Relationship between Corneal Sensation, Blinking, and Tear Film Quality.

PURPOSE: To examine the possible role of corneal sensitivity and tear film quality in triggering a blink by investigating the relationship between blink rate, central corneal sensitivity threshold (CST), ocular surface temperature (OST), tear meniscus height (TMH), tear film quality (noninvasive tear break-up time [NIBUT]), and tear film lipid pattern under normal conditions. METHODS: Forty-two volunteers (average age, 27.76 ± 5.36 years; 11 males) with good ocular health (Ocular Surface Disease Index, <15.0) were recruited for this cross-sectional cohort study. Blink rate, CST (noncontact corneal air gas aesthesiometry, NCCA), minimum and maximum OST in the central and inferior cornea between blinks (thermal infrared camera), TMH, NIBUT, and lipid pattern of the tear film (Keeler Tearscope Plus) were recorded on the right eye only. RESULTS: Median blink rate was 11 blinks/min (interquartile range [IR], 6.95 to 17.05), CST was 0.35 mbars (IR, 0.30 to 0.40), minimum OST in the central cornea was 35.15°C (IR, 34.58 to 35.50), and NIBUT was 34.55 s (IR, 12.45 to 53.80). Moderate but statistically significant correlations were observed between CST and NIBUT (r = 0.535, p < 0.001), CST and blink rate (r = -0.398, p < 0.001), lipid pattern and OST (r = 0.556, p < 0.001), and between CST and OST (r = 0.371, p = 0.008). The correlations between blink rate and NIBUT (r = -0.696, p < 0.001) and between OST and NIBUT (r = 0.639, p < 0.001; Spearman test) achieved higher significance; this was highlighted by the linear regression model where NIBUT and minimum central and inferior OST were identified as significant predictor variables. CONCLUSIONS: There is strong evidence for significant interactions between corneal sensitivity, NIBUT, OST, and blink frequency, emphasizing that ocular surface conditions represent a possible important trigger for the initiation of a blink. However, the mechanisms involved in the initiation of a blink are complex, with local ocular sensory input as only one trigger, along with other external influences and internal factors under cortical control.

Dynamic Contour Tonometry (DCT) over a thin daily disposable hydrogel contact lens.

UNLABELLED: Dynamic Contour Tonometry (DCT) has been shown to measure the intraocular pressure (IOP) independent of corneal physical properties such as thickness, curvature and rigidity. The aim of this study was to find out if DCT remains accurate when it is applied on regularly shaped corneas while a thin, daily hydrogel contact lens (CL) is worn. METHODS: This was a prospective, randomised study and included 46 patients (46 right eyes): 26 females and 20 males. The age varied from 22 to 66 years (mean: 43.0+/-12.70 years). IOP and ocular pulse amplitude (OPA) measurements were taken with and without a daily disposable hydrogel CL (-0.50 D), Filcon IV) in situ (using the DCT), with a randomised order of measurements. RESULTS: The average value for the IOP measurements without CL was 16.51+/-3.20 mmHg, and with CL in situ it was 16.10+/-3.10 mmHg. The mean difference was 0.41 mmHg and not found to be statistically significant (p=0.074). The average value for the OPA measurement without CL was 2.20+/-0.79 mmHg. With CL in situ it was 2.08+/-0.81 mmHg. This gave a mean difference of 0.11 mmHg and was statistically significant (p=0.025). The Bland-Altman plot showed a maximum difference in IOP of +2.44 and -2.00 mmHg (CI 0.95). Regarding OPA, the maximum difference was +0.81 and -0.60 mmHg (CI 0.95). CONCLUSION: The presence of a thin hydrogel CL did not affect the accuracy of IOP measurements using the DCT. The ocular pulse amplitude was measured on average 5.45% lower with a CL in situ.

Contact lens profile: a tale of two countries.

INTRODUCTION: This study investigated the modality, type and duration of contact lens wear as well as compliance and hygiene related issues (hand and case hygiene, use of tap water, dozing and overnight wear) in the UK and Germany. Questionnaires were collected anonymously from 417 UK and 767 German patients attending optometric practices for contact lens appointments. It is the seventh of a series of contact lens wearer profiles conducted since 2000. RESULTS: The proportion of rigid gas permeable lenses worn was significantly higher at 55.4% in Germany, compared to 16.1% in the UK. Overall, a significantly larger proportion of German participants used tap water to rinse their lenses and cases (P<0.001). Also, German respondents changed their lens cases less frequently (p<0.001). Fewer UK than German respondents stated they washed their hands before lens insertion (p=0.009), removal (p=0.01), before eating (p<0.001). German participants were less likely to wash their hands before preparing food (p=0.042) and after using the toilet (p=0.002). The two sample groups differed significantly regarding the care regimens they used for their CLs (p<0.001). CONCLUSION: The differences between Germany and the UK highlighted in this study were caused by differences in legal regulations, plumbing and practitioners' guidance. Although many of the questions relating to hygiene differed statistically between the two participating sample groups, the absolute differences in figures were not considered to be large.