Tear-film evaporation flux and its relationship to tear properties in symptomatic and asymptomatic soft-contact-lens wearers

PURPOSE

With soft-contact-lens wear, evaporation of the pre-lens tear film affects the osmolarity of the post-lens tear film and this can introduce a hyperosmotic environment at the corneal epithelium, leading to discomfort. The purposes of the study are to ascertain whether there are differences in evaporation flux (i.e., the evaporation rate per unit area) between symptomatic and asymptomatic soft-contact-lens wearers, to assess the repeatability of a flow evaporimeter, and to assess the relationship between evaporation fluxes, tear properties, and environmental conditions.

METHODS

Closed-chamber evaporimeters commonly used in ocular-surface research do not control relative humidity and airflow, and, therefore, misestimate the actual tear-evaporation flux. A recently developed flow evaporimeter overcomes these limitations and was used to measure accurate in-vivo tear-evaporation fluxes with and without soft-contact-lens wear for symptomatic and asymptomatic habitual contact-lens wearers. Concomitantly, lipid-layer thickness, ocular-surface-temperature decline rate (i.e., °C/s), non-invasive tear break-up time, tear-meniscus height, Schirmer tear test, and environmental conditions were measured in a 5 visit study.

RESULTS

Twenty-one symptomatic and 21 asymptomatic soft-contact-lens wearers completed the study. A thicker lipid layer was associated with slower evaporation flux (p < 0.001); higher evaporation flux was associated with faster tear breakup irrespective of lens wear (p = 0.006). Higher evaporation flux was also associated with faster ocular-surface-temperature decline rate (p < 0.001). Symptomatic lens wearers exhibited higher evaporation flux than did asymptomatic lens wearers, however, the results did not reach statistical significance (p = 0.053). Evaporation flux with lens wear was higher than without lens wear but was also not statistically significant (p = 0.110).

CONCLUSIONS

The repeatability of the Berkeley flow evaporimeter, associations between tear characteristics and evaporation flux, sample-size estimates, and near statistical significance in tear-evaporation flux between symptomatic and asymptomatic lens wearers all suggest that with sufficient sample sizes, the flow evaporimeter is a viable research tool to understand soft-contact-lens wear comfort.

Quantifying Meibomian Gland Morphology Using Artificial Intelligence

SIGNIFICANCE

Quantifying meibomian gland morphology from meibography images is used for the diagnosis, treatment, and management of meibomian gland dysfunction in clinics. A novel and automated method is described for quantifying meibomian gland morphology from meibography images.

PURPOSE

Meibomian gland morphological abnormality is a common clinical sign of meibomian gland dysfunction, yet there exist no automated methods that provide standard quantifications of morphological features for individual glands. This study introduces an automated artificial intelligence approach to segmenting individual meibomian gland regions in infrared meibography images and analyzing their morphological features.

METHODS

A total of 1443 meibography images were collected and annotated. The dataset was then divided into development and evaluation sets. The development set was used to train and tune deep learning models for segmenting glands and identifying ghost glands from images, whereas the evaluation set was used to evaluate the performance of the model. The gland segmentations were further used to analyze individual gland features, including gland local contrast, length, width, and tortuosity.

RESULTS

A total of 1039 meibography images (including 486 upper and 553 lower eyelids) were used for training and tuning the deep learning model, whereas the remaining 404 images (including 203 upper and 201 lower eyelids) were used for evaluations. The algorithm on average achieved 63% mean intersection over union in segmenting glands, and 84.4% sensitivity and 71.7% specificity in identifying ghost glands. Morphological features of each gland were also fed to a support vector machine for analyzing their associations with ghost glands. Analysis of model coefficients indicated that low gland local contrast was the primary indicator for ghost glands.

CONCLUSIONS

The proposed approach can automatically segment individual meibomian glands in infrared meibography images, identify ghost glands, and quantitatively analyze gland morphological features.

Ocular surface cooling rate associated with tear film characteristics and the maximum interblink period

The surface of the human eye is covered with a protective tear film that refreshes with each blink. Natural blinking occurs involuntarily, but one can also voluntarily blink or refrain from blinking. The maximum time one can refrain from blinking until the onset of discomfort is the maximum interblink period (MIBP). During the interblink period the tear film evaporates and thins from the ocular surface. Infrared thermography provides a non-invasive measure of the ocular surface temperature (OST). Due to evaporation, ocular surface cooling (OSC) generally occurs when the eyes are open and exposed to the environment. The purpose of our study was to investigate the effect of OSC rate on the MIBP, and to investigate the association of the MIBP with tear film characteristics in subjects who do and do not exhibit OSC. The MIBP was measured simultaneously with OST over time. Non-invasive tear breakup time, tear meniscus height, tear lipid layer thickness, and Schirmer I test strip wetted lengths were measured on a day prior to the thermography visit. Subjects were divided into cooling and non-cooling groups based on OSC rate, and demographic and tear film characteristics were tested for inter-group differences. A faster OSC rate was associated with an exponentially shorter duration of the MIBP overall and within the cooling group alone. Faster non-invasive tear breakup time was significantly associated with a shorter MIBP in both groups. These results suggest that tear film evaporation initiates a pathway that results in the onset of ocular discomfort and the stimulus to blinking. The presence of a subset of subjects with no or minimal OSC who nevertheless have a short MIBP indicates that evaporative cooling is not the only mechanism responsible for the onset of ocular discomfort.

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

Purpose

To 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.

Methods

667 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).

Results

Pre-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.

Conclusions

Despite 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.

Human Lacrimal Production Rate and Wetted Length of Modified Schirmer's Tear Test Strips

Purpose

To assess and compare the wetting kinetics of sheathed and unsheathed Schirmer's tear test (STT) strips, and to determine the repeatability of 5-minute wetted length (WL) and basal tear production rate (BTPR).

Methods

Seventeen subjects underwent two sheathed and unsheathed STTs each for both eyes on four visits on separate days. After administration of topical anesthetic, WLs were measured every 30 seconds for 5 minutes, and BTPRs were calculated for sheathed strips. Limits of agreement (LoA), difference-versus-mean plots (DVM), and the coefficient of repeatability (CR) assessed WL and BTPR repeatabilities. Variance estimates were used to calculate sample sizes for future study.

Results

For the unsheathed STT, the mean (SD) difference in WLs between visits was 0.74 (5.05) mm, LoA were [−9.17, 10.64], and CR was 9.17 mm; for the sheathed STT, the mean (SD) intervisit difference was 0.16 (5.94) mm, LoA were [−11.49, 11.8], and CR was 10.53 mm. Eight of 48 sheathed STTs and 20 of 44 unsheathed STTs showed constant WL for the final 90 seconds of the test. The mean (SD) difference between repeated visits for BTPR was approximately 0.0 μL/min, LoA were [−1.82, 1.82], and CR was 1.91 μL/min.

Conclusions

Repeatability of sheathed and unsheathed 5-minute WL and BTPR is inadequate for measuring within-subject changes, but is sufficient for group studies with moderate sample sizes. Constant WL for the final 90 seconds with the eight sheathed STT measurements suggests varying BTPR, whereas constant WL with the unsheathed STT can be explained by balancing evaporation and BTPR.

Translational Relevance

Repeatability of the modified STT is evaluated clinically to establish quantitative BTPRs rather than inference from a strip WL.

Effects of corneoscleral topography on soft contact lens performance: A pilot study

To quantify corneoscleral junction (CSJ) topography in soft contact lens (SCL) wearers, and assess the association between the CSJ and SCL performance and subjective comfort, forty-four adapted SCL wearers (16 Asians, 16 Caucasians, 12 Latinos) were recruited for the present study. Corneal topography was taken with a Medmont E300 (Medmont International, Pty Ltd.). CSJ images were taken with a commercial OCT (Bioptigen, Inc.). Our published CSJ image analysis technique was used to describe the geometric properties of the CSJ using the sum of squared orthogonalized residuals (SSRo). Multivariable mixed effects models were employed to examine associations between SSRo and subject demographics, ocular characteristics, SCL fit and performance, and comfort. The SSRo was significantly related to quadrant (p < 0.001), ethnicity (p = 0.014), and horizontal corneal shape factor (p = 0.044). The nasal quadrant had the largest SSRo, indicating the steepest CSJ profile and/or the most irregular CSJ surface, followed by the inferior quadrant. The superior and temporal quadrants had the smallest SSRo, indicating relatively flat and even CSJ topography. Caucasians had the steepest and/or most irregular CSJ compared with Latinos and Asians. Less inferior-superior heterogeneity in the SSRo was associated with greater comfort after 6 h of lens wear. The SSRo was proved to be a useful tool to quantify CSJ geometry in SCL wearers. Significant differences in the SSRo were found among quadrants and ethnic groups. Better subjective comfort after 6 h of SCL wear was associated with a smaller difference in the SSRo between the superior and inferior quadrants.

The Berkeley Dry Eye Flow Chart: A fast, functional screening instrument for contact lens-induced dryness

PURPOSE

In this article, we introduce a novel flow chart-based screening tool for the categorization of contact lens-induced dryness (CLIDE) and its impact on daily visual activities: the Berkeley Dry Eye Flow Chart (DEFC).

METHODS

One hundred thirty (130) experienced soft contact lens wearers discontinued lens wear for 24 hrs, passed a baseline screening and eye health examination, completed the Ocular Surface Disease Index (OSDI) then were dispensed fresh pairs of their habitual lenses. After 6 hrs of wear, subjects were administered a battery of symptom questionnaires, and underwent non-invasive tear breakup time (NITBUT) measurement, grading of distortion in reflected topographer mires, grading of lens surface wettability, and a fluorescein examination of the ocular surface. Subjects returned after at least 48 hrs and repeated all assessments after 6 hrs of wear of a second fresh pair of habitual lenses.

RESULTS

The repeatability of the DEFC between visits was within 1%, and Limits of Agreement and Coefficient of Repeatability were comparable to those of the other CLIDE assessments. Higher DEFC score was significantly related to shorter pre-lens NITBUT, higher OSDI score, and higher Visual Analog Scale (VAS) ratings of average and end-of-day severity and frequency of dryness (all p < 0.001). For CLIDE as diagnosed based on DEFC score, the highest sensitivities and specificities were achieved by the OSDI and VAS ratings; pre-lens NITBUT exhibited good sensitivity but poor specificity. The optimum pre-lens NITBUT diagnostic threshold was found to be ≤ 2.0 sec for debilitating CLIDE, and the OSDI threshold was ≥ 11.4.

CONCLUSIONS

The DEFC provides a means of quickly categorizing CLIDE patients based on severity and frequency of symptoms, and on the degree to which symptoms impact daily life. The DEFC has several potential advantages as a CLIDE screening and monitoring tool, has good repeatability, and is significantly related to commonly employed clinical assessments for CLIDE.

Understanding Ocular Discomfort and Dryness Using the Pain Sensitivity Questionnaire

PURPOSE

To utilize the Pain Sensitivity Questionnaire (PSQ) to assess the influence of pain sensitivity on perceptions of ocular discomfort and dryness.

METHODS

Subjects completed a battery of questionnaires, including history of ocular and general health, contact lens wear history, the Ocular Surface Disease Index (OSDI) questionnaire, visual analog scale (VAS) 100-point rating scales to assess severity and frequency of average and end of day (EOD) discomfort and dryness, and the PSQ to assess pain sensitivity level. Masked subjects were then instructed to wear one inverted and one normally oriented soft contact lens contralaterally for 30 minutes to induce an inter-eye difference in comfort and dryness sensations. Subjects rated comfort and dryness in each eye on VAS every 5 minutes during contact lens wear. A slit lamp examination was performed to evaluate ocular surface health and to assess contact lens fit.

RESULTS

One hundred and fifty-three subjects (111 females, 42 males) completed the study. In separate models, a higher PSQ score was significantly associated with higher OSDI score (p = 0.002), lower average and EOD comfort (p = 0.005 and 0.001, respectively), and greater EOD dryness (p = 0.04). The minimum (0.14) and maximum (7.14) PSQ scores observed in our subject cohort (i.e., from the subjects who were the least and most sensitive to pain, respectively) corresponded to an estimated difference of 11 points on the OSDI, 20 points on the VAS scale for average comfort, 31 points for EOD comfort and 17 points for EOD dryness. In a mixed effects model, a higher PSQ score was significantly associated with a greater inter-eye difference in comfort (p = 0.013) and dryness (p = 0.010) during CL wear.

CONCLUSIONS

Pain sensitivity influences perceptions of ocular discomfort and dryness, and should be taken into account when evaluating subjective assessments of these symptoms.

Contact lens care solutions: a pilot study of ethnic differences in clinical signs and symptoms

OBJECTIVES

To determine whether Asian and white subjects differ in clinical signs or subjective symptoms in response to the use of different biguanide-preserved contact lens care solutions.

METHODS

Forty-two subjects (15 Asian and 27 white) wearing lotrafilcon B silicone hydrogel contact lenses used a preservative-free lens care solution bilaterally for 2 weeks, then used two biguanide-preserved solutions (solution 1: ReNu MPS; solution 2: AQuify MPS) contralaterally in randomly assigned eyes for 4 weeks. Comprehensive ocular surface examinations were performed and symptomatology questionnaires were administered every 2 weeks. Investigators were masked as to solution assignment during examinations, whereas subjects were not to avoid potential difficulties in compliance with the protocol.

RESULTS

With solution 1, most Asian and white subjects had grade 2 or greater corneal staining after 2 weeks (67% and 59%, respectively) and 4 weeks (60% and 67%, respectively). With solution 2, grade 2 or greater corneal staining occurred in 40% of Asians after 2 weeks and in 13% after 4 weeks, but in only 4% of whites after 2 weeks and 0% after 4 weeks. Whites reported significantly better average comfort (P=0.046) and less dryness (P<0.001) than did Asians.

CONCLUSIONS

Asians and whites differ in both ocular response to the use of contact lens care solutions and in reporting subjective symptoms. Racial and ethnic differences should be considered when evaluating and treating contact lens patients in a clinical setting.

Ethnic differences in dry eye symptoms: effects of corneal staining and length of contact lens wear

PURPOSE

To explore the relationships among length of contact lens (CL) wear, degree of corneal staining and severity of dryness symptoms, and to determine whether these relationships differ between Asians and non-Asians.

METHODS

Adapted soft CL wearers (n=395; 180 Asian, 215 non-Asian) were required to discontinue CL wear for at least 24h and report to the University of California, Berkeley Clinical Research Center (UCB-CRC). Fluorescein corneal staining was graded according to Brien Holden Vision Institute scales. Length of CL wear was reported by subjects and subjective dryness ratings were collected using the UCB-CRC Dry Eye Flow Chart (DEFC).

RESULTS

More Asian CL wearers exhibited corneal staining compared to non-Asians, and Asian CL wearers had a higher mean grade of corneal staining (p<0.001), as well as a higher mean DEFC classification (p<0.001). The difference between Asians and non-Asians in grades of corneal staining extent and depth were significant (p<0.001). Among non-Asian CL wearers, dryness symptoms decreased with more years of CL wear and increased in the presence of corneal staining, which was not the case for Asian CL wearers.

CONCLUSIONS

Asian soft CL wearers reported more severe dryness symptoms and demonstrated more severe corneal staining overall compared to non-Asians. Among non-Asians, dryness symptoms were less severe on average with increased years of CL wear and more severe in the presence of corneal staining. Dryness severity does not appear to be related to years of CL wear or corneal staining among Asians.

Corneal epithelial permeability: ethnic differences between Asians and non-Asians

PURPOSE

To ascertain whether a difference in the permeability of the corneal epithelium to fluorescein (Pdc) exists between Asians and non-Asians.

METHODS

From a multi-study database we extracted 632 records of baseline, open-eye Pdc measurements taken on both eyes of 176 subjects. Subjects were awake for a minimum of 4h before measurement, and were free of ocular disease and central corneal staining. Pdc was transformed by natural logarithm to better approximate normality for statistical tests.

RESULTS

The mean ln(Pdc) in the Asian group was significantly greater than in the non-Asian group [-2.34 ln(nm/s) vs. -2.58 ln(nm/s); p<0.001].

CONCLUSIONS

Compared with non-Asians, Asians exhibited a less negative ln(Pdc), which translates to a higher Pdc and a more permeable corneal epithelium. We speculate that this may be related to anatomic differences responsible for greater eyelid tension in Asians.

Rapid screening of tissue microarrays for Her-2 FISH testing is a safe, accurate, efficient and economic method enabling provision of an entirely FISH-based Her-2 testing service

Abstract #2070

Introduction: FISH (fluorescence in situ hybridisation) testing is the gold standard method for Her-2 status assessment in breast cancer yet is only employed in about 30% of tests carried out partly due to cost and labour considerations. Previously we described TMA-based (tissue microarray) testing1 to reducing cost constraints and now describe a rapid screening approach to eliminate unequivocally negative and positive cases and reduce time spent testing.&#x2028; Materials and methods: We examined TMAs (6 cores per case) from 89 cases of invasive breast cancer comparing formal FISH scoring with a rapid screening method using systematic examination of the entire core at x100 magnification without formal counting. Each core was screened by two observers and results recorded for each core as positive (P), equivocal (E) or negative (N). Formal counting and rapid screening methods were timed.&#x2028; Results: The results are given in Table 1. Where both observers agreed that every core in a particular case was negative (43 cases) or positive (10 cases) the predictive value was 100%. The three “Mixed” Groups were constituted as follows: (1) a predominance of positive observations, (2) a predominance of negative observations and (3) a predominance of equivocal observations. Comparison of the FISH scores for the five observational groups using Student's T Test showed significant or highly significant differences (Range: p=0.02-p=0.0001). Screening each 6 TMA core case at x100 magnification took 2 minutes and formal counting of each case took 12 minutes.&#x2028; &#x2028; Conclusion: Using stringent criteria we show that rapid screening of TMAs for routine Her-2 FISH testing provides a safe, economical and time-efficient method for the assessment of Her-2 status in breast cancer. The technique ensures that all patients receive gold standard testing. 65% of Her-2 negative cases can be rapid screened and eliminated from formal counting with 100% confidence. Unanimous positive cases can also be appropriately categorised. The remaining cases require formal counting which takes no longer than is normally the case with whole section techniques. The TMAs also provide a valuable resource for future analyses.&#x2028; Reference: 1. Graham AD, Faratian D, Rae F, Thomas J St J. Tissue microarray technology in the routine assessment of Her-2 status in invasive breast cancer: a prospective study of the use of immunohistochemistry and fluorescence in situ hybridization. Histopathology 2008; 52: 847-855.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2070.

Impact of rigid gas-permeable contact lens extended wear on corneal epithelial barrier function

PURPOSE

To measure the effect of hypoxia and eye closure on epithelial permeability to fluorescein (P(dc)) during rigid lens extended wear (EW).

METHODS

Central corneal thickness (CT) and P(dc) were measured in 42 subjects with an optical pachometer and automated scanning fluorophotometer, respectively. All subjects had been successfully wearing rigid gas-permeable (RGP) lenses on a 6-night EW regimen, and each individual was randomized to wear either medium- or high-oxygen-permeable (Dk) RGP lenses (two types of siloxane-fluorocarbon polymer lenses with Dk of 49 and 92). CT and P(dc) measurements were performed at an afternoon visit (baseline) and were repeated in the morning after 8 hours of overnight wear. Subjects slept with a patch over the right eye. The patch was not removed until immediately before the morning measurement.

RESULTS

The mean overnight swelling response for subjects in the medium-Dk group was greater than that in the high-Dk group. Results of a paired t-test indicate that the eye wearing the medium-Dk lens with a patch overnight had a significant increase in epithelial permeability. Results of mixed-effect models suggest that eye closure and lens-induced hypoxia are significant factors in altering P(dc).

CONCLUSIONS

The results indicate that corneal epithelial permeability increases with hypoxic dose and that epithelial barrier function is impaired by overnight rigid lens wear.

Predicting extended wear complications from overnight corneal swelling

PURPOSE

To examine the hypothesis that the corneal overnight swelling response (ONSR) is a predictor of ocular complications in contact lens extended wear (EW).

METHODS

The Berkeley Contact Lens Extended Wear Study (CLEWS) was a randomized, concurrently controlled clinical trial in which more than 200 subjects in EW with rigid gas-permeable (RGP) lenses were observed for 1 year. After adapting to EW, subjects were randomized to either medium or high oxygen-permeable (Dk) RGP lenses and underwent clinical assessments, keratometry, and corneal pachometry at 3-month intervals.

RESULTS

The ONSR was directly related to lens Dk (P = 0.01) and exhibited substantial variability across subjects. The probability of remaining free of complications over time was not significantly lower for subjects with a mild ONSR compared with those with greater edema (P = 0.84). The risk of development of keratopathy was not significantly related to the ONSR (relative risk = 1.00).

CONCLUSIONS

The corneal ONSR is not a good predictor of ocular complications in 1 year of RGP EW. Lenses that cause little or no corneal edema are not necessarily safer for overnight wear.

The Berkeley Contact Lens Extended Wear Study. Part I : Study design and conduct

OBJECTIVE

The primary aim of the Berkeley Contact Lens Extended Wear Study (CLEWS) was to test the hypotheses that extended wear of rigid gas-permeable (RGP) contact lenses with greater oxygen permeability (Dk) reduces the incidence of contact lens-associated keratopathy (CLAK) and increases the survival rate in RGP extended wear (EW). In this article we describe the clinical trial design in detail, present the results of subject recruitment and retention, and provide the baseline demographic and ocular characteristics of the CLEWS subjects, whose data will be analyzed to address the study aims in a companion article.

DESIGN

A randomized, concurrently controlled clinical trial.

INTERVENTION

Subjects were fitted with day wear (DW) high-Dk RGP lenses and then adapted to EW. Subjects who adapted to EW were then randomly assigned to either high- or medium-Dk RGP lenses for 12 months of 6-nights/week EW.

MAIN OUTCOME MEASURES

Slit-lamp assessment and grading of 17 possible keratopathies, measurement of refractive error and corneal curvature, and symptoms. Follow-up data were collected every 3 months.

RESULTS

From 545 subjects entering the DW adaptation phase, 201 adapted to EW and were randomly assigned to medium- or high-Dk lenses for 12 months of EW. The baseline characteristics of the two study groups were similar and did not differ from the 344 DW subjects who failed to adapt to EW. The distributions of oxygen transmissibility for the two study groups were disjoint, indicating that each group received distinctly different levels of hypoxia.

CONCLUSIONS

We show that CLEWS was appropriately designed to address the study hypotheses, was conducted with regard for the safety of the subjects, and adhered to rigorous protocols designed to control for bias and ensure the integrity of study data. We establish the internal validity of between-group statistical comparisons and characterize our study population to permit informed evaluation of the applicability of our results to the contact lens-wearing population in general.

The Berkeley Contact Lens Extended Wear Study. Part II : Clinical results

OBJECTIVE

To describe the principal clinical outcomes associated with 12 months use of rigid gas-permeable (RGP) extended wear contact lenses and address two primary study questions: (1) does extended wear (EW) of high oxygen transmissibility (Dk/t) RGP lenses reduce the incidence of ocular complications, and (2) does the wearing of high-Dk/t lenses reduce the rate of failure to maintain 6-night RGPEW over 12 months?

DESIGN

A randomized, concurrently controlled clinical trial.

INTERVENTION

Subjects who adapted to EW with high Dk (oxygen permeability) RGP lenses were randomized to either high Dk or medium-Dk RGP lenses for 12 months of 6-night EW.

MAIN OUTCOME MEASURES

Contact lens-associated keratopathies (CLAK), changes in refractive error and corneal curvature, and survival in EW.

RESULTS

Two hundred one subjects were randomized to medium or high-Dk lenses for 12 months of EW. Sixty-two percent of the subjects in each group completed 12 months of EW; however, the probability of failure was significantly greater for the medium-Dk group. Although the risk of complications was similar for the two groups, the number of CLAK events that led to termination were 16 versus 5 for the medium-Dk and high-Dk groups, respectively. This suggests that the type of adverse response or the inability to reverse an adverse event was different for the group being exposed to the lower oxygen dose.

CONCLUSIONS

The level of oxygen available to the cornea has a significant impact on maintaining successful RGP extended contact lens wear, but not on the initial onset of CLAK. The number of clinical events leading to termination was substantially higher for the medium Dk group, which suggests that corneal hypoxia is an important factor in the development of CLAK. Although overnight contact lens wear should be recommended with caution and carefully monitored for early detection of ocular complications, it appears that high-Dk RGP lenses can be a safe and effective treatment for correction of refractive error for most individuals who can adapt to EW.

The effects of one-hour wear of high-Dk soft contact lenses on corneal pH and epithelial permeability

PURPOSE

Previous studies have shown that 1-hour closed-eye contact lens wear with a low-Dk lens causes a significant reduction in corneal pH and an increase in epithelial permeability. In the present study, we evaluated the effects of super-high-Dk/t soft lenses on corneal epithelial barrier function and stromal pH.

METHODS

Corneal thickness was measured by optical pachometry, while epithelial permeability and stromal pH were measured by fluorophotometry. A paired-eye design was used in which one eye was randomly allocated to wear a high-oxygen-permeable soft lens (CIBAVision Focus/NIGHT & DAY (Dk/t= 175) while the other eye did not wear a lens.

RESULTS

After 1-hour closed-eye lens wear, neither the difference in corneal swelling (P = 0.206) nor the permeability (P = 0.055) between both eyes was significantly different. The mean pH values under open-eye conditions were 7.66 vs. 7.57 for the treatment and control eyes, respectively (P = 0.082), dropping to 7.27 vs. 7.25 after 1-hour eye closure (P = 0.283).

CONCLUSIONS

Although our results are limited to a 1-hour observation period, they do provide evidence that high-Dk materials may eliminate corneal acidosis and reduced epithelial barrier function that accompany closed-eye contact lens wear with lower-Dk soft lens materials.

Does head positioning influence anterior chamber depth in pseudoexfoliation syndrome?

PURPOSE

Phacodonesis can occur in pseudoexfoliation syndrome because of impaired zonular support. This study investigates whether the increased mobility of the lens influences anterior chamber depth in patients with pseudoexfoliation while assuming a prone position.

METHODS

Central anterior chamber depth was measured in 39 patients with clinically apparent unilateral pseudoexfoliation and elevated intraocular pressure. Patients were placed in a face-up position for 5 minutes, at which time anterior chamber depth and axial length were measured by A scan, and intraocular pressure was measured by Tonopen (Oculab, La Jolla, CA) in both eyes. The measurements were repeated on both eyes after 5 minutes in a face-down position.

RESULTS

No significant differences in intraocular pressure or axial length between the prone and supine positions were found in either eye. Anterior chamber depth in eyes with pseudoexfoliation decreased from a mean of 3.08 mm in the supine position to a mean of 2.95 mm in the prone position, whereas mean anterior chamber depth in the fellow eyes decreased from 3.01 mm to 2.97 mm. The decrease in anterior chamber depth when facing down in the eyes with pseudoexfoliation was significantly greater than in the fellow eyes.

CONCLUSIONS

In patients with clinically apparent unilateral pseudoexfoliation, the lens seems to be more mobile in the affected eye. This results in a shallower anterior chamber when the head is placed in a prone position. Whether this fact might potentially lead to transient pupillary block when engaging in activities such as facing down while reading warrants further study.

Measurement of post-lens tear thickness

PURPOSE

A method to measure the tear film beneath a soft contact lens, referred to as post-lens tear thickness (PLTT), would have many applications to contact lens research. In this study a noninvasive technique for measuring the PLTT is presented.

METHODS

The feasibility of measuring the tear layer by optical pachometry was first assessed using a model eye. The baseline corneal thickness (B) of both eyes of 21 subjects was measured, etafilcon-A ionic disposable soft contact lenses (58% water) were inserted, and the total thickness (T) of the cornea, contact lens, and PLTT were measured. After the pachometry readings the lenses were removed and their center thickness (C) determined. The PLTT was calculated using the equation: PLTT = T-(B+C). Two sets of measurements of T were performed at 15 and 25 minutes after lens insertion. The entire procedure was repeated at a second visit.

RESULTS

The pachometry measurements of the small aqueous reservoir between the model eye and the lens closely matched those obtained by direct microscopic measurement. For human PLTT, the mean values (and 95% confidence intervals) for right eyes on visits 1 and 2 were 11 (8, 13) and 12 (10, 15) microm, respectively, and for left eyes were 12 (10, 15) and 11 microm (8, 14) microm, respectively.

CONCLUSIONS

It is possible to measure the post-lens tear thickness using optical pachometry. The variability between repeated measurements suggests that with careful sample size planning, the technique is sufficiently precise to be useful in group assessments of PLTT.

Saccades reduce latency and increase velocity of ocular accommodation

Horizontal vergence can be stimulated binocularly with disparity (disparity vergence) or monocularly with accommodation (accommodative vergence). The latter results from a neural cross-coupling that causes both horizontal vergence and accommodation to respond when either one is stimulated [Alpern, M., & Ellen, P. (1956). American Journal of Ophthalmology, 42, 289-303]. The velocity of disparity and accommodative vergence is enhanced when accompanied by saccades [Enright, J. T. (1984). Journal of Physiology (London) 350, 9-31; Enright, J. T. (1986). Journal of Physiology (London) 371, 69-89]. Based upon the coupling between accommodation and vergence, we predicted that accommodation should also be facilitated by saccades. An SRI Dual Purkinje Eyetracker was used to measure left and right eye position, and the accommodation of the left eye, in response to stimulation. Horizontal saccades were stimulated by targets separated by 2-6 degrees and accommodation was stimulated monocularly over a range of +/- 2 diopters (D). When saccades occurred within 0-400 ms following a monocular step stimulus to accommodation, latency of accommodation decreased and the associated accommodative-vergence response was synchronized with the saccade. Saccades also enhanced the velocity of accommodation and accommodative-vergence, and this facilitation increased with saccade amplitude. Transient vergence responses that are normally associated with saccades [Erkelens, C. J., Steinman, R. M., & Collewijn, H. (1989). Proceedings of the Royal Society of London B. Biological Sciences, 236, 441-465; Maxwell, J. S., & King, W. M. (1992). Journal of Neurophysiology, 68 (4), 1248-1260] did not affect accommodation when it was not stimulated by defocus. Because saccades and accommodation utilize separate plants and final common pathways, the synchronization of saccades and accommodation and the enhanced velocity of accommodation and accommodative-vergence must occur at more central sites. Possibilities include the superior colliculus, which represents both accommodation and saccades [Nagasaka, Y., & Ohtsuka, K., (1998). Investigative Ophthalmology AVRO supplement], vestibular nuclei which project to regions near the oculomotor nuclei [Lang, W., Buttner-Ennever, J. A., & Buttner, U. (1979). Brain Research, 177, 3-17], and interactions between omni pause neurons and near response cells of the mesencephalic reticular formation (MRF) [Mays, L. E., & Gamlin, P. D. R. (1995a). Current Opinions in Neurobiology, 5, 763-768; Mays, L. E., & Gamlin, P. D. R. (1995b). Eye movement research: Mechanisms, processes and applications. New York: Elsevier] which represent both accommodation and vergence [Judge, S. J., & Cumming, B. G. (1986). Journal of Neurophysiology, 55, 915-930; Zhang, Y., Mays, L. E., & Gamli, P. D. R. (1992). Journal of Neurophysiology, 67, 944-960].

Predicting RGP daily wear success

PURPOSE

While most clinicians agree that fitting of rigid gas permeable (RGP) lenses is the preferred treatment strategy for some types of patients, many patients have difficulty adapting to full-time daily wear of these lenses. The Contact Lens Extended Wear Study (CLEWS) is a randomized, controlled clinical trial in which subjects are first adapted to full-time RGP daily wear prior to randomization to either high or medium oxygen transmissibility (Dk/L) RGP lenses for 12 months of extended wear. The CLEWS pre-randomization data provide an opportunity to examine the reasons some patients fail to adapt to RGP daily wear and to determine whether a patient's demographic, historical, and ocular characteristics can be used to predict RGP daily wear success.

METHODS

From 1,809 individuals who expressed interest in RGP lenses, 411 subjects passed the CLEWS screening criteria and were fit with high Dk lenses (mean Dk = 92 x 10(-11) [cm2/sec][mL 02/mL x mmHg]). The fitting strategy included minimum apical alignment, lid attachment, centration, and average lens diameters of 9.2 mm. Success was defined as a minimum of 14 hours per day without adverse ocular responses that would contraindicate either full-day daily wear or extended wear.

RESULTS

Of the 411 subjects, 286 (69.6%) were successful with RGP extended wear. Among the 125 failures, 50 were based on clinician findings (e.g., cornea, vision, compliance), while 75 subjects chose to discontinue wear because of unacceptable comfort or poor vision. Multivariate linear logistic regression modeling shows that younger patients with greater corneal curvature (K) and less predicted residual astigmatism have a higher probability of RGP daily wear success.

CONCLUSIONS

Our study showed that RGP lenses can be fit with a relatively high rate of success and that many of those patients who elect to discontinue RGP daily wear report unacceptable comfort as the primary reason. We propose a Bayesian statistical method that will assist clinicians in selecting those candidates for RGP daily wear who are most likely to adapt successfully.

Tear mixing under a soft contact lens: effects of lens diameter

PURPOSE

Tear exchange under a soft contact lens is modest, and higher exchange rates may be necessary to reduce extended-wear complications; what is not known is the optimal soft lens design to increase tear mixing. We explored the effect of lens diameter on tear mixing.

METHODS

Twenty-three subjects wore four different soft contact lenses with diameters of 12.0, 12.5, 13.0, and 13.5 mm. Tear mixing was quantified by placing fluorescein isothiocyanate-dextran on the posterior lens surface, inserting the lens, and monitoring the changes in fluorescence intensity in the postlens tear film. Tear mixing, expressed as the percentage decrease in fluorescence intensity per blink, was estimated using an exponential model. Lens movement was videotaped and lens comfort was graded on a 50-point scale (50 = excellent comfort). Subjects reporting a comfort level of less than 35 were excluded.

RESULTS

The mean +/- SE tear mixing rates were 1.82% +/- 0.17%, 1.61% +/- 0.16%, 1.34% +/- 0.17%, and 1.24% +/- 0.17% per blink for the 12.0-, 12.5-, 13.0-, and 13.5-mm diameter lenses, respectively. By regression analysis we found that, on average, mixing under the 12.0-mm lens was 0.59% per blink greater than with the 13.5-mm lens (P = .0024). Lens diameter was a significant predictor of lens comfort, and adjusting for the effects of comfort weakened the relationship between diameter and tear replenishment rate, although the mean rate under the 12.0-mm lens was still 0.43% per blink greater than with the 13.5-mm lens (P = .0468).

CONCLUSIONS

These data suggest that smaller-diameter soft lenses provide substantially better tear mixing than larger lenses; however, even small lenses provide modest tear mixing compared with rigid contact lenses.

Angiotensin II infusion increases thoracic duct lymph flow in chronically catheterized sheep

Both pregnancy and estrogen administration are associated with a decrease in the systemic vasculature pressor response to angiotensin II infusion; however, the lymphatic vessel system response is not clear. In the present study we infused angiotensin II to nine nonpregnant splenectomized ewes with 0.1, 10, or 1,000 ng X kg-1 X min-1 for a 5-min period at each dose. At the lowest dose the mean arterial pressure increased from 10 to 20% over base line. At the highest dose, the left thoracic duct flow rate peaked at 361% 10 min after the infusion was started, whereas arterial pressure peaked at 183% of the control value. Peak lymph flow occurred 4-6 min after the maximal increase in mean systemic arterial pressure. Neither hematocrit nor venous pressure were altered at any of the doses administered. This suggests that the interstitial fluid space pressure remained unchanged and that the increase in lymph flow was not secondary to fluid transfer from the intravascular system. We postulate, therefore, that the effect of angiotensin II in the increase of lymph flow rate is by direct action on the lymphatic vessels themselves.

Catecholamine secretion from the adrenal medulla of the fetus, regulation by hormones

In the ovine fetus, the adrenal medulla activity secretes catecholamines into the circulation under normal and stress conditions. Little is known regarding the endocrine regulation of adrenal medullary catecholamine secretion in the fetus. The present study was undertaken to investigate the direct effects of the hormones prolactin, angiotensin II and cortisol on catecholamine release from fetal adrenal medulla, and to determine whether the effect of the hormones change during development into adulthood. Adrenal medulla from fetal, newborn and adult pregnant sheep was collected, dispersed into single cells and plated. Following preincubation, the cells were treated with ovine prolactin or angiotensin II at 8, 40 and 200 micrograms/ml; or cortisol at 10(-8), 10(-7) and 10(-6)M for 24 h. Catecholamine release into the medium were measured at 3, 6, 12 and 24 h. Ovine prolactin at 8 to 200 micrograms/ml significantly stimulated the release of total catecholamines after 12 h of incubation. The effect of prolactin was dose-dependent such that the magnitude of the response increased and the response time shortened with increasing concentrations of prolactin. In addition, the release of all three catecholamines--dopamine, norepinephrine and epinephrine--was significantly elevated. In newborn cells, only the highest concentration of 200 micrograms/ml ovine prolactin stimulated total catecholamine release at 6 h and 12 h, with significant increases of the three catecholamines at 12 h. In maternal cells, stimulation of catecholamine release was observed also with the highest concentration of prolactin tested (200 micrograms/ml) and after 12 h of incubation, when only the release of epinephrine was significantly enhanced by 324%.(ABSTRACT TRUNCATED AT 250 WORDS)

Rectal gunshot wounds. Management of civilian injuries

The diagnosis and operative management of 43 consecutive low velocity wounds of the rectum were evaluated with regard to postoperative morbidity and mortality. Rectal and proctoscopic examinations, although frequently positive (80% and 91%, respectively), were not uniformly reliable in making the preoperative diagnosis. Diversion of the fecal stream by colostomy occupies a key role in operative management. Loop colostomy appears not only as efficacious as end colostomy and mucus fistula, but also requires less time to perform and subsequently close. Distal rectal washout is an important adjunct which reduces the incidence of rectal and intra-abdominal infectious complications. Civilian and military wounds of the rectum appear to differ in terms of the postoperative complications, mortality rate, and management techniques.

Radioisotope-assisted diagnosis of traumatic rupture of the diaphragm

Traumatic rupture of the diaphragm is usually not diagnosed early after injury. We hypothesized that the diagnostic yield could be improved by injecting 50 uC of Tc99m macroaggregated albumin in 300 ml of normal saline solution and using simple scintillation counting. Thirty dogs were divided into four groups, anesthetized, and mechanically ventilated. In all groups, counting was done bilaterally 5 cm from the midline at the sternal notch and at 8, 16, 24, 32, 40, 48, and 56 cm below that level immediately and at 10, 20, and 30 min after instillation of the nuclide. In group I, the nuclide was instilled through a left thoracostomy tube, and counting was done with the dogs in reversed Trendelenberg position. In group II, blunt diaphragmatic rupture was simulated before instillation of the nuclide, and counting was done as in group I. In group III, the nuclide was instilled through a standard peritoneal lavage catheter, and counting was done with the dogs in Trendelenberg position. In group IV, blunt diaphragmatic rupture was simulated, nuclide was instilled, and counting was done as in group III. In each dog, there was no significant difference in the counts per minute (cpm) taken immediately and at 10, 20, and 30 min after instillation. In group I, radioactivity was concentrated in the areas adjacent to the diaphragm. In group II, radioactivity was concentrated at the sites lowest in the abdomen where the mean cpm differed significantly (p = .034) from group I.(ABSTRACT TRUNCATED AT 250 WORDS)

Polycistronic mRNAs code for polypeptides of the Vibrio harveyi luminescence system

DNA coding for the alpha and beta subunits of Vibrio harveyi luciferase, the luxA and luxB genes, and the adjoining chromosomal regions on both sides of these genes (total of 18 kilobase pairs) was cloned into Escherichia coli. Using labeled DNA coding for the alpha subunit as a hybridization probe, we identified a set of polycistronic mRNAs (2.6, 4, 7, and 8 kilobases) by Northern blotting; the most prominent of these was the one 4 kilobases long. This set of mRNAs was induced during the development of bioluminescence in V. harveyi. Furthermore, the same set of mRNAs was synthesized in E. coli by a recombinant plasmid that contained a 12-kilobase pair length of V. harveyi DNA and expressed the genes for the luciferase subunits. A cloned DNA segment corresponding to the major 4-kilobase mRNA coded for the alpha and beta subunits of luciferase, as well as a 32,000-dalton protein upstream from these genes that could be specifically modified by acyl-coenzyme A and is a component of the bioluminescence system. V. harveyi mRNA that was hybridized to and released from cloned DNA encompassing the luxA and luxB genes was translated in vitro. Luciferase alpha and beta subunits and the 32,000-dalton polypeptide were detected among the products, along with 42,000- and 55,000-dalton polypeptides, which are encoded downstream from the lux genes and are thought to be involved in luminescence.

Diaphragmatic injury: a method for early diagnosis

Traumatic diaphragmatic hernia, whether of blunt or penetrating etiology, is difficult to diagnose in the acute phase. The lesion is presently best diagnosed by chest X-ray, but only occasionally. Chest X-ray appears normal or nonspecific 25 to 50% of the time. For this reason, simple diagnostic technique using radiographic methodology available in emergency rooms was studied in animals in order to devise a way to diagnose this injury. Eight per cent diatrizoate meglumine and diatrizoate sodium (Renografin, Squibb) was placed into the chest or abdomen of animals with either 8-cm simulated blunt or 5-mm simulated penetrating injuries. The Renografin was infused by either a peritoneal lavage or thoracostomy catheter. Serial X-rays showed diagnostic rate of transdiaphragmatic leakage in 24 of 26 animals with blunt injury and seven of 16 animals with penetrating injury. There was no evidence of pleural, peritoneal, or pulmonary injury from the Renografin itself. It was concluded that the experimental technique may prove useful in screening or confirming traumatic diaphragmatic hernia during the acute or latent phases.

Effects of adrenaline and noradrenaline on the heat production of warm- and cold-acclimated sheep

The heat production (HP), heart rate (HR), respiration rate, rumen motility, and body temperature responses to 2.5-h adrenaline (A) and noradrenaline (NA) intrajugular infusions at 0.00, 0.15, 0.30, 0.60, and 0.90 micrograms.kg-1.min-1 were studied in 10 shorn wethers which had been chronically (3-8 weeks) exposed to warm (19-24 degrees C) or moderately cold (8-13 degrees C) temperatures. Heat production, as estimated from respired gas analysis, increased 40-45% with all doses of A and the effect was potentiated by chronic cold exposure. Only the higher dose rates of NA induced an increase in HP. The maximum HP increase due to NA was 30% and the effect was not influenced by chronic cold exposure. Thermoneutral HP was greater by 16-19% in cold-acclimated as compared with warm-acclimated sheep. Corresponding to the HP effects of A and NA, all doses of A and the highest dose of NA resulted in slight increases in rectal temperature. Respiration rate increased with increased dose rate of NA but only the highest dose of a resulted in an increase in respiration rate. HR, rectal temperature, and respiration rate responses to A and NA were not influenced by cold acclimation.