José B. Almeida

Surface AFM microscopy of unworn and worn samples of silicone hydrogel contact lenses

PURPOSEnTo evaluate the qualitative and quantitative topographic changes in the surface of worn contact lenses (CLs) of different materials using atomic force microscopy (AFM).nnnMETHODSnThe topography of five different CL materials was evaluated with AFM over a surface of 25 microm(2) according to previously published experimental setup. Average roughness (R(a)) and root mean square (Rms) values were obtained for unworn and worn samples.nnnRESULTSnThe R(a) value increased for balafilcon A (11.62-13.68 nm for unworn and worn samples, respectively), lotrafilcon A (3.67-15.01 nm for unworn and worn samples, respectively), lotrafilcon B (4.08-8.42 nm for unworn and worn samples, respectively), galyfilcon A (2.81-14.6 nm for unworn and worn samples, respectively), and comfilcon A (2.87-4.63 nm for unworn and worn samples, respectively). Differences were statistically significant for all lenses except Rms and R(a) for comfilcon A, and R(a) parameter for balafilcon A (p > 0.05). The least relative increase was observed for some balafilcon A samples and for some of these samples the roughness decreased after the lenses had been worn.nnnCONCLUSIONnThe changes in surface roughness between unworn and worn lenses are different for different silicone-hydrogel materials. Overall all CLs increased the degree of surface roughness after being worn, even for very short periods of time. However, for samples of balafilcon A, roughness increases at a lower extent or even can decrease as compared to unworn samples of the same material due to filling of the macropores.

Binocular Vision Changes in University Students: A 3-Year Longitudinal Study

Purpose. The aim of this study was to investigate the changes in accommodation and binocular vision parameters during a period of 3 years and to evaluate their potential influence on the refractive changes observed over the same period of time in a population of university students in Portugal. Methods. A 3-year longitudinal study was conducted comprising 118 young adults (34 males and 84 females; mean age: 20.6 ± 2.3 years). Examinations consisted of subjective refraction, dissociated phoria and vergences at distance and near vision, accommodative convergence/accommodative ratio, lag of accommodation, and the negative and positive relative accommodation. Results. There were statistically significant differences between the first (2002) and the second examination (2005) relative to distance and near phoria, and break and recovery points for the base-in and base-out at distance vision. Statistically significant differences were also obtained for the blur and break points for the base-out, and for break and recovery points for the base-in at near vision. As regards accommodation parameters, we verified a statistically significant difference for all parameters measured. Comparing the baseline values of patients who suffered a myopic shift ≥0.50 D with those from patients who did not experience such a shift, we observed a statistically significant difference for the break value of the base-in at distance vision (equal to 12.2 ± 3.6 for the group without refractive error alteration and 15.8 ± 6.8 for the other group) and for the break value of the base-in at near vision (equal to 22.4 ± 5.2 and 24.8 ± 5.5 for the group without refractive error alteration and for the other group, respectively). Conclusions. We observed significant changes in near heterophoria, fusional vergences, and positive relative accommodation. The break values of the base-in fusional vergence account as significant predictors of myopic shift in young adults.

Contact lens fitting profile in Portugal in 2005: strategies for first fits and refits.

Purpose. To evaluate the standards of contact lens practice in Portugal, with particular attention paid to the characteristics of first fits and refits regarding aspects such as symptoms of dryness, overnight wear, silicone hydrogel and multifocal prescriptions, and care systems. Methods. A questionnaire was distributed to 300 contact lens practitioners in Portugal, and they were asked to complete them with the following first 10 fittings (only right eye of each patient). Fifty-six questionnaires were returned to total 529 fittings. Results. The mean age of contact lens wearers was 28.1 ± 10.1 years, and 94.4% of the wearers were fitted with soft contact lenses (67.9% hydrogel lenses, 21.2% silicone hydrogel lenses, and 5.2% biomimetic soft contact lenses). Sixty percent of patients wore their contact lenses for 9 to 12 hours per day. The lenses were replaced on a monthly basis in 71% of cases, and 82.8% of wearers used a multipurpose solution for lens cleaning and disinfection. Significant differences were found between first fits and refits regarding the prevalence of dryness symptoms (higher incidence of frequent symptoms in the evening in the refitting group, P < 0.01, &khgr;2), replacement schedule (lower incidence of monthly disposable lenses in refits compared to first fits, P < 0.05, &khgr;2), and care regimen (lower incidence of multipurpose solutions and higher incidence of hydrogen peroxide in refits, P < 0.01, &khgr;2). Conclusions. Statistical analysis of the current trends in the Portuguese contact lens fitting profile showed that contact lens practitioners in Portugal are receptive to use innovations in contact lens products, such as silicone hydrogel and biomimetic materials, and daily-disposable contact lenses to refit patients who have not succeeded with previous lenses. Multifocal lenses also experienced a significant increase in their prevalence among refits and new fits. Rigid gas-permeable materials maintained and even experienced a slight increase in refits. Conversely, there is still a low incidence of extended-wear prescriptions, most of them being made with low-Dk soft contact lenses.