Scleral cross-linking by riboflavin and blue light application in young rabbits: damage threshold and eye growth inhibition.

BACKGROUND: Scleral cross-linking (SXL) by riboflavin and light application has been introduced as a possible treatment to increase scleral tissue stiffness and to inhibit excessive axial elongation of highly myopic eyes. We evaluated an ocular tissue damage threshold for blue light irradiation, and used SXL treatment to induce eye growth inhibition. METHODS: The sclera of 3-week-old rabbits (39 pigmented and 15 albino rabbits) were treated with different blue light intensities (450 ± 50 nm) and riboflavin. Alterations and a damage threshold were detected in ocular tissues by means of light microscopy and immunohistochemistry. The influence of SXL on the eye growth was examined in 21 young rabbits and was measured by using A-scan ultrasonography, micrometer caliper, and for selected eyes additionally by MR imaging. RESULTS: Light microscopic examinations demonstrated degenerative changes in ocular tissue after irradiation with blue light intensities above 400 mW/cm(2) (with and without riboflavin application). Therefore, that light intensity was defined as the damage threshold. Tissue alteration in retina, choroid, and sclera and activation of retinal microglia cells and Müller cells could be earlier observed at blue light intensities of 150 and 200 mW/cm(2). Albino rabbits were less sensitive to this SXL treatment. A significant reduction of the eye growth could be detected by SXL treatment with the minimal efficient blue light intensity of 15 mW/cm(2) and maintained stable for 24 weeks. CONCLUSIONS: SXL with riboflavin and blue light intensities below a defined damage threshold can induce a long lasting growth inhibitory effect on young rabbit eyes. Therefore, SXL might be a realistic approach to inhibit eye elongation in highly myopic eyes.

Dose-dependent collagen cross-linking of rabbit scleral tissue by blue light and riboflavin treatment probed by dynamic shear rheology.

PURPOSE: To determine the visco-elastic properties of isolated rabbit scleral tissue and dose-dependent biomechanical and morphological changes after collagen cross-linking by riboflavin/blue light treatment. MATERIAL: Scleral patches from 87 adult albino rabbit eyes were examined by dynamic shear rheology. Scleral patches were treated by riboflavin and different intensities of blue light (450 nm), and the impact on the visco-elastic properties was determined by various rheological test regimes. The relative elastic modulus was calculated from non-treated and corresponding treated scleral patches, and treatments with different blue light intensities were compared. RESULTS: Shear rheology enables us to study the material properties of scleral tissue within physiological relevant parameters. Cross-linking treatment increased the viscous as well as the elastic modulus and changed the ratio of the elastic versus viscous proportion in scleral tissue. Constant riboflavin application combined with different blue light intensities from 12 mW/cm(2) up to 100 mW/cm(2) increased the relative elastic modulus of scleral tissue by factors up to 1.8. Further enhancement of the applied light intensity caused a decline of the relative elastic modulus. This might be due to destructive changes of the collagen bundle structure at larger light intensities, as observed by histological examination. CONCLUSION: Collagen cross-linking by riboflavin/blue light application increases the biomechanical stiffness of the sclera in a dose-dependent manner up to certain light intensities. Therefore, this treatment might be a suitable therapeutic approach to stabilize the biomechanical properties of scleral tissue in cases of pathological eye expansion.

Laboratory measurement of the absorption coefficient of riboflavin for ultraviolet light (365 nm).

PURPOSE: Corneal cross-linking (CXL) is an increasingly used treatment technique for stabilizing the cornea in keratoconus. Cross-linking (polymerization) between collagen fibrils is induced by riboflavin (vitamin B2) and ultraviolet light (365 nm). Although reported to reach a constant value at higher riboflavin concentrations, the Lambert-Beer law predicts a linear increase in the absorption coefficient. This work was carried out to determine absorption behavior at different riboflavin concentrations and to further investigate the purported plateau absorption coefficient value of riboflavin and to identify possible bleaching effects. METHODS: The Lambert-Beer law was used to calculate the absorption coefficient at various riboflavin concentrations. The following investigated concentrations of riboflavin solutions were prepared using a mixture of 0.5% riboflavin and 20% Dextran T500 dissolved in 0.9% sodium chloride solution: 0%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%, and were investigated with and without aperture plate implementation. An additional test series measured the transmitted power at selected riboflavin concentrations over time. RESULTS: In diluted solutions, a linear correlation exists between the absorption coefficient and riboflavin concentration. The absorption coefficient reaches a plateau, but this occurs at a higher riboflavin concentration (0.1%) than previously reported (just above 0.04%). Transmitted light power increases over time, indicating a bleaching effect of riboflavin. CONCLUSIONS: The riboflavin concentration can be effectively varied as a treatment parameter in a considerably broader range than previously thought.

Collagen crosslinking with ultraviolet-A and hypoosmolar riboflavin solution in thin corneas.

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.

Efficacy and safety of blue-light scleral cross-linking.

PURPOSE: To evaluate the efficacy of blue-light scleral cross-linking as well as its safety in preventing retinal damage beneath the treated sclera. METHODS: Six rabbits were unilaterally treated with topical riboflavin (0.5%) and blue light (465 nm) on the equatorial sclera using a light emitting diode source with an exposure area of 9 mm in diameter. Four weeks after the treatment, the animals were euthanized and the exposed sclera and contralateral eye sclera excised for comparative testing of biomechanical rigidity and histologic retinal cellular damage. Extensiometry was performed to evaluate the stress-strain curve of treated versus untreated sclera, and light microscopy of the treated sclera and underlying retina were also comparatively evaluated. RESULTS: Blue-light scleral cross-linking showed a three-fold increased stiffening in all tested animals in the stress-strain curve. Histological investigation revealed no retinal damage in any of the treated eyes. CONCLUSIONS: Scleral cross-linking with riboflavin and blue light (465 nm) has a stiffening effect on the sclera without histological tissue damage to the retina.

Pregnancy-related exacerbation of iatrogenic keratectasia despite corneal collagen crosslinking.

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.

Topography-guided surface ablation for forme fruste keratoconus.

PURPOSE: To evaluate the efficacy of customized surface ablation in cases of forme fruste keratoconus. DESIGN: Prospective noncomparative case series. PARTICIPANTS: Eleven eyes of 8 contact lens-intolerant patients with forme fruste keratoconus treated at the Institute of Refractive and Ophthalmic Surgery and the University Eye Clinic Zurich. INTERVENTION: Topography-guided customized surface ablation by means of a scanning spot excimer laser. MAIN OUTCOME MEASURES: Visual acuity, refraction, quality of vision (ghosting), corneal topography including the Zernike parameter Z3. RESULTS: Statistically significant reduction of manifest refractive error, corneal irregularity, and ghosting. The spherical equivalent was reduced by -2.8+/-0.62 diopters (D) (P = 0.0007), the cylinder by 1.34 +/- 0.18 D (P = 0.015), Z3 was reduced by 41% (P<0.001), and all patients had less ghosting compared to their preoperative status. No eye lost > or =1 lines in best spectacle-corrected visual acuity; however, 7 of 11 eyes gained > or = 1 line. CONCLUSION: Topography-guided surface ablation is a promising option to rehabilitate vision in contact lens-intolerant patients with forme fruste keratoconus.

Corneal and total wavefront aberrations in phakic and pseudophakic eyes after implantation of monofocal foldable intraocular lenses.

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.

Q-factor customized ablation profile for the correction of myopic astigmatism.

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.

The effect of phenylephrine and cyclopentolate on objective wavefront measurements.

PURPOSE: To investigate the impact of phenylephrine and cyclopentolate on wavefront refraction and fourth order spherical aberration C12. METHODS: This cohort study comprised 151 eyes with sphere up to -10.00 diopters (D) and cylinder -3.75 D. Aberrometry was performed using the ALLEGRO WAVE (WaveLight Laser Technologies AG, Erlangen, Germany) after instillation of phenylephrine 5% yielding objective phenylephrine refraction in accommodated steady-state, as well as after cyclopentolate 0.5% providing objective cyclopentolate refraction in non-accommodated state. Accommodation target fogging was turned off. Wavefront aberrations were expressed by Zernike expansion up to the sixth order, and paraxial curvature matching with Taylor series was used to calculate objective wavefront sphere. RESULTS: Objective wavefront sphere was not influenced by pupil size. Eyes showed substantial accommodation after phenylephrine with a myopic shift of -0.66 D comparing objective to subjective manifest sphere (r=0.942, P<.001). Cycloplegic eyes behaved like a model eye, with a difference of -0.08 D between objective and subjective cycloplegic sphere (r=0.976, P<.001). C12 increased ten-fold from 4.0- to 7.0-mm pupil size, keeping the same sign. Comparing cyclopentolate with phenylephrine, the sign of C12 changed in a positive direction by an average +0.124 +/- 0.109 microm (range: -0.052 to +0.632 microm) at 7.0 mm, whereas the total higher order aberrations changed very little. A good correlation was found between C12 and the change in objective wavefront sphere between cyclopentolate and phenylephrine (r=0.75, P<.001). CONCLUSIONS: Fogging of the accommodation target should be used for wavefront measurements. Weaker cycloplegic agents, such as tropicamide, may be used to ensure relaxed but not completely paralyzed accommodation, which would yield "manifest" aberration values close to the natural resting state.

Treatment-induced shifts of ocular reference axes used for measurement centration.

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.

Clinical photoablation with a 500-Hz scanning spot excimer laser.

PURPOSE: The aim of this study was to use a 500-Hz scanning spot laser (Concept500, WaveLight Laser Technologie AG, Erlangen, Germany) to investigate potential side effects that might be associated with the use of a high repetition rate laser platform. METHODS: Seven eyes were treated using a 500-Hz scanning spot laser for laser in situ keratomileusis (LASIK). The local frequency of the ablation was kept below 40 Hz to avoid local heating of corneal tissue. With the exception of the high repetition rate (500 Hz), all other laser parameters such as fluence, algorithm, ablation profile, and spot diameter were identical to a standard WaveLight Allegretto laser system. Patients were examined at 1 month and 1 year after initial treatment. Preoperative and postoperative examination included manifest sphere and cylinder, uncorrected and best spectacle-corrected visual acuity (BSCVA). RESULTS: All eyes were treated for myopia or myopic astigmatism. Five eyes received spherocylindrical and two eyes spherical ablation only. No adverse events correlated with the use of a high repetition rate laser system were observed during surgery or at any point during follow-up. All eyes maintained or had improved BSCVA at 12 months after treatment when compared to preoperative values. CONCLUSION: The use of an excimer laser with a maximal repetition rate of 500 Hz and a local repetition rate of less than 40 Hz was free of any specific side effect that might be associated with the use of such a high repetition rate.

Transferring wavefront measurements into corneal ablations: an overview of related topics.

We give an overview of possible side effects that are specific for, or of particular relevance in, customized treatments. Certain processes involved in customized ablations have the potential to alter the quality of the optical correction. Professionals associated with customized treatment should be informed and trained with respect to possible sources of error.

Conservative treatment of vertical diplopia in a patient with silent sinus syndrome.

Silent sinus syndrome is a rare disease of the maxillary sinus characterized by bony absorption processes leading to progressive sinus wall thinning with consecutive enophthalmos and hypoglobus. It represents a benign cause of acquired enophthalmos and is often accompanied by painless vertical diplopia, the latter treated surgically in all cases published to date. We report a 56-year-old patient with silent sinus syndrome in whom vertical diplopia was treated with prisms showing that conservative treatment alone may, in mild cases, be an effective alternative to reconstructive surgery.

Fra-1 substitutes for c-Fos in AP-1-mediated signal transduction in retinal apoptosis.

Lack of the AP-1 member c-Fos protects photoreceptors against light-induced apoptosis, a model for retinal degeneration. In mice, light damage increases the activity of the transcription factor AP-1, while pharmacological suppression of AP-1 prevents apoptosis, suggesting the involvement of pro-apoptotic AP-1 target genes. Recently, however, it was shown that photoreceptors expressing Fra-1 in place of c-Fos (Fos (Fosl1/Fosl1) ) are apoptosis competent despite the lack of transactivation domains in Fra-1. Here, we show that morphological features of light-induced apoptosis were indistinguishable in Fos (Fosl1/Fosl1) and wild-type mice. Furthermore, light exposure comparably increased AP-1 activity in both genotypes. Opposite to wild-type mice, Fra-1, but not c-Fos, was detectable in AP-1 complexes of Fos (Fosl1/Fosl1) mice. Importantly, AP-1 responsiveness for glucocorticoid receptor-mediated inhibition was preserved in Fos (Fosl1/Fosl1) mice. Thus, Fra-1 takes over for c-Fos in pro- and anti-apoptotic signal transduction. As Fra-1 lacks transactivation domains, AP-1 may not induce, but rather suppress genes in retinal light damage.