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This chapter describes how to employ a geometrical analysis of the human cornea in order to detect differences in a sample with healthy corneas and corneas with abnormal corneal topography. We obtained geometrical data from a total of 120 patients divided into two groups: healthy (89) and subclinical keratoconic (31) corneas. The proposed detection method generates a virtual 3D solid custom model of the cornea employing Computer-Aided Geometric Design tools and using raw data from a discrete and finite set of spatial points representative of both sides of the corneal surface provided by a corneal topographer. Determined geometric variables are then extracted from the model and statistically analyzed to detect any corneal deformation. The predictive value of the modeled variables was established through a ROC analysis, achieving the Posterior apex deviation variable the best results. This accurate characterization of the human cornea enables new paths in the detection of this type of corneal pathology and offers a new and more integrated tool that facilitates a better diagnosis and follow-up of keratoconus.

PURPOSE: To analyze the initial data obtained in a group of patients treated with microwave keratoplasty followed by accelerated corneal collagen cross-linking (CXL) for the correction of keratoconus. METHODS: Prospective, nonrandomized clinical study including six eyes from four patients treated with microwave thermal keratoplasty followed by accelerated CXL. Refractive, topographic, anterior aberrometry, and corneal biomechanics outcomes were analyzed during 6-month follow-up. RESULTS: Immediately after the procedure, a significant reduction of >7.00 diopters (D) was observed in mean keratometry ( P =.02). Uncorrected distance visual acuity increased from 0.92±0.52 logMAR (Snellen 20/160) preoperatively to 0.47±0.19 logMAR (Snellen 20/60) postoperatively ( P =.05). No statistically significant change was found in corrected distance visual acuity ( P =.28). Corneal higher order aberration decreased from 1.89±0.90 to 1.51±0.65 μm and corneal primary coma aberration decreased from 1.45±0.68 μm preoperatively to 0.84±0.23 μm postoperatively ( P >.10). No statistically significant changes were found in the biomechanics variables ( P =.40). A significant regression of the effect was assessed in keratometry at the end of follow-up ( P =.03). CONCLUSIONS: The Keraflex procedure may have the ability to improve refractive status in patients who suffer from keratoconus, as well as induce corneal remodeling to a more anterior regular surface. However, the current treatment regimen is not sufficient to maintain the flattening effect achieved and significant regression occurs.

To evaluate the corrective potential of corneal wavefront-guided photorefractive keratectomy (PRK) in patients with high levels of corneal aberrations and symptoms after previous corneal refractive surgery.Vissum-Instituto de Oftalmológico de Alicante, Alicante, Spain.This study comprised 25 eyes (20 patients) that had 1 or more previous unsuccessful keratorefractive procedure. All eyes had PRK retreatment using the Esiris excimer laser and ORK-CAM software for customized ablation design. All eyes had a high preoperative level of corneal higher-order aberrations (HOAs) (coma-like or spherical-like root mean square [RMS]0.5 microm). Changes in refractive outcomes, subjective symptoms, and corneal aberrometry were evaluated during a 6-month follow-up.Uncorrected visual acuity improved significantly from preoperatively (mean 0.48) to 6 months after retreatment (mean 0.75) (P.01). The mean best spectacle-corrected visual acuity (BSCVA) also improved significantly, from 0.78 to 0.90, respectively (P.01). Forty-four percent of patients gained 1 or more lines of BSCVA. The reduction in cylinder at 6 months was statistically significant (P= .01). Corneal aberrometry at 6 months showed a statistically significant reduction in total (P= .01), spherical-like (P.01), coma-like (P= .02), and primary coma (P.01) RMS. At 6 months, 72% of patients had low or no perception of halos and all reported no glare.Corneal wavefront-guided PRK enhancement with the ORK-CAM system minimized corneal HOAs in eyes with previous unsuccessful keratorefractive surgery.

Purpose: To evaluate the relationship between two anterior chamber anatomical parameters, angle-to-angle and iris pigment end-to-iris pigment end distances, and sulcus-to-sulcus diameter. Methods: Twenty eyes without active ocular pathologies or previous ocular surgeries from 20 patients ranging in age from 23 to 51 years were included in this study. Mean spherical equivalent refraction ranged from +5.50 to −7.00 diopters. Angle-to-angle and iris pigment end-to-iris pigment end distances were measured in all cases three times consecutively using two technologies: optical coherence tomography (OCT) and very high-frequency ultrasonography. Sulcus-to-sulcus diameter was additionally obtained by ultrasonography. Correlation, linear regression, intrasession, and interchangeability analysis between parameters was performed. Results: Mean sulcus-to-sulcus diameter was 11.92±0.80 mm. Mean angle-to-angle distance was 12.14±0.52 mm for ultrasonography and 12.23±0.59 mm for OCT. Mean iris pigment end-to-iris pigment end distance was 12.18±0.51 mm for ultrasonography and 12.29±0.61 mm for OCT. No statistically significant differences were found among these anatomical parameters (unpaired Student t test, all P >.10). Statistically significant correlations were found between sulcus-to-sulcus diameter and angle-to-angle distance and between sulcus-to-sulcus diameter and iris pigment end-to-iris pigment end distance for both imaging techniques. For ultrasonography, range of agreement was 0.90 mm between sulcus-to-sulcus diameter and angle-to-angle distance and 0.74 mm between sulcusto-sulcus diameter and iris pigment end-to-iris pigment end distance. These ranges increased to 1.22 mm and 1.14 mm, respectively, for OCT measurements. Conclusions: Angle-to-angle and iris pigment end-toiris pigment end distances are correlated with sulcus-to-sulcus diameter, but they cannot be used as equivalent parameters. [ J Refract Surg. 2009;25:1017–1025.]

To evaluate the improvement in visual and optical performance after corneal wavefront-guided laser in situ keratomileusis (LASIK) enhancement in patients with high levels of corneal coma aberration and complaints about quality of vision.Vissum-Instituto Oftalmológico de Alicante, Alicante, Spain.Corneal wavefront-guided LASIK enhancement was performed in 34 symptomatic eyes of 29 patients aged 26 to 64 years with previous LASIK surgery and a significant level of primary coma aberration. The ablation design was calculated using ORK-CAM software (Schwind eye-tech-solutions). The follow-up period was 6 months. Changes in refraction, corneal aberrometry, and subjective symptoms were analyzed.At 6 months, the mean efficacy index was 0.88 +/- 0.12 and the mean safety index, 1.03 +/- 0.16. The reduction in sphere and cylinder at 1 month was statistically significant (P.01). Of all eyes, 97.06% had a spherical equivalent within +/-1.00 diopter. At 1 month, statistically significant changes were observed: total (P = .01), and primary coma root mean square reduction (P.01), and negativization of the primary spherical aberration coefficient (P.01). At 6 months, patient perception of halos and glare was reduced or eliminated in a high percentage of cases.Corneal wavefront-guided enhancements with the ORK-CAM system are a useful tool for the correction of the second order refractive errors and for the reduction of the corneal primary coma induced by previous keratorefractive procedures.

To determine the equivalence of corneal white-to-white (WTW) diameter and anterior segment angle-to-angle (ATA) measurements.Vissum Instituto Oftalmologico de Alicante, Alicante, Spain.Thirty eyes of 19 patients ranging in age from 20 to 51 years old with no previous ocular surgeries were included in this study. In all cases, the horizontal WTW diameter was measured with a tool provided by the CSO corneal topography system (Costruzione Strumenti Oftalmici) and the horizontal ATA was measured using an optical coherence tomography (OCT) system (Visante, Carl Zeiss Meditec AG). All measurements were repeated 3 times to evaluate intrasession repeatability. The correlation between WTW and ATA measurements was studied, and the interchangeability of the 2 parameters was assessed using the Bland and Altman method.The mean corneal WTW diameter was 12.25 mm +/- 0.49 (SD) (range 11.34 to 13.16 mm), and the mean ATA distance was 11.76 +/- 0.52 mm (range 10.03 to 12.92 mm). The difference between the 2 parameters was statistically significant (P.01). A weak, although statistically significant, positive correlation (r = 0.39; P = .03) and a nonpredictive linear model were found. The Bland and Altman analysis showed large limits of agreement between WTW and ATA measurements that are clinically relevant (limits of agreement, -1.59 mm and 0.61 mm). The intrasession repeatability scores for the WTW and ATA measurements were good.The WTW and ATA distance measurements were not equivalent and thus are not interchangeable. There was no linear model for an accurate prediction of the ATA from the WTW.

PURPOSE: To analyze the outcomes of intracorneal ring segment (ICRS) implantation for the treatment of keratoconus based on preoperative visual impairment. DESIGN: Multicenter, retrospective, nonrandomized study. METHODS: A total of 611 eyes of 361 keratoconic patients were evaluated. Subjects were classified according to their preoperative corrected distance visual acuity (CDVA) into 5 different groups: grade I, CDVA of 0.90 or better; grade II, CDVA equal to or better than 0.60 and worse than 0.90; grade III, CDVA equal to or better than 0.40 and worse than 0.60; grade IV, CDVA equal to or better than 0.20 and worse than 0.40; and grade plus, CDVA worse than 0.20. Success and failure indices were defined based on visual, refractive, corneal topographic, and aberrometric data and evaluated in each group 6 months after ICRS implantation. RESULTS: Significant improvement after the procedure was observed regarding uncorrected distance visual acuity in all grades (P < .05). CDVA significantly decreased in grade I (P < .01) but significantly increased in all other grades (P < .05). A total of 37.9% of patients with preoperative CDVA 0.6 or better gained 1 or more lines of CDVA, whereas 82.8% of patients with preoperative CDVA 0.4 or worse gained 1 or more lines of CDVA (P < .01). Spherical equivalent and keratometry readings showed a significant reduction in all grades (P ≤ .02). Corneal higher-order aberrations did not change after the procedure (P ≥ .05). CONCLUSIONS: Based on preoperative visual impairment, ICRS implantation provides significantly better results in patients with a severe form of the disease. A notable loss of CDVA lines can be expected in patients with a milder form of keratoconus.