Anterior Cornea Research Articles

Improvements to Phakometry Using Bessel Beams.

The main problem with phakometry is the low visibility of the third Purkinje image. We built a phakometer using Bessel beams, which have properties of being resistant to diffraction and the potential for self-reconstruction. This instrument had lenticular images three times brighter than those of a conventional phakometer. To investigate Purkinje image brightness, accuracy, and repeatability of a "Bessel" phakometer compared with those of a conventional phakometer. Phakometers were developed with a telecentric imaging system focused at the pupil plane of the eye to capture anterior cornea, anterior lens (PIII), and posterior lens (PIV) Purkinje images. A Bessel beam was generated by a diode laser beam passing through a high-powered doublet with a central obstruction. Software was used to determine image sizes and estimate lens anterior and posterior surface radii of curvature (Ra, Rp), equivalent refractive index (RI), and equivalent power (F). The Bessel phakometer's accuracy was assessed using a model eye. Repeatability (interobserver and intraobserver) and Purkinje images brightnesses of Bessel and conventional phakometers were assessed with six participants. The lens parameters of the model eye determined by the Bessel phakometer were similar to those provided by the model eye's manufacturer with differences (manufacturer - Bessel) in Ra and Rp, RI, and F of +1.18 mm, 0.18 mm, +0.0053, and -0.55 D, respectively. The intraobserver repeatabilities for the Bessel and conventional phakometers were similar. The interobserver repeatabilities of Ra, Rp, and RI for the Bessel phakometer were almost half those (i.e., two times better) for the conventional phakometer. Brightnesses of PIII and PIV were approximately three times higher with the Bessel phakometer than with the conventional phakometer. The Bessel beam phakometer provided accurate estimates of lens parameters of a model eye and produced brighter Purkinje images and better interobserver repeatability than that of a conventional phakometer.

Long-Term Stability of Keratometry, Scheimpflug-Derived True Net Power, and Total Corneal Refractive Power After Primary Pterygium Excision.

To evaluate long-term changes in mean keratometry, astigmatism, true net power (TNP), and total corneal refractive power (TCRP) of corneas after primary pterygium excision. This is a prospective observational series conducted at a tertiary teaching hospital eye center in Hong Kong. A total of 31 eyes of 31 patients with primary pterygium excision were included. Patients with recurrent or double-headed pterygia or a history of corneal scars from previous trauma, infection, or surgery were excluded. Data were collected prospectively at postoperative weeks 1, 4, 12, and month 18. Mean keratometry of the anterior cornea was 44.3 diopters (D) [95% confidence interval (CI): 43.6-44.9 D] at week 1, 44.3 D (95% CI: 43.6-44.9 D, standard error = 0.3) at week 4, 44.3 D (95% CI: 43.7-44.9 D) at week 12, and 44.1 D (95% CI: 43.5-44.7 D) at month 18. Mean astigmatism of the anterior cornea was 1.1 D (95% CI: 0.7-1.4 D), 1.0 D (95% CI: 0.7-1.3 D), 0.9 D (95% CI: 0.6-1.1 D), and 1.0 D (95% CI: 0.7-1.3 D) at postoperative 1, 4, 12 weeks, and 18 months, respectively. Mean keratometry, astigmatism of the anterior and posterior cornea, TNP and TCRP at 2.0-mm, 3.0-mm, 4.0-mm rings and zones remained unchanged on all follow-up visits (P = 1 for all comparisons). Keratometric values including TNP and TCRP were stable as soon as 1 week after pterygium excision. This information might help clinicians in planning subsequent intraocular surgery that requires biometric assessment for intraocular lens implantation.

A study protocol for a multicentre randomised clinical trial evaluating the safety and feasibility of a bioengineered human allogeneic nanostructured anterior cornea in patients with advanced corneal trophic ulcers refractory to conventional treatment

IntroductionThere is a need to find alternatives to the use of human donor corneas in transplants because of the limited availability of donor organs, the incidence of graft complications, as...

Evaluation of visual quality parameters after Descemet membrane endotelial keratoplasty (DMEK)

Purpose and ObjectivesTo evaluate progressive changes in visual quality parameters in patients who underwent DMEK for Fuchs endotelial dystrophy (FED), and to compare the visual quality results with healthy controls without corneal pathology.MethodsFourteen eyes with FED who underwent DMEK were evaluated for corneal topographic changes using Pentacam (OCULUS, Iberia SL), preoperatively, at 1 month and at 6 months after surgery. Mean keratometry (Km), corneal density (1‐2 mm, central and total), high order aberrations (HOA), low order aberrations (LOA) and total aberrations (total RMS) were analyzed in the anterior and posterior cornea. Fourteen healthy subjects were evaluated using the same protocol and compared with the patient's final evaluation data.ResultsSignificant improvement was observed in patients at 1 month after surgery in the posterior Km (p=0.005), central posterior density (p=0.034), 1‐2 mm posterior density (p=0.006) and central anterior density (p=0.045), and anterior LOA (p=0.026) and total aberrations (p=0.020). After 6 months all densities (anterior and posterior) had improved compared to preoperative results (p<0.05) as well as all posterior aberrations (total, HOA and LOA, p<0.05). Posterior and anterior Km values and corneal densities did not show significant differences compared to healthy subjects (p>0.05). Corneal aberrations (anterior and posterior)remained significantly higher in DMEK subjects (p>0.05)ConclusionsDMEK surgery improves corneal visual quality parameters in FED patients after the first month postoperatively. Corneal density and mean keratometry values are not different from healthy corneas at 6 months after DMEK. However, despite corneal aberrations decrease after surgery they remain higher than those values found in healthy corneas.

Refractive, corneal and ocular residual astigmatism: distribution in a German population and age-dependency - the Gutenberg health study.

Worldwide, the most frequent cause of visual impairment is uncorrected refractive error. This analysis focused on the distribution and associations of refractive, corneal and ocular residual astigmatism. As part of the Gutenberg Health study, a population-based cross-sectional study was conducted in the general population of Germany. A comprehensive ophthalmological examination including refraction, tonometry, and Scheimpflug imaging of the anterior cornea (Pachycam) was performed. In addition to the magnitude and type (with-the-rule, against-the-rule, oblique) of the refractive or corneal astigmatism, we calculated the vector components (J0, J45) of both astigmatisms and calculated the ocular residual astigmatism. We performed multiple quantile regression analysis to evaluate the factors associated with refractive, corneal and ocular residual astigmatisms. A total of 13,558 subjects (49% female) with a mean age of 54.0years (range 35-74years) were included in this study. The prevalence of refractive astigmatism (>1.0D) was 13.0% in right eyes and 12.0% in left eyes, and 85% of these subjects wore spectacles. The distribution of refractive astigmatism showed a two-peak distribution with high astigmatism for with-the-rule and against-the-rule astigmatism. The associated factors were corneal curvature, age and sex for the different astigmatisms (p<0.001). We analyzed the prevalence of different astigmatisms within a European population. We confirmed a shift with aging from with-the-rule to against-the-rule astigmatism to refractive and corneal astigmatism. Astigmatism has a large impact on visual perception; more than 85% of people with astigmatism over one diopter wore glasses for distance vision.

Changes in the anterior cornea during the early stages of severe myopia prior to and following LASIK, as detected by confocal microscopy.

The present study aimed to assess the microscopic changes of the epithelium and Bowman's layer under confocal microscopy during the early stages of severe myopia following laser in situ keratomileusis (LASIK). The study comprised 54 patients (54 eyes) with severe myopia and 65 patients (65 eyes) with low and moderate myopia, who underwent LASIK surgery at Tianjin Medical University Eye Hospital (Tianjin, China). In all patients, the epithelium, Bowman's layer and anterior stroma were examined prior to and 1, 7, 30, 90 and 180 days after the surgery, using in vivo confocal microscopy. Six (6 eyes) of the 54 patients with severe myopia (11.1%) exhibited corneal epithelial changes following the surgery, as examined by a slit lamp. Three patients (3 eyes) exhibited epithelial changes under confocal microscopy. In 40 eyes (74.1%) with severe myopia, brown yellow changes were observed at the epithelial layer and in the central part of the cornea 6 months after the surgery; the same was observed in 35 eyes (53.8%) with low and moderate myopia. Microfolds in the Bowman's layer of eyes with severe myopia were detected in 48 eyes (88.9%), and in 54 eyes (100.0%) in the anterior stroma following LASIK, whereas microfolds were observed in 51 (78.5%) and 65 eyes (100%), respectively, in patients with low to moderate myopia. In the severe myopia group, 54 eyes (100%) exhibited nerve fibers below the epithelium that were detectable 1 day post-surgery; in 16 eyes (29.6%), 1 or 2 sub-epithelial nerve fibers were detected 7 days after the surgery, and in 24 eyes (44.4%), 1 or 2 sub-epithelial nerve fibers were observed 6 months after the surgery. In eyes with low and moderate myopia, the figures were 100, 38.5 and 64.8%, respectively. The nerves of neither group returned to the pre-operative level. In conclusion, neurotrophic epitheliopathy, microfolds in Bowman's layer and anterior stroma were detected in the present patients with severe myopia of the cornea following LASIK, and the recovery of nerve fibers required an extended period of time.

Microstructural evaluation of the mucin balls and their relations to the corneal surface-Insights by in vivo confocal microscopy.

The purpose of the current study was to observe and correlate the characteristics of mucin balls to the ocular surface properties, and furthermore, to report the effect of different mucin balls size and number on structural alteration of the anterior cornea. The study included, two groups of patients fitted with one-month continuous, extended wear lenses for therapeutic (group 1) and optical (group 2) purposes; the later serving as a control group. Group 1 was comprised of patients with recurrent erosion syndrome, while group 2 included subjects with mild myopia and voluntary use of continuous wear lenses. The examination was performed when mucin balls were encountered during a routine visit. Clinical examination was reinforced with laser scanning in vivo confocal microscopy, which provided microstructural observations. The appearance and size of the mucin balls were described and measured at two independent time points. Qualitative analysis included shape (round, elliptical and irregular) and reflectivity (bright, homogenous and dark, heterogonous). Clinically 1460 mucin balls were encountered (822 in group 1 and 638 in group 2). The number of mucin balls analyzed by in vivo confocal microscopy was 820. Diversity was higher in group 1. The mucin balls of group 2, were more uniform - rounded in shape 81,2% and regular in reflectivity 98%. Qualitative analysis revealed a negative correlation between the size of the balls and impact on the basal epithelium morphology and also "activation" of the anterior stroma in adjacent areas. Mucin balls affect corneal surface including both epithelia disintegration as well as keratocyte "activation". The main predisposing factor for mucin ball formation appear to be the corneal surface irregularity. As structural alterations of the cornea are transient, mucin balls might be beneficial for corneal restoration due to mechanical and/or biochemical stimulation. In vivo, confocal microscopy is an innovative tool for evaluating mucin balls in their diversity and dynamics.

48 - Preliminary results of a multicenter randomized clinical trial evaluating the safety and feasibility of an allogeneic nanostructured artificial anterior human cornea

48 - Preliminary results of a multicenter randomized clinical trial evaluating the safety and feasibility of an allogeneic nanostructured artificial anterior human cornea

Differences in retinal shape between East Asian and Caucasian eyes.

To investigate whether retinal shape is different between East Asians and Caucasians. There were 36 East Asian and 40 Caucasian young adults, with refractions between +0.75D and -5.50D. Peripheral eye lengths were obtained after pupil dilation using the Lenstar partial coherence interferometer. Measurements were obtained along the horizontal and vertical meridians of the visual field out to ±35° and ±30°, respectively, in 5° steps. Retinal co-ordinates were estimated using a validated method from the peripheral eye length measurements and ray-tracing through a modified Le Grand full theoretical eye. Rays were directed normally towards the anterior cornea. Retinal shapes were described in terms of vertex radius of curvature (Rv ), asphericity (Q) and equivalent radius of curvature (REq ) along both horizontal and vertical meridians. Rv was smaller in East Asian than in Caucasians (mean difference ± 95% CI -0.7 ± 0.5 mm), along the horizontal meridian than the vertical meridian (-1.2 ± 0.6 mm), and in myopia than in emmetropia (-1.0 ± 0.6 mm). Rv along the horizontal meridian, but not along the vertical meridian, became smaller as myopia increased. Q did not vary significantly with meridian, refraction group or race. The same pattern of results occurred for REq as for Rv . The percentage differences of heights under the estimated retinal surfaces showed steeper retinas in East Asians than in Caucasians; the differences between East Asian and Caucasian emmetropes were 2.5% and <1% along horizontal and vertical meridians, respectively, and corresponding differences for myopes were 4.6% and 1.8%. East Asians had steeper retinas than Caucasians. The horizontal meridian had steeper retinas than the vertical meridian. Myopes had steeper retinas than emmetropes. Racial differences in retinal shape in both emmetropes and myopes, combined with the high prevalence of myopia in East Asia, suggest that retinal shape may play a role in myopia development.

Placido disk-based topography versus high-resolution rotating Scheimpflug camera for corneal power measurements in keratoconic and post-LASIK eyes: reliability and agreement

To compare the repeatability/reproducibility of measurement by high-resolution Placido disk-based topography with that of a high-resolution rotating Scheimpflug camera and assess the agreement between the two instruments in measuring corneal power in eyes with keratoconus and post-laser in situ keratomileusis (LASIK). One eye each of 36 keratoconic patients and 20 subjects who had undergone LASIK was included in this prospective observational study. Two independent examiners worked in a random order to take three measurements of each eye with both instruments. Four parameters were measured on the anterior cornea: steep keratometry (Ks), flat keratometry (Kf), mean keratometry (Km), and astigmatism (Ks-Kf). Intra-examiner repeatability and inter-examiner reproducibility were evaluated by calculating the within-subject standard deviation (Sw) the coefficient of repeatability (R), the coefficient of variation (CoV), and the intraclass correlation coefficient (ICC). Agreement between instruments was tested with the Bland-Altman method by calculating the 95% limits of agreement (95% LoA). In keratoconic eyes, the intra-examiner and inter-examiner ICC were >0.95. As compared with measurement by high-resolution Placido disk-based topography, the intra-examiner R of the high-resolution rotating Scheimpflug camera was lower for Kf (0.32 vs 0.88), Ks (0.61 vs 0.88), and Km (0.32 vs 0.84) but higher for Ks-Kf (0.70 vs 0.57). Inter-examiner R values were lower for all parameters measured using the high-resolution rotating Scheimpflug camera. The 95% LoA were -1.28 to +0.55 for Kf, -1.36 to +0.99 for Ks, -1.08 to +0.50 for Km, and -1.11 to +1.48 for Ks-Kf. In the post-LASIK eyes, the intra-examiner and inter-examiner ICC were >0.87 for all parameters. The intra-examiner and inter-examiner R were lower for all parameters measured using the high-resolution rotating Scheimpflug camera. The intra-examiner R was 0.17 vs 0.88 for Kf, 0.21 vs 0.88 for Ks, 0.17 vs 0.86 for Km, and 0.28 vs 0.33 for Ks-Kf. The inter-examiner R was 0.09 vs 0.64 for Kf, 0.15 vs 0.56 for Ks, 0.09 vs 0.59 for Km, and 0.18 vs 0.23 for Ks-Kf. The 95% LoA were -0.54 to +0.58 for Kf, -0.51 to +0.53 for Ks and Km, and -0.28 to +0.27 for Ks-Kf. As compared with Placido disk-based topography, the high-resolution rotating Scheimpflug camera provides more repeatable and reproducible measurements of Ks, Kf and Ks in keratoconic and post-LASIK eyes. Agreement between instruments is fair in keratoconus and very good in post-LASIK eyes.

Outcomes of corneal collagen cross linking prior to photorefractive keratectomy in prekeratoconus

The combination of corneal collagen cross linking (CXL) and refractive surgery, such as photorefractive keratectomy (PRK) has been studied extensively that it is important for visual function improvement. This combination might improve corneal stabilization and reshape the corneal tissue. The debating issue is regarding the appropriate timing between CXL and PRK combination surgery, whether it should be performed before or after surgery, as well as on the safety and efficacy of this combined surgery. The mechanism of CXL is believed when riboflavin as a photosensitizer is saturated on the cornea while exposed to ultraviolet irradiation, thus it is excited into an activate state that generating some reactive oxygen species. This processes lead to the formation of covalent bond between collagen molecules that increase the cornea biomechanics. Previous studies CXL followed by PRK removed the cross-linked stiffer anterior cornea. We assumed that our finding is important for the basis of further study.

Correlation of IOP with Corneal Acoustic Impedance in Porcine Eye Model.

Purpose The aim of this study is to correlate the intraocular pressure (IOP) change with the acoustic impedance of the cornea, in order to propose a noncontact and noninvasive method for IOP monitoring. Methods and Materials A highly focused transducer (frequency 47-MHz; bandwidth 62%) was made to measure the echo from the anterior and posterior surfaces of intact porcine eyes, respectively. A multilayered transmission and reflection model was used to calculate the acoustic impedance. The linear relationship between acoustic impedance and intraocular pressure was analyzed by statistical method. ResultDuring pressure elevation from 10 mm Hg to 50 mm Hg, the mean acoustic impedance of the posterior cornea increased from 1.5393 to 1.5698 MRayl, which showed a strong linear correlation (R = 0.9849; P = 0.0022). Meanwhile, the mean value of the anterior cornea increased from 1.5399 to 1.5519 MRayl, and a less significant correlation was observed (R = 0.7378; P = 0.0025). Conclusion This study revealed a linear correlation between intraocular pressure and acoustic impedance of the cornea, thus demonstrating a potentially important method to noninvasively measure the intraocular pressure in vivo.

Mid-Term Results of a Single Intrastromal Corneal Ring Segment for Mild to Moderate Progressive Keratoconus.

To study the mid-term effects of implanting a single intracorneal ring segment (ICRS) for treatment of mild to moderate progressive keratoconus. This retrospective study was conducted on patients with progressive keratoconus treated with ICRS. The mean follow-up time was 15.2 ± 8.8 (range, 7-26) months before and 27.8 ± 7.5 (range, 18-35) months after surgery. Patients received no other treatment during this time. Of the cases studied, 59.1% had inferior keratoconus. Thirty eyes of 30 patients with a mean age of 27.5 ± 4.6 years were included in the study. Corrected distance visual acuity decreased by 1 line during the preoperative follow-up and improved by 2 lines after surgery (P < 0.05). Maximum keratometry (Kmax) of the anterior (2.39 ± 0.75 D) and posterior (0.33 ± 0.32 D) corneas at 3 mm and anterior Kmax at 8 mm (2.39 ± 0.95 D) decreased after treatment (all P < 0.05). The posterior Q value shifted toward a more oblate curvature (0.50 ± 0.52, P = 0.023). Decreases in anterior elevation at the thinnest point (5.22 ± 7.21 μm) and posterior corneal central elevation (8.89 ± 11.26 μm) were significant (both P < 0.05). Corneal thickness at the center (11.11 ± 12.38 μm) and thinnest point (15.89 ± 12.75 μm) increased after treatment (all P < 0.001). Other significant changes included postoperative decreases in the keratoconus index (0.12 ± 0.06), index of height decentration (0.06 ± 0.05), index of surface variance (27.32 ± 13.08), index of vertical asymmetry (0.42 ± 0.21), index of height asymmetry (8.42 ± 20.57), and an increase in the center keratoconus index (0.01 ± 0.02) (P < 0.001). This study demonstrates that ICRS implantation provides favorable mid-term outcomes in treatment of mild and moderate progressive keratoconus and can improve corneal indices compared with their preoperative states.

Two-Year Refractive Outcomes After Descemet Membrane Endothelial Keratoplasty.

To monitor refractive changes after Descemet membrane endothelial keratoplasty (DMEK) and to determine what may influence these changes and the time point of stabilization. From 67 pseudophakic DMEK eyes operated on for Fuchs endothelial dystrophy at a tertiary referral center, biomicroscopy, visual acuity, subjective refraction, and Scheimpflug-based corneal tomography data were obtained before and up to 2 years postoperatively. Visual acuity and changes in spherical equivalent (SE), mean anterior and posterior simulated keratometry (Km), and central pachymetry were analyzed. At 3 months postoperatively, both hyperopic (28/67 eyes) and myopic (21/67 eyes) shifts were observed; 18/67 eyes showed no SE change. The mean change in SE at 3 months was +0.33 diopters (D) (95% confidence interval = [0.11, 0.54], P = 0.028), which stabilized thereafter (P > 0.466). Initial flattening of mean anterior Km by 0.66D (95% confidence interval = [-0.81, -0.51], P < 0.001) at 3 months was followed by a slow steepening, which became significant between 1 and 2 years postoperatively (P < 0.001). Posterior Km stabilized after 3 months (P > 0.252). Preoperative to 3 months postoperative absolute changes in anterior Km were positively related to preoperative backscattered light from the central anterior cornea (P = 0.035), and the presence of partial graft detachment postoperatively (P = 0.013). After DMEK, SE and posterior corneal curvature were on average stable at 3 months after surgery, whereas the mean anterior corneal curvature showed an ongoing gradual change. Changes in anterior corneal curvature may be related to preoperative anterior corneal densitometry or postoperative partial graft detachment.

Distribution and compensation mechanism of aberrations between anterior and posterior surface of the cornea in myopia and myopic astigmatism eyes

Objective: To study the compensation mechanism of aberrations between anterior and posterior corneal surface, and to investigate the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Methods: One hundred and sixty-one subjects (300 eyes) with myopia and myopic astigmatism were recruited randomly. Corneal aberrations (anterior, posterior and total) in three different optical zones (2 mm, 4 mm, and 6 mm) centered on the corneal vertex were assessed with a corneal topographer (Sirius). We also calculated compensation factors (CFs) as a measure of the relative efficiency of the aberration compensation mechanism. Astigmatism was divided into corneal astigmatism and non-corneal astigmatism. Mann-Whitney U test was utilized for the comparison of different aberrations and CFs between the two astigmatism groups. Spearman correlation was applied to analyze the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Results: As the order of the aberrations elevated from the second to the seventh, the RMS values decreased significantly. The larger the optical zone, the greater the values of aberrations and the lower the percentage of the compensation mechanism among all the Zernike terms. At the same time, as the order of the aberrations increased, the predominance of the compensation mechanism was increasingly obvious. Slight compensation of spherical aberration (Z40) was observed in the peripheral. In the center of the analyzing zones (2 mm), compensation mechanism represented in coma (Z3±1), and it disappeared in the peripheral. We detected slight compensation of the corneal astigmatism (Z2±2) in the surrounding zone, although the compensation factors were closed to zero in diverse optical zones. Superposition was found in trefoil (Z3±3) straightly. Nevertheless, a tendency towards compensation was discovered with the enlargement of the optical zones. And the secondary spherical aberration (Z60) behaved compensation continuously. However, similar compensation was discovered between the right eye and left eye in different analyzing optical zones. There were significant correlations between the flattest K values and Z2±2, Z3±3and Z40 in the anterior, posterior and total cornea. It was similar with the steepest K values. When the optical zone expanded to 6 mm, Z3±1 and Z40 significantly decreased with intraocular pressure (rcoma=-0.188, P<0.05. rspherical=-0.147, P<0.05). No correlation was found between various aberrations and central corneal thickness (P>0.05). Conclusions: Compensation dominated in the corneal center, while the percentage decreased gradually as the optical zone extended. Slight compensation in astigmatism and spherical aberration between the anterior and posterior cornea may be benificial to the scotopic visual quality. Corneal aberrations were significantly related to K values and intraocular pressure. (Chin J Ophthalmol, 2016, 52: 840-849).

Anterior Corneal, Posterior Corneal, and Lenticular Contributions to Ocular Aberrations.

To determine the corneal surfaces and lens contributions to ocular aberrations. There were 61 healthy participants with ages ranging from 20 to 55 years and refractions -8.25 diopters (D) to +3.25 D. Anterior and posterior corneal topographies were obtained with an Oculus Pentacam, and ocular aberrations were obtained with an iTrace aberrometer. Raytracing through models of corneas provided total corneal and surface component aberrations for 5-mm-diameter pupils. Lenticular contributions were given as differences between ocular and corneal aberrations. Theoretical raytracing investigated influence of object distance on aberrations. Apart from defocus, the highest aberration coefficients were horizontal astigmatism, horizontal coma, and spherical aberration. Most correlations between lenticular and ocular parameters were positive and significant, with compensation of total corneal aberrations by lenticular aberrations for 5/12 coefficients. Anterior corneal aberrations were approximately three times higher than posterior corneal aberrations and usually had opposite signs. Corneal topographic centers were displaced from aberrometer pupil centers by 0.32 ± 0.19 mm nasally and 0.02 ± 0.16 mm inferiorly; disregarding corneal decentration relative to pupil center was significant for oblique astigmatism, horizontal coma, and horizontal trefoil. An object at infinity, rather than at the image in the anterior cornea, gave incorrect aberration estimates of the posterior cornea. Corneal and lenticular aberration magnitudes are similar, and aberrations of the anterior corneal surface are approximately three times those of the posterior surface. Corneal decentration relative to pupil center has significant effects on oblique astigmatism, horizontal coma, and horizontal trefoil. When estimating component aberrations, it is important to use correct object/image conjugates and heights at surfaces.

Changes in Keratometric Values and Corneal High Order Aberrations After Hydrogel Inlay Implantation

We sought to analyze surgically induced refractive change (SIRC) and change in high-order aberration after Raindrop corneal inlay insertion (ReVision Optics, Lake Forest, CA), and assess the extent to which Raindrop corneal inlay insertion could correct presbyopia. Interventional case series. Seventeen patients were included if they had a corneal thickness ≥500μm and a stable manifest spherical equivalent refraction between 0.50 and+1.00 diopters (D). The Raindrop corneal inlay was implanted on the stromal bed of a femtosecond laser-assisted generated flap of nondominant eyes. Manifest refraction, corneal powers, and corneal high-order aberrations were measured preoperatively and at 3 and 12months postoperatively. The SIRC by manifest refraction was 0.99 ± 0.26 D. The changes derived from simulated keratometry (K), true net power, and equivalent K reading (EKR) at 1.0-4.0mm were greater than the SIRC (all P < .01) while the change in EKR at 6.0mm was less than the SIRC (P < .01). The changes in EKR 5.0mm, automated K, and EKR 4.5mm did not differ significantly from the SIRC (P= .81, .29, and .09, respectively), and the difference was the least for EKR 5.0mm. In analysis of high-order aberrations, only spherical aberration showed statistically significant difference between preoperative and postoperative on both anterior cornea and total cornea (all P < .01). Raindrop corneal inlay corrects presbyopia via increasing negative spherical aberration. The equivalent K reading at 5.0mm accurately reflected the SIRC, and would be applicable for intraocular power prediction before cataract surgery.

Construction of a Corneal Stromal Equivalent with SMILE-Derived Lenticules and Fibrin Glue.

The scarcity of corneal tissue to treat deep corneal defects and corneal perforations remains a challenge. Currently, small incision lenticule extraction (SMILE)-derived lenticules appear to be a promising alternative for the treatment of these conditions. However, the thickness and toughness of a single piece of lenticule are limited. To overcome these limitations, we constructed a corneal stromal equivalent with SMILE-derived lenticules and fibrin glue. In vitro cell culture revealed that the corneal stromal equivalent could provide a suitable scaffold for the survival and proliferation of corneal epithelial cells, which formed a continuous pluristratified epithelium with the expression of characteristic markers. Finally, anterior lamellar keratoplasty in rabbits demonstrated that the corneal stromal equivalent with decellularized lenticules and fibrin glue could repair the anterior region of the stroma, leading to re-epithelialization and recovery of both transparency and ultrastructural organization. Corneal neovascularization, graft degradation, and corneal rejection were not observed within 3 months. Taken together, the corneal stromal equivalent with SMILE-derived lenticules and fibrin glue appears to be a safe and effective alternative for the repair of damage to the anterior cornea, which may provide new avenues in the treatment of deep corneal defects or corneal perforations.

Optical coherence tomography analysis of hydrofluoric acid decontamination of human cornea by mannitol solution

PurposeTo evaluate the efficacy of mannitol solution as a decontamination agent on the chemical burn of the human corneas. MethodsEight donor corneas from an eye bank were exposed to 25μl of 2.5% hydrofluoric acid (HF) solution on a filter paper for 20s. Three eyes were rinsed with 1000ml of mannitol 20% for 15min immediately after removal of the filter paper, 3 other were rinsed with sodium chloride (NaCl) 0.9% (1000ml for 15min) and two eyes were not rinsed. Microstructural changes were monitored in the time domain by optical coherence tomography (OCT) imaging for 75min. ResultsNaCl reduced the penetration depth to approximately half the thickness of the cornea at 15min; scattering within the anterior cornea was higher than that for the unrinsed eye. With mannitol, no increased scattering was observed in the posterior part of the corneal stroma within a time period of 1h after rinsing. OCT images revealed low-scattering intensity within the anterior stroma at the end of the rinsing period. ConclusionIn eye bank human corneas, mannitol proved to be an efficient agent to decontaminate HF burn.

Femtosecond laser cutting of human corneas for the subbasal nerve plexus evaluation.

Assessment of various morphological parameters of the corneal subbasal nerve plexus is a valuable method of documenting the structural and presumably functional integrity of the corneal innervation in health and disease. The aim of this work is to establish a rapid, reliable and reproducible method for visualization of the human corneal SBP using femtosecond laser cut corneal tissue sections. Trephined healthy corneal buttons were fixed and processed using TissueSurgeon-a femtosecond laser based microtome, to obtain thick tissue sections of the corneal epithelium and anterior stroma cut parallel to the ocular surface within approximately 15 min. A near infrared femtosecond laser was focused on to the cornea approximately 70-90 μm from the anterior surface to induce material separation using TissueSurgeon. The obtained corneal sections were stained following standard immunohistochemical procedures with anti-neuronal β-III tubulin antibody for visualization of the corneal nerves. Sections that contained the epithelium and approximately 20-30 μm of anterior stroma yielded excellent visualisation of the SBP with minimal optical interference from underlying stromal nerves. In conclusion, the results of this study have demonstrated that femtosecond laser cutting of the human cornea offers greater speed, ease and reliability than standard tissue preparation methods for obtaining high quality thick sections of the anterior cornea cut parallel to the ocular surface.