Central and peripheral corneal thickness measured with optical coherence tomography, Scheimpflug imaging, and ultrasound pachymetry in normal, keratoconus-suspect, and post-laser in situ keratomileusis eyes.

PURPOSE: To compare central (CCT) and peripheral corneal thickness (PCT) using Scheimpflug imaging (Pentacam), high-speed optical coherence tomography (Visante OCT), and ultrasound (US) pachymetry (Sonogage Corneo-Gage Plus) in normal, keratoconus-suspect, and post-laser in situ keratomileusis (LASIK) eyes. SETTING: Department of Refractive Surgery, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA. METHODS: The CCT and PCT were retrospectively measured using US pachymetry, Scheimpflug imaging, and high-speed OCT from January 2006 to March 2008. The influence of age and absolute magnitude of corneal thickness were also analyzed. Analysis was by multivariate generalized estimating equations, multivariate linear regression, and linear regression plots. RESULTS: One hundred sixty-three eyes were analyzed. Ultrasound pachymetry CCT measurements were consistently higher than Scheimpflug and OCT measurements (mean difference 6.5 microm +/- 1.8 [SD] and 7.5 +/- 1.4 microm, respectively) (both P<.0005) in normal eyes; the difference was statistically similar and not greater with keratoconus suspicion, age, or absolute magnitude of corneal thickness (P>.05). Scheimpflug measurements were significantly lower than US pachymetry in post-LASIK eyes (P<.0005). There was no statistically significant difference (mean 0.9 +/- 1.4 microm) in Scheimpflug and OCT CCT measurements (P>.5), although Scheimpflug measurements were significantly lower in post-LASIK eyes (P<.0005). Scheimpflug PCT measurements were higher than OCT measurements, showing more agreement with increasing age (P = .017). CONCLUSIONS: Scheimpflug and OCT CCT measurements were reproducible but always thinner than US pachymetry in normal and keratoconus-suspect eyes. In post-LASIK eyes, OCT pachymetry maps were more accurate than Scheimpflug maps. The influence of age on PCT requires further study.

Effects of Zernike wavefront aberrations on visual acuity measured using electromagnetic adaptive optics technology.

PURPOSE: This study measured the changes in visual acuity induced by individual Zernike ocular aberrations of various root-mean-square (RMS) magnitudes. METHODS: A crx1 Adaptive Optics Visual Simulator (Imagine Eyes) was used to modify the wavefront aberrations in nine eyes. After measuring ocular aberrations, the device was programmed to compensate for the eye's wavefront error up to the 4th order and successively apply different individual Zernike aberrations using a 5-mm pupil. The generated aberrations included defocus, astigmatism, coma, trefoil, and spherical aberration at a level of 0.1, 0.3, and 0.9 microm. Monocular visual acuity was assessed using computer-generated Landolt-C optotypes. RESULTS: Correction of the patients' aberrations improved visual acuity by a mean of 1 line (-0.1 logMAR) compared to best sphero-cylinder correction. Aberrations of 0.1 microm RMS resulted in a limited decrease in visual acuity (mean +0.05 logMAR), whereas aberrations of 0.3 microm RMS induced significant visual acuity losses with a mean reduction of 1.5 lines (+0.15 logMAR). Larger aberrations of 0.9 microm RMS resulted in greater visual acuity losses that were more pronounced with spherical aberration (+0.64 logMAR) and defocus (+0.62 logMAR), whereas trefoil (+0.22 logMAR) was found to be better tolerated. CONCLUSIONS: The electromagnetic adaptive optics visual simulator effectively corrected and generated wavefront aberrations up to the 4th order. Custom wavefront correction significantly improved visual acuity compared to best-spectacle correction. Symmetric aberrations (eg, defocus and spherical aberration) were more detrimental to visual performance.

[Corneal wound healing response following different modalities of refractive surgical procedures]. / Resposta cicatricial corneana em diferentes modalidades de cirurgia refrativa.

The corneal wound healing response following refractive procedures represents a subject of high relevance, due to its direct influence on the postoperative results. Technical modifications of current refractive procedures, like the automated flap creation with the femtosecond laser, LASEK, PRK with mitomycin C and Epi-LASIK have been proposed as alternatives to traditional LASIK and PRK. Several theoretical advantages have encouraged the diffusion of these new techniques; however, a better understanding of the corneal wound healing response following these procedures is required. The present text proposes a review of the corneal wound healing characteristics following different modalities of refractive surgical procedures.

Resposta cicatricial corneana em diferentes modalidades de cirurgia refrativa / Corneal wound healing response following different modalities of refractive surgical procedures

A resposta cicatricial corneana secundária a procedimentos refrativos, representa assunto de alta relevância, pois influencia diretamente nos resultados pós-operatórios. Modificações técnicas nos atuais procedimentos, como a criação automatizada do retalho corneano ("flap") através de pulsos ultra-rápidos de laser ("Femtosecond laser"), novas modalidades de ceratectomia superficial como a criação de um retalho epitelial com ou sem tratamento prévio com álcool (LASEK ou Epi-LASIK) e a utilização de quimioterápicos como a mitomicina C, vêm sendo propostas como técnicas alternativas aos tradicionais LASIK e PRK. Inúmeras vantagens teóricas vêm impulsionando a difusão dessas novas técnicas, entretanto, melhor entendimento da resposta cicatricial subseqüente a esses procedimentos se faz necessário. O presente texto propõe revisão das principais características da cicatrização corneana que ocorrem após diferentes técnicas de cirurgia refrativa.

Alcon CustomCornea wavefront-guided retreatments after laser in situ keratomileusis.

PURPOSE: To evaluate the outcome of wavefront-guided ablations for the correction of residual myopia and astigmatism after standard laser in situ keratomileusis (LASIK). METHODS: Twenty nine eyes of 26 patients who underwent wavefront-guided LASIK retreatment with Alcon CustomCornea (Alcon Laboratories Inc, Fort Worth, Tex) were evaluated. Complete ophthalmologic examination, corneal topography, and wavefront measurements were performed. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and wavefront analysis were evaluated preoperatively, 1 week, 3 months, and 6 months after surgery. Wavefront measurements were assessed using the LADARWave device. Statistical analysis was performed using the McNemar test and percentages of success. RESULTS: One week postoperatively, UCVA was > or =20/40 in 100% of eyes (> or =20/20 in 31%) and BSCVA was > or =20/40 in 100% (> or =20/20 in 73%). Wavefront analysis showed a decrease in total aberrations, high order aberrations, defocus, coma, spherical aberration, and other terms of higher order aberrations at 1-week follow-up. Three months postoperatively, UCVA was > or =20/40 in 100% of eyes (> or =20/20 in 38%) and BSCVA was > or =20/40 in 100% (> or =20/20 in 81%). Six months postoperatively, UCVA was > or =20/40 in 100% of eyes (> or =20/20 in 60%) and BSCVA was > or =20/40 in 100% (> or =20/20 in 90%). Wavefront analysis showed decrease in total aberration, high order aberration, defocus, coma, and spherical aberration. CONCLUSION: Wavefront-guided LASIK retreatment in post-LASIK eyes represents a good option for laser vision correction. All eyes showed reduction in pre-existing total aberrations. Some high order aberration components decreased in this initial series. Further follow-up is necessary to assess the initial predictability of wavefront-guided LASIK upgrade.

Correlation of aberrations with visual acuity and symptoms.

Standard refractive surgery (photorefractive keratectomy and laser in situ keratomileusis)induces optical changes in the wavefront aberrations of the eye. Higher-order optical changes are induced, especially spherical aberration and coma. Wavefront sensing performed after refractive surgery has revealed a decrease in low-contrast acuity and contrast sensitivity, comprising the patient's night vision and leading to symptoms such as halos, starburst, and glare.