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Corneal collagen crosslinking (CXL) with riboflavin and ultraviolet-A light is a method for treating progressive keratectasia. The currently accepted treatment parameters induce collagen crosslinking in the anterior 250 to 350 microm of corneal stroma. To protect the endothelium, CXL inclusion criteria require a minimum corneal thickness of 400 microm after removal of the epithelium. In advanced keratoconus, however, progressive corneal thinning often leads to a remaining stromal thickness of less than 400 microm. We have therefore modified the current treatment protocol by preoperatively swelling thin corneas to a stromal thickness of at least 400 microm using hypoosmolar riboflavin solution. This treatment protocol was performed in a case series of 20 patients, and no complications were observed. Preoperative swelling of the cornea safely broadens the spectrum of CXL indications to thin corneas that would otherwise not be eligible for treatment.

Iatrogenic keratectasia after laser in situ keratomileusis (LASIK) represents a serious complication of refractive laser surgery. We describe a woman who developed bilateral iatrogenic keratectasia during her first pregnancy 26 months after LASIK. Corneal collagen crosslinking (CCL) with riboflavin and ultraviolet-A was performed in March 2005 (right eye) and April 2005 (left eye). This treatment stopped the progression and even caused the keratometric steepness to regress over a postoperative follow-up of 22 months, as demonstrated by preoperative and postoperative corneal topographies and maximum K-readings. During the patient's second pregnancy, the keratectasia exacerbated. To our knowledge, this is the first case showing exacerbation of keratectasia despite CCL and, as the exacerbation occurred only during pregnancy, suggesting that hormonal changes might affect corneal biomechanical stability.

Purpose: To compare the correlation between corneal and total wavefront aberrations in normal phakic and pseudophakic eyes after implantation of foldable monofocal intraocular lenses (IOLs)., Setting: University Hospital, Eye Clinic, Zurich, Switzerland., Methods: Wavefront aberrations and corneal topography of 29 eyes that had cataract surgery with implantation of hydrophobic monofocal foldable IOL (AcrySof, Alcon Labs) were measured at least 2 months postoperatively and compared with wavefront measurements performed in 33 normal young phakic eyes. The total wavefront aberrations were measured by means of a Tscherning wavefront sensor at a wavelength of 660 nm (Allegro Wave Analyzer, WaveLight Laser Technology). The corneal aberrations were derived from corneal topography measurements ascertained with a Placido-based topography system (Keratograph 70600, Oculus). The correlations between corneal and total wavefront aberrations were calculated for all Zernike coefficients from 2nd up to 6th order., Results: There was a significant correlation between corneal and total wavefront aberrations in astigmatism C3 and C5 as well as for all 3rd-order Zernike coefficient in both groups (except C8 in the pseudophakic group). The correlation between corneal and total astigmatism (C3 and C5) was higher in the pseudophakic than in the phakic eyes. In contrast, the correlation for the coma-like aberrations was weaker in the pseudophakic eyes (R>0.18) than in the group of phakic eyes (R>0.58). In both groups, there was no significant correlation between spherical aberration C12 of the cornea and the C12 of the total eye., Conclusion: After cataract surgery with an IOL implantation, both vertical and horizontal coma, as well as spherical aberration, were of higher value than in normal eyes. The compensation effect for corneal aberrations of the natural lens is absent in the IOL and explains these findings. The corneal aberrations in pseudophakic eyes reflect better the optical quality of the total eye than the phakic eyes. Nevertheless, the missing correlation in some specific aberrations, such as C8 and C10, shows the inability of corneal topography to provide suitable information on the optical quality of the total eye after cataract surgery. Thus, both corneal and total wavefront measurements are relevant for the assessment of outcomes after cataract surgery.

Purpose: To compare the results of the Q-factor customized aspheric ablation profile with the wavefront-guided customized ablation pattern for the correction of myopic astigmatism., Setting: Institute for Refractive and Ophthalmic Surgery, Zurich, Switzerland., Methods: Thirty-five patients were enrolled in a controlled study in which the nondominant eye was treated with the Q-factor customized profile (custom-Q study group) and the dominant eye was treated with wavefront-guided customized ablation (control group). Preoperative and 1-month postoperative high-contrast visual acuity, low-contrast visual acuity, and glare visual acuity, as well as aberrometry and asphericity of the cornea, were compared between the 2 groups. All eyes received laser in situ keratomileusis surgery, and the laser treatment was accomplished with the Wavelight Eye-Q 400 Hz excimer laser., Results: For corrections up to -9 diopters (D) of myopia, there were no statistically significant differences between the 2 groups regarding any visual or optical parameter except coma-like aberrations (3rd Zernike order), where the wavefront-guided group was significantly better 1 month after surgery (P = .002). For corrections up to -5 D (spherical equivalent), the Q-factor optimized treated eyes had a significantly smaller shift toward oblate cornea: DeltaQ15 = 0.25 in Q-factor customized versus DeltaQ15 = 0.38 in wavefront-guided treatment (P = .04)., Conclusions: Regarding safety and refractive efficacy, custom-Q ablation profiles were clinically equivalent to wavefront-guided profiles in corrections of myopia up to -9 D and astigmatism up to 2.5 D. Corneal asphericity was less impaired by the custom-Q treatment up to -5 D of myopia.

Purpose: To determine the shifts of the main corneal reference points in dependence of the chosen centration axis for the treatment., Setting: Federal Institute of Technology Zurich, Institute of Biomedical Engineering, Zurich, Switzerland., Methods: Computer simulations were performed on several variants of the Gullstrand-Emsley schematic eye, which was modified by an off-axis fovea. Refractive corrections were simulated by centering Munnerlyn's formula on each of the 4 corneal reference points determined in the preoperative eye: the optical axis, the line of sight, the visual axis, and the first corneal reflex. Subsequently, the postoperative locations of these axes were determined and compared with the preoperative values., Results: The postoperative line of sight was found to depend least on the choice of the preoperative centration axis for both myopic and hyperopic treatments. It undergoes a maximum movement of 0.040 mm when centering a +5 diopter correction on the preoperative line of sight, whereas the corneal reflex, which is used for centering most topography systems, can move by more than 0.10 mm., Conclusions: Centration of the correction on the preoperative line of sight enabled good comparability between preoperative and postoperative measurements that use the line of sight as a reference axis. Yet, centration of the treatment on the preoperative line of sight does not ensure comparability between preoperative and postoperative measurements that use the corneal reflex as a reference axis such as most corneal topography systems. Axis shifts might lead to misinterpretation of data such as a wrong diagnosis of a decentered ablation or changes in the Zernike representation.