Joan Gispets

Blink rate, blink amplitude, and tear film integrity during dynamic visual display terminal tasks.

Purpose: The present study aimed at investigating the influence of the level of dynamism of two different visual display terminal tasks on spontaneous eyeblink rate, blink amplitude, and tear film integrity. Material and Methods: A total of 25 healthy, young volunteers participated in the study. Blink rate and blink amplitude were recorded in silent primary gaze conditions and while subjects were playing two computer games of similar cognitive demands but different rate of visual information presentation. For each experimental condition, tear volume was evaluated by measuring meniscus height and with the red phenol thread test. Fluorescein and non-invasive break-up time tests, as well as the observation of interference patterns and the estimation of the dry area extension, were employed to assess tear stability. Results: Statistically significant differences were revealed in blink rate (F = 595.85, p < 0.001) and blink amplitude (χ2 = 34.00, p < 0.001), with blink rate during fast- and slow-paced game play decreasing to almost 1/3 and 1/2 of baseline levels, respectively, and with a larger percentage of incomplete blinks during dynamic tasks. Fluorescein and non-invasive break-up time tests and dry area extension were able to differentiate between experimental conditions in general (F = 408.42, p < 0.001; F = 163.49, p < 0.001; χ2 = 20.74, p < 0.001), as well as between fast- and slow-paced games, thus suggesting that tear quality was more affected than tear volume. Conclusions: Blink rate, blink amplitude, and tear film stability were compromised during the most dynamic visual display terminal task, suggesting a negative influence of not only the cognitive aspects of the task, but also of the rate at which new visual information is presented. Frequent breaks and blinking awareness training are recommended for visual display terminal users requiring prolonged periods of visually demanding dynamic computer play or work.

Optical performance in eyes wearing two multifocal contact lens designs

The optical performance of eyes wearing soft multifocal contact lenses was studied using the double‐pass technique. Retinal image quality was measured in a group of six eyes wearing two different designs of multifocal lenses: an aspheric design and a spheric multicurve design. Measurements were performed for far, intermediate and near vision conditions and with two different pupil diameters: 3 and 5 mm. The results show that the best optical performance is obtained for far vision conditions when no lens is worn. For near vision conditions, the optical performance when the lens is worn is, in general, better than when no lens is worn. When the lens is worn, the optical performance for far and intermediate vision conditions is similar for the aspherical design, but it decreases for near vision conditions. For the spherical multicurve design, the optical performance obtained for far vision conditions is similar to that obtained for intermediate vision conditions for low values of object vergence, but decreases when the object vergence is high and therefore also for near vision. In general, the differences in optical performance are greater for small pupil diameters (3 vs 5 mm). The general trends of the results obtained by computing the modulation transfer function of the contact lens–eye system can also be shown qualitatively by means of double‐pass images or quantitatively by computing the Imax/Imed of the image.

Image quality in wearers of a centre distance concentric design bifocal contact lens

The optical performance of eyes wearing bifocal concentric contact lens was studied using the double‐pass technique. Retinal image quality was measured for four subjects wearing CIBA Bisoft contact lenses presenting the central zone for correcting distance vision. Lenses with two different central optic zone diameter (COZD), 3.2 and 3.8 mm, were studied and the influence of pupil diameter and viewing distance were analysed. Results show that the best optical performance is obtained for far vision conditions when no lens is worn even if the pupil coverage by the COZD is complete. For near vision conditions, the optical performance when the lens is worn is, in general, better than when no lens is worn. When the lens is worn the best optical performance corresponds to a pupil diameter of 3 mm and far vision conditions. For this pupil diameter, variations in the situations analysed can be explained by changes in the percentage of pupil coverage corresponding to the far or the near vision zone of the lens. For a pupil diameter of 5 mm, the retinal image quality is more similar in all situations studied and pupil coverage alone cannot explain the results obtained and the influence of other parameters related to the design or contact lens fitting characteristics must be considered.

Task oriented visual satisfaction and wearing success with two different simultaneous vision multifocal soft contact lenses

Purpose: A longitudinal prospective, cross-over, double masked study was designed to evaluate task oriented visual satisfaction and wearing success with two types of simultaneous vision multifocal soft contact lenses. Methods: Twenty-two presbyopic subjects followed two 14-day trial periods in which they were alternatively and randomly fitted with two types of multifocal lenses. Habitual tasks were described in terms of observation distance, visual demand level and time allocation. Subjects graded visual satisfaction with each pair of lenses and each habitual task at different times during each trial. Overall satisfaction was evaluated after completion of the two trial periods. Wearing success was determined by the percentage of subjects opting to continue multifocal lens wear and by the number of subjects still wearing their lenses six months later. Results: Viewing distance and visual demand level were found to infl uence visual satisfaction (p < 0.001). Visual satisfaction decreased for tasks involving higher visual demands and for near and far viewing distances, rather than for intermediate vision or a combination of near and far vision. A combined effect of lens type and evaluation time was discovered (p = 0.046). Although 78 % of subjects decided to continue lens wear, only one subject was wearing them on a daily basis 6 months after the completion of the study. Insuffi cient quality of vision was reported as the main reason for multifocal contact lens discontinuation. Conclusions: A task oriented visual satisfaction evaluation may prove helpful in lens design selection, as well as in predicting wearing success.

Central thickness of hydrogel contact lenses as a predictor of success when fitting patients with tear deficiency.

A randomized, double masked, study was designed in order to investigate the relationship between the central thickness of hydrogel contact lenses and the overall comfort of patients with tear deficiency. To allow for statistical analysis, a thin lens was fitted in one eye and a thicker lens of the same characteristics in the contralateral eye. Subjects were asked to wear the lenses for 30 days on a normal daily wear basis and to graduate several factors such as comfort, dryness sensation, redness, photophobia, tearing, quality of vision and others. The results indicate that thicker lenses were preferred in terms of comfort, dryness sensation, photophobia and handling whereas thinner lenses were considered to give a better quality of vision. As a whole, thicker lenses were better tolerated by the patient. Central thickness was found to be of significant relevance when choosing a contact lens, especially when the tear film is deficient.

The variability of corneal and anterior segment parameters in keratoconus

PURPOSE To analyse, describe and test diverse corneal and anterior segment parameters in normal and keratoconic eyes to better understand the geometry of the keratoconic cornea. METHOD 44 eyes from 44 keratoconic patients and 44 eyes from 44 healthy patients were included in the study. The Pentacam System was used for the analysis of the anterior segment parameters. New ad-hoc parameters were defined by measuring the distances on the Scheimpflug image at the horizontal diameter, with chamber depth now comprising of two distinctive distances: corneal sagittal depth and the distance from the endpoint of this segment to the anterior surface of the lens (DL). RESULTS Statistically significant differences (p<0.05) between normal and keratoconic eyes were found in all of the analysed corneal parameters. Anterior chamber depth presented statistical differences between normal and keratoconic eyes (3.06±0.43mm versus 3.34±0.45mm, respectively; p=0.004). This difference was found to originate in an increase of the DL distance (0.40±0.33mm in normal eyes against 0.61±0.45mm in keratoconic eyes; p=0.014), rather than in the changes in corneal sagittal depth. CONCLUSION These findings indicate that keratoconus results in central and peripheral corneal manifestations, as well as changes in the shape of the scleral limbus. The DL parameter was useful in describing the forward elongation and advance of the scleral tissue in keratoconic eyes. This finding may help in the monitoring of disease progression and contact lens design and fitting.

Sources of variability of the van Herick technique for anterior angle estimation

The purpose of the present study was to investigate two potential sources of variability of the traditional van Herick technique for temporal anterior chamber angle estimation, namely the need to compare the depth of the peripheral anterior chamber (PACD) with the thickness of the peripheral cornea (PCT), and the possible loss of information resulting from restricting the assessment of the anterior chamber angle (ACA) to the temporal limbus.

Attitudes towards contact lenses: A comparative study of teenagers and their parents

PURPOSE This two-phase survey aimed to identify the beliefs and attitudes that create a barrier towards contact lens (CL) fitting among adolescents (aged 12-18 years) and their parents attending eye care practitioner clinics in Italy (phase 1) and Iberia (Spain and Portugal; phase 2). In phase 2, the sample was further focused, by limiting it to those adolescents who did not already wear CL. METHODS The extent to which CL satisfy aesthetic, visual, and practical needs and their effectiveness, safety, and comfort in the general population and in adolescents was rated by respondents on a 5-point Likert scale. RESULTS In phase 1, approximately one-third of adolescents (n=146) and parents (n=114) were CL wearers. Most adolescents (77.5% of 223) and parents (66.2% of 230) expressed a high interest in CL use in phase 2 despite none of the adolescents currently wearing CL. Parents, but not adolescents, perceived that CL were significantly less safe in adolescents than in the general population (p<0.05) in phases 1 and 2. Across both phases, adolescents and parents agreed that CL met an aesthetic need in adolescents (p<0.05 versus general population). Among 50% of parents (mainly mothers), significant concerns regarding CL were difficulties following instructions and taking care of the CL and potential eye damage, which, in mothers, led them to show less agreement towards CL use by the adolescent (p<0.001). CONCLUSIONS These findings highlight an essential need for improved education on CL use in the population.

Comparative Analysis of Peripheral Corneal Geometry in Health and Keratoconus

Objectives: To describe and compare corneal peripheral angles in normal and keratoconic eyes, to gain a better understanding of the topography of the periphery of the cornea in keratoconus and assist practitioners in the selection and fitting of large diameter contact lenses. Methods: Eighty-eight eyes were included in the study, divided into three groups: healthy (A0, 28 eyes), keratoconus at stage I according to the Amsler-Krumeich classification (AI, 33 eyes) and keratoconus at stages II to IV (AII, 27 eyes). The Pentacam Scheimpflug system was used to manually measure the corneal peripheral angles corresponding to a chord length range between 8.6 and 12.6 mm at 8 different peripheral locations. Results: The peripheral angle was influenced by ocular condition and by the peripheral location, with no interaction effect between both factors. Statistically significant differences were found in mean corneal peripheral angles between groups A0 (30.84°±2.33°) and AI (31.63°±2.02°) (P=0.001) and between A0 and AII (31.37°±2.11°) (P=0.030). The differences between AI and AII were not significant. In all eyes, the largest and smallest peripheral angles were found at the temporal inferior and temporal superior locations, respectively, with a mean difference between largest and smallest of 3.37°±1.42° in healthy eyes and 2.96°±1.54° in keratoconus (AI+AII). Conclusion: Clinically insignificant differences were found in peripheral angles between keratoconus and healthy eyes, giving support to the use of large diameter, intralimbal contact lenses with peripheral designs, and resting on the same corneal region, as those fitted on normal corneas.

Blinking supervision in a working environment

Abstract. The health of the ocular surface requires blinks of the eye to be frequent in order to provide moisture and to renew the tear film. However, blinking frequency has been shown to decrease in certain conditions such as when subjects are conducting tasks with high cognitive and visual demands. These conditions are becoming more common as people work or spend their leisure time in front of video display terminals. Supervision of blinking frequency in such environments is possible, thanks to the availability of computer-integrated cameras. Therefore, the aim of the present study is to develop an algorithm for the detection of eye blinks and to test it, in a number of videos captured, while subjects are conducting a variety of tasks in front of the computer. The sensitivity of the algorithm for blink detection was found to be of 87.54% (range 30% to 100%), with a mean false-positive rate of 0.19% (range 0% to 1.7%), depending on the illumination conditions during which the image was captured and other computer–user spatial configurations. The current automatic process is based on a partly modified pre-existing eye detection and image processing algorithms and consists of four stages that are aimed at eye detection, eye tracking, iris detection and segmentation, and iris height/width ratio assessment.