Relationships between central tear film thickness and tear menisci of the upper and lower eyelids

PURPOSE. To investigate the relationship between central tear film thickness (TFT) and tear menisci of the upper and lower eyelids using real-time optical coherence tomography (OCT). METHODS. Both eyes of healthy subjects were imaged with a real-time OCT to obtain height, curvature, and area of upper and lower tear menisci simultaneously. Central TFT was indirectly measured by calculating the difference between baseline measurements of the central corneal thickness plus tear film and the true corneal thickness obtained after instillation of artificial tears. Results from two normal blinks were obtained from one eye at each visit and repeated the next day. RESULTS. The average central TFT was 3.4 Ϯ 2.6 m. The upper tear meniscus curvature, height, and area were 239 Ϯ 112 m, 268 Ϯ 68 m, and 22,732 Ϯ 11,974 m 2 respectively. There were no significant differences in curvatures, heights, or areas between upper and lower tear menisci, nor were there any differences in measured variables between the two blinks at each visit or between the two repeated visits in the right and left eye groups (P Ͼ 0.05). The upper and lower tear menisci in each eye group on each day correlated strongly with curvature, height, and area (all P Յ 0.03). However, no tear meniscus variable was a significant predictor of TFT (all P Ͼ 0.44). CONCLUSIONS. OCT is a promising tool in the measurements of TFT and dimensional variables of tear menisci. Upper and lower tear menisci have nearly identical dimensions. (Invest Ophthalmol Vis Sci. 2006;47:4349 -4355

Effect of Blinking on Tear Volume After Instillation of Midviscosity Artificial Tears

To determine by optical coherence tomography (OCT) the effect of blinking on ocular surface tear volume after instillation of artificial tears. Experimental study. Normal human eyes (n = 21) were imaged to obtain dimensions of the tear film and menisci during blinking. The imaging was carried out immediately and five minutes after the instillation of 35 μl midviscosity artificial tears (1.0% carboxymethylcellulose; Refresh Liquigel; Allergan, Irvine, California, USA). The exposed ocular surface area and the lid lengths were used to calculate the volumes. Immediately after the instillation, total tear volume was increased ( P < .001) compared with five minutes after the instillation, with the major increases in the lower tear meniscus volume and tear film volume. After the instillation, blinking caused tear loss in total tear volume because of the decrease of the lower tear meniscus volume ( P < .05). In contrast, blinking increased the tear film volume ( P < .05). At the end of the eye-opening period, tear film volume decreased and lower tear meniscus volume increased significantly ( P < .05), with no significant changes in total tear volume ( P > .05). During the blink cycle immediately after the instillation, net loss was evident in tear film volume, lower tear meniscus volume, and total tear volume ( P < .05). Blinking plays a crucial role in distribution and removal of instilled tears. When the tear system is overloaded, the increase in blink output helps restore balance

Correlations Among Upper and Lower Tear Menisci, Noninvasive Tear Break-up Time, and the Schirmer Test

To determine the relationships among tear meniscus parameters, noninvasive tear break-up time (NITBUT), and the Schirmer test. Experimental study. Thirty-six subjects were tested on one randomly selected eye. Real-time corneal optical coherence tomography (OCT) was used to image the upper and lower tear menisci during normal and delayed blinking followed by measurement of NITBUT and the Schirmer test. Digital images of the eye were taken for measuring the lid lengths to estimate tear volume in the menisci. Compared with normal blinking, significant increases of tear menisci occurred during delayed blinking (post hoc, P < .01). NITBUT was weakly but significantly correlated with the height ( r = 0.36; P = .03) and area ( r = 0.37; P = .03) of the lower tear meniscus during normal blinks. NITBUT was also correlated with the lower tear meniscus volume ( r = 0.45; P < .05) and total tear meniscus volume ( r = 0.43; P < .05) during normal blinking. The Schirmer test was not significantly related to any parameters of the tear menisci, volumes, or NITBUT; however, it was negatively correlated with the age of the subjects ( r = −0.47; P = .004). The age was negatively correlated with the upper tear meniscus ( r ranged from 0.36 to 0.37 for the radius, height, and area, P < .05) measured during delayed blinking. NITBUT appears correlated with the lower tear meniscus during normal blinking, and the Schirmer test appears not correlated with the noninvasively measured tear meniscus

Repeated measurements of dynamic tear distribution on the ocular surface after instillation of artificial tears

PURPOSE: To determine the repeatability of real-time optical coherence tomography (OCT) measurements of tear film thickness (TFT) and variables of tear film menisci. METHODS: Forty eyes were imaged with a custom-built, real-time OCT to obtain heights, curvatures, and cross-sectional areas of upper and lower tear menisci simultaneously. The central TFT was indirectly determined as the difference between the combined thickness of the central cornea and tear film and the true corneal thickness obtained after instillation of artificial tears. Dynamic tear distribution was determined by OCT imaging immediately and 5, 20, 40, and 60 minutes after tear instillation. Measurements taken after two blinks of one eye at each visit were repeated on the next day. Measurements from the companion eye were made on separate days. RESULTS: There were no significant differences between the two measurements of each variable made on consecutive days. At baseline, upper tear meniscus variables were strongly correlated with the comparable lower meniscus variables. However, there were no significant correlations between TFT and any tear meniscus variable. Immediately after instillation of artificial tears, all measured variables increased significantly. TFT, upper and lower menisci heights, and upper meniscus area remained elevated for at least 5 minutes. In addition there were significant correlations between TFT and the lower tear meniscus height and area. CONCLUSIONS: The custom-built OCT showed good repeatability and holds promise in measuring the dynamic distribution of artificial tears on the ocular surface

Effect of blinking on tear dynamics

PURPOSE. Optical coherence tomography (OCT) was used to study the impact of blinking on tear dynamics. METHODS. One eye of 21 subjects was imaged at the same time of day on two consecutive days. Dimensional information of the tear film and of the upper and lower tear menisci during normal and delayed blinking were obtained from OCT images using custom software. Digital camera images were used to measure eyelid length and ocular surface area for tear volume estimation. RESULTS. No significant changes in any measured variable occurred between the two repeat visits. During normal and delayed blinking sessions, the tear film thickness increased significantly after each blink (P Ͻ 0.05) and then decreased (P Ͻ 0.05) during the open-eye period. For normal blinks, the tear meniscus did not change significantly during blinking or during the open-eye period. Except for upper tear meniscus curvature, all other parameters of tear menisci during delayed blinks were higher than those measured during normal blinks (P Ͻ 0.05). For delayed blinks, the lower tear meniscus height decreased after the blink (P Ͻ 0.05). Also for delayed blinks, the height and area of both upper and lower tear menisci significantly increased during the open-eye period. The total estimated tear volume on the ocular surface was greater during the delayed blinks (P Ͻ 0.01), and most of the volume was located in the lower tear meniscus (P Ͻ 0.01). CONCLUSIONS. OCT is a promising tool for studying the impact of blinking on tear dynamics. Tear distribution is dynamically balanced and consistent during normal blinking, but it becomes altered during delayed blinking. (Invest Ophthalmol Vis Sci. 2007;48:3032-3037) DOI:10.1167/iovs.06-1507 T he tear system is highly dynamic, maintaining balance between tear secretion and tear loss so that the ocular surface is protected while the eye is open. Each blink initiates a cycle of tear secretion, spreading, evaporation, and drainage of tears. 1-3 Not much is known about the effect of blinking on the dynamically balanced tear system, mainly due to the extreme difficulty in real-time quantification of each tear compartment on the ocular surface. Many studies provide either snapshot information 4 -6 or averaged performance 5 about the tear system. Real-time videography SUBJECTS AND METHODS The Research Review Boards of the University of Rochester and University of Miami approved the study. Twenty-one subjects (10 women and 11 men, mean age: 32.1 Ϯ 8.7 years) in good health and with no history of contact lens wear or any current ocular or systemic diseases were recruited in Rochester for a prospective study. Informed consent was obtained from each subject, and all were treated in accordance with the tenets of the Declaration of Helsinki. The temperature (15-25°C) and humidity (30%-50%) in the small consulting room where the study was conducted were controlled by central air conditioning and two humidifiers. OCT imaging was performed on one randomly selected eye of each subject at the same time of day on two consecutive days. A real-time corneal OCT, developed as described previously, 9 was used to perform vertical 12-mm scans across the central cornea (apex) including the upper and lower tear menisci simultaneously. During imaging, the subjects were exposed only to ambient room light and were asked to look at an external target. OCT images were recorded continuously when the subjects blinked normally for three to five blinks. After the normal blinks, the subjects were asked to delay each blink for as long as possible for another set of three to five blinks. After that, the study eye was given a drop of artificial tears (Refresh Liquigel; Allergan, Irvine, CA) followed by OCT scanning to obtain true corneal thickness for the calculation of the tear film thickness, as described in detail previously. Image processing and data analysis were performed at the University of Miami by two of the authors (JW, JRP). Eight OCT images corresponding to a 1-second interval immediately before and after each blink were analyzed for measuring the total corneal thickness. One of these eight images showing upper and lower tear menisc