The ChromaGen contact lens system: colour vision test results and subjective responses.

The ChromaGen lens system is designed to enhance colour perception in colour vision deficiency (CVD). To investigate its efficacy, 14 CVD subjects were prescribed ChromaGen contact lenses. Colour vision tests (Ishihara, Farnsworth Munsell D-15, Farnsworth Lantern) were administered at baseline, lens dispensing, and after a 2-week lens-wearing trial during which subjective responses were recorded daily using visual analogue scales. ChromaGen lenses significantly reduced ishihara error rates (p < 0.001; ANOVA), particularly for deutan subjects. There was also a significant reduction in errors (p < 0.005) on the D-15 test. Conversely, lens wear had no significant effect on Farnsworth Lantern test performance. Subjectively, subjects reported enhanced colour perception, but poor vision in dim light. Judgement of distance and motion were only slightly affected. We conclude that ChromaGen lenses may enhance subjective colour experience and assist in certain colour-related tasks, but are not indicated as an aid for CVD in occupations with colour vision-related restrictions.

Corneal response to orthokeratology.

PURPOSE: The technique of orthokeratology produces a corneal response to the mechanical pressures exerted by rigid contact lenses. This paper reports a study which investigated the topographic and pachometric corneal changes induced by orthokeratology. METHODS: Six young myopic subjects (11 eyes) wore "accelerated orthokeratology" lenses (OK-74; Contex Inc., Sherman Oaks, CA) in a high Dk material (AirPerm; Dk = 88) for 28 days. Corneal and epithelial thickness were measured topographically using the Holden-Payor optical micropachometer, and corneal topography was monitored using the EyeSys system. RESULTS: Refractive error change reached 1.71 +/- 0.59 D reduction in myopia after 28 days. After 1 day of lens wear, statistically significant central corneal flattening was noted, which progressed to reach 0.22 +/- 0.07 mm (1.19 +/- 0.38 D) at 28 days. A trend toward central epithelial thinning was apparent, reaching statistical significance on day 28 (7.1 +/- 7.1 microm; 9.6%). Midperipheral corneal thickening was also found approximately 2.5 mm from the corneal center, which was statistically significant by day 14 (13.0 +/- 11.1 microm; 2.4%). Calculations using Munnerlyn's formula indicate that changes in corneal sagittal height based on topographical thickness changes across the flattened central 5.25-mm zone can account for the refractive changes observed. CONCLUSIONS: These findings suggest that the initial corneal response to orthokeratology may be explained by redistribution of corneal tissue, rather than by overall bending of the cornea.

Contact lens induced peripheral ulcers during hydrogel contact lens wear.

PURPOSE: Ulcerative keratitis is the most serious adverse response associated with contact lens wear. However, some reports of microbial keratitis in the literature may refer to a less severe form of corneal ulceration, which we have termed contact lens induced peripheral ulcers (CLPU). METHODS: We present details of 11 cases of CLPU which occurred in clinical trials at our research unit. RESULTS: CLPU episodes are characterized by a single, small (< 2 mm diameter) circular lesion in the corneal mid-periphery or periphery, involving a focal loss of the full thickness of the epithelium associated with subepithelial stromal infiltrates. Patient symptoms may include ocular irritation, pain, photophobia, and lacrimation. They are usually associated with the use of hydrogel extended wear contact lenses. The lesions are self-limiting, typically healing within 7 days without treatment. After resolution, a small circular scar remains, which does not affect vision because of its peripheral location. The etiology of CLPU is unclear. In our studies, the incidence of CLPU was similar in conventional (2.9% per patient year) and disposable (2.0% per patient year) hydrogel extended wear, but lower during intermittent extended wear (1.6% per patient year); only one case occurred during daily wear (< 0.5% per patient year). CONCLUSIONS: A conservative approach to patient management of all suspected cases of corneal ulceration is encouraged. However, we suggest that future reports of ulcerative keratitis associated with various lens types and wearing schedules should differentiate between potentially devastating microbial keratitis and the relatively innocuous peripheral ulceration described in this paper.

Ocular characteristics associated with rigid gas-permeable lens adherence.

PURPOSE: Rigid gas-permeable (RGP) lens adherence after overnight lens wear is clearly a patient-dependent phenomenon. However, no previous study has attempted to determine whether specific ocular characteristics are associated with an increased frequency of lens adherence. METHOD: In this study, clinically applicable tests were used to measure a range of ocular characteristics, including central and peripheral corneal curvature, tear film status, eyelid characteristics, central corneal thickness, and ocular rigidity in a group of 22 young adult subjects for whom reliable estimates for frequency of overnight RGP lens adherence had been obtained from earlier studies. RESULTS: Linear discriminant analysis revealed that a higher frequency of lens adherence was associated with lower ocular rigidity, thinner central corneas, greater eyelid tension, and lower amounts of corneal astigmatism. CONCLUSIONS: These findings suggest a clinical approach for identifying patients who may develop clinically significant lens adherence during RGP extended wear, and also provide support for the "thin film adherence" theory of RGP lens adherence.

Effects of lens parameter variation on rigid gas-permeable lens adherence.

The influence of lens parameter variation on the frequency and persistence of rigid gas-permeable (RGP) lens adherence after overnight lens wear was investigated. In 3 separate studies, 11 subjects wore lenses of different designs in each eye over 5 nights. No significant differences in the frequency of lens adherence were found with loose vs. tight peripheral fittings (49% vs. 42%), or with 9.6-mm vs. 8.7-mm diameter lenses (42% vs. 52%). However, a significantly higher frequency of adherence was found for flat-fitting lenses compared to steep-fitting lenses (84% vs. 49%; p < 0.05, Binomial test). Adherence was also significantly more persistent after eye opening with flat-fitting lenses, whereas steep-fitting lenses regained mobility more rapidly than the other lens designs tested. These findings suggest that the "suction cup" theory of RGP lens adherence does not adequately explain this phenomenon, and that the lens parameter variations investigated in this study do not reliably reduce or eliminate lens adherence during RGP extended wear.

Temporal sequence of changes in tear film composition during sleep.

Overnight eye closure induces a shift in the nature and composition of the tear film, from a dynamic reflex tear-rich to a stagnant secretory IgA-rich layer. This is accompanied by the induction of a state of sub-clinical inflammation, as evidenced by increases in albumin levels, plasminogen activation, conversion of complement C3 to C3c, and the recruitment of polymorphonuclear (PMN) cells into the tear film. To determine the time course and functional relationship between these potentially interdependent processes, tear samples were collected from ten non-contact lens wearers after 1, 2, 3 and 5 hours of sleep. A subgroup of 6 subjects also self-collected tear samples after 8 hours of sleep. Tear samples were analysed for albumin by quantitative immunofixation assay, secretory IgA (sIgA) by radial immunodiffusion assay, plasmin-like activity using a chromogenic substrate, and complement C3 to C3c conversion by immunoblot assay. Epithelial and PMN cells in the precorneal tear film were recovered from corneal washings from the same subjects after 1, 3, 5 and 8 hours of sleep, and quantified. Results revealed that, unlike epithelial cells which exhibited a slow progressive accumulation as a function of the period of sleep, PMN cell concentration exhibited a lag phase, with recruitment occurring after between 3 and 5 hours of eye closure. This was preceded by plasminogen activation, increases in albumin and sIgA levels, and complement C3 to C3c conversion, all of which occurred within 1 to 3 hours after eye closure. Plasmin-like activity appeared to plateau after 3 hours and then decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Rigid gas-permeable lens adherence: a patient-dependent phenomenon.

Ten unadapted subjects participated in a study to investigate the incidence and intrasubject repeatability of rigid gas-permeable (RGP) lens binding (adherence) over a 7-day period of overnight lens wear. An overall incidence of lens binding of 49% was found, based on subject self-assessment on eye opening. Seven of the 10 subjects experienced lens binding on at least one occasion. Two-thirds of lenses assessed as bound on eye opening were mobile at a clinical examination approximately 2 h after eye opening. The apparent incidence of lens binding at this time, based on lenses still bound and positive clinical signs of lens binding, was 36%. Despite equivalent lens fittings across the subject group, there were significant individual differences in the incidence of lens binding over the 7-day period, ranging from no binding to 100% incidence. This suggests that lens binding is primarily a patient-dependent phenomenon.

Rigid gas permeable lens binding: significance and contributing factors.

A retrospective analysis of lens binding was performed using records from 279 cases of overnight wear of rigid gas permeable (RGP) lenses in a variety of materials and designs. The overall incidence of lens binding on eye opening was 22%. Typically, the lens was bound nasally, became mobile spontaneously in less than 1 h, and produced staining of the central cornea and inferior conjunctiva. A corneal indentation ring was noted in 53% of eyes that experienced a bound lens. A statistical analysis was performed to determine whether RGP lens binding was associated with particular lens parameters, patient characteristics, or lens fitting factors. Overnight lens binding was found to occur more frequently with lenses of large diameter, flat base curve and minimal axial edge lift, fitted "on-K" or flat relative to central corneal curvature, and exhibiting less than optimal on-eye lens movement before eye closure.

Strategies for minimizing the ocular effects of extended contact lens wear--a statistical analysis.

In a study reported recently, the effects of long-term extended wear of soft contact lenses on the human cornea were found to include epithelial thinning, a reduction in epithelial oxygen uptake, induction of epithelial microcysts, stromal thinning, and an increase in endothelial polymegathism. A multiple regression analysis was performed on data from this study to identify lens or patient characteristics associated with these effects. Although generalization to the population of conclusions based on associations identified using a small sample should be treated with caution, results from this analysis suggest that lens-induced effects on the cornea may be minimized by fitting lenses that are thinner and more mobile, and by encouraging more frequent lens removal and replacement. Patients with thinner corneas and with high endothelial cell density and low polymegathism before commencing lens wear tended to show fewer effects from extended lens wear.

Severe corneal infections associated with contact lens wear.

An analysis of acute contact lens-related complications, with particular emphasis on severe microbial keratitis, was undertaken at the Department of Ophthalmology, Sahlgren's Hospital in Gothenburg. A total of 224 contact lens wearers presented with acute complications over a 2-year period (1981-1982). The lowest incidence of acute complications was found with hard contact lens wear. Similar numbers of daily wear and extended wear soft contact lens wearers presented with acute complications. The highest incidence of severe microbial keratitis was found in patients wearing soft contact lenses on an extended-wear basis. Inappropriate topical steroid therapy was implicated as a major factor contributing to the severity of these cases. Less severe sequelae of contact lens-related complications were also over-represented in the extended lens wear group. These findings emphasize the need for a conservative approach to the use of an extended wear regimen with soft contact lenses.

The vascular response to long-term extended contact lens wear.

The effects of long-term extended wear of soft contact lenses on human conjunctival and limbal vasculature were determined by examining 27 patients who had worn a high water content hydrogel contact lens in one eye only for an average of 62 ± 29 months (mean ± SD). The levels of general conjunctival hyperaemia (p > 0.01), limbal hyperaemia (p > 0.001), and the extent of limbal vessel penetration (p > 0.001) were found to be significantly greater in the lens-wearing eye, relative to the control eye, immediately on lens removal. The patients ceased lens wear for up to one month, and changes in the levels of vascular response were monitored during this period. General conjunctival hyperaemia and limbal hyperaemia recovered to levels observed in the non-lens-wearing eye within two and seven days after lens removal, respectively. However, limbal vessel penetration was still significantly greater in the lens-wearing eye 33 days after ceasing lens wear (p > 0.05).

Topographical corneal oedema.

Corneal thickness changes were monitored across the cornea in 10 subjects during 7 days continuous wear of 3 types of hydrogel contact lenses of different back vertex powers. Analysis of topographical corneal thickness changes indicates that the periphery of the cornea swells significantly less than the central cornea. The effect is more dramatic with higher levels of central corneal oedema, and with lenses of higher minus power, in spite of their thicker lens periphery. An anoxic stimulus was also found to produce greater central than peripheral corneal swelling, indicating that tear exchange under the periphery of the contact lens is not a significant factor in limiting peripheral corneal swelling. It was concluded that the topographical swelling profile is not contact lens-related, but reflects a reduced swelling capability of the peripheral cornea, due to physical restraint in the limbal region.