Tear Break-up Research Articles

Instability of tear film and loss of meibomian glands in patients with acne vulgaris.

In this prospective study, we compared ocular clinical variables in patients with acne vulgaris with those of healthy controls. These variables included tear film break-up time, meibomian gland dropout rate, and anterior chamber parameters. Our sample comprised 73 eyes from 73 patients with acne vulgaris and 67 eyes from 67 healthy controls. All participants underwent a non-invasive first tear film break-up time test and the average tear film break-up time was evaluated. Meibography was used to identify any meibomian gland dropout. The parameters of the cornea and anterior chamber were measured using Scheimpflug topography imaging. Finally, the ocular surface disease index questionnaire was administered to score each participant on their subjective experience of ocular complaints. The noninvasive first tear film break-up time values of the acne vulgaris Group and the control Group were 4.7 ± 2.8 and 6.4 ± 3.5 sec, respectively. There was a significant difference between the groups (p=0.016). The number of eyes with tear break-up at any time during the measurement period was also significantly higher in the acne Group (p=0.018). In the acne vulgaris Group, the mean meibomian gland dropout rates were 33.21 ± 15.5% in the upper lids and 45.4 ± 14.5% in the lower lids. In the control group, these rates were 15.7 ± 6.9% and 21 ± 9.7% respectively. Dropout was significantly higher in the acne group for both the upper and lower lids (p=0.000). We found impaired tear stability in patients with acne vulgaris and a high rate of meibomian gland dropout. These glands play a key role in tear stability and their dropout is likely to result in evaporative dry eye. Measurement of the variables in this study allows objective diagnosis of this condition using a non-invasive, dye-free methodology, with minimum contact.

Dynamics and mechanisms for tear breakup (TBU) on the ocular surface

<abstract> The human tear film is rapidly established after each blink, and is essential for clear vision and eye health. This paper reviews mathematical models and theories for the human tear film on the ocular surface, with an emphasis on localized flows where the tear film may fail. The models attempt to identify the important physical processes, and their parameters, governing the tear film in health and disease. </abstract>

Smartphone induced eye strain in young and healthy individuals

Background: Usage of digital devices has become one's basic need. Digital eye strain is repeatedly noticed sequelae in optometry practice.&#x0D; Objectives: This study aims to estimate the different aspects of eye strain.&#x0D; Methodology: Altogether, 55 students with a mean age of 21.25 years, vision (≥6/9) were enrolled. A survey related to common asthenopic (eyestrain) symptoms was carried before and after reading an extract from a novel. Accommodative facility and non-invasive first tear breakup (NTBUT) time were measured before and after the reading. The viewing distance to a smartphone was measured every 20 minute.&#x0D; Results: The total eye strain symptom score was significantly greater post-experiment (score = 7.07±2.84) than pre-experiment (score = 1.54±1.60, p &lt; 0.001). Symptoms of tired eyes, sore eyes, and sleepy eyes increased significantly after 60 min of a smartphone use (p &lt; 0.05). The mean viewing distance while using a smartphone over 60 min was 30.15 ± 3.29 cm. There was a significant correlation between change in total symptom score and change in viewing distance (r = ˗0.301, p = 0.026). The symptom that correlated with a change in viewing distance was ‘sore eyes’ (r = ˗0.382, p = 0.04) and sleepy eyes (r= ˗0.363, p=0.06). There was a significant decrease in monocular and binocular accommodative facilities and NTBUT after 60 min of reading.&#x0D; Conclusion: Closer viewing distance and eyestrain symptoms are obvious after a smartphone reading. Prolonged use of smartphones appears to have important implications for accommodative function, causing ocular symptoms having an impact on quality of life.

Kinetic visual acuity is correlated with functional visual acuity at higher speeds

ObjectiveTo measure the kinetic visual acuity (KVA) which is the ability to identify approaching objects and the functional visual acuity (FVA) which is continuous VA during 1 min under binocular...

Changes in Corneal Detection Thresholds After Repeated Tear Film Instability.

PurposeTo use a human-based model to study the effects of repeated tear film instability on corneal detection thresholds to cold, mechanical, and chemical stimuli.MethodsTwenty-five subjects participated in three study visits. A computer-controlled Belmonte esthesiometer was used to estimate corneal detection thresholds to cold, mechanical, and chemical stimuli before, after, and 30 minutes following 10 consecutive sustained tear exposure (STARE) trials. Subjects turned a pain knob (0–10) to indicate discomfort during STARE trials. The area of tear breakup and thinning in each trial was analyzed. Symptoms were evaluated by the Current Symptom Questionnaire (CSQ).ResultsThere was a significant time effect on CSQ symptoms during both visits (Friedman test, P < 0.001), with immediately after repeated STARE and 30 minutes later significantly differing from before STARE (Wilcoxon, P < 0.017). Tear breakup occurred in every trial, ranging from 25% to 88% of the exposed corneal area and all subjects indicated discomfort during trials. There was a significant time effect on mechanical thresholds between before STARE mechanical thresholds and 30 minutes later (repeated measures analysis of variance [ANOVA] P < 0.001), but not cold (P = 0.057) or chemical (P = 0. 565) thresholds.ConclusionsIn this study, tear breakup during STARE trials was associated with discomfort, which when repeated, resulted in increased symptoms of ocular discomfort and alterations of mechanical sensory thresholds after 30 minutes. These results suggest that tear film instability, which is thought to occur repeatedly during normal blinking among dry eye patients over the day, can produce neurosensory alterations.

Mathematical modelling of glob-driven tear film breakup.

Evaporation is a recognized contributor to tear film thinning and tear breakup (TBU). Recently, a different type of TBU is observed, where TBU happens under or around a thick area of lipid within a second after a blink. The thick lipid corresponds to a glob. Evaporation alone is too slow to offer a complete explanation of this breakup. It has been argued that the major reason of this rapid tear film thinning is divergent flow driven by a lower surface tension of the glob (via the Marangoni effect). We examine the glob-driven TBU hypothesis in a 1D streak model and axisymmetric spot model. In the model, the streak or spot glob has a localized high surfactant concentration, which is assumed to lower the tear/air surface tension and also to have a fixed size. Both streak and spot models show that the Marangoni effect can lead to strong tangential flow away from the glob and may cause TBU. The models predict that smaller globs or thinner films will decrease TBU time (TBUT). TBU is located underneath small globs, but may occur outside larger globs. In addition to tangential flow, evaporation can also contribute to TBU. This study provides insights about mechanism of rapid thinning and TBU which occurs very rapidly after a blink and how the properties of the globs affect the TBUT.

A mouse dry eye model induced by topical administration of the air pollutant particulate matter 10

AimTo introduce a novel dry eye mouse model induced by topical administration of the air pollutant particulate matter 10 (PM10). MethodA total of 60 male BALB/c mice were used in this study and divided into two groups: group A (PBS eye drops, n=30) and group B (PM10 eye drop group, n=30). Each treatment was dosed four times a day, every time 50ul with the concentration of 5mg/ml PM10, for 14 consecutive days in the right eye. The clinical manifestations of dry eye were measured before therapy and 4, 7 and 14days post-treatment respectively, which included the tear volume, tear break-up (BUT) time, corneal fluorescein staining, rose bengal staining, Lissamine Green staining and inflammatory index. Eye samples were collected on D14 and examined by histologic light microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), corneal cytokeration 10 (K10) immunnostaining, and tumor necrosis factor-α (TNF-α), NF-κB-p65 and NF-κB Western Blot analysis. ResultsAt 0d, 7d and 14d, there were no statistical changes in tear volume, BUT after treatment (P>0.05) with PBS in group A. In group B, all items showed statistical differences at each time point (P<0.05). At 14d after therapy, the fluorescein staining score of group B was higher than group A (P<0.05). The score of rose bengal staining and Lissamine Green staining in group B was also higher than that in group A (P<0.05). The number of mean layers of corneal epithelial cells in the group A was significantly lower than that in the group B (P<0.05). TEM and SEM revealed that the number of corneal epithelial microvilli were drastically reduced in group B. The number of corneal chondriosome/desmosomes was also reduced in group B by TEM. PM10 induced apoptosis in the superficial and basal corneal epithelium, and leaded to abnormal differentiation and proliferation of the ocular surface with higher expression levels of K10 and reduced number of goblet cells in the conjunctival fornix in group B. PM10 significantly increased the levels of TNF-α, NF-κB-p65 and NF-κB in the cornea. ConclusionPM10 can damage the tear film function and cause the destruction of the structural organization of ocular surface in mice. Topical administration of PM10 in mice induces ocular surface changes that are similar to those of dry eye in humans, representing a novel model of DES.

A link between tear breakup and symptoms of ocular irritation

PurposeWe used the presence or absence of a soft contact lens (CL) as a barrier to test the hypothesis that tear breakup (TBU) presents a direct noxious stimulus to the ocular surface. MethodsTen subjects kept one eye open as long as possible, termed sustained tear exposure (STARE), for 10 consecutive trials while discomfort was monitored with and without a CL in place. The area of TBU was quantified in each frame. Discomfort was measured during and after each STARE trial and symptoms of ocular irritation were assessed before and after all testing. ResultsTBU increased at the end of trials to an average of 19.89% ± 17.91% and 20.58% ± 15.33% and discomfort to 9.09 ± 1.44 and 1.97 ± 2.19 in trials without and with a CL, respectively. Discomfort was significantly higher during trials without CLs (Friedman test, p < 0.005), but there was no significant difference in the area of TBU between trials (Friedman test, p = 0.296) with and without a CL (Friedman test, p = 0.527). Discomfort after each STARE trial increased significantly across trials (Friedman, p < 0.005). Symptoms of ocular irritation increased significantly from pre- to post-testing (Wilcoxon signed rank test, p < 0.005). ConclusionsTBU during STARE trials was associated with increasing ocular discomfort, which was partially blocked by wearing a CL, supporting the hypothesis that TBU directly stimulates the corneal surface. Repeated STARE trials led to increasing discomfort and dry-eye like symptoms of ocular irritation, suggesting that repeated bouts of TBU can lead to alterations in ocular surface sensory processing.

써클콘택트렌즈가 눈물막 안정성에 미치는 영향

목적: 본 연구에서는 써클콘택트렌즈의 착색이 눈물막 안정성에 미치는 영향을 알아보고자 하였다. 방법: 눈물량이 정상인 20대 54안을 대상으로 콘택트렌즈 착용 전후의 비침입성 눈물막파괴시간 및 눈물막 깨짐이 시작되는 부위를 측정하였으며, 콘택트렌즈 전후면의 표면 거칠기를 주사전자현미경으로 관찰하였다. 콘택트렌즈는 hilafilcon B재질의 투명 및 써클콘택트렌즈, polymacon 재질 및 HEMA NVP 공중합 재질의 써클콘택트렌즈를 대상으로 하였다. 결과: 콘택트렌즈 착용 시 나안에 비해 눈물막파괴시간이 통계적으로 유의하게 감소하였으며 써클콘택트렌즈 간에 눈물막파괴시간이 통계적으로 유의한 차이를 보이는 경우도 있었다. 일반적으로 콘택트렌즈의 상방부 보다는 하방부에서, 코방향 보다는 귀방향에서 좀 더 높은 빈도로 눈물막이 깨지기 시작하였으나 렌즈의 종류에 따라 다소 차이가 있었다. Hilafilcon B 투명렌즈에 비해 동일 재질 써클콘택트렌즈 주변부(착색부분)에서의 눈물막 깨짐이 더 많았다. 결론: 써클콘택트렌즈의 착용으로 인해 눈물막 안정성이 영향을 받음을 알 수 있었으며, 본 연구결과는 써클콘택트렌즈 착용 시 착색으로 인하여 나타날 수 있는 문제점 해결의 기초자료로 사용될 수 있을 것으로 보인다. Purpose: The effect of pigmentation in circle contact lens on lens wearers' tear film stability was investigated in this study. Methods: Non-invasive tear film break-up times of 54 normal eyes before and after lens wearing in twenties and the portion of first tear breakup were measured. The frontal and back surface roughness of circle contact lens was further observed with a scanning electron microscope. The clear lens which was made of hilafilcon B and circle contact lenses which were made of hilafilcon B, polymacon and copolymer of HEMA NVP were tested. Results: Non-invasive tear film breakup time was significantly reduced compared with it before lens wearing. In some case, statistically significant difference in tear film breakup time was also observed between circle contact lenses. The tear file break-up was usually early started in lower than upper portion, and in temporal than nasal portion although there was variation in the lens material. The tear film break-up of circle contact lenses made of hilafilcon B was more commonly observed in peripheral portion(pigmented area) compared with clear contact lens made of same material. Conclusions: The present study revealed that the stability of tear film was affected by wearing circle contact lens and the result seems to be used as the basis for the problem solving that can occur due to the pigmentation when wearing circle contact lens.

Dynamics and function of the tear film in relation to the blink cycle.

Great strides have recently been made in quantitative measurements of tear film thickness and thinning, mathematical modeling thereof and linking these to sensory perception. This paper summarizes recent progress in these areas and reports on new results. The complete blink cycle is used as a framework that attempts to unify the results that are currently available. Understanding of tear film dynamics is aided by combining information from different imaging methods, including fluorescence, retroillumination and a new high-speed stroboscopic imaging system developed for studying the tear film during the blink cycle. During the downstroke of the blink, lipid is compressed as a thick layer just under the upper lid which is often released as a narrow thick band of lipid at the beginning of the upstroke. "Rippling" of the tear film/air interface due to motion of the tear film over the corneal surface, somewhat like the flow of water in a shallow stream over a rocky streambed, was observed during lid motion and treated theoretically here. New mathematical predictions of tear film osmolarity over the exposed ocular surface and in tear breakup are presented; the latter is closely linked to new in vivo observations. Models include the effects of evaporation, osmotic flow through the cornea and conjunctiva, quenching of fluorescence, tangential flow of aqueous tears and diffusion of tear solutes and fluorescein. These and other combinations of experiment and theory increase our understanding of the fluid dynamics of the tear film and its potential impact on the ocular surface.

Changes in Corneal Sensation, Epithelial Damage, and Tear Function After Descemet Stripping Automated Endothelial Keratoplasty

To study the ocular surface changes in eyes after Descemet stripping automated endothelial keratoplasty (DSAEK) compared with those after penetrating keratoplasty (PKP). This prospective study compared the changes in 31 eyes of 28 patients who underwent DSAEK (DSAEK group) with those in 15 disease-matched eyes of 15 patients who underwent PKP (PKP group). Corneal epithelial integrity was evaluated using a fluorescein staining score. Corneal sensation was measured with a Cochet-Bonnet esthesiometer. Tear function was evaluated using the Schirmer test, tear clearance test, tear function index, and tear break-up time. The postoperative fluorescein staining score was significantly higher in the PKP group than in the DSAEK group (P = 0.02). Postoperative corneal sensation was significantly better in the DSAEK group than in the PKP group (P < 0.01). Corneal sensation after DSAEK was significantly better than the preoperative value (P = 0.02). There were no statistically significant changes in the Schirmer test, tear clearance test, tear function index, or break-up time before and after the surgery in both the DSAEK and PKP groups. No significant differences were observed between the DSAEK and PKP groups after the surgery. Corneal sensation was preserved, and epithelial damage was less severe after DSAEK compared with PKP. Preservation of corneal sensation may contribute to the early recovery of visual function and long-term maintenance of ocular surface health after DSAEK.

Quantitative Analysis of Tear Film Fluorescence and Discomfort During Tear Film Instability and Thinning

The purpose of this study was to test the association between tear film fluorescence changes during tear break-up (TBU) or thinning and the concurrent ocular sensory response. Sixteen subjects kept one eye open as long as possible (MBI), indicated their discomfort level continuously, and rated ocular sensations of irritation, stinging, burning, pricking, and cooling using visual analog scales (VAS). Fluorescence of the tear film was quantified by a pixel-based analysis of the median pixel intensity (PI), TBU, and percentage of dark pixels (DarkPix) over time. A cutoff of 5% TBU was used to divide subjects into either break-up (BU) or minimal break-up (BUmin) groups. Tear film fluorescence decreased (median PI) and the percentage of TBU and DarkPix increased in all trials, with the rate significantly greater in the BU than the BUmin group (Mann-Whitney U test, P < 0.05). The rate of increasing discomfort during trials was highly correlated with the rate of decrease in median PI and developing TBU (Spearman's, r ≥ 0.70). Significant correlations were found between corneal fluorescence, MBI, and sensory measures. Concentration quenching of fluorescein dye with tear film thinning best explains decreasing tear film fluorescence during trials. This was highly correlated with increasing ocular discomfort, suggesting that both tear film thinning and TBU stimulate underlying corneal nerves, although TBU produced more rapid stimulation. Slow increases in tear film hyperosmolarity may cause the gradual increase in discomfort during slow tear film thinning, whereas the sharp increases in discomfort during TBU suggest a more complex stimulus.

Scale and Spatial Distribution of Aberrations Associated with Tear Breakup

We examined the spatial correlation between tear breakup (TBU) and the associated optical anomalies on multiple spatial scales. Five subjects refrained from blinking while the time course and patterns of TBU were sequentially observed using fluorescein, retroillumination, and Shack-Hartmann (SH) aberrometry. Wavefront error maps were developed using Zernike polynomials, as well as local zonal analysis of measured wavefront slopes. The difference between these maps reveals the presence of very high-order aberrations missed by standard modal fitting methods. Size of SH spots was also quantified to estimate optical perturbations on a microscopic scale. The spatial correlation between TBU and optical aberrations was also computed. Degradation of the tear film increased wavefront aberrations over all spatial scales measured. Consistent with tear thinning, blink suppression induced an irregular pattern of phase advances in regions of TBU. SH spot size also increased in regions of TBU, which indicates the presence of optical aberrations on a scale smaller than individual lenslets. The optical signature of TBU caused by blink suppression is a combination of wavefront aberrations on macroscopic and microscopic scales due to non-uniform tear film thinning and possible exposure of a rough epithelial surface. Localized optical defects correspond temporally and spatially with TBU revealed by fluorescein and retroillumination. In addition to gross wavefront aberrations, scatter develops in areas of TBU that will further contribute to image degradation and visual disturbances after TBU.

Measurement of the Time Course of Optical Quality and Visual Deterioration during Tear Break-Up

To compare changes in optical quality and visual performance that accompany tear break-up (TBU) during blink suppression. A three-channel optical system was developed that simultaneously measured refractive aberrations (Shack-Hartmann aberrometer), 20/40 letter contrast sensitivity (CS), and TBU (retroillumination, RI). Ten wearers of silicone hydrogel contact lenses were asked to keep one eye open for approximately 18 seconds, while CS, wavefront aberrations, and RI images were collected. The wavefront was reconstructed by zonal methods, and image quality was quantified with a series of metrics including RMS fit error. Novel metrics for quantifying TBU over the contact lens surface were developed by quantifying the contrast of the RI image and by using Fourier descriptors of the first Purkinje (PJ) image shape. There was a full range of TBU over the lens surface, with four subjects showing TBU across the corneal center and one subject with TBU in the inferior peripheral pupil. Among the four subjects with central corneal TBU, RMS fit error, RI contrast, and PJ Fourier descriptors showed high correlation with CS (r(2) range, 0.9187-0.9414, 0.6261-0.975, and 0.4917-0.8986, respectively). Some of the general optical-quality metrics such as blur strength, neural sharpness, and area of modulation transfer function (MTF) also showed that change correlated with CS loss. Optical metrics of tear quality and retinal image quality are associated with the decline in vision that occurs with TBU. The evidence supports the hypothesis that blurry vision symptoms reported by contact lens wearers are caused by poor quality of the retinal image due to TBU.

Application of a Novel Interferometric Method to Investigate the Relation between Lipid Layer Thickness and Tear Film Thinning

The lipid layer of the tear film forms a barrier to evaporation. Evaporation is a major cause of tear thinning between blinks and tear breakup. The purpose of this study was to investigate the relation between tear film thinning and lipid layer thickness before and after instillation of an emulsion eye drop. Fifty non-contact lens wearers were studied. Spectral interferometry was used to measure the thinning rate of the precorneal tear film for up to 19 seconds after a blink. Simultaneously, lipid layer thickness was measured based on an absolute reflectance spectrum. After a 2-minute recovery, the measurement was repeated. A drop of the lipid emulsion was then instilled; 15 minutes later, two interferometry measurements were performed similarly. A histogram of thinning rates was fitted by a bimodal distribution with narrow and broad peaks corresponding to slow and rapid thinning, respectively. The correlation between repeated thinning rate measurements was modest, but repeatability was considerably more significant when analyzed in terms of the slow/rapid dichotomy. Similarly, the correlation between thinning rate and lipid thickness was modest but was more evident when analyzed in terms of the slow/rapid dichotomy. Instillation of an emulsion eye drop significantly increased the thickness of the lipid layer but did not significantly alter the thinning rate. The proposed slow/rapid dichotomy of thinning rates presumably relates to a good/poor barrier to evaporation of the lipid layer. The imperfect correlation between thinning rate and lipid thickness indicates that other factors, such as the composition and structure of the lipid layer, are important (e.g., sufficient polar lipids may be needed to form good interface between nonpolar lipids and the aqueous layer).

A Link between Tear Instability and Hyperosmolarity in Dry Eye

Tear film instability and tear hyperosmolarity are considered core mechanisms in the development of dry eye. The authors hypothesize that evaporation and instability produce transient shifts in tear hyperosmolarity that lead to chronic epithelial stress, inflammation, and symptoms of ocular irritation. The purpose of this study was to provide indirect evidence of short-term hyperosmolar conditions during tear instability and to test whether the corneal epithelium responds to transient hyperosmolar stress. Five subjects kept one eye open as long as possible, and overall discomfort and sensations associated with tear break-up were scaled. Later, the same subjects used the same scales to report discomfort sensations after instillation of NaCl and sucrose hyperosmolar drops (300-1000 mOsM/kg). A two-alternative, forced-choice experiment was used to obtain osmolarity thresholds. In the second experiment, primary cultured bovine corneal epithelial cells were transiently stressed with the same range of hyperosmolar culture medium, and proinflammatory mitogen-activated protein kinase (MAPKs) were measured by Western blot analysis. Tear instability led to an average discomfort rating of 6.13 and sensations of burning and stinging. These sensations also occurred with hyperosmolar solutions (thresholds, 450-460 mOsM/kg) that required 800 to 900 mOsM/kg to generate the same discomfort levels reported during tear break-up. MAPK was activated at 600 mOsM/kg of transient hyperosmolar stress. These experiments provide a link between hyperosmolarity and tear instability, suggesting that hyperosmolar levels in the tear film may transiently spike during tear instability, resulting in corneal inflammation and triggering sensory neurons.

Blinking and Tear Break-Up During Four Visual Tasks

This study investigates the relationship between blinking, tear film break-up, and ocular symptoms for normal and dry eye subjects performing four different visual tasks. Sixteen control and sixteen dry eye subjects performed four visual tasks (looking straight ahead, watching a movie, identifying rapidly changing letters, and playing a computer game) while blink patterns and fluorescein images of the tear film were videotaped. Pre and posttesting symptom questionnaires, querying the intensity of nine symptoms of ocular irritation, were completed by all subjects. Blink rate and blink amplitude were computed from digitized videos. The percentage of tear film break-up before the blink was calculated. Dry eye subjects had a significantly higher blink rate (p = 0.017, t-test). Both groups blinked significantly less during the game and letter tasks (p < 0.04, t-test). Partial blinks were common as were clusters or "flurries" of rapid blinks, but there was no significant difference in blink amplitude for control and dry eye subjects. Tear film break-up in normal subjects was typically inferior; whereas dry eye subjects showed more tear break-up centrally and superiorly. Real-time video recording of tear break-up and blink behavior pointed to complex interaction between the two. Dry eye subjects shifted more toward intense ocular symptoms at posttesting (p < 0.05, Wilcoxon signed rank) than controls. Both groups showed a shift toward more corneal staining at posttesting (p < 0.05, Wilcoxon signed rank), which was typically inferior. Reduced and incomplete blinking along with increased tear film break-up during normal visual tasks may explain the increased level of ocular discomfort symptoms reported at the end of the day, particularly in dry eye patients.

Effect of Artificial Tears on Visual Performance in Subjects With Dry Eye

Disruption of the anterior refracting surface of the eye (i.e., the tear layer) reduces visual performance. Tear layer breakup occurs soon after a blink in contact lens wearers and patients with dry eye. This study determined whether artificial tears stabilize the tear film and improve visual performance in contact lens wearers who also exhibit a dry eye. Five subjects with mild to moderate dry eye (probably as a result of an evaporative dry eye) during spectacle and contact lens wear were fitted with a Focus Night & Day hydrogel lens for this study. A temporal, two-alternative, forced-choice paradigm was used to measure contrast sensitivity. The stimuli were vertically oriented sine wave gratings (between 0.5 and 14 cpd) presented for 16.67 msec. The stimuli were presented at two different times after blink detection: 2 sec after blink detection (i.e., before tear layer breakup) or 4 sec after tear film breakup. Four conditions were investigated at 4 sec after tear layer breakup: 1) without artificial tears added, 2) with Clerz2 (Alcon, Fort Worth, TX) instilled, 3) with Sensitive Eyes (Bausch & Lomb, Rochester, NY), and 4) with GenTeal (Novartis, Basel, Switzerland) applied. The artificial tears were instilled at 10-min intervals during the data collection. The short-term visual effects of drop instillation were also investigated by continually monitoring contrast sensitivity for a 14-cpd grating after a single-drop administration. High spatial frequency contrast sensitivity and visual acuity were found to be reduced after tear film breakup in the absence of supplementation with artificial tears. For the group data (and four of five subjects), the instillation of Sensitive Eyes improved the contrast sensitivity and visual acuity to the level attained before tear breakup, thus prolonging visual performance. Clerz2 and GenTeal did not produce any enhancement in visual performance. A short-term decrease in contrast sensitivity was also observed with a single administration of Clerz2 and GenTeal. This study indicates that there was a benefit of Bausch & Lomb Sensitive Eyes tear supplementation on visual performance in subjects with an evaporative dry eye. This may be the result of 1) aqueous supplementation in these subjects and/or 2) the minimal tear layer disruption found with Sensitive Eyes drop administration. The results suggest that practitioners need to identify those patients who can benefit from the use of appropriate artificial tear supplements.

Double lateral shearing interferometer for the quantitative measurement of tear film topography

A lateral shearing interferometer designed and built for the study of the precorneal tear film topography dynamics and its effect on visual performance is presented. Simple data processing algorithms are discussed and tested on data illustrating different tear topography features: postblink tear undulation, tear breakup, eyelid-produced bumps and ridges, bubbles, and rough precontact lens tear surfaces.

Breakup and dewetting of the corneal mucus layer. An update.

The normal precorneal tear film usually remains intact between consecutive blinks, but holes begin to appear and grow at random spots in about 10–60 sec when blinking is prevented. Although the exact mechanism of the tear film breakup has eluded our understanding, it is certain that the breakup is secondary to the nonwettability of the corneal surface. We had earlier proposed a mechanism based on the possibility of the rupture and dewetting of the precorneal mucus layer due to the long-range van der Waals forces.1–4 The tear breakup was thought to be triggered by the “hydrophobicity,” or nonwettability, of the underlying corneal epithelial surface devoid of its mucus covering.