de 4,10±1,12 dioptrias para -0,85±0,86 (P = 0,001), 0,74±1,26 (P=0,001), 1,05±1,34 (P = 0,001) e 3,84±1,13 dioptrias (P=0,16), respectivamente aos 4, 12 e 24 semanas após a cirurgia e na última consulta. O aumento induzido de curvatura corneana regrediu significantemente entre 4 semanas e a última avaliação. Setenta e cinco por cento dos pacientes apresentaram melhora na acuidade visual não corrigida de pelo menos duas linhas. Em nenhum dos pacientes avaliados observou-se erosões recorrentes, neovascularização ou necroses estromais. Em dois pacientes onde foi realizada microscopia especular seis meses após a cirurgia não se detectaram alterações endoteliais. Este estudo confirma o efeito limitado e temporário da termoceratoplastia na correção da hipermetropia.

Palavras-chave:
Hipermetropia; Termoceratoplastia; Córnea

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Publication Dates

• Publication in this collection
  Apr 1997