Short term wear of high Dk soft contact lenses does not alter corneal epithelial cell size or viability

Abstract

Background/aims-Current contact lenses (CLs) when worn on an extended wear basis cause corneal epithelial alterations. The aim of this study was to evaluate changes in corneal epithelial cell morphology and physiology following short term (3 months) wear of highly oxygen permeable CLs and to compare this with disposable CLs. Methods-Subjects were wearers of highly oxygen permeable CLs (n=11, wearing CLs on a 30 night schedule), disposable CL users (n=6, wearing CLs on a 6 night schedule), and non-CL wearers (n=20). Mean CL wear experience was 3 months. Epithelial cells were harvested using corneal cytology and were stained using acridine orange and ethidium bromide. Epithelial cell size and viability were determined. Results-The majority of epithelial cells recovered were non-viable (71%), and the mean longest cell diameter was 38 (SD 8) µm. Disposable CLs caused an increase in cell size (42 (7) µm) compared with both non-wear (39 (7) µm, p=0.01) and wear of highly oxygen permeable CLs (37 (10) µm, p=0.0049). There was no diVerence in cell viability between groups. Conclusions-Extended wear of disposable CLs caused an 8% increase in cell diameter in harvested corneal epithelial cells following 3 months of CL wear. Cells harvested following 3 months' wear of highly oxygen permeable CLs were indistinguishable from those recovered from non-CL wearers. (Br J Ophthalmol 2001;85:143-146) Long term overnight contact lens (CL) wear causes profound changes in corneal epithelial metabolism and physiology. In animal studies these eVects manifest as increased corneal epithelial fragility, due to epithelial oedema and loss of desmosomal contacts between cells, 1 and reduced epithelial adhesion, due to a reduction in the number of hemidesmosomes in the basement membrane adhesion complex.2 3 Lens related metabolic changes have manifested as impaired mitosis with lactate accumulation in the anterior chamber. 4 Studies in humans have demonstrated epithelial thinning and reduced oxygen uptake rate with long term extended lens wear. 5 More recently, overnight lens wear has been shown to impair epithelial barrier function, measured by an increase in permeability to sodium fluorescein. 6 Direct evaluation of corneal epithelial cell alterations has been possible using specular and confocal microscopy. Morphological changes following extended wear of hydrogel lenses have included increased corneal epithelial cell size on specular microscopy, 7 8 which has been attributed to a prolonged residence time of mature cells on the surface epithelium. Short term wear of disposable hydrogel lenses on a 6 night extended wear schedule has been shown to increase superficial cell area by 28% 9 and this eVect appears to be proportional to the duration of continuous wear. 10Both morphological and metabolic alterations associated with extended wear of hydrogel lenses have been primarily attributed to chronic hypoxia or corneal acidosis and, perhaps secondarily, to factors such as reduced tear exchange, mechanical eVects, and the impact of t...

Have Silicone Hydrogel Lenses Eliminated Hypoxia?

“…52 Daily wear of conventional hydrogels and silicone hydrogels has been shown not to significantly affect central epithelial thickness. 54 Taken together hypoxia, direct lens pressure, and modulation of epithelial homeostasis are possible mechanisms underlying the epithelial changes observed during all soft lens wear. Epithelial surface cells harvested using corneal cytology from high Dk silicone hydrogel lens wearers after 3 months of continuous wear are indistinguishable in size, morphology, or viability from cells taken from nonlens wearers.…”

The effect of long-term wear of soft lenses of low and high oxygen transmissibility on the corneal epithelium

“…For those subjects, previous low Dk daily wear was considered equivalent to half a year of extended wear. On the basis of this, total wear experience for the low Dk group was 14 (4) years (range: [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Four low Dk subjects wore lenses on a 13 nights/week extended wear schedule with fortnightly replacements.…”

“…These include central [1][2][3][4][5] and peripheral 3,6 epithelial thinning, basal cell fragility, 7 reduced surface cell shedding, 1,2,8 and cell death, 1,9,10 reduced mitosis, 11 a lower number of epithelial cell layers, 4,7 and reduced oxygen uptake. 5 Increases in surface cell size, 1,2,8,[12][13][14][15] bacterial adhesion, 1,2,8 epithelial permeability, 16 and the number of microcysts 5,17 have also been observed. Although alterations to the corneal epithelium in the short term have been well described, the appearance of the epithelium after long-term lens wear is often poorly characterized, particularly in the case of lens materials and modalities of wear introduced to the market in more recent years.…”

The Effects of Short-Term Lens Wear and Eye Rubbing on the Corneal Epithelium

“…Although high oxygen-transmissible (Dk) lens wear has reduced some of the hypoxic-related effects on the corneal epithelium such as epithelial microcysts, 3,4 reduced oxygen uptake, 3 epithelial acidosis, 5 and epithelial permeability, 6 they have been shown to alter the epithelium in the following ways: epithelial thinning, 7,8 increased surface cell size, [7][8][9][10][11] reduced surface cell shedding, [7][8][9] and reduced mitosis. 12 Most of these studies have investigated the effects of high Dk lens wear over weeks and months of wear with little being known, to date, on possible alterations in the shorter term.…”