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Biomedical subjects

A S Bruce

Publications and source records attributed to A S Bruce.

At least 19 recordsLinked to original sources
PubMed2001

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.

Biocompatible Materials↗
PubMed2001

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) < 10 s 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.

Administration, Topical↗
PubMed2000

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 patient's 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.

Adult↗
PubMed1998

Morphological variants in keratoconus: anatomical observation or aetiologically significant?

PURPOSE: Two morphological cone variants are identified in keratoconus; nipple and oval. The present study was designed to assess the impact of aetiological factors on cone morphology. METHODS: As part of a prospective controlled study, keratoconic subjects from a suburban practice (n = 89) underwent videokeratograph examination and completed a questionnaire detailing aetiological factors. RESULTS: Comparison of 95% confidence limits (CL; bootstrap method) for apical power between the two cone morphology groups showed no statistical significance. Oval cones were located at a greater eccentricity than nipple cones, as their definitions suggest. Associations between aetiological factors examined and the morphology of the cone were not significant (bootstrapped 95% CL). CONCLUSION: Despite the suggestion of morphological variants in keratoconus, the results of the present study suggest a common cone aetiology.

Age of Onset↗
PubMed1997

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.

Administration, Topical↗
PubMed1996

Lens adherence and postlens tear film changes in closed-eye wear of hydrogel lenses.

BACKGROUND: Lens adherence and a reduced postlens tear film circulation have been suggested as factors contributing to some adverse reactions in extended wear of hydrogel contact lenses. In this study, we determined lens fitting and postlens tear film characteristics during closed-eye wear. METHODS: Twenty subjects wore hydrogel lenses for 3 h of eye closure, followed by 30 min of open-eye wear. Lens movement was measured with a video biomicroscope. Postlens tear film appearances in specular reflection were classified as either amorphous, or as one of four color intensity grades, where a colored appearance was taken as indicative of a depleted postlens tear film. RESULTS: All subjects showed lens adherence (movement < 0.1 mm) and postlens tear film depletion within 45 min of eye closure. These changes were sustained for the remainder of the closed-eye period, but were reversed within 15 min of eye opening. Lens adherence was associated with colored postlens tear film patterns of any intensity. CONCLUSION: Closed-eye wear was invariably associated with the onset of lens adherence and postlens tear film depletion. This finding emphasizes the need for adequate lens movement during the open-eye phase of extended wear.

Adhesiveness↗
PubMed1996

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.

Aged↗
PubMed1995

Soft lens movement: effect of blink rate on lens settling.

Little is understood about the mechanism by which soft lenses settle on the eye, although it has been suggested that lens base curve, steepening with in-eye lens dehydration or tear film changes may influence lens movement in the initial period of wear. In this study, we investigated the role of postlens tear fluid expulsion by assessing lens movement in 20 subjects wearing 38% water content hydrogel lenses for 10 min under three different conditions: 10 blinks/min, 30 blinks/min and eye closure. Over the 10 min wearing period, the total decrease in median lens movement for the 10 blinks/min condition was 0.07 mm, which was not a significant change (Friedman ANOVA, p = 0.13), while significant decreases occurred with conditions of 30 blinks/min (0.19 mm, p = 0.004) and eye closure (0.43 mm, p = 0.0001). As expected, lens movement under the three conditions was the same at insertion, but was significantly higher thereafter for the slower blink rate condition compared to the faster blink rate or eye closure conditions (Wilcoxon test, Z = 2.8 and -3.0, p = 0.006 and 0.003, respectively). Based on these findings, we postulate the model that the extent of lens settling and the degree of postinsertion lens movement are determined by the timeaverage pressure for postlens tear film expulsion exerted on the lens by the eyelids.

Adult↗
PubMed1995

Role of the post-lens tear film in the mechanism of inferior arcuate staining with ultrathin hydrogel lenses.

We studied the depletion of the post-lens tear film as contributing to inferior arcuate staining with ultrathin high water content hydrogel lenses. We monitored the post-lens tear film specular reflection of hydrogel lenses (0.04 mm center thickness, 67% nominal water content), which caused inferior arcuate staining. A standard thickness (0.12 mm) lens was worn in the contralateral eye as a control condition. Lenses were worn for a 2 hour period by 20 subjects. Post-lens tear film appearances were categorized as amorphous, faint colored, or colored, where the colored patterns represented a relatively depleted post-lens tear film. We also measured lens dehydration, lens adherence, and pre-lens tear film stability in order to evaluate their role in inferior arcuate staining. The ultrathin and standard lenses caused staining in 100 and 75% of subjects, respectively; the severity of staining was much greater with the ultrathin lenses (Wilcoxon signed ranks test, P = 0.0004). The ultrathin lenses were associated with a higher incidence of post-lens tear film depletion (P = 0.018), had greater front surface dehydration (P = 0.0004), and were more adherent to the eye (paired t-test, P = 0.001). However, pre-lens tear thinning times were not significantly different between the two lens types (Wilcoxon signed ranks test, P > 0.05). These findings support the contention that post-lens tear film depletion is a component of a lens adherence or lens dehydration mediated mechanism of inferior arcuate staining.

Adult↗
PubMed1995

Osmotic determinants of postlens tear film morphology and hydrogel lens movement.

The determinants of postlens tear film (PTF) composition in hydrogel lens wear are poorly understood, although this layer has important roles in lens movement and corneal integrity. We investigated the hypothesis that the PTF could be depleted by instillation of hypotonic saline, using a randomized, double masked, placebo controlled study design. Solutions of 0.90, 0.60 and 0.45% NaCl were instilled into the eyes of 12 subjects wearing ionic and non-ionic high water content hydrogel lenses. Postlens tear film appearances in specular reflection were categorized as amorphous, faint coloured or coloured, where the coloured patterns represent a progressive thinning of the PTF. With instillation of the hypotonic solutions (0.60 and 0.45% NaCl), the appearance of the PTF in specular reflection changed to a faint coloured or coloured pattern in at least 67% of subjects for each lens type (Friedman ANOVA, P < 0.002). For the 0.45% NaCl solution, median lens movement decreased from 0.50 to 0.10 mm (Friedman ANOVA, P = 0.02); however, there were no significant changes in measured lens parameters and no difference between lens types. Postlens tear film depletion due to a hypotonic shift in tear osmolality, as demonstrated here, may explain the clinically observed phenomenon of lens binding.

Adult↗
PubMed1995

Accommodation-convergence relationships and age.

PURPOSE: The objective of this study was to determine if there are differences in accommodative-convergence/accommodation (AC/A) and convergence-accommodation/convergence (CA/C) ratios in subjects with increasing age. The authors aimed to relate the findings to the present theories of the development of presbyopia. METHODS: Using a Canon AutoRef R-1 to measure accommodation and an IRIS eye movement monitor to measure eye movements, the authors determined objective AC/A and CA/C ratios for 23 subjects between 17 and 42 years of age with normal binocular vision. Changes in accommodation and convergence responses were stimulated by lenses (-1.00 DS and -2.00 DS) and prisms (4 and 8 prism diopters), respectively. Measures were made at two visits on consecutive days. RESULTS: A moderate linear relationship was found between AC/A ratio and age (P < .002), and a strong linear relationship was found between CA/C ratio and age (P < .0001). The decrease in CA/C ratio with age was due to a decreased accommodative response to prisms (P = .0001). Measurements were reliable, with 95% confidence intervals at +/- 1.28 delta/D and +/- 0.02 D/delta for AC/A and CA/C ratios, respectively. A reciprocal relationship existed between the AC/A and CA/C ratios. CONCLUSION: The AC/A ratio increases, and the CA/C ratio decreases, in persons between 20 and 40 years of age. This may be because increasing ciliary muscle contraction is required to produce a given change in accommodation with increasing age or because of changes in the adaptability of the tonic accommodation and vergence systems with age.

Accommodation, Ocular↗
PubMed1994

Comparison of clinical diagnostic tests in hydrogel extended wear.

We compared the relative value of biomicroscopy, pachometry, esthesiometry, and corneal oxygen flux measurements for the detection of corneal hypoxia in myopic patients wearing hydrogel extended wear lenses. Measurements were standardized by relating the change in each parameter to its test-retest reliability. After 3 months of extended wear the greatest change occurred in biomicroscopic signs (microcysts and vacuoles, fluorescein staining, inferior conjunctival hyperemia) and in stromal edema measured with pachometry. These four signs were poorly correlated to each other (Pearson's r < 0.3), indicating that none could be considered redundant. Stromal striae, endothelial edema (blebs), esthesiometry, and corneal oxygen flux measurements showed relatively little change during the period of lens wear.

Contact Lenses, Extended-Wear↗
PubMed1994

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, 31% 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. In-office 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.

Blinking↗
PubMed1994

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.

Adult↗
PubMed1994

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 blinking), and subjects' symptoms were assessed using a questionnaire. Non-amorphous appearances were present in 25% of subjects and occurred approximately 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.

Adolescent↗
PubMed1993

Epithelial, stromal, and endothelial responses to hydrogel extended wear.

Corneal epithelial, stromal, and endothelial edema were assessed in 19 subjects before and after a 4-month period of hydrogel contact lens extended wear. A thick hydrogel lens was worn under closed-eye conditions for 3 hours to induce stromal edema and endothelial edema (blebs), and eye bathing with a hypotonic solution was used to induce epithelial edema. Initial central stromal edema (corneal thickness) was 14.4 +/- 0.6% in response to the stress lens compared with 2.1 +/- 0.4% in the control eye (mean +/- SE). After 4 months of lens extended wear, stromal edema was significantly reduced (P < 0.0001) to 12.3 +/- 0.6% and 0.5 +/- 0.2% in test and control eyes, respectively. Adjustment of the stromal edema response at the second visit for residual edema from the extended wear accounted for some of the reduction, but the edema response remained significantly decreased (stress lens: 13.6 +/- 0.7%; and control eye: 1.2 +/- 0.4%). Endothelial edema response to the stress lens, as measured on a scale of 1 to 7, decreased from 4.6 +/- 0.3 to 2.8 +/- 0.3 over the period of extended wear. The final level was indistinguishable from that of the eye not wearing the stress lens. The epithelial edema response to hypotonic exposure was not altered with extended wear. These findings indicate that the stromal and endothelial edema responses may be unreliable diagnostic signs of the physiologic impact of hydrogel extended wear.

Adult↗
PubMed1991

Esthesiometry as an indicator of corneal health.

We review the literature regarding changes in the structure and function of the cornea as an index of the physiological status of the tissue. Accurate measurement of corneal sensitivity may be the most reliable test of long-term corneal compromise inasmuch as the edema response, the most popular test of corneal physiological integrity, shows "adaptation". Although reduced sensitivity has been associated with corneal hypoxia, decreased corneal pH may also play a major role. Certainly, small departures of pH from normal levels in the body can lead to major depression of neural function. Traditionally, mechanical sensitivity of the cornea has been measured with procedures based on the von Frey hair. More recently, esthesiometry has been performed with the use of a puff of air, a chemical stimulant, and heat. Results from early trials with these procedures are encouraging in terms of the development of a viable clinical method for assessing metabolic effects on the cornea from contact lens wear.

Adaptation, Physiological↗