Adrian S. Bruce

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.

Corneal pathophysiology with contact lens wear

Contact lens wear induces a wide spectrum of changes in the appearance and function of the cornea. The most salient effect of lens wear is the hypoxically induced reduction in the rate of metabolic activity of the corneal epithelium and its sequellae. Other important alterations to corneal health associated with contact lens wear may be caused by antigenic and toxic stimuli, mechanical forces, osmotic effects and carbon dioxide retention. Perhaps the most important task facing the contact lens clinician is to distinguish between an acceptable state of physiological modification and an anomalous or pathological state of hypofunction. In this article, we review the assortment of corneal changes primarily on the basis of the causative agents and time scale with reference to the physical and chemical processes leading to the observed signs or symptoms. This procedure allows a strong foundation for understanding the etiology and management principles for the variety of effects that contact lenses may have on the cornea.

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.

The conjunctival epithelium in dry eye subtypes: Effect of preserved and non-preserved topical treatments

Purpose. To determine the effect of topical treatments on the conjunctiva in dry eye. Methods. N = 134 dry eye subjects were diagnosed using a protocol of McMonnies dry eye symptom survey score > 14, fluorescein break up time (FBUT) < 10s and presence of rose Bengal staining. Differential diagnosis of dry eye subtypes was based on biomicroscopic signs and ocular/medical history. Superficial perilimbal bulbar conjunctival epithelial samples were collected using impression cytology. The nucleo-cytoplasmic ratio (N/C), goblet cell density (GCD) and expression of monoclonal antibodies HLA DR and CD23 were determined. The ocular surface characteristics of untreated subjects, those receiving preserved dry eye treatments and those receiving non-preserved treatments were compared with each other and with controls. Ocular surface characteristics of dry eye subtypes were also examined. Results. An increase in N/C (p = 0.011), reduction in GCD (p = 0.0001) and increase in expression of HLA DR (p = 0.0001) and CD23 (p = 0.0001) were detected in the untreated group compared to controls. No significant differences were found between the group receiving non-preserved dry eye treatments and untreated dry eye group. The group receiving preserved treatments had a reduced GCD (p = 0.0003) and increased expression of HLA DR (p = 0.0003) and CD23 (p = 0.0001) compared to the group receiving non-preserved treatments. Dry eye subtype specific differences in HLA DR and CD23 expression were noted. Conclusions. The conjunctival inflammation and reduced goblet cell density of dry eye is exacerbated by use of preserved topical agents, and is not significantly improved by use of non-preserved artificial tear supplements alone. Therapeutic strategies for dry eye should aim to increase goblet cell density and control ocular surface inflammation.

Postlens tear film morphology, lens movement and symptoms in hydrogel lens wearers

Postlens tear film morphology, lens movement and symptoms were assessed in 100 subjects wearing hydrogel contact lenses on a daily wear schedule. Postlens tear film appearance in specular reflection was categorized as amorphous, coloured, striated or dynamic (variable with bliniking), and subjects’symptoms were assessed using a questionnaire. Non‐amorphous appearances were present in 25% of subjects and occurred approximateiy equally with HEMA, Acuvue. Igel 55 and other lens types. Patterned appearances were found to be associated with reduced lens movement (Kruskal‐Wallis ANOVA, P < 0.001). The most common symptom (dryness) was not significantly related to postlens tear film appearance. Postlens tear film morphology was shown to be a determinant of lens movement, but may be unrelated to common symptoms.

Repeatability of the phenol-red thread and tear thinning time tests for tear film function

Reliable tear function tests are required both in clinical practice and for research. Between‐sessions repeatability of the phenol‐red thread and tear thinning time tests was assessed for 17 young normal Caucasian subjects on two consecutive days. A single phenol‐red thread result and the mean of three tear thinning times were recorded on each day. The minimum phenol‐red thread result was 11 mm, and the 68 per cent and 95 per cent confidence intervals for repeatability were ± 5 mm and ± 10 mm, respectively. We propose diagnostic criteria of less than 11 mm for low tear secretion and less than 16 mm for a borderline result, based on the 68 per cent confidence interval. A level of measurement effect on repeatability of tear thinning time was present (Spearmans rho = 0.79, p = 0.002), with longer times showing greater variability: this relationship was eliminated by logarithmic data transformation. The tear thinning time test was not sufficiently reliable for clinical use; for a result of 15 seconds, there was 95 per cent confidence that subsequent times would lie between 57 and three seconds. We recommend further investigation into the use of log scales for tear stability tests.

Keratoconus associated with continual eye rubbing due to punctal agenesis.

Purpose. To highlight a possible causal effect of eye rubbing in the etiology of keratoconus. Methods. A 43-year-old man presented to the practice of one of the authors (I.F.G.) with the complaint of gradual onset reading difficulty. History revealed the patient to have experienced constant epiphora in the right eye throughout his life as a result of punctal agenesis, which necessitated frequent wiping of this eye. Vision in the patients right eye had been reduced for approximately 20 years. Results. Based on ocular examination, the patient was diagnosed as having unilateral keratoconus in the right eye. Conclusion. It is thought by some that keratoconus is associated with, or indeed caused by, persistent rubbing of the anterior eye. While a number of studies support a genetic basis for keratoconus in some patients, it is possible that mechanical factors play a role in the development of this condition in other patients. This paper presents a case of unilateral keratoconus, where there is a confirmed history of habitual eye rubbing and wiping of excess tears as a result of punctal agenesis in the ipsilateral eye, thereby suggesting a possible causal relationship of eye rubbing in the etiology of keratoconus.

Dehydration of hydrogel lenses: environmental influences during normal wear

ABSTRACT To examine whether certain aspects of the environment can have a significant effect upon the steady‐state water content of hydrogel contact lenses during normal wear, nine volunteers monitored ambient temperature, ambient humidity, and the water content of their contact lenses over a 5‐day period of daily lens wear. Three subjects wore Hydron zero‐6 lenses (38% nominal water content), three wore Hydrocurve II lenses (55%), and three wore Permalens contact lenses (71%). The results indicate that a knowledge of ambient temperature and humidity is of little value in predicting the water content of hydrogel lenses under normal wearing conditions, at least with respect to the range of environmental conditions encountered in the course of this experiment.

Hydrogel (acuvue) Lens Movement is Influenced by the Postlens Tear Film

The determinants of hydrogel lens movement with thin mid-water content lenses may be better understood by taking into account the lubrication properties of the tear film. We assessed lens movement, postlens tear film (PTF) status, and tear meniscus height with 58% water content (Acuvue) lenses worn over 6 h on each of 2 consecutive days. Median lens movement was near zero initially and increased within the first hour to 0.34 and 0.30 mm on days 1 and 2, respectively (Friedman analysis of variance by ranks, days 1 and 2, p<0.001). The small lens movement at 15 min was related to the increased PTF depletion (Kruskal-Wallis analysis of variance; day 1, p=0.02; day 2, p=0.007). In some subjects, lens movement and PTF status co-varied throughout the lens wearing periods. These findings suggest the PTF is a determinant of hydrogel lens movement.

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.