Dorota H. Szczesna-Iskander

Future directions in non-invasive measurements of tear film surface kinetics.

Purpose. To review the methods for dynamic, non-invasive, and objective assessment of tear film surface quality and to outline their current state-of-the-art and their future potential. Methods. Among the methods available, high-speed videokeratoscopy, lateral shearing interferometry, and dynamic wavefront sensing are being considered. Results. The principles of operations, their advantages and disadvantages, and limitations of each method are being outlined. The possible future directions of each method are also discussed. Conclusions. To gain a better understanding of tear film, its structure and function, it is essential to combine macroimaging technologies with those focusing on tear film microstructure. In this way, one can envisage a clinical device that could help, in future, early diagnosis of dry eye syndrome and development of better materials for contact lenses and eye lubricants.

Noninvasive In Vivo Assessment of Soft Contact Lens Type on Tear Film Surface Quality

PURPOSE To evaluate the effect of soft contact lens type on the in vivo tear film surface quality (TFSQ) on daily disposable lenses and to establish whether two recently developed techniques for noninvasive measurement of TFSQ can distinguish between different contact lens types. METHODS Thirteen subjects wearing four different types of daily soft contact lenses participated in the study. Dynamic area high-speed videokeratoscopy (HSV) and lateral shearing interferometry (LSI) were used to quantitatively assess TFSQ in natural blinking conditions in the morning soon after lens insertion and in the afternoon following 8 hours of lens wear. RESULTS All considered contact lenses caused a significant reduction in TFSQ compared with bare eye measures. Significant differences (P < 0.05) in the average TFSQ were also observed between all contact lens materials in LSI measurements and in the majority of dynamic area HSV measurements. The potential relationship between the contact lens parameters and the observed decline in the prelens TFSQ was explored. CONCLUSIONS Noninvasive techniques of tear film surface assessment have the potential to discriminate contact lens type/material on eye. LSI was found to more effectively perform this discrimination than the dynamic area HSV technique.

Automatic dynamic tear meniscus measurement in optical coherence tomography

An image processing algorithm is developed for quantitative assessment of tear meniscus dynamics from continuous optical coherence tomography (OCT) measurements. Clinical utility of dynamic OCT tear meniscus measurement is assessed in studies of tear meniscus parameters. The results indicate that any apparent changes in the early post-blink phase meniscus parameters are essentially related to the longitudinal movements of the eye and not to the formation of tear meniscus corresponding to tear film build-up. Dynamic acquisition of tear film meniscus is essential for providing reliable estimates of its parameters such as height, depth, and area.

Measurement variability of the TearLab Osmolarity System.

PURPOSE To independently assess the measurement variability of TearLab System in a clinical setting of one visit and to estimate the minimum number of measurements required for reliable readings of tear osmolarity. METHODS Ten consecutive osmolarity measurements were taken from both eyes by the same examiner at one visit for fourteen subjects. The ocular surface disease index symptoms questionnaire and tear film break up time were also performed. Group average cumulative mean and cumulative coefficient of variation were calculated to assess the TearLab measurement variation. Repeated application of Thompsons tau method was performed to identify the outliers in tear osmolarity readings for each eye. Results from both eyes were analysed separately. RESULTS Up to two randomly occurring outlying values in 10 consecutive measurements were found in 19 out of 28 measured eyes. No statistically significant differences between the left and right eye were found for the group mean and group standard deviation (paired t-test, p=0.099 and p=0.068, respectively), however the cumulative coefficient of variation indicated higher measurement group variability on one eye. Estimated cumulative coefficient of variation indicated the minimum of three consecutive acquisitions required for the measurement to be reliable. CONCLUSIONS TearLab Osmolarity System required at least three consecutive measurements to be taken in order to provide clinically reliable tear osmolarity readings. Also, taking the maximum osmolarity value for detecting dry eye disease should be viewed with caution since outlying readings of tear osmolarity frequently occur.

Tear film dynamics on soft contact lenses.

Purpose To analyze and model the dynamics of tear film surface quality (TFSQ) in a group of subjects with healthy eyes, before and during contact lens (CL) wear, and in a group of subjects with dry eyes (DEs). Methods Four sets of TFSQ measurements with lateral shearing interferometry were retrospectively analyzed on two groups of subjects. The first group included 13 CL wearers for which TFSQ measurements corresponding to baseline, Best CL, and Worst CL were selected. The second group included 13 DE subjects. The acquired TFSQ time series were fit with a power-exponential model. Tear film surface quality stability time, best TFSQ, and integrated poststability time characterizing the tear film deterioration process were derived. Results The proposed power-exponential model was better suited (higher correlation values) for the TFSQ dynamics on CL rather than for those of baseline and DE measurements. The average baseline TFSQ Stability Time was significantly longer (p < 0.001) than those in the DE group and with both the best and worse CL. The average Best TFSQ achieved at baseline was statistically significantly better (p = 0.03) than that for the DE group. The average best TFSQ was significantly better (p < 0.01) for the Best CL than for that of the Worst CL. Deterioration of TFSQ on both best and Worst CL was substantially faster than that achieved for the DE group. Conclusions The observed distinct change in the sign of the TFSQ velocity on contact lenses suggests a two-phase dynamics in which the postblink stability phase is followed by a phase of dewetting. Lens material properties influence the first phase but play little role after the dewetting process occurs.

Objective measures of pre-lens tear film dynamics versus visual responses

Purpose To ascertain whether there is a correlation between objective measures of pre-lens tear film surface quality (TFSQ) dynamics and visual quality responses. Methods Thirty one subjects wore a pair of silicone hydrogel lenses for 1 hour before measurements. Acquisition of TFSQ dynamics was conducted for each subject in suppressed blinking conditions. A Placido disk videokeratoscope was fitted with an internal target and a video streaming output. Subjects were asked to focus on the target and indicate the just noticeable decrease in visual quality. The recorded videos and the subjective responses were saved for further analysis, for which a new videokeratoscopy image processing technique, based on calculating a texture feature (homogeneity), was developed. The estimated times of lens dewetting were then associated with the subjective responses. Results The dewetting point of the lens was identified in 82% of recordings. The group median time of subjective response was 3.5 s post-dewetting point, which corresponded to about 4.3% decrease in TFSQ. In the remaining measurements, either no substantial change in TFSQ or changes related to post-blink slow movement of the lipid layer were observed. The former was not associated with any noticeable change in subjective visual quality whereas the latter usually created visually identifiable temporal disturbance resulting in a subjective response. A small but statistically significant correlation (r2 = 0.32, p < 0.001) was found between objectively estimated point of dewetting and the subjective response, corresponding to just noticeable change in visual quality. Conclusions The new technique proved to be sufficiently sensitive to identify the distinct two-phase process of pre-lens TFSQ dynamics. Changes in objectively determined pre-lens TFSQ can also be identified subjectively, but there exists, in general, a certain lag between the two responses. The estimated times of lens dewetting could be utilized for in vivo assessment of contact lens wetting parameters.

Non-invasive pre-lens tear film assessment with high-speed videokeratoscopy☆

PURPOSE To evaluate the effect of two types of daily contact lenses (delefilcon A and omafilcon A) on the tear film and establish whether it is dependent on pre-corneal tear film characteristics using a new method to analyse high-speed videokeratoscopy recordings, as well as to determine the sensitivity of the method in differentiating between contact lens materials on eye. METHODS High-speed videokeratoscopy recordings were analysed using a custom made automated algorithm based on a fractal dimension approach that provides a set of parameters directly related to tear film stability. Fifty-four subjects participated in the study. Baseline measurements, in suppressed and natural blinking conditions, were taken before subjects were fitted with two different daily contact lenses and after four hours of contact lens wear. RESULTS The method for analysing the stability of the tear film provides alternative parameters to the non-invasive break up time to assess the quality of the pre-corneal and pre-lens tear film. Both contact lenses significantly decreased the quality of the tear film in suppressed and natural blinking conditions (p<0.001). The utilised method was able to distinguish between contact lens materials on eye in suppressed blinking conditions. The pre-corneal tear film characteristics were not correlated with the decrease in pre-lens tear film quality. CONCLUSION High-speed videokeratoscopy equipped with an automated method to analyse the dynamics of the tear film is able to distinguish between contact lens materials in vivo. Incorporating the assessment of pre-lens tear film to the clinical practice could aid improving contact lens fitting and understand contact lens comfort.

The utility of measuring tear film break-up time for prescribing contact lenses

PURPOSE To evaluate the clinical value of non-invasive keratograph tear film breakup time (NIKBUT) in the assessment of pre-corneal and pre-lens tear film quality for prescribing contact lenses (CLs). METHODS Forty-six subjects aged 25.5±4.3 (mean±standard deviation) years were recruited. Visual acuity (VA), anterior eye health checks and NIKBUT were evaluated. On the following day, subjects were fitted with a daily Silicon Hydrogel (SiHy) CL in one eye and a Hydrogel (Hy) CL in the other. After four hours one material for both eyes was chosen based on a qualitative analysis which included VA, CL fitting and comfort. Information about the first and the mean NIKBUT was then contrasted against the prescription decision. RESULTS Thirty-four subjects were fitted with SiHy and twelve with Hy CL. No statistically significant differences were found for both NIKBUT parameters between left and right eye at baseline (p=0.38 and p=0.50, respectively) and post four hours of CL wear (p=0.61 and p=0.06). The chosen lens did not always correspond to longer NIKBUT. In 39.1% and 34.8% of cases (i.e., 18 and 16 out of 46), there was a match between prescription decision and the first and the mean NIKBUT results, respectively. CONCLUSIONS Although there is no evidence whether tear film surface quality measurement has a superior diagnostic values compared to other traditional clinical measures used in practice, NIKBUT measurements have provided additional information that could be of interest during CL fit.