Comparison by contact lens cytology and clinical tests of three contact lens types.

PURPOSE: To determine if hydrogel lens materials from different FDA groups have different effects on the human ocular surface. METHODS: Contact lenses from Groups I and II, and Group IV were tested on 10 healthy adapted hydrogel contact lens wearers. For each comparison, the subject wore 2 new contact lenses for approximately 45 min. Lens movement was measured, and comfort evaluated using a subjective scale. After removal of the lenses, fluorescein staining and tear break-up time were measured. Cells were collected by contact lens cytology (CLC), and the size and number of cells harvested from each lens were determined. RESULTS: There were differences between lens groups in lens movement and comfort, but no differences in fluorescein staining or tear break-up time. CLC showed no differences in cell counts or cell size. There was no correlation between the results of CLC and the clinical tests for lens movement, lens comfort, tear break-up time, and fluorescein staining. CONCLUSIONS: With short durations of lens wear, differences in ionicity and water content have no effect upon the size and number of cells collected from a contact lens. This suggests that, in the short-term, the shedding of cells beneath a hydrogel lens is not affected by the choices of lens material.

Fitting characteristics of Dailies daily disposable hydrogel contact lenses.

PURPOSE: We evaluated the fitting characteristics of nelfilcon A contact lenses to determine the optimal time for judging lens performance during trial fitting. METHODS: Twenty subjects wore a pair of DAILIES (daily disposable soft lenses) for 8 hours. A slit lamp camera was used to videotape lens fit every 5 minutes during the first 30 minutes and at 8 hours. Lens movement and centration were measured in 0.1 mm increments by a single observer. RESULTS: Lens movement decreased significantly during the first 30 minutes of wearing time (P < 0.001). Mean lens movement measured 0.31 mm initially, decreased to 0.17 mm at 25 minutes of wear, and then increased to 0.33 mm at 8 hours (P < 0.001). At 5 minutes, 93% of eyes showed lens movement within 0.2 mm of the value at 8 hours. Lens centration did not change during the first 30 minutes of wear and was comparable to centration measured at 8 hours. CONCLUSIONS: During trial fitting, the optimal time for evaluating movement of nelfilcon A contact lenses is during the first 5 minutes of wear. Lens movement measured at 8 hours will likely be greater than lens movement measured 10 to 30 minutes after insertion.

Day to day variations in ocular surface staining of the bulbar conjunctiva.

PURPOSE: The purpose of this study was to characterize the variability of bulbar conjunctival staining over time in response to a single application of fluorescein. METHODS: Sixteen subjects were stained Monday through Friday for a 2-week period. Appointments were scheduled from 9:00 a.m. to 12:00 p.m. to minimize variance due to diurnal variation. Fluorescein stain was applied by touching a separate Ful-Glo strip wetted with nonpreserved saline to the lower palpebral conjunctiva of each eye, with the right eye being stained first. Immediately after application of the fluorescein, conjunctival staining was graded in a randomized order by two examiners, using cobalt blue illumination and a no. 15 Wratten enhancement filter. Conjunctival staining was assessed based upon a 0 to 4 grading scale with 0.5 grade increments. By evaluating the variability in staining over time for each subject, a representation of overall fluctuation for the group was obtained. RESULTS: The average duration for an episode of staining graded higher than the group median (grade 0.5) was found to be 2.0 +/- 2.4 days. Overall, a mean staining grade of 0.5 for the right eye and 0.6 for the left eye was found. Right and left eyes were found to correlate well (r = 0.67, p < 0.01, Spearman's correlation) and the mean difference was not statistically significant [p = 0.73, multi-way, repeated measures analysis of variance (ANOVA)]. The mean difference in grading between the two examiners was 0.1 grades (p = 0.67, multi-way, repeated measures ANOVA), with a correlation coefficient of r = 0.68 (p < 0.01, Spearman's correlation). CONCLUSIONS: Characterization of conjunctival staining over time may be useful in evaluating clinically suspect staining, and in determining its potential duration. The appearance and variability of the conjunctival staining patterns noted in this study indicate a potential relationship to normal physiological processes, such as desquamation. This study also demonstrated a low amount of variability between right and left eyes, supporting the use of contralateral studies in the assessment of conjunctival staining. It also demonstrated a good consistency between separate examiners despite not being standardized.

Corneal staining patterns in normal non-contact lens wearers.

Corneal fluorescein staining was evaluated in 16 subjects over a 2-week period by 2 practitioners. Using a scale of 0 to 4 with 0.5 grade steps, the average duration for an episode of staining above the group median (grade 0.5) was found to be 1.2 +/- 0.4 days. For both eyes, the most prevalent location of staining was the inferior region (50%), followed by the nasal region (20%). Overall, a mean staining grade of 0.5 for the right eye and 0.6 for the left eye was found. Practitioners also demonstrated a difference in grading of 0.1 in the right and left eyes. These data may be most useful in determining the normality of suspect corneal fluorescein staining and its duration until resolution. This study demonstrated a low amount of variability between right and left eyes, and established a good consistency between separate examiners.

Soft toric lens power accuracy and reproducibility.

Lens power accuracy is the most frequently cited requirement for reproducible soft toric lens performance. Power accuracy is even more critical with planned replacement soft toric lenses because of the increased rate at which lenses are replaced. However, no reproducible methodology exists for making such an evaluation. We developed a power measurement method from which measurement error was eliminated. Geometric optical calculation was used to calculate the resulting optical error. The relationship between visual acuity loss and optical errors was used to predict the effect on visual acuity. This method was applied to a sample of 457 Focus Toric soft contact lenses. We found that 83.5 +/- 1.7% of the lenses were accurate enough to deliver one line or less of loss in visual acuity. Our estimate of the clinical problem rate associated with power reproducibility was 3.3 +/- 0.9% of lens pairs. If lenses were replaced on a monthly basis, this would amount to one problem pair every 30 months.