Stability Of Precorneal Tear Film Research Articles

Experience in the Treatment of Dry Eye Syndrome in Students with Myopic Refraction

Objective: to study the effectiveness of the hypromellose-based medicine Artificial Tears®, eye drops, in the treatment of dry eye syndrome in students with myopic refraction. Patients and methods. A total of 147 students of Academician E.A. Wagner Perm State Medical University with different types of clinical refraction were examined. Among them 63 students with myopic refraction of various degrees in 110 eyes were included in the study (mean age — 22.6 ± 0.16 years, 49 (78 %) women, 14 (22 %) men). Dry eye syndrome was detected in 49 (78 %) participants in 82 eyes (74.5 %). According to the myopia correction method, 3 groups were formed: Group 1 — students with eyeglasses; Group 2 — students constantly using soft contact lenses; Group 3 — students who had excimer laser correction by LASIK method. The remaining students (n = 14) had no dry eye syndrome. The study was conducted in two stages: at baseline and then repeated after 4 weeks in students with dry eye syndrome who used daily the medicine Artificial Tears®. Subjective assessment was based on the Ocular Surface Disease Index (OSDI) questionnaire. Оbjective assessment included function tests, characterizing the precorneal tear film stability and total tear production level. Results. In the process of treatment a good tolerance of the given medicine was reported. Analysis of the overall results showed that the mean OSDI score decreased statistically significantly from 26.92 to 20.29 seconds (p ≤ 0.0001). The mean tear film break-up time increased from 7.95 to 11.25 (p ≤ 0.0001). The mean Schirmer’s test score was slightly changed: from 13.98 to 14.07 mm due to the presence of increased tear production in some students, which is characteristic of the dry eye syndrome initial manifestations. Conclusion. The medicine Artificial Tears® in the form of eye drops is well tolerated and is sufficiently effective in eliminating the dry eye syndrome manifestations after only 4 weeks of use. The treatment with the medicine Artificial Tears® showed a statistically significant reduction in the disease severity (according to the OSDI questionnaire data) and an increase in the tear film break-up time. The received results allow us to recommend the medicine Artificial Tears® for medical use in patients with various degrees of myopic refraction, regardless of the myopia correction method used.

Influence of Active and Passive Smoking on the Tear Film in the Saudi Population

Purpose: To investigate the effects of different types of smoking on the precorneal tear film stability and quality using questionnaire, clinical tests and noninvasive keratography. And to provide community awareness about the dangers of dry eye and its connection to smoking. Methods: Prospective cross-sectional study with a total of 33 participants was enrolled in this study. The participants’ ages ranged between 17 to 40 years old. They were divided into 3 groups: Control non smokers, Passive smokers, and Active smokers. All participants of control and passive smokers’ groups are females (100.0%), while there are (45.5%) male participants in active smokers’ group and (54.5%) females. there were no statistically significant differences between groups (non – passive - active) smokers related to spherical equivalent; p value was (0.403). All subjects replied to questionnaire for dryness evaluation then went through full ophthalmological examinations. Also, we examined subjects for dryness using clinical tests (Tear break up time TBUT and Schirmer) and non-invasive keratography. Results: Dry Eye Questionnaire analysis: all control group participants were normal and not dry. There are (54.5%) dry, while (45.5%) in passive Group were not. And participants of active smokers’ group with percentage of (54.5%) were dry, (45.5%) were not dry. As regards clinical parameters (TBUT and Shirmer): we concluded that there were no statistically significant differences between groups related to TBUT & Schirmer tests, where p value was 0.095, 0.993 respectively. Noninvasive keratograph dryness tests (TBUT & tear meniscus height TMH) we concluded that there were statistically significant differences between groups related to TBUT where p value was 0.026, with insignificant reduction of TMH values in active smoker group as P value was 0.283. Conclusion: These findings suggest that chronic smoking has a negative effect on the ocular surface and affects some tear characteristics. Moreover, the chronic ocular irritative effects of cigarette smoking may lead to defects in ocular surface defense.

Developing a diagnosis model for dry eye disease in dogs using object detection.

The purpose of this study was to develop an object detection method for the diagnosis of dry eye disease (DED) in dogs. To this end, a methodology was designed to evaluate ocular surface video images using the YOLOv5 model, which is an object detection algorithm that has been widely used because of its simple network structure and fast detection speed. Because the cornea is a transparent organ, an illuminator plate with grid squares was used to provide grid lines, which were analyzed as the reflected straight lines of the light source representing the precorneal tear film (PTF) stability. The original video consisted of the number of 12 normal images(normal, [Formula: see text] = 17) and the number of 15 abnormal images(abnormal, [Formula: see text] = 17), converted to JPEG images for labeling, learning, and model validation. The labeled image data were divided into a training image data set (normal, [Formula: see text] = 15,276; abnormal, [Formula: see text] = 26,196) to a validation image data set (normal, [Formula: see text] = 6546; abnormal, [Formula: see text] = 11,228). As a result of the experiment, the mean average precision ([Formula: see text]) achieved 0.995. This study proposes a method to effectively determine ocular surface status in dogs by using YOLOv5 and concludes that an object detection model can be used in the veterinary field.

Хвороба сухого ока у студентів з міопією під час пандемії COVІD-19

Актуальність. На сьогодні актуальною проблемою є пандемія коронавірусної хвороби 2019 (COVID-19) в усьому світі. Вжито заходів безпеки, зокрема використання масок, дистанційне навчання. Однак офтальмологи, як і населення в цілому, повинні знати, що маска для обличчя разом із тривалим використанням цифрових пристроїв призводить до збільшення кількості повідомлень про сухість очей у великої кількості пацієнтів. Мета дослідження: вивчити частоту виникнення хвороби сухого ока у студентів з міопією. Матеріали та методи. У дослідженні взяли участь 96 студентів медичного університету, які спостерігались у офтальмолога з діагнозом «міопія», обраних методом випадкової вибірки. Всім пацієнтам, крім стандартного офтальмологічного обстеження, проводилась оцінка стабільності прерогової слізної плівки (CП) за допомогою кератотопографії рогівок, та проба Норна (час розриву слізної плівки (ЧРСП)). Також використовувався стандартний опитувальник, призначений для оцінки вираженості симптомів хвороби сухого ока, «Індекс ураження очної поверхні» (Ocular Surface Disease Index). Результати. Під час проведення кератотопографії в 47 пацієнтів ЧРСП не був знижений. У середньому за часом стабільність концентричних кілець зберігалась тривалий час, 20,2 ± 3 с. Але у 49 пацієнтів спостерігались ознаки нестабільності СП за часом порівняно з 47 пацієнтами без порушення ЧРСП. У 47 пацієнтів без порушень при дослідженні на корнеотопографі даний показник при пробі Норна варіював від 25 до 18 с, тобто також не виходив за рамки вікової норми (у середньому 21,5 ± 3,5 с). У 3 пацієнтів з мінімальним показником ЧРСП за кератотопографією його значення за пробою Норна становило 9 с. У 36 пацієнтів з укороченням ЧРСП, відповідно до обох методів, відзначався слабкий ступінь сухого ока, у 10 — помірний, у 3 — виражений. Найбільш частими скаргами були: відчуття піску в очах, зоровий дискомфорт при роботі за комп’ютером і в вітряну погоду та при тривалому користуванні захисною маскою. Висновки. Серед студентів, які перебували на дистанційному навчанні, в 51,04 % випадків відзначається підтверджена об’єктивними методами хвороба сухого ока. Більш виражений ступінь сухого ока відзначається в користувачів контактних лінз, тому в обов’язковому порядку офтальмологам слід призначати їм зволожуючі краплі.

Выбор оптимального способа предоперационной оценки риска развития синдрома «сухого глаза» у пациентов с миопией

Aim. Comparative analysis of the effectiveness of keratotopography methods and classical Norn’s test in assessing the stability of the tear film (TF) in patients with myopia before photorefractive surgery. Methods. The study involved 26 patients. All of them were planned for keratorefractive surgery to correct myopic refraction and astigmatism. Their age averaged 32.5±14.5 years (18-47 years). The stability of pre-corneal tear film was assessed using computed keratotopography and Norn’s test - the tear film rupture time (TFRT) was determined. A standard questionnaire was also used to assess the severity of symptoms of dry eye syndrome (DES). A comparison was made of the indicators of tear film, stability obtained by the methods of keratotopography and Norn’s test, with their subsequent comparison with the data of the questionnaire. Results. In 17 patients (65.4 %), TFRT index corresponded to the age norm. In the remaining 9 people (34.6 %), indicators of tear film stability were reduced both by keratotopography (12±4 sec) and by Norn’s test (13.5± 4.5 sec), and there were also subjective signs of dry eye syndrome according to questionnaire data. The data turned out to be comparable. Conclusion. The incidence of impaired stability of the TF and subjective manifestations of DES among patients planned for keratorefractive surgery for myopia and myopic astigmatism was significant and, according to our data, made 34.6 %. To prevent complicated postoperative course of photorefractive surgery, it is necessary to assess the condition of the ocular surface immediately before refractive surgery, to identify the risk group for DES development. Key words: dry eye syndrome; tear film; keratotopography; Norn’s test; tear film rupture time.

The relationship of pre-corneal to pre-contact lens non-invasive tear breakup time.

PurposeTo examine the relationship between pre-corneal and pre-contact lens tear film stability (TFS), and to determine whether pre-corneal TFS is a reliable predictor of subsequent pre-lens TFS after a contact lens is placed on the eye.Methods667 records met inclusion criteria and were extracted from a soft contact lens multi-study database. Multivariable linear mixed effects models were fit to examine the association between pre-corneal and pre-lens TFS, adjusting for potential confounders and accounting for repeated measures. Receiver Operating Characteristic (ROC) analysis was employed to assess the predictive performance of pre-corneal TFS for subsequent pre-lens TFS. TFS was quantified for this analysis as the non-invasive tear breakup time (NITBUT).ResultsPre-corneal NITBUT was significantly related to the pre-lens NITBUT at both 10 min (p<0.001) and 2–6 hrs (p<0.001) post-lens insertion. However, the sensitivities of pre-corneal NITBUT for predicting symptom-associated thresholds of pre-lens NITBUT ranged from 50–65%, and specificities ranged from 57–72%, suggesting poor-to-moderate diagnostic performance.ConclusionsDespite the association of pre-corneal and pre-lens TFS, the inherent lability and sensitivity to environmental exposures of the tear film introduce significant variability into NITBUT measurements. Using pre-corneal NITBUT to identify likely successful contact lens candidates prior to fitting is thus not sufficiently accurate to be relied upon in the clinical setting.

Clinical study of the precorneal tear film in relation with duration of diabetes

Context: The study objective was to compare precorneal tear film in terms of amount and stability in diabetic individuals. Aims: The aim was to study the effect of diabetes on the amount and stability of precorneal tear film. Settings and Design: This is a hospital-based, prospective, case-controlled, observational study of 1-year duration. Sixty-five sequentially collected patients with diabetes attending the Ophthalmology outpatient department/inpatient department at AVBRH were selected for the study after taking the inclusion and exclusion criteria into consideration. Informed consent was obtained from all participants after approval by the Institutional Ethical Committee of the college. Subjects and Methods: After enrollment of the participants in the study, all underwent a thorough ophthalmic examination. Tear film break up time (TBUT) and Schirmer test without anesthesia followed by with anesthesia were calculated. Statistical Analysis Used: Statistical analysis was done using descriptive and inferential statistics using Chi-square test and Student's unpaired t-test, SPSS 17.0 version and GraphPad 6.0 version software (Biomatters, Ltd. NZ and GSL Biotech, USA) were used in the analysis, and P < 0.05 was considered the level of statistical significance (P < 0.05). Results: Patients with diabetes showed unstable tear film. The amount of tear film measurement also decreases in diabetics. A higher number of positive test results for both Schirmer test and TBUT test were found in patients having a duration of diabetes >5 years. Conclusions: Longer duration of diabetes is associated with dry eye. Diabetes is associated with a reduction in the amount of precorneal tear film as well as an unstable precorneal tear film.

Differential time-course tear film quantitative changes following limbal relaxing incisions

BackgroundThe study aims at evaluating the time-course changes of pre-corneal tear film after simultaneous phacoemulsification and limbal relaxing incisions (LRIs) performed in 2 groups of patients; group-A had vertical and group-B had horizontal LRIs.MethodsFourty-two eyes of 28 patients with co-existing cataract and corneal astigmatism were studied before and after simultaneous cataract surgery and LRIs (at weeks 1, 4 and 12), patients were classified into 2 groups according to the orientation of LRIs; vertical (A) and horizontal (B) groups. Pre-corneal tear film stability was assessed by measuring the tear break-up time (TBUT) and the tear volume was determined using Schirmer’s I test (Basic Schirmer’s test; BST), both preoperatively and postoperatively.ResultsTBUT was significantly reduced in both the study groups (P = 0.001) without significant reduction regarding basic Schirmer’s test values except for the first postoperative week in the horizontal LRI group-B (P = 0.04).ConclusionsPrecorneal tear film stability is altered in the early postoperative period after simultaneous cataract and LRI incisions shown by TBUT measurement values. These changes do not appear to differ significantly depending on the orientation of LRI incisions.

Engineered metal oxide nanomaterials inhibit corneal epithelial wound healing in vitro and in vivo

Ocular exposure to metal oxide engineered nanomaterials (ENMs) is common as exemplified by zinc(II) oxide (ZnO), a major constituent of sunscreens and cosmetics. The ocular surface that includes the transparent cornea and its protective tear film are common sites of exposure for metal ENMs. Despite the frequency of exposure of the ocular surface, there is a knowledge gap regarding the effects of metal oxide ENMs on the cornea in health and disease. Therefore, we studied the effects of metal oxide ENMs on the cornea in the presence or absence of injury. Cell viability of immortalized human corneal epithelial (hTCEpi) cells was assessed following treatment with 11 metal oxide ENMs with a concentration ranging from 0.5 to 250 μg/ml for 24 h. An epithelial wound healing assay with a monolayer of hTCEpi cells was then performed using 11 metal oxide ENMs at select concentrations based on data from the viability assays. Subsequently, based on the in vitro results, in vivo testing of precorneal tear film (PTF) quantity and stability as well as a corneal epithelial wound healing were tested in the presence or absence ZnO or vanadium(V) oxide (V2O5) at a concentration of 50 μg/ml. We found that WO3, ZnO, V2O5 and CuO ENMs significantly reduced hTCEpi cell viability in comparison to vehicle control or the other metal oxide ENMs tested. Furthermore, ZnO and V2O5 ENMs also significantly decreased hTCEpi cell migration. Although ZnO and V2O5 did not alter PTF parameters of rabbits in vivo, corneal epithelial wound healing was significantly delayed by topical ZnO while V2O5 did not alter wound healing. Finally, hyperspectral images confirmed penetration of ZnO and V2O5 through all corneal layers and into the iris stroma. Considering the marked epithelial toxicity and corneal penetration of ZnO, further investigations on the impact of this ENM on the eye are warranted.

A comparative clinical study of the precorneal tear film in diabetic and nondiabetic persons

Context: The study objective was to compare precorneal tear film in terms of amount and stability in diabetic and nondiabetic individuals. Aims: The aim was to study the effect of diabetes on the amount and stability of precorneal tear film. Settings and Design: This is a hospital-based, prospective, case–controlled, observational study of 1-year duration. Sixty-five sequentially collected patients with diabetes and 65 age- and sex-matched nondiabetics, attending the ophthalmology outpatient department/inpatient department at AVBRH were selected for the study after taking the inclusion and exclusion criteria into consideration. Informed consent was taken from all participants after approval by the Institutional Ethical Committee of the college. Subjects and Methods: After enrollment of the participants to the study, all underwent a thorough ophthalmic examination. Tear film break-up time (TBUT) and Schirmer's test without anesthesia followed by with anesthesia were calculated. Statistical Analysis Used: Statistical analysis was done by using descriptive and inferential statistics using Chi-square test and Student's unpaired t-test, SPSS 17.0 version and GraphPad 6.0 version software were used in the analysis, and P 5 years. Conclusions: Longer duration of diabetes is associated with dry eye. Diabetes is associated with reduction in the amount of precorneal tear film as well as an unstable precorneal tear film.

External eye symptoms in indoor environments.

Eye irritation, for example dry or irritated eyes, is generally among top three reported symptoms in office-like environments, in particular among workplaces with cognitive demanding visual display unit (VDU) work. The symptoms are especially among middle and advanced ages and particularly among women more than men. The symptoms are also among the most commonly reported complaints in the eye clinic. To be in a position to interpret the high prevalence of eye symptoms, a multidisciplinary and integrated approach is necessary that involves the external eye physiology (separate from internal eye effects), eye diseases (evaporative dry eye (DE), aqueous-deficient DE, and gland dysfunctions), and risk factors that aggravate the stability of precorneal tear film (PTF) resulting in hyperosmolarity and initiation of inflammatory reactions. Indoor environmental, occupational and personal risk factors may aggravate the PTF stability; factors such as age, contact lenses, cosmetics, diet, draft, gender, low humidity and high temperature, medication, outdoor and combustion pollutants, and VDU work. Psychological stressors may further influence the reporting behavior of eye symptoms. The impact of the risk factors may occur in a combined and exacerbating manner.

Efficacy of 0.01% dexamethasone solution in comprehensive therapy of dry eye disease

Introduction. The officinal dosage of dexamethasone solution (0.1%) has a marked localized antiinflammatory effect. But the widespread use of this dose in the management of dry eye diseases is limited by the risk of damage to the cornea. Therefore, the authors developed a solution containing 0.01% dexamethasone phosphate in combination with 6% polyvinylpyrolidone and 1.5%–5.5% dextrose [3]. Aim. To study the effects of this novel anti-inflammatory solution on corneal inflammatory processes. Materials and methods. This study included a cohort of 25 patients (50 eyes) with corneal–conjunctival xerosis. Lower tear meniscus index, precorneal tear film production, stability and osmolarity, and the degree of staining of the ocular surface epithelium with vital solutions were assessed prior to the treatment and on day 28 of the study. The presence of the cytokines IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-17A, IL-1Ra, TNF-α, INF-α, and INF-γ in patients’ tear fluid and blood plasma was quantified using ELISA. All patients were asked to complete a questionnaire to evaluate subjective signs of xerosis of the ocular surface. Results. Statistically significant increases in tear meniscus index, precorneal tear film stability, and main and total tear production, with a significant decrease in tear film osmolarity were observed by day 28 of the study. In addition, positive changes in objective parameters relating to the ocular surface epithelium were further confirmed by the patients’ evaluations of their quality of life. Furthermore, the degree of staining of the ocular surface epithelium with vital solutions also decreased. Conclusions. The results of the study demonstrate the high level of effectiveness of the developed medication as a treatment for dry eye diseases of various etiologies.

Efficiency of 0.01% Dexamethasone Solution in Comprehensive Therapy of Dry Eye Disease

Introduction: At present anti-inflammatory therapy of patients with dry eye disease is based mainly on glucocorticoids' instillations. In spite of the fact that dexamethasone in officinal dosage (0.1%) has a marked local anti-inflammatory effect, its wide use is limited by the presence of a destructive process in the cornea. Taking this into account, the authors developed a drug containing 0.01% dexamethasone phosphate in combinations with 6% polyvinylpyrolidone and 1.5-5.5% dextrose solution. Objective: To study the impact of the developed medication on the inflammatory process dynamics in the tissues of the eye surface in patients with dry eye disease of various etiology. Materials and Methods: The material of this study was based on the results of the examination and treatment of 25 volunteers (50 eyes) with corneal-conjunctival xerosis developed on the background of 7 cases of meibomian blepharitis (14 eyes), 8 cases of perimenopause (16 eyes), and 10 cases of Sjögren's syndrome (20 eyes). All patients used the developed medication in the form of eye drops 3-4 times daily on the background of tear replacement therapy. Prior to the therapy and on day 28 of the study the following parameters were assessed, lower tear meniscus index, precorneal tear film production, stability and osmolarity, staining of eye surface epithelium with sodium fluoresce in solution, as well as bengal rose and lissamine green. The quantity of cytokines was determined in the tear fluid and blood plasma with ELISA method: interleukins-1β, 2, 4, 6, 8, 10, 17A, interleukin 1 receptor antagonist, TNF α, interferons α and γ. Besides, all the subjects were asked to fill in a questionnaire to evaluate subjective signs of the ocular surface epithelium xerosis or Ocular Surface Disease Index (OSDI). Results: By day 28 of the study statistically valid increase of the tear meniscus index, precorneal tear film stability, main and total tear production and decrease of tear film osmolarity were observed. Besides, the staining degree of the ocular surface epithelium with bengal rose and lissamine green (van Bijsterv?ld scale) and with sodium fluoresce in (Oxford scale) decreased. Also, the positive dynamics of the objective parameters of the ocular surface epithelium is confirmed by the subjects' patients evaluation of their quality of life. Conclusion: The results of the study performed prove the high clinical efficiency of the developed medication that has a marked local anti-inflammatory effect in the therapy of dry eye disease of various etiology.

A new, specular reflection-based, precorneal tear film stability measurement technique in a rabbit model: viscoelastic increases tear film stability.

To develop a safe, noninvasive, noncontact, continuous in vivo method to measure the dehydration rate of the precorneal tear film and to compare the effectiveness of a viscoelastic agent in maintaining the precorneal tear film to that of a balanced salt solution. Software was designed to analyze the corneal reflection produced by the operating microscope's coaxial illumination. The software characterized the shape of the reflection, which became distorted as the precorneal tear film evaporated; characterization was accomplished by fitting an ellipse to the reflection and measuring its projected surface area. Balanced salt solution Plus (BSS+) and a 2% hydroxypropylmethylcellulose viscoelastic were used as the test agents. The tear film evaporation rate was characterized and compared over a period of 20 minutes in 20 eyes from 10 New Zealand white rabbits. The ellipse axes ratio and surface area were found to decrease initially after each application of either viscoelastic or BSS+ and then to increase linearly as the tear film began to evaporate (P < 0.001) for eyes treated with BSS+ only. Eyes treated with BSS+ required 7.5 ± 2.7 applications to maintain sufficient corneal hydration during the 20-minute test period, whereas eyes treated with viscoelastic required 1.4 ± 0.5 applications. The rates of evaporation differed significantly (P < 0.043) between viscoelastic and BSS+. The shape and surface area of the corneal reflection are strongly correlated with the state of the tear film. Rabbits' corneas treated with viscoelastic remained hydrated significantly longer than corneas treated with BSS+.

Iris colour and the influence of local anaesthetics on pre-corneal tear film stability

Using non-invasive methods we report here that the stability of the pre-corneal tear film is lower in the brown eye than in the blue eye. The average stability in the blue eye is 15.8 sec (SD +/- 5.8) and in the brown eye it is 12.3 sec (SD +/- 2.9). On average, instillation of topical anaesthetics, benoxinate hydrochloride (0.4%) or amethacaine hydrochloride (0.5%), depress the stability of the pre-corneal tear film in blue eyes but not in brown eyes.

Numerical analysis of interferograms for evaluation of tear film build‐up time

The lateral shearing interferometer was applied to the in vivo dynamic investigation of the external surface of the pre-corneal tear film after an eye blink. Sequences of interferograms were recorded at a sampling frequency of 25 Hz. Immediately after every eye blink, a bright pattern was observed under the interference fringes. This disappeared after a short time interval (around 0.5-2 s): smooth interference fringes were then observed, corresponding to the creation of a smooth anterior optical surface over the cornea. The purpose of this study is to describe in detail the kinetics of pre-corneal tear film stability and to propose quantitative measures of the stabilisation process in healthy eyes during the 3 s period after a blink. Two methods of quantitative assessment of the tear film build-up time are presented. The first is based upon the evaluation of the inhomogeneity of the background of the interferogram; the second evaluates the orientation of the structure of the background by the analysis of the zero order of the Fast Fourier Transform (FFT) spectrum. The quasi-vertically oriented bright line patterns observed in interferograms immediately after a blink and the mirror-symmetry of their tilts for right and left eyes indicate that the pattern is related to the wiping movements of the upper eyelids during the eye blink.

Interferometric measurements of dynamic changes of tear film

Tear film stability plays an important role in the quality of vision. We present an interferometric method for assessing the stability of precorneal tear film in real time. A lateral shearing technique is applied as a noninvasive and sensitive method for investigating tear film stability and the smoothness of the tear film surface by quantitative evaluation of the interference fringe pattern. The evaporation of tears and the appearance of tear film break-up between blinks cause changes in the fringe geometry. For quantitative assessment of the fringe smoothness and consequently of the tear film structure, the fast Fourier transform (FFT) is applied. Four parameters are used to quantitatively estimate dynamic changes in the tear film stability of the cornea 20 s after the eye blink. Examples of examined interferograms recorded in patients with healthy eyes, patients suffering from dry-eye syndrome, and patients wearing contact lenses are given. Significant differences between the stability of the tear film in the healthy eye and that in the dry eye and the eye with a contact lens are observed. The favorable influence of artificial tears applied in patients with dry-eye syndrome or contact lenses is also discussed.

Evaluating Tear Film Stability in the Human Eye With High-Speed Videokeratoscopy

High-speed videokeratoscopy (HSV) is an emerging technology that has the potential to acquire information on the dynamics of corneal topography and tear-film behavior. We show that the surface regularity and asymmetry indices, which are traditionally used for characterizing the stability of precorneal tear film, have limitations in the context of HSV because they are highly sensitive to natural ocular microfluctuations. To overcome this problem, we propose a new microfluctuation-independent surface indicator. It is based on the root-mean-square of the error of the parametric model fit to the surface. Further, we develop techniques for estimating the tear film build-up and break-up times. The tear film build-up time estimator is based on the proposed RMS fit surface indicator while the tear film break-up time estimator is derived directly from a set of consecutive HSV digital images, without the need for estimating the resulting corneal surface.

Comparison of the Short-Term Effects on the Human Corneal Surface of Topical Timolol Maleate With and Without Benzalkonium Chloride

To compare the short-term effects of timolol maleate with and without preservative (0.005% benzalkonium chloride) on pre-corneal tear film stability and corneal epithelial barrier function. The study population consisted of 20 healthy volunteers. To obtain baseline values, 7 days before the experiment the non-invasive breakup time of the pre-corneal tear film was measured using a tear specular microscope; corneal fluorescein uptake was measured with a fluorophotometer. Unpreserved or preserved 0.5% timolol was applied to one eye; the contralateral eye was exposed to the other drug. At 30 minutes after instillation, the pre-study tests were repeated. Preserved timolol did, while unpreserved timolol did not, significantly reduce the non-invasive breakup time from the baseline values (baseline and post-exposure values 11.4 and 6.8 seconds, respectively, P = 0.008 for preserved timolol, and 11.7 vs. 11.0 seconds, P = 0.55 for unpreserved timolol). Corneal fluorescein uptake, on the other hand, was significantly increased upon exposure to either preserved or unpreserved timolol (baseline and post-exposure values 37.5 and 82.0 ng/ml, P < 0.001 for preserved timolol, and 35.4 vs. 57.6 ng/ml, P < 0.001 for unpreserved timolol). Preserved timolol exerted the greater effect (P = 0.028). Exposure to preserved timolol resulted in significant instability in the pre-corneal tear film. Moreover, it disrupted the corneal epithelial barrier function to a greater degree than unpreserved timolol. The elimination of preservatives may be desirable in efforts to protect the integrity of the corneal surface and its interaction with the tear film.

The effect of benoxinate on the tear stability of Hong Kong-Chinese

We conducted a series of experiments to examine the effect of local anaesthetic instillation on tear stability measurements. All experiments were conducted with the examiner masked with respect to treatments. We measured tear break-up time (TDUT) and non-invasive tear break-up time (NITBUT) 30s after instillation of benoxinate (0.4%) in a single masked experiment and found that NITBUT was significantly increased while TBUT was unaffected. In separate experiments tear stability was assessed 5 min after instillation of benoxinate and there was no significant effect on either TBUT or NITBUT measurements. In a control experiment to examine the effect of instilling a drop of liquid into the eye, neither TBUT nor NITBUT were affected 30s after the instillation of saline. No corneal staining was observed in any of the subjects after instillation of benoxinate. The results suggest that benoxinate does not affect the stability of the precorneal tear film, and that tear stability can be assessed after the instillation of unpreserved benoxinate.