Guadalupe Rodriguez

Optical aberrations in the mouse eye.

PURPOSE The mouse eye is a widely used model for retinal disease and has potential to become a model for myopia. Studies of retinal disease will benefit from imaging the fundus in vivo. Experimental models of myopia often rely on manipulation of the visual experience. In both cases, knowledge of the optical quality of the eye, and in particular, the retinal image quality degradation imposed by the ocular aberrations is essential. In this study, we measured the ocular aberrations in the wild type mouse. METHODS Twelve eyes from six four-week old black C57BL/6 wild type mice were studied. Measurements were done on awake animals, one being also measured under anesthesia for comparative purposes. Ocular aberrations were measured using a custom-built Hartmann-Shack system (using 680-nm illumination). Wave aberrations are reported up to fourth order Zernike polynomials. Spherical equivalent and astigmatism were obtained from the 2nd order Zernike terms. Modulation Transfer Functions (MTF) were estimated for the best focus, and through-focus, to estimate depth-of-focus. All reported data were for 1.5-mm pupils. RESULTS Hartmann-Shack refractions were consistently hyperopic (10.12+/-1.41 D, mean and standard deviation) and astigmatism was present in many of the eyes (3.64+/-3.70 D, on average). Spherical aberration was positive in all eyes (0.15+/-0.07 microm) and coma terms RMS were significantly high compared to other Zernike terms (0.10+/-0.03 microm). MTFs estimated from wave aberrations show a modulation of 0.4 at 2c/deg, for best focus (and 0.15 without cancelling the measured defocus). For that spatial frequency, depth-of-focus estimated from through-focus modulation data using the Rayleigh criterion was 6D. Aberrations in the eye of one anesthetized mouse were higher than in the same eye of the awake animal. CONCLUSIONS Hyperopic refractions in the mouse eye are consistent with previous retinoscopic data. The optics of the mouse eye is far from being diffraction-limited at 1.5-mm pupil, with significant amounts of spherical aberration and coma. However, estimates of MTFs from wave aberrations are higher than previously reported using a double-pass technique, resulting in smaller depth-of-field predictions. Despite the large degradation imposed by the aberrations these are lower than the amount of aberrations typically corrected by available correction techniques (i.e., adaptive optics). On the other hand, aberrations do not seem to be the limiting factor in the mouse spatial resolution. While the mouse optics are much more degraded than in other experimental models of myopia, its tolerance to large amounts of defocus does not seem to be determined entirely by the ocular aberrations.

Longitudinal changes of optical aberrations in normal and form-deprived myopic chick eyes

We performed measurements of refraction (with retinoscopy), axial length (with ultrasound biometry) and ocular aberrations (with a custom-built Hartmann-Shack aberrometer) on seven awake White-Leghorn chicks occluded monolaterally with diffusers for two weeks. Treatment started on the first day after hatching (day 0) and measurements were conducted on several days between day 0 and 13. Non-occluded eyes experienced normal emmetropization (decreasing hyperopia at 0.2 +/- 0.09 D/day and increasing axial length at 0.05 +/- 0.03 mm/day), while occluded eyes developed axial myopia (1.50 +/- 0.2 D/day and 0.12 +/- 0.02 mm/day). Interocular differences in refraction and axial length by day 13 were on average 17.43 D and 0.86 mm, respectively. Monochromatic high order aberrations decreased with age in both eyes. Average RMS (for 1.5 mm pupil diameter) decreased from 0.11 +/- 0.03 at day 0 to 0.06 +/- 0.03 microm (day 13) in occluded eyes, and from 0.12 +/- 0.05 to 0.03 +/- 0.01 microm in non-occluded eyes. MTF-based optical quality metrics also show an improvement with age. However, while this improvement occurs in both eyes, after day 8 myopic eyes tend to show significantly higher amounts of aberrations (and consequently worse best-corrected optical quality) than normal eyes. The degradation imposed by aberrations is small compared to that imposed by defocus and the diffuser. These results suggest a decrease of aberrations during development which does not seem to be visually guided. Myopic eyes showed slightly worse optical quality than normal eyes, suggesting that the geometrical changes resulting from excessive ocular axial growth also affect the optical quality of the ocular components.

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.

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.

Emmetropization and optical aberrations in a myopic corneal refractive surgery chick model

We studied the potential of myopic corneal refractive laser surgery to induce myopia (axial elongation) and potential interactions between aberrations (generally resulting from the procedure) and myopia development in chicks (Gallus domesticus). Ten white Leghorn chicks were monolaterally treated one day post-hatching with photorefractive keratectomy (PRK), with a nominal dioptric change of -9.9 D (imposed hyperopia). Axial length was measured using an adapted ultrasonic biometer; corneal radius of curvature was measured using a custom-built videokeratometer and spherical error and high order aberrations were measured using custom-built Hartmann-Shack aberrometer post-operatively on days 9, 12, 14 and 16 after hatching. Two-weeks after surgery, there were no significant differences in corneal radius of curvature between treated and control eyes. Astigmatism increased on average by a factor of 2.6 and 3rd and higher order aberrations by a factor of 4.3 after PRK. Both treated and control eyes were close to emmetropia, and no axial elongation was found in the treated eyes. The inability of the refractive procedure to achieve significant reductions in the corneal power could be attributed to the biomechanical properties of the chick eye. High order aberrations induced significant contrast decrease (by a factor of 1.7 at 4.5c/deg). However, reduced image quality neither produced myopic refractive error nor axial elongation in the treated eyes. Both normal and treated eyes emmetropized, indicating that increased amounts of aberrations do not appear to be a risk factor for myopia.

Experimental Model of Laser in situ Keratomileusis in Hens

PURPOSE To develop an experimental animal model of laser in situ keratomileusis (LASIK) in hens. METHODS One hundred adult hens underwent a 60-microm corneal flap followed by -4 diopter excimer laser ablation. Surgical technique, clinical course, and pathology correlations are presented. RESULTS Sixty percent of animals had a successful LASIK outcome according to clinical observations. Pathology showed the integrity of Bowmans layer and homogeneous flap in all eyes with good clinical outcomes. Flap complications such as buttonholes (5%), free-flaps (2%), and slipped flaps (3.4%) occurred with the surgical technique. Corneal abscess (2.9%) was also present. Loss of transparency was noted in 26.4%, which correlates with epithelial ingrowth detected by light histology study. CONCLUSIONS An experimental animal model of LASIK was successfully developed in adult hens. This model could be useful in the study of wound healing and pharmacological modulation after LASIK in an animal with Bowmans layer.

Refractive stabilization and corneal swelling after cataract surgery.

Purpose To determine the earliest time after cataract surgery when corneal swelling and automated refraction are stabilized sufficiently to allow reliable refractive prescription. Methods This was a prospective, nonrandomized, case series study of 124 consecutive eyes undergoing uneventful cataract surgery. Automated refraction and central corneal thickness (CCT) measurements were made at baseline before cataract surgery and on follow-up visits 1 day and weekly for 4 weeks afterward. Corneal swelling was determined as the percentage change in CCT after surgery. To determine the validity of automated refraction, it was compared with subjective refraction at the final visit. Results Corneal swelling decreased between the first postsurgical day and the first week and again between postsurgical weeks 1 and 2 (p < 0.01 each). Although thinning continued through the fourth postsurgical week, the changes were not significant. Both spherical and cylindrical refraction were stable 1 week after surgery, with the greatest change between the first postsurgical day and 1 week (p < 0.01). In replicate measurements of automated spherical refraction taken on the last visit, the intraclass correlation coefficient was 0.93. For automated cylindrical refraction, it was 0.81. Conclusions Automated refraction is highly repeatable and can be used to monitor postsurgical refractive changes. Whereas corneal swelling becomes stable 2 weeks after cataract surgery, automated refraction becomes stable after 1 week and can be used to accurately prescribe corrective lenses at that time.

Constancy of the Orbscan acoustic factor to detect contact lens‐induced corneal swelling

Purpose:  The aim of the present study was to compare central and peripheral corneal thickness measurements in corneas with and without contact lens (CL)‐induced corneal swelling, in order to establish the constancy of the Orbscan acoustic factor (AF) for reliability in detection of CL‐induced corneal swelling.

Repeatability of Wavefront Aberration Measurements With a Placido-Based Topographer in Normal and Keratoconic Eyes

PURPOSE To determine and compare the repeatability of anterior corneal higher order aberrations (HOAs) using a Placido-based topographer (Allegro Topolyzer; WaveLight Technologie AG, Alcon Laboratories, Erlangen, Germany) in a sample of normal and keratoconic eyes. METHODS Three repeated measurements of each cornea of normal and keratoconic eyes were taken with the Allegro Topolyzer. Repeatability of the HOAs (3rd- and 4th-order individual values and normalized polar Zernike coefficients, coma-like, root mean square (RMS) up to 8th-order values, HOA RMS, and total RMS for 6-mm pupil diameter) and central corneal power (3-mm pupil) were analyzed. Within-subject standard deviation (Sw), precision, repeatability, coefficient of variation (CV), and the intraclass correlation coefficient (ICC) were calculated. RESULTS Zernike coefficients were significantly different between the normal (36 eyes of 36 patients) and keratoconus (36 eyes of 36 patients) groups (P ≤ .03) except in Z(+1) 3, Z(+3) 3, Z(-4) 4, and Z(+4) 4. In the normal group, Sw was 0.031 µm or less, CV ranged from 6.49% (spherical aberration) to 37.18% (secondary astigmatism), and ICC values ranged from 0.227 to 0.982. In the keratoconus group, Sw was 0.059 µm or less, CV ranged from 2.06% (total RMS) to 25.82% (tetrafoil), and ICC values ranged from 0.839 to 0.996. In analyzing the keratoconus stages (Amsler-Krumeich classification), the repeatability of the Zernike coefficients tended to improve with increasing keratoconus stage. CONCLUSIONS The repeatability of corneal wavefront aberration provided by the Allegro Topolyzer was better in keratoconic eyes (good and moderate repeatability) than in normal eyes (moderate and poor repeatability). These results are important to eye care practitioners and refractive surgeons during refractive surgery planning or keratoconus detection, classification, and management. [J Refract Surg. 2016;32(5):338-344.].