Bandage soft contact lens barrier function: a clinical research note.

Corneal thickness pre- and post-operatively was measured on 18 volunteer subjects within the context of a clinical investigation of laser refractive surgery. All measurements were taken with regard for time of day, in order to counter any complicating diurnal influence on data accuracy. Of the 18 subjects, six lost or had accidently displaced their overnight bandage soft contact lenses the first night immediately after surgery, and 12 retained theirs. The individuals with lost bandage lenses exhibited uniformly thick, swollen corneas. In contrast, the other 12 subjects, with retained lenses, exhibited a stable corneal thickness map, displaying the characteristic relatively thick periphery that transitions to a thinner central region. Moreover, in the six affected subjects, application of a new overnight bandage lens resulted in recovery of the normal thickness pattern on day 2, as opposed to the uniform swelling or oedema of the previous day. In combination, these findings indicate a fluid barrier function on behalf of the bandage soft contact lenses, which allowed the corneal endothelial pump mechanism to counteract any extreme swelling or fluid accumulation. This previously unreported phenomenon helps explain the historical effectiveness of this treatment regimen for corneal bullous, or excessive fluid-retention, conditions.

Orbscan pachymetry: implications of a repeated measures and diurnal variation analysis.

INTRODUCTION: Corneal thickness changes reflect alterations in hydration and metabolism. Ultrasound pachymetry determinations may be adversely influenced by fluctuations in tissue hydration, whereas optical systems are apparently unaffected by these fluxes. A recently marketed, optical-based, topographic mapping system (Orbscan; Orbtek, Inc.) uses anterior and posterior corneal surface data to calculate corneal thickness. OBJECTIVE: This new instrumentation presents as a potentially useful pachymetry tool for evaluation of corneas under hydration flux or challenge (e.g., postphotorefractive keratectomy [PRK] healing studies) and was therefore evaluated for accuracy and variability. MEASUREMENTS: Three calibrated standards were measured in repeated fashion. Additionally, 1 test subject was measured 30 times in 1 day (5 measurements each at 8:00, 9:30, and 11:00 AM and at 1:00, 2:30, and 4:00 PM). Corresponding measurements were made at 8:00 and 11:00 AM and at 4:00 PM on 3 separate days to assess repeatability. Grouped data from 18 volunteer subjects were compared to the data of the test subject as well. RESULTS: Pachymetry accuracy on a calibrated standard was determined to be +/-2 microm (standard deviation, n = 12). Repeated measures on the subject demonstrated a mean standard deviation of 9.08 microm for 750 thickness data points across the central 7 mm of the cornea; peripheral measurement points exhibited progressively greater variability than at the apex (analysis of variance; P<0.0001). A plot of thickness by corneal location and time of day exhibited a diurnal pattern, with the peripheral cornea exhibiting progressively greater thickness changes than the central cornea (two-way analysis of variance; P<0.00001). The data significantly correlated across days when all times of day were considered (r = 0.999). However, thickness values obtained at 8:00 AM were significantly different across days (t test; P<0.0002). The subject's data correlated very well (r = 0.9996) with the grouped volunteer data. CONCLUSIONS: These data show this system to be useful in corneal research and in clinical settings. The data confirm early morning pachymetry to be highly variable. Additionally, the data not only indicate a diurnal variation of corneal hydration over time, but also imply the presence of a diurnal-based hydration gradient across the peripheral cornea, both of which can have significance for PRK, since excimer tissue ablation effectiveness is influenced by tissue hydration.

A store-forward ophthalmic telemedicine case report from deployed U. S. Army forces in Kuwait.

This telemedicine test was developed to determine the relative ease with which an off-the-shelf ophthalmic telemedicine package could be successfully applied from within a remote theatre of operations. The project was conducted at the Camp Doha Health Clinic, located just outside Kuwait City, during the period from April 12(th) through April 23(rd), 1998. The deployed signal unit had contracted for a direct T-1 commercial satellite link (via MCI), which allowed for direct internet connectivity using a PCMCIA network card. Digital images were sent via this connection to 140 e-mail sites throughout the world, including an unsolicited image to each of 134 Army optometry officers for their review, analysis, and diagnosis. Return responses to this unsolicited survey were 53 out of 134, for a 39.7% response rate. Half of the respondents were able to view the image with ease and clarity, rendering an accurate clinical diagnosis. The other half of the respondents either did not have the software to display an image on their clinical desktop PC, or did not know how to use their provided software. This project clearly indicates that an off-the-shelf ophthalmic digital system can be successfully used from a remote deployed site. However, the consulting clinicians require up-to-date training, and their computer packages should have as wide a capability base as possible.

Exercise Mountain Shield, Task Force 11, and visual readiness.

This report, in an effort to assist in the development of future operational and planning guidelines, presents data from a no-notice exercise involving an aviation brigade in Germany preparing for possible deployment to Bosnia. One hundred twenty-two soldiers (of 918) requested vision screening during predeployment processing. Twenty-four possessed 20/20 vision or better and simply required duplicate orders of needed eyewear. Ninety-eight required an updated refraction. The three battalion-level units provided equal numbers of soldiers requiring screening and examination. Although the lower enlisted grades presented in the greatest numbers, the distribution in terms of percentage was equivalent across all ranks. Myopes outnumbered hyperopes with a spherical distribution peak at -1.50 diopters, and a majority possessed 1.00 diopter of astigmatism or less. Assuming 40% of all soldiers are spectacle wearers (ametropic), this brigade of 518 soldiers had, then, roughly 210 ametropes, with 60% of them (122) requiring last-minute ordering of required eyewear, 98 of those after refractive examination. Possible solutions to this readiness issue have been developed but require sufficient command emphasis to be effective.

An apparent pH-induced effect on extended wear hydrogel lens water content.

Numerous studies have examined the separate issues of precorneal tearfilm pH and hydrogel lens water content. None have examined the two issues in an associated, clinical fashion. Earlier research by this author has shown that stabilized hydrogel lens anterior surface pH correlates with established values for the precorneal tearfilm pH. This technique was therefore paired with two different methods of hydrogel lens water content assessment to determine if there was a predictable tear pH-related effect on soft lens hydration. Sixty-five volunteer subjects were fitted with either 38% (polymacon) or 58% (etafilcon A) water content hydrogel lenses on an extended-wear basis. The in situ hydrogel lens anterior surface pH was measured with a flat-surfaced, self-referenced pH electrode 5 min after initial fitting, and on subsequent extended wear follow-up examinations. On each follow-up, associated lens water content was determined by gravimetric and/or refractive analysis, yielding a total of 517 paired data points over a 33 month period. While the anterior lens surface pH increased in a nonlinear fashion with immediate duration of extended lens wear [p < 0.001 analysis of variance (ANOVA) by number of days extended lens wear], the water content decreased in a nonlinear fashion under the same conditions (p < 0.001 by ANOVA). Correlation of these two nonlinear functions yielded a negatively sloped linear regression (r = 0.99 and 0.97) for each material. The slopes of the resultant linear functions were significantly different (p < 0.01) by t-test; the higher water content material exhibited a greater sensitivity to pH. The routine labeling of pH-induced water content changes by hydrogel lens manufacturers would provide an objective model for clinical lens behavior, and assist in lens type and parameter selection when fitting extended-wear soft lenses. Additionally, as other lens materials are characterized, it may be possible to model the "ideal" hydrogel material in terms of apparent pH-dependent or-independent behavior.

Influence of extended soft contact lens wear on the comparative measurement of central corneal thickness.

The clinical performance of a portable ultrasound pachometer was compared with a digital, 'optical' pachometer attachment of a contact specular microscope. The two separate methods were used to assess central corneal thickness (CCT) in 214 extended-wear soft contact lens subjects over a cumulative 33 month period. The two test methods did not correlate well (r = 0.56). Mean ultrasound CCT was 0.542 mm +/- 0.004 SEM; mean CSM 'optical' attachment CCT was 0.562 mm +/- 0.004 SEM (significantly different by t-test; p < 0.05). A two-way anova (each CCT method by immediate duration of extended lens wear, and by duration in study) revealed an apparent underestimation of central corneal thickness by the ultrasound pachometer. While this presumed ultrasound bias or error can be explained by concurrent morphological and physiological changes associated with long-term contact lens wear, other methodological errors could have influenced the results. Pending additional study, physiologically stressed corneas might be better evaluated by some method of corneal thickness measurement other than ultrasound.

Refractive error distribution and incidence among U.S. Army aviators.

Spectacle incompatibility has been a major problem in the fielding of advanced Army avionic and electro-optical systems. As a result, routine contact lens wear may be instituted as an option to spectacles. Refractive error data were extracted from the Aviation Epidemiological Data Registry, a computer-accessible repository of flight physical medical information on the entire Army aviation population. Refractive error distribution patterns in the class 1 and class 2 flight physical populations were analyzed in order to provide a contact lens supply reference database, estimate the annual incidence of refractive error development, and estimate costs of possible spectacle-wearer flight-duty deselection. Contact lens wear appears to be a more cost-effective alternative than deselection.

Subjective assessment of contact lens wear by army aircrew.

Because 23% of Army aviators are ametropic, contact lenses have drawn increased attention as a spectacle substitute to solve system compatibility problems. From November 1988 until October 1991, a series of contact lens research protocols were conducted to develop a comprehensive database on contact lens wear in varied environments. Questionnaires were used to assess suitability and acceptability of routine contact lens wear. Responses from 202 subjects were obtained from September 1989 through September 1991. The questions explored operational and safety of flight issues of contact lens wear. Subjects overwhelmingly approved of contact lens use in all settings: 95% expressed greater combat readiness and effectiveness with contact lenses, 98% felt contact lens use (and maintenance) in the cockpit had no adverse impact on safety of flight, and 98% endorsed the routine use of contact lenses. These data highlight Army aircrew acceptance of contact lens use.

Contact lenses in the U.S. Army attack helicopter environment: an interim report.

Recent technological advances have had a major impact on military aviation. While modern methods of providing visual information via electro-optics/visionics systems have extended the aviator's operational envelope, these devices are becoming increasingly incompatible with spectacle wear. Since close to 22 percent of Army aviators are ametropic (spectacle wearing), alternative means of providing a refractive error correction need to be investigated. One alternative being considered is the use of a contact lens correction. Since November 1988, the U.S. Army Aeromedical Research Laboratory (USAARL) has been conducting two AH-64 "Apache" contact lens research projects in order to develop a comprehensive database on contact lens wear in a variety of environments. A three-tier contact lens fitting system is being used: two different types of soft lenses and one rigid gas permeable (RGP) lens type. The wearing schedule is set at a maximum of 7 days/6 nights of extended lens wear. Fundamental operational data is being chronicled by unit flight surgeons. Standard clinical data is being used in ongoing command deliberations on future medical policy decisions concerning contact lens wear by Army aviators. Basic research information is being gathered in an effort to determine the fundamental physiological response of the cornea to the presence of a contact lens. Data through July 31, 1990 are presented. The subjective assessment of contact lens applications within the aviation community is universal acceptance. While current clinical data indicate some ocular health risk, flight safety risks are minimal. Establishment of long-term contact lens efficacy will likely depend on the ensuing analysis of physiological data.

Disposable soft lens ulcerative keratitis in an Army aviator: a case report.

A synopsis of Army aviation interest in soft contact lenses is presented. A case report of one volunteer subject's experience with presumed contact lens-associated infectious ulcerative keratitis then is summarized. The clinical significance of this case is highlighted.

Prevalence of spectacle wear among U.S. Army aviators.

The advanced avionic and electro-optical systems installed in Army rotary wing aircraft are becoming increasingly incompatible with spectacle wear. Therefore, the prevalence of spectacle wear among Army aviators is an important consideration in the development of future systems. A review of spectacle prevalence data from the Aviation Epidemiology Data Register (AEDR) for the years 1986, 1987, 1988, and 1989 was performed. Data were consistent across all 4 years, with mean prevalence of spectacle wear being 22% for active component forces. Reserve and National Guard components displayed mean spectacle wear prevalences of 27% and 32%, respectively. These prevalence rates are higher than those previously obtained in 1985 by a similar, but slightly different paradigm. Spectacle-wearing aviators exist in greater numbers than previously documented and represent a segment of the aviation population that will have increasing compatibility problems with advanced flight systems. Therefore, system planners will need to address these incompatibilities in future hardware developments.

Military aviation: a contact lens review.

The military aviation communities have benefitted from the development of advanced electro-optical avionics systems. One drawback that has emerged is an increasing system incompatibility with traditional spectacle visual corrections. An alternative solution to the refractive error correction problem that some services have been investigating is that of contact lens wear. Since this much-debated topic is currently of command interest, a general overview of contact lens issues is presented as a framework for future discussions.

Effects of ultraviolet radiation on the oxygen uptake rate of the rabbit cornea.

Ultraviolet radiation (UVR) has been demonstrated to be involved in a number of adverse ocular effects. One aspect of UVR-induced corneal stress only recently documented is an alteration of epithelial energy metabolite levels. In this study, in order to examine wavelength and dose dependency issues concerning metabolic effects of UVR, exposures were made at four different wavelengths (290, 300, 310 and 360 nm) and five different mean radiant exposures (0.05, 0.10, 0.15, 0.20, and 0.25 J.cm-2). Pre- and postexposure levels of relative metabolic activity of the corneal epithelium were monitored in vivo by recording the corneal oxygen uptake rate with a micropolarographic electrode. A paired difference analysis demonstrated a decrease in relative corneal metabolic activity that was both wavelength- and dose-dependent. These relative metabolic effects provide some insight toward the understanding of underlying damage mechanisms, and imply a broader radiant energy susceptibility range of the eye than previously thought.

Effect of ultraviolet radiation on the energy metabolism of the corneal epithelium of the rabbit.

The present research was directed at quantifying possible alterations in corneal epithelial metabolic activity secondary to in vivo exposure to ultraviolet radiation (UVR). Microfluorometric energy metabolite assays on microgram (microgram) sized, freeze-dried tissue samples were used as an in vitro means of assessing overall metabolic activity in the epithelium of control rabbit corneas and in the epithelium of UVR-exposed rabbit corneas 2 min after discontinuation of exposure. The specific assays were for glucose, glycogen, adenosine triphosphate (ATP), and phosphocreatine (PCr). The radiant exposures were kept constant at 0.05 J cm-2 for all UVR wavelengths utilized (290, 300, 310 and 360 nm). Experimental UVR exposure conditions served to increase epithelial glucose and glycogen concentrations. Although the epithelial ATP concentrations were unchanged, the epithelial PCr concentrations (a high energy phosphate bond reservoir) decreased as a result of UVR exposure. Overall, the data demonstrate a decrease in corneal epithelial metabolic activity, which may be wavelength-dependent, as a result of UVR exposure. It is suggested that immediate metabolic stress can be responsible for the pattern of epithelial cell loss seen in photokeratitis.

Glucose concentration profiles of normal and ultraviolet radiation-exposed rabbit corneas.

The passage of glucose within the cornea has been thought to occur by passive diffusion processes. However, corneal glucose concentration profiles have not been established to support this notion. While microfluorometric methods of metabolite assay typically have been used as a means of assessing regional brain metabolism, this unique methodology of tissue isolation and metabolite determination has not previously been applied to the cornea. Since this technique permits metabolite quantification on microgram-sized tissue samples, a co-ordinated corneal glucose concentration profile can be obtained. Tissue preparation consisted of liquid nitrogen freezing, cryo-sectioning, and freeze-drying, with storage at -20 degrees C. The sections were thawed under vacuum pump, subsectioned, weighed, and assayed for glucose concentration (by dry weight). This study established a glucose concentration profile of the epithelium, anterior stroma, midstroma, posterior stroma, and endothelium for the normal pigmented rabbit cornea. A glucose concentration profile for UV radiation-exposed rabbit corneas also was documented. The UV radiation glucose profile data indicate the presence of an active transport mechanism capable of delivering glucose into the corneal epithelium against a concentration gradient. The presence of a transport system that 'pulls' glucose through the deeper corneal layers thus would make epithelial integrity important for the maintenance of overall corneal viability.