Spectroscopic measurements in scleritis: bluish-red or deep red?

PURPOSE: To design a slit-lamp mountable spectrometer for the assessment of ophthalmic patients and to illustrate a potential clinical application by measuring the spectral characteristics of inflamed eyes of differing aetiologies. METHODS: A slit lamp mountable instrument was designed and built, and methods for data analysis developed. Reflectance spectra were recorded from two patients with scleritis, three with non-scleritic red eyes and from two controls with non-inflamed eyes. RESULTS: Measurements were reproducible and demonstrated statistically significant differences in the spectral characteristics between the three groups. Spectra from scleritic eyes revealed a relative increase in intensity of long wavelength red light, 650-740 nm, compared with non-scleritic red eyes. These longer wavelengths will be appreciated as dark red. There was no increase in relative intensity in the blue part of the spectrum in scleritic eyes. CONCLUSIONS: Reproducible measurements of the eye were made using an innovative, slit-lamp mountable spectrometer and its functionality demonstrated by differentiating the spectra from eyes with differing pathologies. While intending only to illustrate one potential application; for the cases examined, our results indicate that inflamed scleritic eyes exhibit a longer wavelength red light with no increase in shorter wavelength blue light. Thus our measurements would seem to confirm that the perceived redness of scleritis differs from other red eyes. However, it is a deeper darker red and not a bluish one as traditionally described.

A new customized artificial iris diaphragm for treatment of traumatic aniridia.

UNLABELLED: We report the use of a custom hand painted iris implant, which offers outstanding cosmetic results in the treatment of aniridia. In the past artificial Irides has been a poor match to the healthy eye and of limited cosmetic benefit. This artificial iris produced by Dr. Schmidt Intraocularlinsen GmbH, Germany is fully customized with handmade colour composition, which structurally matches the appearance of natural iris restoring the aesthetic appearance with higher patient satisfaction. CONCLUSION: Custom made artificial iris is an excellent product, which gives patients a cosmetically normal looking eye and better quality of life.

The pharmacokinetics of linezolid in the non-inflamed human eye.

AIM: This study describes the ocular pharmacokinetics of linezolid, an antibiotic with broad spectrum activity against those Gram positive bacteria that are the most frequent cause of postoperative endophthalmitis. METHOD: Patients undergoing routine cataract surgery were given a single oral 600 mg dose of linezolid at a variable time before surgery. Aqueous and serum levels of linezolid were assayed by high performance liquid chromatography, and a pharmacokinetic curve constructed from the pooled results. RESULTS: Orally administered linezolid rapidly achieves levels in the aqueous of non-inflamed eyes that exceed the concentration required to kill Gram positive bacteria (maximum mean concentration 6.8 (SD 1.2) microg/ml at 2-4 hours post-dose). An effective concentration is maintained for at least 12 hours, the standard interdose interval for this antimicrobial. CONCLUSION: Linezolid offers the possibility of a rapid, oral approach to effective treatment of most cases of postoperative endophthalmitis, with the potential of improving visual outcome.

Keratocyte density and size in conscious humans by digital image analysis of confocal images.

PURPOSE: Confocal microscopy can give images of high magnification and resolution in undisturbed living tissue. It provides new information about the cellular structure of the cornea. Our aim was to measure the density, size and distribution of keratocytes. METHODS: Healthy cornea in four subjects was examined using tandem scanning confocal microscopy. Methods for digital analysis of images were developed. RESULTS: Keratocyte density in confocal cross-sections was greatest immediately under Bowman's membrane (maximum 800 cells/mm2) and decreased sharply towards posterior cornea (minimum 65 cells/mm2). Cross-sectional cell size ranged from 78 to 211 microns2, but did not correlate with depth in the tissue. CONCLUSIONS: Results are consistent with those of earlier work using histological and biochemical techniques in isolated tissue. The methods we have developed enable studies of ongoing processes in conscious humans and can be used to examine diseased tissue as well as the response to injury.

Confocal microscopy using oblique sections for measurement of corneal epithelial thickness in conscious humans.

PURPOSE: Thickness measurements by confocal microscopy in conscious human subjects may be liable to error as a result of instability of the eye or instrument. Our aim was to evaluate a technique which was expected to be less sensitive to such problems. METHOD: Thickness of corneal epithelium was determined from oblique confocal sections through cornea. A contact lens of known thickness worn by subjects was used to calibrate images. RESULTS: There were two layers in images which could have corresponded to the stromal/epithelial interface. The mean result in each subject ranged from 38 to 53 microm using the more superficial layer and 46 to 60 microm using the deeper one. The smaller values gave the distance between the epithelial surface and the sub-epithelial nerve plexus and thus seemed to correspond to epithelial thickness. CONCLUSIONS: Measurements of epithelial thickness by our new method are comparable with results of earlier studies.

An in vivo investigation of the structures responsible for corneal haze after photorefractive keratectomy and their effect on visual function.

PURPOSE: To make serial measurements of corneal haze and microscopic anatomy after photorefractive keratectomy (PRK) and compare the results with visual function measured at the same time points in the same single group of human subjects. METHODS: Ten patients underwent -6.00-diopter, 6-mm PRK. The patients were reviewed frequently for 12 months. Corneal haze was measured objectively in two ways: (1) an opacification index was determined from the variance in digitized retroillumination images; and (2) light reflected and scattered back from the cornea was assessed by gray-scale analysis of video slit images. In vivo confocal microscopy recorded the anatomic changes occurring in the cornea, and computer analysis of the images quantified the keratocytes and subepithelial deposit. Visual performance was assessed by Snellen visual acuity, contrast sensitivity, and glare-induced visual dysfunction. RESULTS: In the first week, epithelial irregularity resulted in a transient reduction in all aspects of visual function. In the first month, keratocyte disturbances reduced contrast sensitivity at high frequencies and produced glare. Over the next couple of months, the subepithelial deposit resulted in a more prolonged loss of contrast sensitivity at low frequencies and glare-induced visual dysfunction due to the scattering of light. In several patients, these visual defects persisted after 1 year. CONCLUSIONS: Epithelial and keratocyte disturbances only transiently affect visual function. The subepithelial deposit is more persistent and can have a lasting effect on visual performance. Therefore, attempts to improve the visual outcome of PRK must be aimed at controlling the synthesis of subepithelial material.

Comparison of tear film thickness in three species determined by the glass fibre method and confocal microscopy.

Using optical methods to measure tear film thickness we previously found that values were substantially larger than earlier estimates by mechanical and chemical techniques. The predominant component was found to be mucus, not aqueous fluid. This article describes the results of using confocal microscopy to re-examine an earlier method of measuring thickness, the glass fibre technique. Confocal microscopy enabled visual identification of tear and epithelial surfaces and accurate measurement of the separation between them, giving the full film thickness. Consecutive measurements were made by each method in eyes of 22 animals of three species. Measurements using fibres in rabbits gave results of 7 microns, replicating earlier findings. However, the fibre technique gave the same result in all species. Values were not correlated with measurements by microscopy, which ranged from 10 to 14 microns. We propose that fibres were too flexible to be pressed through all mucus layers and contact epithelium, and as a result this method underestimated film thickness.

Study of precorneal tear film thickness and structure by interferometry and confocal microscopy.

Past measurements of precorneal tear film thickness in rabbits and humans gave values of 4-7 microns. These have been the accepted values. However, measurements presented in this report are much higher. Earlier techniques may have changed film thickness or not have fully included the layer containing mucus. Little is known about the mucus component. Thickness was measured in freshly killed animals of 10 species using two independent optical techniques. Coherent light was reflected from eyes and thickness was determined from spacing of interference fringes. Clear images of tissue structure were obtained with confocal microscopy, the tear film was visually identified, and thickness measured. Measurements by the two methods were closely correlated in each animal. No film was detected in trout or carp. In other species, thickness ranged from 9 microns in frogs to 15 microns in gerbils. Values are significantly larger than earlier estimates. Film thickness in three living rabbits was not significantly different from that measured shortly after death. There was no variation in thickness at five positions across the cornea in three species. Mucus content of rat tear film was examined by measuring thinning after application of 4, 8, and 20% (weight/volume) acetylcysteine, a mucolytic agent. Thickness was considerably reduced compared to controls, and the film almost completely removed by the highest concentration. The authors propose that the film is largely composed of mucus, not free aqueous solution. Our methods include such layers, and measurements are correspondingly larger than earlier ones.

Study of human precorneal tear film thickness and structure using laser interferometry.

The authors previously found that measurements of precorneal tear film thickness in animals, using laser interferometry and confocal microscopy, were larger than earlier estimates. They proposed that this occurred because optical methods did not disturb film structure and measured full thickness, including mucus. In the present study, tear film thickness was measured in humans. Coherent light was reflected from eyes and formed interference patterns. Thickness was determined from spacing of fringes. Mean thickness in six subjects was 34-45 microns, more than four times larger than earlier values. Validity and accuracy of measurements by interferometry were examined in our earlier study using confocal microscopy. Here it provided supportive evidence. Tear film thickness was estimated from optical sections through the corneas of three subjects to be 41-46 microns. Mucus content of the film also was examined. Interferometry was used to measure thinning after application of a mucolytic agent. There was no change in thickness after 5 min exposure to 0.1% (weight/volume) acetylcysteine. Solutions of 20% caused thinning to 11 microns, and thickness slowly increased to reach its original value over 40 min. Thus, the film seemed to be composed substantially of mucus, not aqueous fluid. The results also provided evidence that measurements by interferometry did not include underlying epithelium. Earlier nonoptical methods probably did not include the portion of the film that contained mucus. They seem to have greatly underestimated human tear film thickness.

Precorneal residence times of sodium hyaluronate solutions studied by quantitative gamma scintigraphy.

Sodium hyaluronate solutions have been advocated in the management of a variety of dry-eye states. By virtue of their non-Newtonian rheological properties, formulations exhibiting high zero-shear viscosities may be used as an artificial tear with the expectation of prolonged precorneal residence times and improved tolerance. Quantitative gamma scintigraphy was used to evaluate the residence times of 0.2% and 0.3% sodium hyaluronate solutions and a polymer-free solution of buffered saline in 12 patients with keratoconjunctivitis sicca and a group of six normal volunteers. Using several indices of residence time, mean values for the sodium hyaluronate solutions were significantly longer than those for buffered saline. Parallel changes in tear film thickness were also demonstrated using a technique based on laser interferometry.