Timothy R. Golding

Tear meniscus measurement in the diagnosis of dry eye

PURPOSE Assessment of the tear film meniscus is a quantitative, minimally invasive, direct measurement of tear film quantity. The aim of this study was to assess the efficacy of tear meniscus parameter measurement in the diagnosis of dry eye. METHODS Tear meniscus radius of curvature, height, width and cross-sectional area (TMC, TMH, TMW, XSA) were determined by photographing an optic section of the inferior tear meniscus (colored with a min volume of fluorescein) at 12 x magnification, and then scanning developed images into a computer analysis program. Fifteen dry eye subjects and 15 age-matched controls were assessed. Dry eye subjects satisfied the criteria of a rose bengal staining score >/= 1, and a mean phenol red thread 15s wetted length </= 10 mm. RESULTS TMC, TMH and XSA were all reduced in magnitude in the dry eye group compared to the control group (mean +/- SD; TMC: 0.314 +/- 0.160 mm vs. 0.545 +/- 0.259 mm, TMH: 0.244 +/- 0.089 mm vs. 0.461 +/- 00.173 mm, XSA: 0.0082 +/- 0.0048 mm2 vs. 0.0176 +/- 0.0103 mm2, ANOVA, p < 0.05). Both TMC and TMH showed good diagnostic accuracy (166.7% and 160% respectively), with a dry eye referent value of </=0.35 mm for each parameter. TMC and TMH also showed strong correlations with the cotton thread test, non-invasive breakup time, and ocular surface staining scores (p < 0.01). TMH was the most powerful predictor of tear film insufficiency. CONCLUSIONS This study has shown tear meniscus assessment to be a useful alternative to existing tests for dry eye.

Relationship between tear-meniscus parameters and tear-film breakup.

PURPOSE Several flaws exist with the lipid-diffusion model for tear-film breakup. The aim of this study was to test an alternative model of tear-film rupture in which the negative hydrostatic pressure in each tear meniscus (related to the tear-meniscus radius of curvature) is proposed to influence the formation of breaks in the tear film. METHODS Measurements of noninvasive breakup time (NIBUT) and tear-meniscus radius of curvature, height, width, and cross-sectional area (TMC, TMH, TMW, and XSA) were made for 15 aqueous-deficient dry-eye and 15 age-matched control subjects. An optic section of the inferior tear meniscus (colored with a minute volume of fluorescein) was photographed at x120 magnification, and images were computer analyzed. RESULTS A significant positive correlation was found between log NIBUT and TMC (r2 = 0.141; p < 0.05). Furthermore, all subjects with TMC < 0.340 mm had NIBUT < 15 s, and two thirds of subjects with TMC > 0.340 mm had NIBUT > 15 s. There was a moderate linear relationship between TMH and log NIBUT, indicating an association between tear volume and tear stability. TMC, TMH, and tear meniscus XSA measurements all showed good reliability. CONCLUSIONS The association between highly curved tear menisci and rapid tear-film breakup times is consistent with the meniscus model of tear-film rupture. However, a causal relationship has yet to be established.

Effect of Hydrogel Lens Wear on Tear Film Stability

Noninvasive break-up time (NIBUT) of the tears was measured in a controlled, randomized, double-masked study to assess: (1) the stability of the prelens tear film during wear of new high and low water content lenses and (2) the stability of the precorneal tear film following lens removal after 1 h of wear. The prelens tear film NIBUT of 6 subjects was found to be relatively constant over a 1-h wearing period, averaging 6.1 ± 1.1 s (mean ± SEM). These values were significantly (Scheffes S test, p<0.05) lower than those recorded for the precorneal tear film before lens insertion (33.5 ± 10.6; mean ± SEM), although 85% of prelens tear film Nl- BUTs were greater than the 3-s average interblink period reported previously for soft lens wearers. After lens removal, precorneal tear film NIBUT was reduced significantly compared to prewear levels (Scheffes S test, p<0.05) for up to 15 min. Application of the monomolecular growth model to the NIBUT recovery data revealed a half-time for recovery of 6.0 min, with recovery 95% complete 25.8 min after lens removal. Lens type was not a significant factor in tear film stability, either during wear or after lens removal. The basis for reduced precorneal tear film NIBUT after lens removal is unknown; however, a disruption of the mucin layer coating the corneal epithelium is the most likely mechanism. Indeed, the technique of measuring precorneal tear film NIBUT after lens removal may be a useful determinant of the extent to which contact lens wear disrupts the precorneal mucin layer, providing an indication of the susceptibility of the cornea to a variety of complications.

Soft lens lubricants and prelens tear film stability.

Soft contact lens wearers complaining of “dry eye” are frequently prescribed rewetting drops, although the mode of action and efficacy of this treatment have not been established. Enhancement of prelens tear film (PLTF) stability could provide a basis for symptomatic relief with solution instillation. Thirty symptomatic hydroxyethyl methacrylate (HEMA) lens wearers participated in 4 separate trials of no solution (baseline), saline, and 2 soft lens lubricants. Solutions were applied for a 6-h adaptation period, and PLTF noninvasive break-up time (NIBUT) was monitored for 1 h after a final instillation. PLTF NIBUT was significantly elevated 1 min after instillation of all solutions (p<0.001, logrank test) but this effect persisted for less than 5 min. The transient enhancement of PLTF stability arising from the instillation of these rewetting solutions is unlikely to provide a basis for prolonged symptomatic relief.

X-ray and scanning electron microscopic analysis of the structural composition of tear ferns.

Dried tears from keratoconjunctivitis sicca eyes fail to exhibit the fern-like crystallization patterns observed with tears from eyes with normal tear function. To test our hypothesis that the extent of ferning depends on the ratio of salts to protein and mucin in the tear sample, dried tears from six normal subjects were subjected to scanning electron microscopy (SEM) and X-ray analyses. X-ray diffraction identified sodium chloride and potassium chloride as the major components of tear fern crystals. X-ray fluorescence detected the elements potassium, chlorine, calcium, and sulfur in the dried tear samples, with sulfur indicating the presence of protein and/or mucin. As well as confirming the presence of cubic fern nuclei, SEM revealed two kinds of material, having crystalline and globular appearances, that are hypothesized to be composed of salts and protein/mucin, respectively. Globular material appeared to block extension of crystal fern arms or to coat crystalline material, but did not crystallize. These findings suggest that tear fern crystals are composed of sodium and potassium chloride, with proteinaceous material controlling crystallization indirectly by coating crystal faces and blocking fern extension. This structural composition is consistent with the hypothesis that the ratio of salt to macromolecular species is an important determinant of tear ferning.

Analysis of tear film breakup on Etafilcon A hydrogel lenses

PURPOSE There is a need to understand better the biomaterial characteristics responsible for tear film stability during hydrogel lens wear. The underlying cause of pre-lens tear film instability may be indicated by the distribution of sites of breakup. The purpose of this study was to compare the distribution of rupture sites during wear of a common biomaterial to that without lenses. METHODS A videokeratography unit, the Topographic Modeling System, was used to capture an image of the tear film at the moment of breakup. Forty measurements were made for each of ten subjects, and the resultant rupture site distributions evaluated. The pre-lens tear film breakup locations were studied for Acuvue (Etafilcon A) disposable contact lenses using the same technique. RESULTS There was a statistically significant trend for pre-corneal tear film breaks to occur more commonly in parameniscal zones than in areas overlying the central cornea (ANOVA, p = 0.002). With the Etafilcon A lenses, a significant difference in breakup frequency between the two regions was not observed. CONCLUSIONS The pre-corneal tear film findings are consistent with the meniscus model of tear film stability; however, the biomaterial surface characteristics of Etafilcon A give other factors a more dominant role in tear film rupture.

Soft lens movement: temporal characteristics.

The time-course of on-eye hydrogel lens movement has not been carefully scrutinized, despite the importance of lens movement in optimizing lens fit and corneal physiology. We conducted a study to define the time-course of soft lens movement using 26 subjects. Video slitlamp recordings were made of lens movement at 5-min intervals for 30-min wear and after 8-h wear of 38 or 67% water content lenses (N=14 and 12, respectively). Lens mobility profiles were statistically indistinguishable for high and low water content lenses, and for experienced and neophyte lens wearers. Lens movement displayed biphasic temporal characteristics, decreasing significantly over the first 25 min from a median of 0.6 to 0.3 mm (Wilcoxon matched-pairs signed-rank test, p=0.002), then increasing significantly to 0.5 mm after 8 h of wear (p=0.03). Although some subjects exhibited little alteration in lens movement, 3 1% showed a decrease in lens movement >0.25 mm during the first half-hour of wear. Optimal predictability of lens mobility after 8-h wear was achieved 5 min after insertion, with 77% of subjects displaying lens movement within ±0.25 mm of the final value. Inoffice assessment of lens movement is best achieved 5 min after insertion, although clinical and real world lens mobility will differ significantly in about one in four patients.

Mechanisms of dryness in soft lens wear— role of BUT and deposits

Background: The symptom of dryness in hydrogel lens wear is common but its origins remain poorly understood. To assess the theory that anterior lens surface interactions are responsible for the sensation of dryness during lens wear, 50 contact lens wearers were evaluated.

Differential diagnosis and management of common dry eye subtypes

Dry eye is a prevalent disease causing chronic eye irritation, ocular surface damage and increase risk of eye infection. Six dry eye case studies are presentted to illustrate differential diagnosis and management of dry eye subtypes commonly encountered in optometric practice: autoimmune and non‐autominnune aqueous tear deficiency (ATD), liqid anomally, lid surfacing anomaly, allergic dry eye and marginal dry eye. A two‐stage diagnostic process is described: (1) identification of dry eye using a preliminary test protocol of the McMonnies dry eye survey, fluorescein break‐up time (FBUT) and rose bengal of the McMonnies dry eye suryvey, fluroescein break‐up time (FEBUT) and rose bengal staining and (2) differential diagnosis using a battery of specific tests for diagnosing each dry eye subtype. Subtype‐specific tests included: the cotton thread tear test (CTTT) and Lactoplace® for ATD diagnosis; biomicroscopy of the precorneal lipid layer, lid margins, lashes, and meibomian excreta for lipid anomaly; biomicroscopy for evidence of lid surfacing anomalies such as incomplete blining, ectropion and pterygia; and positive history and slit‐lamp signs of allergy to diagnose allergic dry eye. Impression cytoglogy, a technique enabling the grading of conjunctival squamous metaplasia and goblet cell density, was useful in differenting autoimmune from non‐autoimmune ATD. Specific management strategic for each of the comom dry eye subtypes are described, with the severity of symptoms also influencing the nature of treatment. Correct classification of a patients dry eye enable the practitioner to better comprehend the aetiology and therefore initiate appropriate, effective treatement form the outset. In the absence of a cure for dry eye, patient reiview is essential to promote compliance, monitor improvement and modify treatement accrodingly.