Stephan J. Linke

Retinal cells integrate into the outer nuclear layer and differentiate into mature photoreceptors after subretinal transplantation into adult mice

Vision impairment caused by degeneration of photoreceptors, termed retinitis pigmentosa, is a debilitating condition with no cure presently available. Cell-based therapeutic approaches represent one treatment option by replacing degenerating or lost photoreceptors. In this study the potential of transplanted primary retinal cells isolated from neonatal mice to integrate into the outer nuclear layer (ONL) of adult mice and to differentiate into mature photoreceptors was evaluated. Retinal cells were isolated from retinas of transgenic mice ubiquitously expressing enhanced green fluorescence protein (EGFP) at either postnatal day (P) 0, P1 or P4 and transplanted into the subretinal space of adult wild-type mice. One week to 11 months post-transplantation experimental retinas were analyzed for integration and differentiation of donor cells. Subsequent to transplantation some postnatal retinal cells integrated into the ONL of the host and differentiated into mature photoreceptors containing inner and outer segments as confirmed by immunohistochemistry and electron microscopy. Notably, the appearance of EGFP-positive photoreceptors was not the result of fusion between donor cells and endogenous photoreceptors. Retinal cells isolated at P4 showed a significant increase in their capacity to integrate into the ONL and to differentiate into mature photoreceptors when compared with cells isolated at P0 or P1. As cell suspensions isolated at P4 are enriched in cells committed towards a rod photoreceptor cell fate it is tempting to speculate that immature photoreceptors may have the highest integration and differentiation potential and thus may present a promising cell type to develop cell replacement strategies for diseases involving rod photoreceptor loss.

Association between ocular dominance and spherical/astigmatic anisometropia, age, and sex: analysis of 10,264 myopic individuals.

PURPOSE To determine the association between ocular dominance and spherical or astigmatic anisometropia, age, and sex. METHODS Medical records of 10,264 myopic refractive surgery candidates were filtered. Ocular dominance was assessed with the hole-in-the-card test. Manifest refractive error was measured in each subject and correlated to ocular dominance. Only subjects with corrected distance visual acuity (CDVA) of >20/22 in each eye were enrolled, to exclude amblyopia. Associations between ocular dominance and refractive state were analyzed by means of the t-test, χ(2) test, Spearman correlation, and multivariate logistic regression analysis. RESULTS Right and left eye ocular dominance was noted in 61.7% and 35.6% of the individuals. Ocular dominance had no significant impact on SE refraction in subjects with SE or cylindrical anisometropia <0.5 D. For anisometropia >2.5 D (n = 278) the nondominant eye was more myopic in 63.7% (SE -5.8 ± 2.64 D) compared to 36.3% (-4.69 ± 2.39 D; P < 0.001; adjusted P (Padj) < 0.001) for the dominant eye being more myopic. Nondominant eyes showed higher astigmatic power than dominant eyes (-0.95 ± 0.91 D versus -0.89 ± 0.84 D; P < 0.001). For astigmatic anisometropia >2.5 D, nondominant eyes exhibited a higher amount of astigmatism in 75% of subjects. Nondominant eyes of subjects <29 years and 30 to 39 years of age had a significantly higher astigmatic power than did dominant eyes of the same age group. CONCLUSIONS In contrast to previous reports, this study, including myopic refractive surgery candidates, revealed that the nondominant eye was more myopic for SE anisometropia >2.5 and more astigmatic for cylindrical anisometropia >0.5 D.

LASIK versus photorefractive keratectomy for high myopic (> 3 diopter) astigmatism.

PURPOSE To compare the efficacy, safety, predictability, and vector analysis indices of LASIK and photorefractive keratectomy (PRK) for correction of high cylinder of greater than 3 diopters (D) in myopic eyes. METHODS The efficacy, safety, and predictability of LASIK or PRK performed in 114 consecutive randomly selected myopic eyes with an astigmatism of greater than 3 D were retrospectively analyzed at the 2- to 6-month follow-up visits. Vector analysis of the cylindrical correction was compared between the treatment groups. RESULTS A total of 57 eyes receiving PRK and 57 eyes receiving LASIK of 114 refractive surgery candidates were enrolled in the study. No statistically significant difference in efficacy [efficacy index = 0.76 (±0.32) for PRK vs 0.74 (±0.19) for LASIK (P = .82)], safety [safety index = 1.10 (±0.26) for PRK vs 1.01 (±0.17) for LASIK (P = .121)], or predictability [achieved astigmatism < 1 D in 39% of PRK- and 54% of LASIK-treated eyes, and < 2 D in 88% of PRK- and 89% of LASIK-treated eyes (P = .218)] was demonstrated. Using Alpins vector analysis, the surgically induced astigmatism and difference vector were not significantly different between the surgery methods, whereas the correction index showed a slight and significant advantage of LASIK over PRK (1.25 for PRK and 1.06 for LASIK, P < .001). CONCLUSIONS LASIK and PRK are comparably safe, effective, and predictable procedures for excimer laser correction of high astigmatism of greater than 3 D in myopic eyes. Predictability of the correction of the cylindrical component is lower than that of the spherical equivalent.

Efficacy and predictability of laser in situ keratomileusis for low astigmatism of 0.75 diopter or less

Purpose To examine the refractive and visual outcomes of wavefront‐optimized laser in situ keratomileusis (LASIK) in myopic eyes with low astigmatism of 0.75 diopter (D) or less. Setting University Medical Center Hamburg‐Eppendorf, Germany, and Care Vision private clinics, Germany and Austria. Design Retrospective cross‐sectional data analysis. Methods This study comprised consecutive myopic patients with a preoperative refractive cylinder of 0.75 D or less and a preoperative subjective sphere between −2.75 D and −11.50 D. Three subgroups were formed based on preoperative refractive cylinder magnitude (0.25 D, 0.50 D, and 0.75 D). Manifest refraction, uncorrected distance visual acuity (UDVA), and corrected distance visual acuity were assessed preoperatively and postoperatively. The astigmatic changes were determined using Alpins vector analysis. Results This study enrolled 448 eyes of 448 patients (145 men, 303 women; mean age at surgery 37.8 years ± 9.4 [SD]). By 4 months (mean 116.8 ± 27.7 days) postoperatively, the mean UDVA was 0.10 ± 0.13 logMAR and the mean manifest refraction spherical equivalent (MRSE) −0.05 ± 0.68 D. There was no statistically significant difference in efficacy or safety between the preoperative cylinder groups. Astigmatic overcorrection for a preoperative cylinder of 0.25 D and 0.50 D was suggested by the correction index, the magnitude of error, the index of success, and the flattening index. Conclusions Although the mean UDVA and mean MRSE obtained by the 4‐month follow‐up were appropriate, a preoperative cylinder of 0.50 D or less was significantly overcorrected. Accordingly, caution should be used when considering full astigmatic correction for manifest cylinder of 0.50 D or less. Financial Disclosure Mr. Frings was supported by a grant from Wavelight GmbH, Erlangen, Germany. No author has a financial or proprietary interest in any material or method mentioned.

Screening for Keratoconus With New Dynamic Biomechanical In Vivo Scheimpflug Analyses.

Purpose: To improve keratoconus (KC) screening with new in vivo biomechanical Scheimpflug analyses. Methods: After adjusting for intraocular pressure and corneal thickness, predefined static and new dynamic Scheimpflug curve analyses [Pentacam HR and Corvis ST (CST); Oculus] of 87 normal eyes, 27 subclinical KC eyes, 42 suspected KC, and 65 manifest KC eyes were reviewed retrospectively. A t test (for a normal distribution), Wilcoxon matched-pairs test (if not normally distributed), and receiver operating characteristics were used to test for statistically significant differences between these groups. In addition, new dynamic curve analyses were performed to analyze corneal dynamics throughout the entire response to the CST air puff impulse. Results: Comparing normal and KC-suspect eyes, the parameters A1 length, A2 length, radius of the inward-bended cornea, and deflection length at the highest concavity revealed statistically significant differences. In addition, the newly calculated “applanation length level” and “deflection length level” demonstrated consistently increasing differences with increasing statistical significance between normal eyes and those with advancing KC stages. However, when comparing normal and subclinical KC eyes, none of the analyzed parameters demonstrated statistically significant differences. Conclusions: In vivo biomechanical analyses (CST) at their current state only marginally improve KC screening protocols. Newly generated parameters such as the applanation length level and deflection length level might further improve early KC screening.

Risk factors for donor cornea contamination: retrospective analysis of 4546 procured corneas in a single eye bank.

Purpose: Microbiological contamination is a common cause for elimination of organ-cultured donor corneas. The aims of the present study were to analyze contamination rates and identify risk factors for contamination. Methods: Retrospectively, the contamination rates of 4546 organ-cultured corneas and the causative species were studied. The impact of sex, age, death-to-explantation interval, explantation technique, cause of death, and mean monthly temperature on contamination rate was analyzed. Results: The median annual contamination rate was 5.3% (range: 3%–19%). Most contaminations were of fungal origin (61.9%), with Candida species (45%) being predominant. Bacterial contaminations (34.4%) were dominated by Staphylococcus species (12.8%). Sex, donor age, and mean monthly temperature had no statistically significant influence on the contamination rate. The median death-to-explantation interval of contaminated corneas (44 hours) was longer than that of sterile corneas (39 hours; P < 0.001; n = 4437). Cardiopulmonary failure was associated with the highest contamination rate (13.6%) of all death causes. The switch from whole globe to in situ excision was followed by a temporary increase in contamination rate (12.5%–19.4%). Conclusions: Although the genesis of donor cornea contamination seems to be multifactorial, resident species from physiological skin flora are the main contaminants indicating that the donor corpses could be the main source of microbiological contamination. A change in the explantation technique was followed by an increase in the contamination rate.

effects of laser in situ keratomileusis (lasiK) on corneal biomechanical measurements with the Corvis sT tonometer

Purpose This study was initiated to evaluate biomechanical changes using the Corvis ST tonometer (CST) on the cornea after laser in situ keratomileusis (LASIK). Setting University Medical Center Hamburg-Eppendorf, Germany, and Care Vision Refractive Centers, Germany. Design Retrospective cohort study. Methods This retrospective study included 37 eyes of 37 refractive patients. All CST measurements were performed 1 day before surgery and at the 1-month follow-up examination. The LASIK procedure included mechanical flap preparation using a Moria SBK microkeratome and an Allegretto excimer laser platform. Results Statistically significant differences were observed for mean first applanation length, mean first and second deflection lengths, mean first and second deflection amplitudes, radius of curvature, and peak distance. Significant positive correlations were found between the change (Δ) of radius of curvature and manifest refraction spherical equivalent (MRSE), ablation depth, and Δintraocular pressure as well as between AD and ΔHC-time. Each diopter of myopic correction in MRSE resulted in an increase in Δradius of curvature of 0.2 mm. Conclusion Several CST parameters were statistically significantly altered by LASIK, thereby indicating that flap creation, ablation, or both, significantly change the ability of the cornea to absorb or dissipate energy.

Anterior and posterior corneal changes after crosslinking for keratoconus.

Purpose To evaluate anterior and posterior changes in corneal topography and tomography after corneal crosslinking (CXL) in eyes with progressive keratoconus. Methods Scheimpflug analyses (Pentacam, Oculus) of 20 eyes with keratoconus performed before and after corneal CXL were included into retrospective analysis. Mean follow-up was 2 years. Changes in topographic, tomographic, and pachymetric values were statistically analyzed applying analysis of variance. Further, the distance and direction between the anterior maximum keratometry (Kmax) and the apex as well as the distance and direction between the thinnest point in corneal thickness (TPCT) and the corneal apex before and after CXL were studied. Results Two years after CXL, a statistically significant reduction of the keratometry at the flat meridian (−0.8 D, p < 0.05), the steep meridian (−0.5 D, p < 0.05), the “index of surface variance” (−5.3, p < 0.05), and the “index of highest decentration” (−0.05, p < 0.05) could be demonstrated. While the elevation of the front surface at the apex decreased (−1.5 &mgr;m, p < 0.05), the back elevation at the apex (+2 &mgr;m, p < 0.05) increased. Although not reaching statistical significance, the maximum front and back elevation demonstrated the same trend; while maximum front elevation data remained stable (−0.3 &mgr;m, p = 0.961), maximum back elevation data increased (+6.7 &mgr;m, p = 0.122). The corneal thickness at the apex (−22.0 &mgr;m, p < 0.001) and the TPCT (−20.0 &mgr;m, p < 0.001) decreased, leading to an increase of the corneal thickness progression from the corneal apex to the periphery. The position of Kmax and TPCT remained stable. Conclusions Corneal topography proved to be useful in the follow-up for CXL because of significant changes in the keratometry. Increasing posterior elevation values, despite a stabilized anterior corneal surface, might be a sign of ongoing ectatic changes in the posterior corneal surface.

Relationship between minimum corneal thickness and refractive state, keratometry, age, sex, and left or right eye in refractive surgery candidates

PURPOSE: To evaluate the relationship between the thinnest point in corneal thickness and the refractive state, keratometry, age, sex, and the ocular side. SETTING: Eye clinics in Germany and Austria and the Department of Ophthalmology, University Medical Center Hamburg‐Eppendorf, Hamburg, Germany. DESIGN: Cross‐sectional study. METHODS: Medical records of refractive surgery candidates from 2006 to 2010 were reviewed. Univariate variance analysis, covariance analysis, Bravis‐Pearson correlations, Spearman rank correlations, and t tests were performed to analyze the relationship between the thinnest point in corneal thickness and the biometric parameters. RESULTS: The study evaluated 4600 eyes. The mean thinnest point in corneal thickness was 549 μm ± 33 (SD). Refractive state, mean keratometry, and age had a statistically significant impact on the thinnest point in corneal thickness. The mean thinnest point in corneal thickness was 548 ± 33 μm in myopia, 555 ± 34 μm in hyperopia, and 553 ± 35 μm in high astigmatism, with a statistically significant difference between hyperopic eyes and myopic eyes (P<.001). No correlation was found between the thinnest point in corneal thickness and sex or ocular side. Refractive state (r = 0.07, P<.001) and age (r = 0.05, P<.001) showed a positive correlation and keratometry (r = −0.09, P<.001) a negative correlation with the thinnest point in corneal thickness. CONCLUSIONS: Refractive state, mean keratometry, and age had a statistically significant, although marginal impact, on the thinnest point in corneal thickness. Sex and the ocular side had no effect. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Correlation of the KISA% index and Scheimpflug tomography in ‘normal’, ‘subclinical’, ‘keratoconus‐suspect’ and ‘clinically manifest’ keratoconus eyes

To analyse tomographic changes in eyes classified as ‘normal’, ‘keratoconus‐suspect’ and ‘clinically manifest keratoconus’ based on the established KISA% definition of Rabinowitz and Rasheed and to develop the category of ‘subclinical keratoconus eyes’ to expand the classification into a ‘subtopographic’ range.