Effect of blinking on tear volume after instillation of midviscosity artificial tears.

PURPOSE: To determine by optical coherence tomography (OCT) the effect of blinking on ocular surface tear volume after instillation of artificial tears. DESIGN: Experimental study. METHODS: 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 microl 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. RESULTS: 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). CONCLUSIONS: 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.

Dynamic distribution of artificial tears on the ocular surface.

OBJECTIVE: To study the effects of artificial tear viscosity on tear film thickness, upper and lower tear menisci, and tear volume using optical coherence tomography. METHODS: The central tear film and tear menisci before and immediately after the instillation of different artificial tears were imaged in 40 eyes of 20 healthy individuals. Carboxymethylcellulose sodium, 1.0% (viscosity, 70 cP), propylene glycol, 0.3%, and polyethylene glycol, 0.4% (10 cP), carboxymethylcellulose, 0.5% (3 cP), and isotonic sodium chloride solution (1 cP) were tested on 2 consecutive days. All measurements, including tear film thickness, the height, radius, and area of the tear meniscus, and the estimated tear volume, were obtained at 0, 5, 20, 40, and 60 minutes after instillation. RESULTS: At instillation, all artificial tears and isotonic sodium chloride solution caused an increase in all tear variables (P < .001). Tear film thickness remained significantly elevated for all drops at 5 minutes (P < .001) and returned to baseline at 20 minutes. Other variables returned to baseline at 5 minutes. Comparing the different drops, tear film thickness and lower meniscus variables at instillation were increased with the more viscous drops (P < .05). CONCLUSION: Optical coherence tomography demonstrated that all tear preparations, including isotonic sodium chloride solution, increased tear film thickness for at least 5 minutes and other variables immediately after instillation.

Correlations among upper and lower tear menisci, noninvasive tear break-up time, and the Schirmer test.

PURPOSE: To determine the relationships among tear meniscus parameters, noninvasive tear break-up time (NITBUT), and the Schirmer test. DESIGN: Experimental study. METHODS: 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. RESULTS: 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. CONCLUSIONS: NITBUT appears correlated with the lower tear meniscus during normal blinking, and the Schirmer test appears not correlated with the noninvasively measured tear meniscus.

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 < 0.05) and then decreased (P < 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 < 0.05). For delayed blinks, the lower tear meniscus height decreased after the blink (P < 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 < 0.01), and most of the volume was located in the lower tear meniscus (P < 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.

Keratoprosthesis: current techniques.

PURPOSE: To compare and contrast the techniques and results of keratoprosthesis (KPro) using the Cardona device (1975-1985) with those related to the use of the Dohlman-Doane type 1 device (2003-2005). METHODS: We conducted a retrospective review of 31 cases of Cardona KPro implanted between 1975 and 1981 and a review of 25 cases of Dohlman-Doane type 1 KPro implanted between 2003 and 2005. Procedures were limited to eyes with a poor prognosis for traditional penetrating keratoplasty. RESULTS: In the Cardona cases, 39% (12/31) of patients achieved a visual acuity of 20/40 or better at some point postoperatively, degrading to 16% (5/31) at the end of the observation period. Fifty percent (15/31) required subsequent surgical revision of the KPro. Sixteen percent of cases (5/31) developed endophthalmitis, and 58% (18/31) developed retroprosthetic membranes. There were 5 dislocations of the prosthesis and an additional 3 frank extrusions (26%). Of the 25 Dohlman-Doane cases, there have been no reoperations, endophthalmitis, dislocations, or extrusions to date (8/15/05). Forty-eight percent (12/25) achieved 20/200 acuity or better, and 12% (3/25) achieved 20/40 or better. Retroprosthetic membranes formed in 3 cases. CONCLUSION: Although KPro remains a technique to be used in poor prognosis keratoplasty, improvements in the design of the device and surgical technique over the past 30 years have reduced the overall morbidity and severity of complications and improved the prognosis for visual rehabilitation.

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 +/- 2.6 microm. The upper tear meniscus curvature, height, and area were 239 +/- 112 microm, 268 +/- 68 microm, and 22,732 +/- 11,974 microm2 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 > 0.05). The upper and lower tear menisci in each eye group on each day correlated strongly with curvature, height, and area (all P < or = 0.03). However, no tear meniscus variable was a significant predictor of TFT (all P > 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.

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.

Keratoprosthesis: the Dohlman-Doane device.

PURPOSE: To determine the usefulness of the Dohlman-Doane type I keratoprosthesis for visual rehabilitation in cases of poor prognosis for traditional penetrating keratoplasty. DESIGN: A retrospective, noncomparative interventional series of 25 patients who had sustained multiple graft failure or who were otherwise deemed poor candidates for conventional keratoplasty. METHODS: Candidates were evaluated for potential acuity, intraocular pressure, inflammation, the quality of the ocular surface, and overall prognosis for penetrating keratoplasty. The keratoprosthesis was assembled and mounted on an 8.5- or 9.0-mm diameter donor corneal button and sutured into an 8.0- or 8.5-mm diameter recipient bed with 12 to 16 9-0 nylon sutures. Patients were examined on the first day and subsequently in 1 week and 1 month and then at 3-month intervals. RESULTS: All devices were retained without dislocation or extrusion. There were no instances of endophthalmitis or surface infection. Fundus details were visible on the first postoperative day. Patients achieved their best acuity in an average of 2 months (range, 1 to 180 days). Improvement in acuity was observed in an average of 13 days (range, 1 to 60 days). Retroprosthetic membranes occurred in three cases, with multiple recurrences in one instance. Visual acuity ranged from no light perception to 20/25. CONCLUSION: We conclude that this prosthesis can be implanted routinely and maintained with minimal complications in poor prognosis keratoplasty, which presents the potential for visual rehabilitation.