Hypersensitivity responses and contact lens wear.

Hypersensitivity diseases that involve the eye are common reasons why patients present to eyecare practitioners. Common ocular hypersensitivity disorders include allergic conjunctivitis, giant or contact lens induced papillary conjunctivitis and atopic keratoconjunctivitis. The diagnosis and management of ocular hypersensitivity can present a challenge to eyecare practitioners and an understanding of the mechanisms that underlie the signs and symptoms of such conditions is necessary for their appropriate management. This article reviews the mechanisms by which the eye responds to antigenic challenges, the pathogenesis of ocular hypersensitivity responses, particularly in relation to contact lens wear, and illustrates possible management strategies.     

Non-inflammatory corneal complications of contact lens wear.

Contact lenses can induce changes in the epithelium, stroma and endothelium of the cornea, all of which can be observed clinically using the slit-lamp biomicroscope. These complications include epithelial microcysts, vacuoles and staining, stromal oedema and vascularization, and endothelial polymegethism and blebs. Each complication can be attributed to one or more aetiological factors such as hypoxia, hypercapnia, tissue acidosis, trauma, hypersensitivity and toxicity. This review outlines the way in which these complications manifest clinically, and consideration is given to management strategies and likely prognoses. Early detection of these conditions and appropriate action can usually prevent more serious ocular complications.     

Amiodarone keratopathy and rigid contact lens wear.

Two cases are presented of patients wearing rigid gas permeable contact lenses who exhibited the typical fan-shaped patterns of corneal pigment deposition related to long-term medication containing amiodarone. The vortex corneal epitheliopathy and contact lens tolerance were monitored over several years. In both cases, the lens material was replaced with one incorporating an ultra-violet light inhibitor in view of the possibility of medically induced photosensitivity.     

Corneal erosions in contact lens wear

Contact lens wear continues to be the highest single risk factor for microbial keratitis, particularly when worn in the extended wear modality. For microbial keratitis to occur, the presence of at least a bacterial load as well as a break in the corneal surface is required. One such break occurs in the case of a corneal erosion. These well-circumscribed areas of full thickness epithelial loss can occur both with and without contact lens wear, however the risk of infection is greater in the presence of a lens due to its capacity to provide a vector for the entry of bacterial pathogens. While erosions in non-contact lens wearers are thought to result from defective epithelial basement membrane anchoring, the underlying causes during contact lens wear are yet unknown. This article sets out to review corneal erosions associated with contact lens wear, their associated risk factors such as extended wear, the mechanisms that may be responsible for their formation and the factors that differentiate them from other contact lens related adverse events. Appropriate diagnosis and understanding of the relevant pathophysiology is important to the effective treatment and an understanding of the aetiological factors responsible for erosions is critical to the development of preventative strategies and effective clinical care.     

Spherical aberration in contact lens wear

INTRODUCTION: The aim of the present studies was to investigate the effect on spherical aberration of different non custom-made contact lenses, both with and without aberration control. METHODS: A wavefront analyser (Zywave, Bausch & Lomb) was used to measure the aberrations in each subject's right eye uncorrected and with the different contact lenses. The first study evaluated residual spherical aberration with a standard lens (Focus Dailies Disposable, Ciba Vision) and with an aberration controlled contact lens (ACCL) (Definition AC, Optical Connection Inc.). The second study evaluated the residual spherical aberrations with a monthly disposable silicone hydrogel lens with aberration reduction (PureVision, Bausch & Lomb). RESULTS: Uncorrected spherical aberration was positive for all pupil sizes in both studies. In the first study, residual spherical aberration was close to zero with the standard lens for all pupil sizes whereas the ACCL over-corrected spherical aberration. The results of the second study showed that the monthly disposable lens also over-corrected the aberration making it negative. The changes in aberration were statistically significant (p<0.05) with all lenses. CONCLUSION: Since the amount of aberration varies individually we suggest that aberrations should be measured with lenses on the eye if the aim is to change spherical aberration in a certain direction.     

Effects of contact lens wear on corneal ultrastructure.

Over the past 30 years, a number of studies employing the techniques of light and electron microscopy have been conducted on the corneas of human and animal eyes in an effort to more fully understand the histopathological basis of clinically-observed contact lens-related phenomena. This paper reviews studies that have sought to explain such effects, including epithelial abrasion, punctate staining and thinning; stromal oedema and thinning, and endothelial polymegethism. It is demonstrated that an understanding of contact lens-induced changes to corneal ultrastructure can have a significant impact on the clinical appreciation of the severity or otherwise of various conditions as observed with the slit-lamp biomicroscope.     

UVB-induced epidermal pigmentation in mice eyes with no contact lens wear and non-UVB blocking and UVB blocking contact lens wear

PurposeIrradiation by ultraviolet (UV) B is known to increase the number of Dopa-positive melanocytes in the skin. This study examines the effectiveness of a contact lens for the defense of UVB eye irradiation-induced pigmentation.MethodsA 2.5 kJ/m² dose of UVB radiation was delivered by a sunlamp to the eye of C57BL/6j male mice, and changes in the expression of Dopa-positive melanocytes in the epidermis and the plasma level of alpha-melanocyte-stimulating hormone (α-MSH) was analyzed.ResultsThe degree of change in the Dopa-positive melanocytes expression was reduced by UVB blocking contact lens using mice given UVB irradiation to the eye. The plasma level of α-MSH increased in the C57BL/6j mice after irradiation to the eye, but there was no increase in the UVB blocking contact lens mice given UVB irradiation to the eye. Both the increase of the expression of Dopa-positive melanocytes and the plasma level of α-MSH were strongly suppressed by an alignment fitting UVB blocking contact lens and only a slightly suspended UVB blocking contact lens. In addition, these changes were successfully inhibited by a UVB blocking contact lens but not by a non-UVB blocking contact lens with a similar absorbance.ConclusionThese observations suggest that the UVB blocking contact lens inhibits the pigmentation of the epidermis in mice by suppressing of the α-MSH.     

Corneal epithelial homeostasis following daily and overnight contact lens wear.

This report reviews and integrates our recent clinical and laboratory findings of the effects of daily (DW)/overnight (EW) contact lens wear on corneal epithelial homeostasis. In a prospective, double-masked human clinical study, three lens types (high and hyper Dk/t soft; hyper Dk/t RGP) were used to assess the effects of daily and overnight lens wear on corneal epithelial thickness, cell surface size, Pseudomonas aeruginosa (PA) binding to exfoliated epithelial cells and exfoliation rates. Concomitantly, we studied in a rabbit model, the effects of overnight lens wear on corneal epithelial surface cell viability (live/dead assay, TUNEL-labeling, Annexin-V staining, Bcl-2 expression), basal cell proliferation and migration patterns. The comprehensive results obtained yield important new insights on both the normal homeostasis of the corneal epithelium and the biological changes induced by contact lens wear.     

Corneal changes following short-term miniscleral contact lens wear

PurposeTo examine the influence of short-term miniscleral contact lens wear on corneal shape, thickness and anterior surface aberrations.MethodsScheimpflug imaging was captured before, immediately following and 3 h after a short period (3 h) of miniscleral contact lens wear for 10 young (mean 27 ± 5 years), healthy participants. Natural diurnal variations were considered by measuring baseline diurnal changes obtained on a separate control day without contact lens wear.ResultsSmall but significant anterior corneal flattening was observed immediately following lens removal (overall mean 0.02 ± 0.03 mm, p < 0.001) which returned to baseline levels 3 h after lens removal. During the 3 h recovery period significant corneal thinning (−13.4 ± 10.5 μm) and posterior surface flattening (0.03 ± 0.02 mm) were also observed (both p < 0.01). The magnitude of posterior corneal flattening during recovery correlated with the amount of corneal thinning (r = 0.69, p = 0.03). Central corneal clearance (maximum tear reservoir depth) was not associated with corneal swelling following lens removal (r = −0.24, p > 0.05). An increase in lower-order corneal astigmatism Z(2,2) was also observed following lens wear (mean −0.144 ± 0.075 μm, p = 0.02).ConclusionsFlattening of the anterior corneal surface was observed immediately following lens wear, while ‘rebound’ thinning and flattening of the posterior surface was evident following the recovery period. Modern miniscleral contact lenses that vault the cornea may slightly influence corneal shape and power but do not induce clinically significant corneal oedema during short-term wear.     

Corneal stability after discontinued soft contact lens wear

PURPOSE: To determine the time needed to reach corneal stability after discontinued daily wear of soft contact lenses and to identify corneal topographic and pachymetric changes during this period. METHODS: We prospectively studied the eyes of 21 consecutive soft contact lens wearers evaluated for keratorefractive surgery. Each eye was examined once immediately after lens removal, 3 and 7 days later, and weekly thereafter. At each visit, manifest refraction, keratometry, corneal topography (EyeSys Corneal Analysis system, EyeSys Laboratories, Houston, TX) and pachymetry were performed. Incidence of associated corneal warpage and changes in corneal curvature and thickness during corneal stability time were determined. RESULTS: Of the 42 eyes examined, 26 corneas showed no significant change after the initial evaluation (stable group). The minimum stability time was 3 days in the remaining 16 eyes (unstable group), 7 of which had significant evidence of abnormal topography. Statistical analysis showed no significant differences between two groups regarding age, sex, duration of contact lens wear, and refractive and topographic measures. The mean central corneal thickness on the final visit was significantly different between two groups (P<0.05). CONCLUSION: Contact lens induced corneal warpage may occur in a considerable proportion of soft contact lens wearers. A 2-week contact lens free period seems to be adequate for the cornea to stabilize; however, one cannot predict the minimum time needed for each individual patient. Repeating examinations to document corneal stability before refractive surgery may be a safer alternative.     

Corneal changes following short-term rigid contact lens wear

PurposeThe aim of this cross-over study was to investigate the changes in corneal thickness, anterior and posterior corneal topography, corneal refractive power and ocular wavefront aberrations, following the short term use of rigid contact lenses.MethodFourteen participants wore 4 different types of contact lenses (RGP lenses of 9.5 mm and 10.5 mm diameter, and for comparison a PMMA lens of 9.5 mm diameter and a soft silicone hydrogel lens) on 4 different days for a period of 8 h on each day. Measures were collected before and after contact lens wear and additionally on a baseline day.ResultsAnterior corneal curvature generally showed a flattening with both of the RGP lenses and a steepening with the PMMA lens. A significant negative correlation was found between the change in corneal swelling and central and peripheral posterior corneal curvature (all p ≤ 0.001). RGP contact lenses caused a significant decrease in corneal refractive power (hyperopic shift) of approximately 0.5 D. The PMMA contact lenses caused the greatest corneal swelling in both the central (27.92 ± 15.49 μm, p < 0.001) and peripheral (17.78 ± 12.11 μm, p = 0.001) corneal regions, a significant flattening of the posterior cornea and an increase in ocular aberrations (all p ≤ 0.05).ConclusionThe corneal swelling associated with RGP lenses was relatively minor, but there was slight central corneal flattening and a clinically significant hyperopic change in corneal refractive power after the first day of lens wear. The PMMA contact lenses resulted in significant corneal swelling and reduced optical performance of the cornea.     

The significance of oxygen during contact lens wear

In order to establish the relevance of oxygen to contemporary contact lens practice, a review of the literature was conducted. The results indicate that there are a number of processes occurring in the normal healthy eye where oxygen is required and which are potentially affected by the presence of a contact lens. These activities appear to take place at all corneal levels, as well as at the limbus. Evidence from laboratory, clinical and modelling studies indicates that what constitutes normal oxygenation (normoxia) depends on, among other things, the physiological system under consideration, corneal location and the state of eye closure. This diversity is reflected in the wide range of minimum lens oxygen transmissibility (Dk/t) requirements that are present in a literature.     

Profile,knowledge, and attitude of contact lens users regarding contact lens wear in Ghana

BackgroundContact lenses are gaining popularity in developing countries as an alternative to spectacles for the correction of refractive errors. It is needful, therefore, to generate information to guide the mode of practice, and assist the industry in developing products for the increasing contact-lenses-user population. The purpose of this study was to identify the demographic profile, as well as the knowledge, attitude to wear and care regimen of wearers of contact lenses in Ghana.MethodsIn a cross-sectional study, case folders of 87 users of contact lenses were selected from the database eye contact lenses practices. The folders were reviewed for the demographic profile, type, and purpose for which the contact lenses were prescribed. Forty-two (42) contact lenses users were then randomly surveyed, using a semi-structured questionnaire to collect information on their knowledge, lens wear regimen, and attitudes regarding lens hygiene. Chi-square test was used to test associations between demographics and lens wear variables.ResultsOut of the 87 cases reviewed, 46 (52.9%) were females and 41 (47.1%) males. Their ages ranged from 15 to 68 years with a mean age of 28.62 ± 9.38 years. The majority- 65 (75%) - were youthful (≤ 40 years), with the highest proportion of them - 46 (53%) - being between 20–29 years. The majority - 60 (68.9%) - had a tertiary level of education. Soft contact lenses were commonly worn by 68 (78.2%) users while 19 (21.8%) wore rigid gas permeable lenses. The purpose for wearing contact lenses included for vision correction – 46 (52.9%), followed by for cosmesis - 23 (26.4%) - and therapeutic reasons -18 (20.7%). The commonest refractive error corrected was myopia - 38 (43.7%), followed by astigmatism -19 (21.8%) and hyperopia 6 (6.9%). Among the 42 users who responded to the questionnaire, by proportion, the majority -17 users (40.5%) - were introduced to contact lenses by optometrists. All respondents reported previous symptoms associated with the use of their contact lenses, but slightly more than half, 25 (57.1%) did yearly follow-up visits.ConclusionThe majority of contact lenses used in Ghana are soft lenses, for the purpose of vision correction. The use of contact lenses was common among individuals in their early adulthood and those with tertiary education.     

The effect of contact lens wear on dynamic ocular surface temperature.

AIM: To determine the dynamic emitted temperature changes of the anterior eye during and immediately after wearing different materials and modalities of soft contact lenses. METHOD: A dynamic, non-contact infrared camera (Thermo-Tracer TH7102MX, NEC San-ei) was used to record the ocular surface temperature (OST) in 48 subjects (mean age 21.7 +/- 1.9 years) wearing: lotrafilcon-A contact lenses on a daily wear (LDW; n=8) or continuous wear (LCW; n=8) basis; balafilcon-A contact lenses on a daily wear (BDW; n=8) or continuous wear (BCW; n=8) basis; etafilcon-A contact lenses on a daily disposable regimen (EDW; n=8); and no lenses (controls; n=8). OST was measured continuously five times, for 8s after a blink, following a minimum of 2h wear and immediately following lens removal. Absolute temperature, changes in temperature post-blink and the dynamics of temperature changes were calculated. RESULTS: OST immediately following contact lens wear was significantly greater compared to non-lens wearers (37.1 +/- 1.7 degrees C versus 35.0 +/- 1.1 degrees C; p < 0.005), predominantly in the LCW group (38.6 +/- 1.0 degrees C; p < 0.0001). Lens surface temperature was highly correlated (r=0.97) to, but lower than OST (by -0.62 +/- 0.3 degrees C). There was no difference with modality of wear (DW 37.5 +/- 1.6 degrees C versus CW 37.8+/-1.9 degrees C; p=0.63), but significant differences were found between etafilcon A and silicone hydrogel lens materials (35.3 +/- 1.1 degrees C versus 37.5 +/- 1.5 degrees C; p < 0.0005). Ocular surface cooling following a blink was not significantly affected by contact lens wear with (p=0.07) or without (p=0.47) lenses in situ. CONCLUSIONS: Ocular surface temperature is greater with hydrogel and greater still with silicone hydrogel contact lenses in situ, regardless of modality of wear. The effect is likely to be due to the thermal transmission properties of a contact lens.     

Environmental impact of three replacement modalities of soft contact lens wear.

Purpose: To illustrate the environmental impact of three contact lens replacement modalities, and to place this into a broader environmental context. Methods: Environmental impact was calculated by sorting the packaging used in the supply of three representative contact lens systems into their constituent materials (liquid, plastic, paper, metal and glass), determining their mass, calculating the annualised consumption by a typical contact lens wearer, and factoring the data against published indices of the environmental impact of the constituent materials. Results: Conventional lens wear had the highest impact and planned replacement lens wear (monthly disposable) had the lowest impact. Conclusions: The overall environmental impact of waste generated thorough the use of contact lens products by the end consumer is insignificant (0.5%) compared with the amount of waste generated in our everyday life.     

Repeatability and reliability of ocular aberration measurements in contact lens wear.

BACKGROUND: To assess repeatability and within- and between-observer reliability when measuring ocular aberrations with and without soft contact lens wear. METHODS: The irx3 aberrometer was used to measure second to tenth radial order aberrations on 13 subjects with and without their habitual soft contact lenses. This was first performed by one observer, who took three separate measurements to determine repeatability. In addition, two observers each took a set of three measurements on two occasions, to determine within- and between-observer reliability. Data were normalized to a constant pupil size for all measurements made on each subject. RESULTS: There was no difference in repeatability with or without contact lenses for Zernike polynomial numbers 3-20. There was no difference between within- and between-observer relative reliability either with lenses (t=1.9, p=0.07) or without lenses (t=1.1, p=0.29). However, both within-observer and between-observer reliability were worse when lenses were worn (t=3.6, p=0.0009 and t=2.8, p=0.0074, respectively). CONCLUSION: The reduction in within- and between-observer reliability when measuring aberrations in contact lens wearers may be due to variability resulting from a variety of factors, such as lens flexure, lens movement, lens decentration and reduced stability of the pre-lens tear film.