Anterior Cornea Research Articles

Riboflavin-UV--a crosslinking for fixation of biosynthetic corneal collagen implants.

To evaluate riboflavin-UV-A crosslinking as an alternative suture-free fixation method for biosynthetic corneal collagen implants. A range of cell-free corneal implants consisting of recombinant human collagen type III were examined. In vitro, the implants were crosslinked with different riboflavin solutions and irradiations. Ex vivo, the biosynthetic corneal implants were placed on the anterior cornea of porcine and rabbit eyes after performing deep anterior lamellar keratoplasty with a trephine, femtosecond laser, or excimer laser. UV-A crosslinking was performed with isotonic or hypotonic riboflavin at either standard or rapid procedure. The corneas were excised, fixed in PFA 4%, and embedded in paraffin. Crosslinking effects on the implants and the adhesion between implant and corneal bed were evaluated by slit-lamp biomicroscopy, optical coherence tomography (OCT) images, and histologically. After the crosslinking procedure, the implants showed different degrees of thinning. The accuracy of cutting the corneal bed was highest with the excimer laser. Good adhesion of the implant in the corneal bed could be demonstrated in OCT images. This was more accurate in porcine eyes than in rabbit eyes. Histologically, crosslinks between implant and corneal stroma were demonstrated. There was no difference between standard and rapid crosslinking procedures. Riboflavin-UV-A crosslinking as a fixation method for biosynthetic corneal collagen implants was demonstrated to be promising. It can reduce suture-related complications such as haze formation and surface irregularity. Stability of the implants, especially shrinkage after riboflavin-UV-A crosslinking, needs to be further evaluated. Biostability, integration, and long-term outcome are further evaluated in in vivo animal experiments.

Evaluation of the adhesive properties of the cornea by means of optical coherence tomography in patients with meibomian gland dysfunction and lacrimal tear deficiency.

ObjectiveThe aim was to determine the influence of meibomian gland dysfunction (MGD) and aqueous tear deficiency dry eye (ADDE) on the adhesive properties of the central cornea by means of optical coherence tomography (OCT), and to investigate the relationship between corneal adhesiveness and classical tear tests, as well as the reliability of results, in these lacrimal functional unit disorders.DesignProspective, case-control study.MethodsTwenty-eight patients with MGD and 27 patients with ADDE were studied. A group of 32 healthy subjects of similar age and gender distribution served as a control group. The adhesive properties of the anterior corneal surface were measured by OCT, based on the retention time of adhesion marker above it, in all participants.ResultsAn excellent (≥5 minutes), borderline (within 3–5 minutes), fair (within 1–3 minutes) and poor (<1 minute) values of corneal adhesiveness were found, respectively, in 0%, 7.1%, 64.3% and 28.6% of MGD, in 0%, 7.4%, 63% and 29.6% of ADDE, and in 31.3%, 65.6%, 3.1% and 0% of healthy patients. The differences in time of corneal adhesiveness between MGD and healthy patients, as well as between ADDE and healthy patients, were found to be statistically significant (p<0.001; p<0.001; respectively). Conversely, no statistical significant differences between MGD and ADDE were found (p = 0.952). Data analysis revealed a statistically significant correlation between corneal adhesiveness and clinical tests of dry eye, as well as an excellent degree of inter-rater reliability and reproducibility for OCT measurements (p<0.001).ConclusionADDE and MGD share similar abnormalities on OCT imaging. Decreased adhesive properties of the anterior cornea were identified as a common feature of MGD and ADDE. This simple OCT approach may provide new clues into the mechanism and evaluation of dry eye syndrome.

Numerical model of optical coherence tomographic vibrography imaging to estimate corneal biomechanical properties.

Most techniques measuring corneal biomechanics in vivo are biased by side factors. We demonstrate the ability of optical coherence tomographic (OCT) vibrography to determine corneal material parameters, while reducing current prevalent restrictions of other techniques (such as intraocular pressure (IOP) and thickness dependency). Modal analysis was performed in a finite-element (FE) model to study the oscillation response in isolated thin corneal flaps/eye globes and to analyse the dependency of the frequency response function on: corneal elasticity, viscoelasticity, geometry (thickness and curvature), IOP and density. The model was verified experimentally in flaps from three bovine corneas and in two enucleated porcine eyes using sound excitation (100–110 dB) together with a phase-sensitive OCT to measure the frequency response function (range 50–510 Hz). Simulations showed that corneal vibration in flaps is sensitive to both, geometrical and biomechanical parameters, whereas in whole globes it is primarily sensitive to corneal biomechanical parameters only. Calculations based on the natural frequency shift revealed that flaps of the posterior cornea were 0.8 times less stiff than flaps from the anterior cornea and cross-linked corneas were 1.6 times stiffer than virgin corneas. Sensitivity analysis showed that natural vibration frequencies of whole globes were nearly independent from corneal thickness and IOP within the physiological range. OCT vibrography is a promising non-invasive technique to measure corneal elasticity without biases from corneal thickness and IOP.

Analysis of the viscoelastic properties of the human cornea using Scheimpflug imaging in inflation experiment of eye globes.

PurposeTo demonstrate a Scheimpflug-based imaging procedure for investigating the depth- and time-dependent strain response of the human cornea to inflation testing of whole eye globes.MethodsSix specimens, three of which with intact corneal epithelium, were mounted in a customized apparatus within a humidity and temperature-monitored wet chamber. Each specimen was subjected to two mechanical tests in order to measure corneal strain resulting from application of cyclic (cyclic regimen) and constant (creep regimen) stress by changing the intra-ocular pressure (IOP) within physiological ranges (18–42 mmHg). Corneal shape changes were analyzed as a function of IOP and both corneal stress-strain curves and creep curves were generated.ResultsThe procedure was highly accurate and repeatable. Upon cyclic stress application, a biomechanical corneal elasticity gradient was found in the front-back direction. The average Young's modulus of the anterior cornea ranged between 2.28±0.87 MPa and 3.30±0.90 MPa in specimens with and without intact epithelium (P = 0.05) respectively. The Young's modulus of the posterior cornea was on average 0.21±0.09 MPa and 0.17±0.06 MPa (P>0.05) respectively. The time-dependent strain response of the cornea to creep testing was quantified by fitting data to a modified Zener model for extracting both the relaxation time and compliance function.ConclusionCyclic and creep mechanical tests are valuable for investigating the strain response of the intact human cornea within physiological IOP ranges, providing meaningful results that can be translated to clinic. The presence of epithelium influences the results of anterior corneal shape changes when monitoring deformation via Scheimpflug imaging in inflation experiments of whole eye globes.

Evaluation of posterior astigmatism measured with Scheimpflug imaging.

Our aim was to assess the corneal power, axis, and age dependence of the anterior and posterior corneal surfaces with Scheimpflug imaging. Patients older than 10 years without a history of ocular surgery, corneal diseases, contact lens wearing, or severe dry eye were enrolled. Data regarding the anterior and posterior cornea were analyzed by means of Scheimpflug imaging (Pentacam HR). The median age was 46.8 years (range: 10.0-90.3), and involved 827 eyes of 827 patients. Posterior corneal astigmatism was a median of -0.30 diopters (D) and exceeded 0.50 D in 12.56%. The ratio of the anterior-to-posterior corneal radius was a median of 1.217 (range: 1.021-1.402). The correlation between this ratio and age was significant (r = -0.219; P < 0.001). The correlation between anterior and posterior corneal astigmatism and age was significant. At the anterior surface, the ratio of with-the-rule astigmatism was 80.0% for the age range 10 to 20, decreasing to 36.0% for those aged over 81 years, whereas the ratio of against-the-rule astigmatism increased from 7.1% to 44.0%. At the posterior surface, the ratio of with-the-rule astigmatism was 94.3% for the age range 10 to 20 years, decreasing to 84.0% for those aged over 81 years, whereas the ratio of against-the-rule astigmatism increased from 1.4% to 8.0%. The posterior cornea significantly influences corneal astigmatism. Its power value and orientation are much more stable with advancing age compared with anterior surface values.

Total spherical aberration of the cornea in patients with cataract.

To investigate the distribution of corneal spherical aberration in patients with cataract using the Pentacam HR. Consecutive cataract patients were examined using the Pentacam HR high-resolution rotating Scheimpflug camera (Oculus, Wetzlar, Germany). In one eye of each patient, the root-mean-square (RMS) of anterior, posterior, and total corneal spherical aberration Z4(0) was calculated by ray-tracing on an area of 6 mm diameter. The Pearson correlation coefficient (r) was used to assess correlations between Z4(0) RMS values and age/total corneal refractive power. The χ2 test was used to compare the proportion of eyes qualifying for spherically neutral or negatively aspheric (-0.17 and -0.27 μm) intraocular lenses (IOLs) by targeted level of residual spherical aberration. Fifty-seven men and 92 women were included (mean [±SD] age, 71.73 [±9.12] years). The RMS mean (±SD) values of Z4(0) were +0.353 (±0.132) μm, -0.121 (±0.034) μm, and +0.328 (±0.132) μm, respectively, for the anterior, posterior, and total cornea. The anterior, posterior, and total Z4(0) were on average significantly higher (p < 0.001) in women than in men. In both sexes, statistically significant (p < 0.05) age-related changes were found for the anterior and total Z4(0) but not for the posterior Z4(0) (p > 0.05). The total Z4(0) and total corneal refractive power were significantly correlated in men (p = 0.01) but not in women (p = 0.14). For postoperative targets of 0 ± 0.05/+0.10 ± 0.05 μm residual Z4(0), the proportion of eyes that would have qualified for implantation of negatively aspheric IOLs with -0.17 and with -0.27 μm was similar (61.1 and 56.3%, respectively; p = 0.09); significantly fewer eyes (6.7%) would have qualified for implantation of neutrally aspheric IOLs (p > 0.05). Total corneal Z4(0) measured by Pentacam HR might be higher than that reported in previous studies. In most patients, the implantation of commercially available negatively aspheric IOLs would partially compensate for the positive total corneal Z4(0).

Impact of Posterior Corneal Surface on Toric Intraocular Lens (IOL) Calculation

Purpose: To quantify the impact of posterior cornea on toric IOL calculation accuracy using Placido-topography of anterior corneal surface and Scheimpflug measurements of corneal thickness.Materials and Methods: Three-hundred seventy-nine non-selected eyes undergoing cataract surgery with non-toric intraocular lens (IOL) implantation were measured with TMS-5 (Tomey, Japan), IOLMaster (Zeiss, Germany) and Lenstar (Haag-Streit, Switzerland). Anterior, posterior and total measured corneal astigmatisms were compared with astigmatisms from postoperative refraction by calculating vector differences.Results: The average absolute vector difference between anterior astigmatism and total astigmatism combining the measurements of anterior and posterior cornea was only 0.3 ± 0.2 D, with a median of only 0.27 D, but a maximum of 1.5 D. Measurements of anterior cornea alone show a systematic difference from refractive cylinder of 0.3–6 D at 90, 0.38 D at 89° and 0.28 D at 91° (IOLMaster, Lenstar and anterior TMS5), whereas the total TMS5 cylinder differs on average by only 0.14D at 81° from the refractive cylinder. With-the-rule (WTR) corneal astigmatism is slightly reduced and against-the-rule (ATR) astigmatism slightly increased on average when posterior corneal surface is taken into account additionally. This could also be confirmed by the calculation of an average pachymetry of all eyes in which the thinnest central part shows an ellipsoidal shape with horizontally long axis.Conclusion: Measurements of posterior cornea have on average only a small but significant impact on the outcome of toric IOL calculation, however, they are nevertheless recommended to detect outliers in which corneal irregularities (e.g. beginning keratokonus) may be overlooked.

Biomechanical changes in the human cornea after transepithelial corneal crosslinking using iontophoresis.

To evaluate the corneal response to variable intraocular pressure (IOP) in human eye globes after ultraviolet-A (UVA) transepithelial corneal crosslinking using iontophoresis. Fondazione G.B. Bietti IRCCS, Rome, Italy. Experimental study. Four human donor eye globes were treated with transepithelial crosslinking using iontophoresis and rapid UVA corneal irradiation, and 4 globes had standard crosslinking. Inflation experiments were performed on the globes before and after crosslinking. Topographic maps of the anterior and posterior cornea were acquired using Scheimpflug topography. Images were obtained using a mechanical regimen to analyze corneal strain in response to cyclic stress. Corneal shape changes were analyzed as a function of IOP, and corneal stress-strain curves were generated. Before crosslinking, instillation of hypotonic riboflavin-5-phosphate sodium 0.1% solution using iontophoresis increased corneal thickness by 5% and instillation of dextran-enriched riboflavin 0.1% solution decreased corneal thickness by 13%. Five minutes after treatment, both crosslinking procedures reduced corneal thickness by 2%. Young's modulus (E) of the anterior cornea increased by a mean of 1.8 times (from 1.6 to 2.9 MPa) and 1.9 times (from 1.3 to 2.5 MPa) after transepithelial crosslinking using iontophoresis and standard crosslinking, respectively. The E value of the posterior cornea also increased after both procedures (mean 1.7 times versus 3.1 times). Transepithelial crosslinking using iontophoresis increased the biomechanical strength of human corneal tissue in inflation testing of donor eye globes. The effect on corneal stiffness was almost comparable to that of standard crosslinking. No author has a financial or proprietary interest in any material or method mentioned.

English

We present in this paper the quantification of the geometrical features of the anterior segment of the eye using Anterior Segment Optical Coherence Tomography (AS-OCT). This quantification was achieved by following our own developed methodology including the device development and their distortion calibration (Fan and refraction) for 3-D imaging, and automatic analysis tools as well. The stastistical comparison of the corrected topographies of the anterior cornea with topographies from state-of-the art clinical topography systems represents a valuable contribution toward the development All-OCT-based topographic systems. In addition, we first reported topographies of the crystalline lens in vivo, which is a promising tool to investigate the lens optical properties, the contribution of the lens to the overall retinal image quality, and understanding the change of the physical properties of the lens with accommodation and aging. Furthermore, our quantitative AS-OCT allowed the analysis of the keratoconic cornea and the changes produced by Intra Corneal Ring Segment (ICRS) treatment, as well as monitoring of the ICRS 3-D location. Finally, OCT-based biometry we present in this paper is a promising tool to investigate the changes after cataract surgery; the contribution of the (Intra Ocular Lens) IOL location and tilt to the overall retinal image quality, and in the design of new IOLs.

Ocular forward light scattering and corneal backward light scattering in patients with dry eye.

To evaluate ocular forward light scattering and corneal backward light scattering in patients with dry eye. Thirty-five eyes in 35 patients with dry eye and 20 eyes of 20 healthy control subjects were enrolled. The 35 dry eyes were classified into two groups according to whether superficial punctate keratopathy in the central 6-mm corneal zone (cSPK) was present or not. Ocular forward light scattering was quantified with a straylight meter. Corneal backward light scattering from the anterior, middle, and posterior corneal parts was assessed with a corneal densitometry program using the Scheimpflug imaging system. Both dry eye groups had significantly higher intraocular forward light scattering than the control group (both P<0.05). The dry eye group with cSPK had significantly higher values in anterior and total corneal backward light scattering than the other two groups. Moderate positive correlations were observed between the cSPK score and corneal backward light scattering from the anterior cornea (R=0.60, P<0.001) and corneal backward light scattering from the total cornea (R=0.54, P<0.001); however, no correlation was found between cSPK score and ocular forward light scattering (R=0.01, P=0.932). Ocular forward light scattering and corneal backward light scattering from the anterior cornea were greater in dry eyes than in normal eyes. Increased corneal backward light scattering in dry eye at least partially results from cSPK overlying the optical zone.

Short-term corneal changes with gas-permeable contact lens wear in keratoconus subjects: A comparison of two fitting approaches

PurposeTo evaluate changes in anterior corneal topography and higher-order aberrations (HOA) after 14-days of rigid gas-permeable (RGP) contact lens (CL) wear in keratoconus subjects comparing two different fitting approaches. MethodsThirty-one keratoconus subjects (50 eyes) without previous history of CL wear were recruited for the study. Subjects were randomly fitted to either an apical-touch or three-point-touch fitting approach. The lens’ back optic zone radius (BOZR) was 0.4mm and 0.1mm flatter than the first definite apical clearance lens, respectively. Differences between the baseline and post-CL wear for steepest, flattest and average corneal power (ACP) readings, central corneal astigmatism (CCA), maximum tangential curvature (KTag), anterior corneal surface asphericity, anterior corneal surface HOA and thinnest corneal thickness measured with Pentacam were compared. ResultsA statistically significant flattening was found over time on the flattest and steepest simulated keratometry and ACP in apical-touch group (all p<0.01). A statistically significant reduction in KTag was found in both groups after contact lens wear (all p<0.05). Significant reduction was found over time in CCA (p=0.001) and anterior corneal asphericity in both groups (p<0.001). Thickness at the thinnest corneal point increased significantly after CL wear (p<0.0001). Coma-like and total HOA root mean square (RMS) error were significantly reduced following CL wearing in both fitting approaches (all p<0.05). ConclusionShort-term rigid gas-permeable CL wear flattens the anterior cornea, increases the thinnest corneal thickness and reduces anterior surface HOA in keratoconus subjects. Apical-touch was associated with greater corneal flattening in comparison to three-point-touch lens wear.

UV cross-linking of donor corneas confers resistance to keratolysis.

The aim of this study was to develop a modified ex vivo corneal cross-linking method that increases stromal resistance to enzymatic degradation for use as a carrier for the Boston keratoprosthesis. Ex vivo cross-linking of human corneas was performed using Barron artificial anterior chambers. The corneas were deepithelialized, pretreated with riboflavin solution (0.1% riboflavin/20% dextran), and irradiated with ultraviolet A (UV-A) light (λ = 370 nm, irradiance = 3 mW/cm) for various durations. The combined effect of UV-A and gamma (γ) irradiation was also assessed using the commercially available γ-irradiated corneal donors. The corneas were then trephined and incubated at 37°C with 0.3% collagenase A solution. The time to dissolution of each cornea was compared across treatments. Deepithelialized corneas (no UV light, no riboflavin) dissolved in 5.8 ± 0.6 hours. Cross-linked corneas demonstrated increased resistance to dissolution, with a time to dissolution of 17.8 ± 2.6 hours (P < 0.0001). The corneal tissues' resistance to collagenase increased with longer UV-A exposure, reaching a plateau at 30 minutes. Cross-linking both the anterior and posterior corneas did not provide added resistance when compared with cross-linking the anterior corneas only (P > 0.05). γ-irradiated corneas dissolved as readily as deepithelialized controls regardless of whether they were further cross-linked (5.6 ± 1.2 hours) or not (6.1 ± 0.6 hours) (P = 0.43). Collagen cross-linking of the deepithelialized anterior corneal surface for 30 minutes conferred optimal resistance to in vitro keratolysis by collagenase A.

Overview of the Repeatability, Reproducibility, and Agreement of the Biometry Values Provided by Various Ophthalmic Devices

To present an overview of the measurement errors for various biometric devices, as well as a meta-analysis of the agreement between biometric devices using the Pentacam, Orbscan, and IOL Master as a reference. Meta-analysis of the literature. The meta-analysis is based on data from 216 articles that compare a total of 24 different devices with the reference devices for the following 9 parameters: mean, steep and flat curvature of the anterior and posterior cornea; central corneal thickness; anterior chamber depth; and axial length. After the weighted average difference between devices has been determined, the "two one-sided t test" was used to test for equivalence between devices within certain thresholds defined by the measurement errors and the influence of these differences on the calculated refraction. In only 17 of the 70 comparisons a device was equivalent with the reference device within the thresholds set by the measurement error. More lenient thresholds, based on a change in calculated refraction of ±0.25 diopter, increased this number to a maximum of 25/50 comparisons (excluding pachymetry). High degrees of inconsistency were seen in the reported results, which could partially explain the low agreement between devices. As a rule, biometry measurements taken by different devices should not be considered equivalent, although several exceptions could be identified. We therefore recommend that clinical studies involving multiple device types treat this as a within-subject variable to avoid bias. The follow-up of individual patients using different devices should be avoided at all times.

Evaluation of Orbscan II plus non-history double-K method in intraocular lens power calculation for patients after refractive surgery

To explore the accuracy of intraocular lens (IOL) power calculation with non-history method using the keratometric value derived from one zone of Orbscan II topography after laser in situ keratomileusis (LASIK). For this retrospective study, 20 eyes from 20 patients undergoing myopic LASIK were included from August 2008 to November 2011. Posterior corneal curvature in peripheral 7 to 10 mm fitting zone of postoperative cornea was measured with Orbscan II topography. The ratio between anterior cornea and posterior cornea was used to calculate the preoperative total corneal power of each eye. The predicted postoperative spherical equivalent was calculated by the calculated preoperative total corneal power, power of implanted IOL, refractive error before cataract surgery and eye length from IOL-Master into the double-K method for SRK-T formula. The predicted postoperative spherical equivalent was also calculated by double-K method for SRK-T formula with clinical history. The mean difference between actual and predicted postoperative spherical equivalent, i.e. mean absolute error (MAE), were compared. (1) Non-history method: MAE of 11 eyes was within ± 0.5 D (55%), MAE of 15 eyes within ± 1.0 D (75%) and MAE of all eyes within ± 2.0 D. (2) Clinical-history method: MAE of 10 eyes was within ± 0.5 D (50%), MAE of 14 eyes within ± 1.0 D (70%) and MAE of all eyes within ± 2.0 D. (3) Comparison of non-history and clinical-history methods: The MAE of non-history method was (0.61 ± 0.59) D and the MAE of clinical-history method (0.68 ± 0.55) D. Paired t-test showed no statistically significant difference between two methods (t = -1.248, P = 0.227). The non-history method using the keratometric value derived from one zone of Orbscan II topography after LASIK provides an accurate calculation of IOL power and it can be used as a substitute for incomplete clinical data.

DMEK lenticule preparation from donor corneas using a novel ‘SubHyS’ technique followed by anterior corneal dissection

PurposeTo describe a novel submerged hydro-separation (SubHyS) technique followed by anterior corneal dissection to prepare a Descemet endothelial graft (DEG) for Descemet's membrane endothelial keratoplasty from human donor corneas.Methods30 human...

Preliminary investigation of corneal wavefront aberration following femtosecond laser clear corneal incision for cataract surgery.

To investigate the early changes of the anterior corneal wavefront aberration (WA) following femtosecond laser clear corneal incision (FS-CCI) for cataract surgery. Twenty consecutive patients (20 eyes) with cataract underwent phacoemulsification and were divided into 2 groups: the study group received a 2.75-mm FS-CCI using an iFS Intralase; the control group received a 2.75-mm manual CCI using disposable knives. High-order corneal WA was analyzed over 3.5- and 6.0-mm pupils and corneal astigmatism was evaluated using vector analysis preoperatively, 1 week postoperatively, and 1 month postoperatively. At 1 month postoperatively, the mean surgically induced astigmatism (D) of the anterior cornea was 1.22 ± 0.60 at 144° and 1.04 D ± 0.64 at 90° in the study and control groups (p&lt;0.05), respectively. Over 3.5-mm pupil, there were no changes of corneal high-order aberrations (p&gt;0.05) following FS-CCI. Trefoil increased significantly (p&lt;0.01) following manual CCI at 1 week postoperatively. Over 6.0-mm pupil, FS-CCI did not induce any statistically significant change in corneal WA during follow-up. One week after manual CCI, total root mean square-high order aberrations (p&lt;0.01), spherical aberration (p&lt;0.05), and trefoil (p&lt;0.001) were statistically significantly higher than preoperatively. The CCI method was shown to influence changes in corneal WA during the first month postoperatively. The different changes of corneal high-order WA between the study and control groups may depend on the different CCI geometry. These preliminary data are valuable to improve understanding of FS-CCI design.

Scanning laser ophthalmoscopy and optical coherence tomography imaging of spectacular ecdysis in the corn snake (Pantherophis guttatus) and the California king snake (Lampropeltis getulus californiae).

One of the singularities of the eyes of snakes is the presence of the spectacle, a transparent and vascularized integument covering the cornea. The spectacle is completely renewed during ecdysis. Combined scanning laser ophthalmoscopy (SLO), optical coherence tomography (OCT), and conventional macrophotography were used to image this phenomenon. A spectral OCT/SLO examination and macrophotography were performed in four healthy adult corn snakes (Pantherophis guttatus) and one healthy adult California king snake (Lampropeltis getulus californiae) the day before the start of ecdysis and then daily during ecdysis. In all animals, ecdysis lasted 5days. The spectacle was hardly visible at baseline, but became obvious at day one, while the subspectacular space became larger and the superficial cornea presented a hyperechoic band. At day two, eye surface became translucent, and at the same time, vascularization of the spectacle was visible using SLO. At day 3, the vascularization was no longer visible, while the subspectacular space increased and the eye surface remained translucent. At day 4, the eye surface was transparent and the superficial hyperechoic band started to become less bright. At day 5, the old spectacle was shed and all the parameters returned to baseline. We hypothesize that the echogenicity modifications of the anterior cornea correspond to major metabolic activity associated with new spectacle formation. This increased metabolic activity may contribute to the neovascularization and play an important role in the accumulation of fluid in the subspectacular space, facilitating the shedding of the old spectacle.

Correlation of Anterior Corneal Higher-order Aberrations With Age

The aim of this study was to investigate the distribution of higher-order aberrations (HOAs) of the anterior cornea of eyes with cataract in a senior Chinese population and their correlations with age. Four hundred ten Chinese patients (male/female: 196/214; age: 67.9 ± 10.0 years) with cataract were categorized into 5 groups according to their age. The HOAs in the central 6-mm zone of the cornea were measured with an iTrace wavefront analyzer. The correlations between age and total HOA, coma aberration, trefoil aberration, and spherical aberration were assessed using Spearman analysis. The differences in total HOA, coma aberration, trefoil aberration, spherical aberration among various age groups were analyzed using the Kruskal-Wallis H test. The corneal HOA exhibited a nonnormal distribution. A weak correlation was found between age and total HOA, coma aberration (Z3), trefoil aberration (Z3) (P < 0.001 for all). No correlation was found between age and spherical aberration (Z4). Differences in the root mean square of the total HOA, Z3, and Z3 were found among various age groups (P < 0.05). No difference was found in the root mean square of Z4, spherical diopter, corneal curvature, corneal astigmatism, corneal effective refractive power, corneal asphericity Q value and corneal central power across the groups. The distribution of anterior corneal HOAs of eyes with cataract in a senior Chinese population is of the nonnormal type. The total HOA, Z3, and Z3 are correlated to age, unlike Z4 of the anterior cornea.

Measurement of Corneal Elasticity with an Acoustic Radiation Force Elasticity Microscope

To investigate the role of collagen structure in corneal biomechanics, measurement of localized corneal elasticity with minimal destruction to the tissue is necessary. We adopted the recently developed acoustic radiation force elastic microscopy (ARFEM) technique to measure localize biomechanical properties of the human cornea. In ARFEM, a low-frequency, high-intensity acoustic force is used to displace a femtosecond laser-generated microbubble, while high-frequency, low-intensity ultrasound is used to monitor the position of the microbubble within the cornea. Two ex vivo human corneas from a single donor were dehydrated to physiologic thickness, embedded in gelatin and then evaluated using the ARFEM technique. In the direction perpendicular to the corneal surface, ARFEM measurements provided elasticity values of E = 1.39 ± 0.28 kPa for the central anterior cornea and E = 0.71 ± 0.21 kPa for the central posterior cornea in pilot studies. The increased value of corneal elasticity in the anterior cornea correlates with the higher density of interweaving lamellae in this region.

소프트콘택트렌즈의 유형에 따른 각막형태의 변화

목적: 콘택트렌즈의 함수율, 재질, 굴절력의 차이에 따른 착용전후의 각막의 형태 변화를 살펴보고자 하였다. 방법: 5가지 유형의 콘택트렌즈를 사용하여 렌즈 착용 전후의 두께차이를 비교하였다. 각막의 중심부와 각막 중심에 떨어진 거리와 방향에 따른 렌즈 착용 전, 후의 각막의 두께, 각막 전, 후면 곡률, 고위수차의 변화를 조사하였다. 측정에 사용된 장비로는 ORB ScanII(Bausch & Lomb Inc, ver 3.14)로 각막 지형도 및 각막 두께를 측정하였으며, 고위수차(high order aberration) 분석을 위하여 Zywave(Bausch & Lomb Inc, ver 5.20)를 사용 하였다. 결과: 산소투과가 낮은 하이드로겔 재질의 소프트 콘택트렌즈(T2 lens)에서 각막의 두께가 증가하는 경향이 두드러지게 나타났다. 각막 중심에서 가장 많은 변화를 보였으며, 중심에 가까울수록 변화정도가 증가하였다. 각막의 방향에 있어서는 코 쪽이 가장 많이 변하였다. 결론: 본 연구에서 사용한 함수율, 재질, 디자인이 다른 5종의 콘택트렌즈 중 Dk가 28이상의 산소투과도를 가진 렌즈에서는 각막의 형태 변화가 적었으며, 산소투과도가 매우 낮은 렌즈에서 가장 많은 각막형태의 변화가 나타났다. Purpose: This study was to investigate changes in the thickness of cornea, curvature of cornea, and aberration depending on the water contents, materials, and refractive power of contact lens. Methods: The differences in the corneal thickness between pre- and post-wearing the lenses were compared using 5 kinds of lenses. The changes in the corneal thickness, the curvatures of the anterior and posterior cornea, and high order aberration (HOA) before and after wearing the lenses were investigated at the center of the cornea, and the different distance and the direction away from the center of the cornea. For the equipments of measurement, ORB ScanII (Bausch & Lomb Inc, ver 3.14) was used to measure the corneal topography and thickness, and Zywave (Bausch & Lomb Inc, ver 5.20) was used to analyze the high order aberration. Results: Five (S1, S2, S3, T1, T2) of the lens was used for this study, excluding the lens T2 lens has four lenses and the thickness of the corneal shape, but the impact is minimal. In the case of the hydrogel soft contact lenses (T2 lens) with low oxygen permeability, the corneal thickness showed distinct increasing patterns. The high order aberration and coma aberration were most changed in the silicon hydrogel toric lens, while the depth of anterior was most changed in the hydrogel toric lens. Conclusion: Among the 5 kinds of contact lenses with different water contents, materials, and refractive power used for this study, the corneal shape change was small for the lenses with an oxygen permeability (Dk) of more than 28, and the largest for the lenses with a very low oxygen permeability.