Mechanical Stability of the Cornea After Radial Keratotomy and Photorefractive Keratectomy

Abstract

BACKGROUND: Corneal refractive surgical procedures alter the shape and structure of the tissue, possibly compromising its mechanical stability. METHODS: One or both eyes of 87 subjects were studied: 26 of these 87 had been treated for myopia by excimer laser ablation and 36 by radial keratotomy; 25 without previous corneal surgery functioned as controls. Corneal topography was evaluated by TMS-I videophotokeratography before and after 180° tilting of the patient, and the pressureinduced ring-wise changes in spherical equivalent power (axial power) were calculated. Changes in corneal shape also were evaluated by computing the instantaneous radius of curvature. The intraocular pressure was measured before and after tilting by a hand-held applanation tonometer. RESULTS: The mean intraocular pressure increased from 13.9 + 2.3 nun Hg before tilting to 30.0 ± 3.8 mm Hg during tilting. In the control eyes, the mean power of the central cornea during tilting decreased 0.187 + 0.045 diopters (D) (p<.05); in the excimer-laser-ablated eyes, 0.038 ± 0.056 D (not statistically significant); and in those treated with radial keratotomy, 0.523 ± 0.054 D (p<.01). After radial keratotomy, the cornea steepened outside the clear zone in response to pressure loading, whereas it did not change significantly in the laserablated or control eyes. CONCLUSIONS: Pressure-induced deformation of normal and excimer laser-ablated human cornea is small, whereas radially incised corneas have significantly decreased mechanical stability. [J Refract Surg. 1996;12:459-466.]

Relationship between postoperative intraocular pressure and refractive outcomes in patients after deep anterior lamellar keratoplasty

“… 14 The human cornea has been found to change curvature in response to IOP increments of 5 mmHg, 8 mmHg, and 16 mmHg. 15 16 17 With limbal integrity being affected during DALK, cylindrical changes might be more pronounced with higher IOP.…”

Long-Term Stability of Femtosecond Astigmatic Keratotomy After Treatment of High Postkeratoplasty Astigmatism

“…For example, radial keratotomy (RK) stromal incisions which have been used in the past for the correction of myopic refractive errors were associated with significant long-term instability. 6 Böhringer et al 7 evaluated longer-term outcomes of manual astigmatic keratotomy (AK) and found an increase of keratometric astigmatism after the procedure by 0.3 D/year, equalizing the surgical effect after 10 years. The authors concluded that it may be interesting to check whether the use of a femtosecond laser makes FSAK more stable than manual arcuate keratotomy over a longer follow-up time.…”