Sofia C. Peixoto-de-Matos

Prevalence of corneal astigmatism before cataract surgery.

PURPOSE: To analyze the prevalence and presentation patterns of corneal astigmatism in cataract surgery candidates. SETTING: University of Valencia, Valencia, Spain. METHODS: Refractive and keratometric values were measured before surgery in patients having cataract extraction. Descriptive statistics of refractive and keratometric cylinder data were analyzed and correlated by age ranges. RESULTS: Refractive and keratometric data from 4540 eyes of 2415 patients (mean age 60.59 years ± 9.87 [SD]; range 32 to 87 years) differed significantly when the patients were divided into 10‐year subsets. There was a trend toward less negative corneal astigmatism values, except the steepest corneal radius and the J45 vector component, in older groups (Kruskal‐Wallis, P<.01). In 13.2% of eyes, no corneal astigmatism was present; in 64.4%, corneal astigmatism was between 0.25 and 1.25 diopters (D) and in 22.2%, it was 1.50 D or higher. CONCLUSIONS: Corneal astigmatism less than 1.25 D was present in most cataract surgery candidates; it was higher in about 22%, with slight differences between the various age ranges. This information is useful for intraocular lens (IOL) manufacturers to evaluate which age ranges concentrate the parameters most frequently needed in sphere and cylinder powers and for surgeons to evaluate which IOLs provide the most effective power range.

Oxygen diffusion and edema with modern scleral rigid gas permeable contact lenses.

PURPOSE We defined the theoretical oxygen tension behind modern scleral contact lenses (CLs) made of different rigid gas permeable (RGP) materials, assuming different thickness of the tear layer behind the lens. A second goal was to show clinically the effect of the postlens tear film on corneal swelling. METHODS We simulated the partial pressure of oxygen across the cornea behind scleral CLs made of different lens materials (oxygen permeability Dk, 75-200 barrer) and different thickness (Tav, 100-300 μm). Postlens tear film thicknesses (Tpost-tear) ranging from 150 to 350 μm were considered. Eight healthy subjects were fitted randomly with a scleral lens with a thin and a thick postlens tear layer in two different sessions for a period of 3 hours under open-eye conditions. RESULTS The CLs with less than 125 barrer of Dk and a thickness over 200 μm depleted the oxygen availability at the lens-cornea interface below 55 mm Hg for a postlens tear film of 150 μm. For a postlens tear film thickness of 350 μm, no combination of material or lens thickness will meet the criteria of 55 mm Hg. Our clinical measures of corneal edema showed that this was significantly higher (P < 0.001, Wilcoxon signed ranks test) with the thicker compared to the thinner Tpost-tear (mean ± SD, 1.66 ± 1.12 vs. 4.27 ± 1.19%). CONCLUSIONS Scleral RGP CLs must be comprised of at least 125 barrer of oxygen permeability and up to 200 μm thick to avoid hypoxic effects even under open eye conditions. Postlens tear film layer should be below 150 μm to avoid clinically significant edema.

Ocular dominance and visual function testing.

Purpose. To show the distribution of ocular dominance as measured with sensory and eye sighting methods and its potential relationship with high and low contrast LogMAR visual acuity in presbyopic subjects. Method. Forty-four presbyopes (48.5 ± 3.5 years) participated in this study. Ocular dominance was determined by eye sighting (hole-in-card) and sensorial (+1.50 D lens induced blur) methods. According to the dominance detected with each method (RE: right eye or LE: left eye), patients were classified in dominance type 1 (RE/RE), type 2 (RE/LE), type 3 (LE/RE) and type 4 (LE/LE). Results. Baseline refractive error (MSE) was RE:−0.36 ± 1.67 D and LE:−0.35 ± 1.85 D (P = 0.930). RE was the dominant eye in 61.4% and 70.5% of times as obtained from sensorial and sighting methods, respectively. Most frequent dominance was of type 1 (52.3%), in this case the RE showed statistically significant better distance low contrast LogMAR VA (0.04 LogMAR units) compared to the LE (P < 0.05). Conclusions. The dominance was more frequent in RE in this sample. The eye sighting and sensorial methods to define ocular dominance agreed in more than half of cases. Amount of MSE was not significantly different between dominant and non-dominant eye. But in case of right dominance, the RE presented better distance low contrast VA compared to the LE.

Pupil Size, White-to-White Corneal Diameter, and Anterior Chamber Depth in Patients with Myopia

PURPOSE To evaluate anatomical parameters in a population of patients with myopia. METHODS Nine hundred sixty-four myopic eyes (-3.00 to -20.00 diopters [D] spherical equivalent refraction) were evaluated to measure mesopic and photopic pupil size with an infrared pupillometer; anterior chamber depth and white-to-white corneal diameter were obtained with Orbscan II (Bausch & Lomb). Correlation analysis was performed to evaluate the relationships among anatomical parameters of the anterior segment of the eye. RESULTS Average change in pupil size between mesopic and photopic conditions shows a uniform gap of 1.5 mm in patients aged 18 to 62 years with a slight insignificant trend to decrease with age. Photopic and mesopic pupil size were highly correlated (r=0.694, P<.001) and the difference between both measures was positively correlated with mesopic pupil size (r=0.207, P<.001) and inversely correlated with photopic pupil size (r=0.561, P<.001). Anterior chamber depth and white-to-white corneal diameter were positively correlated (r=0.389, P<.001). White-to-white corneal diameter and anterior chamber depth were not correlated with age (r=-0.096, P<.001) or anterior chamber depth (r=-0.183, P<.001-0.183) as a function of age. CONCLUSIONS Average difference between photopic and mesopic pupil size remained constant across the range of ages included in this cohort. A positive correlation was noted between anterior segment dimensions, and anterior chamber depth decreased with age.

Shedding light on night myopia.

First described during the 18th century, the cause of night myopia remains a controversial topic. Whereas several explanations have been suggested in the literature, particularly related with accommodation or chromatic shift in scotopic light conditions, no definitive explanation for its aetiology has been provided. We describe an experiment in which ocular refractive state was objectively and subjectively measured while viewing two kind of stimulus: letters on a bright background and a punctual source of light in a dark background. We found that under photopic conditions the optimum refractive state of the accommodating eye is significantly more myopic when maximizing perceived quality of a point source on a dark background compared to a conventional letter chart with black letters on a white background. Optical modeling suggested this difference in refractive state is due to spherical aberration. Since isolated point sources are more likely encountered at night, whereas extended objects are more likely encountered in the daytime, our results suggest that a significant part of the night myopia phenomenon is determined by the nature of the visual stimulus and the visual task used to assess ocular refractive state.

Strategies to Regulate Myopia Progression With Contact Lenses: A Review

Purpose: Higher myopic refractive errors are associated with serious ocular complications that can put visual function at risk. There is respective interest in slowing and if possible stopping myopia progression before it reaches a level associated with increased risk of secondary pathology. The purpose of this report was to review our understanding of the rationale(s) and success of contact lenses (CLs) used to reduce myopia progression. Methods: A review commenced by searching the PubMed database. The inclusion criteria stipulated publications of clinical trials evaluating the efficacy of CLs in regulating myopia progression based on the primary endpoint of changes in axial length measurements and published in peer-reviewed journals. Other publications from conference proceedings or patents were exceptionally considered when no peer-review articles were available. Results: The mechanisms that presently support myopia regulation with CLs are based on the change of relative peripheral defocus and changing the foveal image quality signal to potentially interfere with the accommodative system. Ten clinical trials addressing myopia regulation with CLs were reviewed, including corneal refractive therapy (orthokeratology), peripheral gradient lenses, and bifocal (dual-focus) and multifocal lenses. Conclusions: CLs were reported to be well accepted, consistent, and safe methods to address myopia regulation in children. Corneal refractive therapy (orthokeratology) is so far the method with the largest demonstrated efficacy in myopia regulation across different ethnic groups. However, factors such as patient convenience, the degree of initial myopia, and non-CL treatments may also be considered. The combination of different strategies (i.e., central defocus, peripheral defocus, spectral filters, pharmaceutical delivery, and active lens-borne illumination) in a single device will present further testable hypotheses exploring how different mechanisms can reinforce or compete with each other to improve or reduce myopia regulation with CLs.

Anterior and posterior corneal elevation after orthokeratology and standard and customized LASIK surgery

Purpose: To quantify the changes in the elevation topography of the front and back corneal surfaces after three different refractive treatments for correcting myopia with standard and custom laser in situ keratomileusis (LASIK) and orthokeratology using corneal refractive therapy. Methods: We evaluated 20 eyes undergoing orthokeratology for correction of myopia spherical equivalent (mean±SD=−3.41±0.76 D), 18 eyes undergoing custom LASIK surgery (mean±SD=−4.14±0.89 D), and 23 eyes undergoing standard LASIK (mean±SD=−3.61±0.67 D). The values of front and back corneal surfaces were derived by using Pentacam (Oculus, Inc. GmbH, Wetzlar, Germany) before and at least 3 months after each treatment, in the center of the cornea and 4 points to each side of the horizontal meridian at intervals of 1 mm. Results: Corneal elevation data before treatment were not statistically different between patients in either group (P>0.070, for back and front elevation). After treatment, both surgical procedures significantly increased the positive value of the front elevation beyond an area of 6 mm. The opposite trend was found within the central 5 mm of the cornea, presenting a statistically significant decrease in elevation (P<0.001). In the case of orthokeratology, the elevation experienced a minor but a statistically significant reduction in the central region (P<0.001). On the back surface, the elevation did not undergo statistically significant alterations in any of the procedures and none of the items discussed (P>0.285). Conclusions: Differences in front corneal elevation changes between LASIK and orthokeratology reveal a much different mechanism for producing corneal power subtraction. The back corneal surface does not suffer significant changes after surgical and nonsurgical treatments for the correction of myopia.

Radiometric characterization of a novel LED array system for visual assessment

Light that enters the eye can be distorted due to several factors leading to a poor visual performance. The purpose of this paper is to describe and characterize the light-emitting diode (LED) display system to be used in a new device to assess visual quality under high glare conditions. The device has a central white LED and surrounding white LEDs distributed in a radial manner. Each LED is controlled independently using special designed software. The spectral power distribution and color of the LEDs were assessed at different voltage intensities to test the response in terms of output luminance and spectral distribution. It was found that the typical maximum luminance was about 2800 cd/m2 and 6 cd/m2 for the central and surrounding LEDs, respectively. Their color was found to be within the ΔE∗ab range of 2.6 and 0.23, respectively, if the minimum and maximum intensities are considered. The characterization of this device was proved successfully, which might indicate its usefulness in future visual assessments.

In situ corneal and contact lens thickness changes with high-resolution optical coherence tomography.

Purpose: To show the use of high-resolution spectral-domain optical coherence tomography (HR-SOCT) for the in situ evaluation of epithelial, stromal, and contact lens (CL) thickness changes under closed-eye conditions without lens removal. Methods: Eight young healthy patients wore a thick soft CL for 90 minutes under closed-eye conditions, and measures of epithelial and stromal corneal thickness were obtained at regular intervals using a HR-SOCT (Copernicus HR; Optopol Tech. SA, Zawiercie, Poland). Results: Minimal changes in epithelial thickness were detected with a transient statistically significant increase in epithelial thickness in the fellow control eye 30 minutes after insertion (P = 0.028). A significant and progressive increase in stromal thickness up to 8% after 90 minutes of lens wear was observed at a constant rate of 2.5% every 30 minutes, being statistically significant in all observations (P < 0.001). Fellow control eyes also showed a significant increase in stromal thickness at a much lower rate of 0.5% every 30 minutes. Lens thickness decreased significantly by 2% after 90 minutes of lens wear under closed-eye conditions (P < 0.001). Individual analysis showed that all eyes displayed stromal swelling, whereas only half of them showed epithelial swelling. Conclusions: Increase in stromal thickness and a slight decrease in lens thickness were observed in response to a hypoxic stimulus under closed-eye conditions. HR-SOCT is a powerful tool to investigate in vivo the physiological interactions between cornea and CLs.

Comfort and vision scores at insertion and removal during 1 month of wear of Paragon CRT for corneal reshaping.

Purpose: The goal of this study was to evaluate the pattern of initial adaptation of neophytes to corneal refractive therapy (CRT) for overnight corneal reshaping in terms of comfort and subjective visual performance at lens insertion at night and lens removal in the morning. Methods: Twenty-two young healthy subjects were enrolled in this study. All of them had been trialed to assess adaptation to conventional alignment-fit rigid gas permeable lenses and were only enrolled in this study after a 2-week wash-out period. Visual analog scales for subjective comfort and vision were recorded on a form given to the patient on days 1, 2, 3, 5, 7, 14, 21, and 28. Additionally, the patient attended the clinic on days 1, 7, 15, and 30 after fitting, for follow-up. Results: Successful adaptation was obtained in 21 of the 22 initially enrolled individuals. The average overnight wearing time remained constant during the study at 8 hrs per day. Overall comfort rates increased significantly up to values of 8.02 and 9.12 out of 10 at insertion and removal, respectively (P<0.001). Subjective vision scores also increased significantly at the end of the 1-month study period (P<0.001). Conclusions: Adaptation to CRT is rapid in terms of subjective comfort and vision. Comfort significantly increases by day 5, whereas subjective vision in the morning reaches its maximum by days 15 to 21 and at the end of the day by days 10 to 15. These results are of interest to clinicians to provide evidence-based information to their patients about the expected time to adapt to CRT in terms of self-reported comfort and vision.