Raul Martin

Corneal assessment technologies: Current status

There are now many devices that acquire data about the cornea: shape, power, pachymetry at any desired point of the cornea, corneal hysteresis, flap thickness (in LASIK procedures), endothelial cell count and morphology, and so forth. We review the literature on corneal assessment techniques and devices available in clinical practice. Specifically, we discuss slit lamp biomicroscopy, specular microscopy, ultrasound pachymetry, confocal microscopy, very-high-frequency digital ultrasound biomicroscopy, optical coherence tomography, Placido disk-based keratoscopy, slit-scanning elevation topography, Scheimpflug imaging, and dynamic applanation procedures-all of which can be used to assess the morphology of the cornea. In addition, we present a critical analysis of the instrumentation described and discuss the necessity of developing new technology for assessing both the morphology and the physiology of the cornea.

Corneal conjunctivalisation in long-standing contact lens wearers.

Background:  There are many contact lens‐related ocular surface disorders. Some can damage the limbal region where stem cells are thought to be located in its basal cell layer. This damage can result in destruction and a deficiency of corneal stem cells. One important sign of this complication is corneal conjunctivalisation. The purpose of this study is to describe clinical characteristics of a series of long‐standing contact lens (CL) wearers with corneal conjunctivalisation (CC).

Experimental Model of Corneal Haze in Chickens

PURPOSE To develop an experimental animal model of corneal haze following photorefractive keratectomy (PRK). METHODS Fifteen Iber Braun hens underwent unilateral PRK for -9.00 D of myopia. The animals were sacrificed at 1, 3, and 6 months postoperatively, and light microscopy was performed. RESULTS Slit-lamp microscopy showed haze in the PRK-treated eyes. Histopathologic study disclosed epithelial hyperplasia, basement membrane abnormalities, and extensive anterior stromal disorganization. CONCLUSIONS An easy and inexpensive model of haze after PRK was developed in an animal with Bowmans layer. This new model could be useful to understand the pathophysiology and pharmacologic modulation of corneal haze.

Prototype of a Nanostructured Sensing Contact Lens for Noninvasive Intraocular Pressure Monitoring

PURPOSE To present the application of a new sensor based on a flexible, highly piezoresistive, nanocomposite, all-organic bilayer (BL) adapted to a contact lens (CL) for non-invasive monitoring intraocular pressure (IOP). METHODS A prototype of a sensing CL, adapted to a pig eyeball, was tested on different enucleated pig eyes. A rigid, gas-permeable CL was designed as a doughnut shape with a 3-mm hole, where the BL film-based sensor was incorporated. The sensor was a polycarbonate film coated with a polycrystalline layer of the highly piezoresistive molecular conductor β-(ET)₂I₃, which can detect deformations caused by pressure changes of 1 mm Hg. The pig eyeballs were subjected to controlled-pressure variations (low-pressure transducer) to register the electrical resistance response of the CL sensor to pressure changes. Similarly, a CL sensor was designed according to the anatomic characteristics of the eye of a volunteer on the research team. RESULTS A good correlation (r² = 0.99) was demonstrated between the sensing CL electrical response, and IOP (mm Hg) changes in pig eyes, with a sensitivity of 0.4 Ω/mm Hg. A human eye test also showed the high potential of this new sensor (IOP variations caused by eye massage, blinking, and eye movements were registered). CONCLUSIONS A new nanostructured sensing CL for continuous monitoring of IOP was validated in an in vitro model (porcine eyeball) and in a human eye. This prototype has adequate sensitivity to continuously monitor IOP. This device will be useful for glaucoma diagnosis and treatment.

Reverse Geometry Contact Lens Fitting After Corneal Refractive Surgery

PURPOSE To describe reverse geometry rigid gas permeable (RGP) contact lens fitting in eyes with irregular surface induced by complications after myopic corneal refractive surgery. METHODS Reverse geometry RGP contact lenses were fit in nine eyes that underwent myopic corneal refractive surgery and experienced a reduction in best spectacle-corrected visual acuity (BSCVA) Snellen lines postoperatively. RESULTS Comparing the BSCVA with contact lenses, 5 (55.6%) eyes improved > or = 2 lines of BSCVA, 2 (22.2%) eyes improved 1 line, and 2 (22.2%) eyes maintained the same BSCVA as the one eye with spectacles (P < .004). No eye lost lines of BSCVA. All patients reported excellent tolerance and subjective visual quality with the contact lenses. The mean time of contact lens wear was 10.44 +/- 0.88 hours per day (95% confidence interval, 9.76 to 11.12). CONCLUSIONS Reverse geometry RGP contact lens fitting is effective in correcting surgically induced irregular surfaces with improved visual acuity and comfortable wear. These lenses may be the best choice in cases in which surgical retreatment is unfeasible or undesirable.

Differences in the daily symptoms associated with the silicone hydrogel contact lens wear.

Objective: To determine the differences in symptoms associated with daily wear of silicone hydrogel (lotrafilcon B) contact lenses (CLs) after CL insertion and at the end of wear and their relationship with environmental factors and multipurpose solutions (Solo-care Aqua, CIBA Vision, Duluth, GA and Hidro Health, Disop, Spain). Methods: Fifty-four patients were fitted with lotrafilcon B CLs. Two multipurpose solutions were randomly assigned and prescribed in a double-masked crossover study with three visits. After each solution was used, two questionnaires were conducted, including a survey produced by us and Contact Lens Dry Eye Questionnaire. Our questionnaire included 10 items addressing discomfort, blurry vision, lens-handling problems, dryness, redness, tearing, burning, itching, discharge, and dissatisfaction. Patients were assigned scores from 0 (without symptoms) to 10 (symptoms unbearable) at two different times (after CL insertion and at the end of wear) and in two environments (outdoors and adverse environments). Results: The average duration of CL wear was 8.32 ± 2.27 hr/day and 5.85 ± 1.30 days/week. All symptoms became worse (P < 0.05 Wilcoxon test, except lens handling) at the end of CL wear in all visits. The results were independent of the multipurpose solution used (P > 0.05 Friedman test), except for tearing, which showed statistical differences between visits (P = 0.03 Friedman test). Contact Lens Dry Eye Questionnaire showed increased dry eye symptoms at the end of wear (P < 0.05 Friedman test). Conclusions: Daily wear symptoms associated with lotrafilcon B CL increase with the time of wear. This increase in symptoms is nonrelated with the multipurpose solutions compared in this study.

Relationships between central and peripheral corneal thickness in different degrees of myopia

PURPOSE To analyze the relationship between the central corneal thickness (CCT) and mid-peripheral corneal thickness (PCT) with the degree of myopia [axial length (AL) and spherical equivalent refractive error (SE)]. METHODS 175 right myopic eyes from 175 patients were divided according to the degree of SE: group #1 (n=76, <6.00 D), group #2 (n=72, between 6.00 and 12.00 D) and group #3 (n=27, >12.00 D). The CCT and PCT (3mm from the apex to the superior, inferior, nasal and temporal locations) were measured with the Orbscan-II. Relative peripheral index (RPI) was calculated by dividing the PCT by the CCT. The AL was measured with the IOL Master, and the SE was obtained with subjective refraction. RESULTS AL was 25.18±1.16 mm, 26.59±1.26 mm and 29.45±2.58 mm and SE was -3.31±1.40 D, -8.32±1.64 D and -16.44±4.48 D for groups #1, #2 and #3, respectively. Non-statistically significant differences in central and peripheral corneal thickness were found between groups (P>0.05 ANOVA). Non-significant relationship was found between central and peripheral corneal thickness with the AL and SE in the three study groups and in the total sample (r<0.24; P>0.05). The RPI values were similar between groups without significant difference between groups (P>0.05 ANOVA). Linear relationship was found between RPI superior location in group #2 (r=-0.23; P=0.04) and RPI nasal location in group #3 with the EE (r=0.41; P=0.03). CONCLUSION There are no significant differences among low, moderate and extremely myopic eyes related to the CCT and PCT. Corneal thickness is very similar in myopic eyes with small differences that are not clinically relevant to myopic patient management.

Contact lens-induced corneal peripheral swelling: Orbscan repeatability.

Purpose. To compare the repeatability and agreement of corneal thickness measurements using central and peripheral ultrasound and Orbscan pachymetry to detect contact lens (CL)-induced corneal swelling after extended wear (EW). Methods. Corneal thickness was measured in five corneal locations (central, superior, inferior, nasal, and temporal) with ultrasound and Orbscan pachymetry 1 week before CL wear commenced and after 1 week of EW. High oxygen permeability (lotrafilcon A) and low oxygen permeability (etafilcon A) CL were randomly fitted for EW in the right and left eyes of 20 subjects with normal ocular health to induce different amount of corneal swelling. Results. Poor repeatability and poor agreement in peripheral ultrasound and Orbscan pachymetry was found between corneas with and without corneal swelling. Ultrasound coefficients of repeatability (central, superior, inferior, nasal, and temporal) in corneas without (0.95, 2.1, 3.2, 3.9, and 3.8%) and with (0.91, 1.89, 2.45, 2.66, and 2.26%) corneal swelling were higher than Orbscan coefficients of repeatability without (0.74, 1.67, 1.29, 1.11, and 1.11%) and with (0.74, 1.47, 1.28, 1.78, and 1.23%) corneal swelling. Lotrafilcon A induced significantly less corneal swelling in all five corneal locations compared with etafilcon A. Peripheral corneal swelling differences between lens types were significant only with Orbscan measurements (p < 0.05, Paired t-test and re-analysis of variance). Conclusions. The assessment of corneal thickness shows higher repeatability using Orbscan pachymetry than using ultrasound to measure corneas with and without corneal swelling and could be useful to study central and peripheral corneal swelling variations in CL EW.

White-to-white corneal diameter differences in moderately and highly myopic eyes: Partial coherence interferometry versus scanning-slit topography

Purpose To evaluate the differences between Orbscan scanning‐slit topography and IOLMaster partial coherence interferometry (PCI) white‐to‐white (WTW) measurements in moderately and highly myopic eyes. Setting IOBA‐Eye Institute, University of Valladolid, Spain. Design Comparative case series. Methods Myopic eyes were divided according to the degree of myopia as follows: Group 1 (<6.00 diopters [D]), Group 2 (between 6.00 D and 12.00 D), and Group 3 (>12.00 D). The WTW distance was measured with the scanning‐slit topography and PCI devices. Results The study enrolled 328 eyes (64 subjects). The mean WTW in all eyes was 0.50 mm ± 0.26 (SD), lower with scanning‐slit topography (11.69 ± 0.37 mm) than with PCI (12.19 ± 0.40 mm) (P<.01, paired t test). A low mean WTW was found in Group 2 (11.65 ± 0.34 and 12.15 ± 0.36 mm, scanning‐slit topography and PCI, respectively) and Group 3 (11.51 ± 0.36 and 12.05 ± 0.46 mm, respectively) compared with Group 1 (11.79 ± 0.38 and 12.26 ± 0.40 mm, respectively) (P<.03, analysis of variance with Games‐Howell correction). There was a low statistically significant relationship between WTW and spherical equivalent (SE) with both devices. Conclusions Eyes with moderate and high degrees of myopia had lower WTW diameters than eyes with low spherical equivalent myopia measured with both devices. Scanning‐slit topography provided less WTW distance than PCI in myopic eyes; thus, the devices are not clinically interchangeable. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Investigation of posterior corneal curvature in CL-induced corneal swelling

PURPOSE To evaluate Orbscan II measurements without contact lens (CL) removal to monitor in vivo posterior corneal curvature in CL (hypoxia)-induced corneal swelling during extended wear (EW). METHODS Orbscan II corneal topographer was used to measure posterior corneal curvature 1 week before CL wearing and during 1 week of EW. Central corneal thickness (CCT) was also measured during the 2-week study with OCT to determine the corneal swelling percentage. High Dk (lotrafilcon A) and low Dk (etafilcon A) soft CL were randomly fitted in EW in the right and left eyes of 20 subjects with normal ocular health. Orbscan and OCT were also performed without CL removal after 3 and 7 days of wear. RESULTS Low Dk lenses induced significantly higher corneal swelling (2.41+/-2.65%), as compared to the high Dk lenses (0.17+/-2.28%; P<0.05 repeated measures ANOVA (Re-ANOVA and paired t-test) measures with OCT. The low Dk lens induced a significantly posterior corneal flattening compared to the high Dk lens (0.036+/-0.06mm versus 0.006+/-0.04mm; P<0.05 Re-ANOVA and paired t-test). High repeatability for Orbscan-measured posterior best fit sphere (BFS) radii with (r(2)=0.15, 95% limits of agreement (LoA)=0.10 to -0.06) and without (r(2)=0.00, 95% LoA=0.08 to -0.08) CL removal was also observed and suggest that posterior corneal changes was not due to Orbscan variability. CONCLUSIONS Orbscan is a non-invasive and reproducible technique to evaluate and monitoring posterior corneal curvature in vivo in CL (hypoxia)-induced corneal swelling during EW.