Clinical Study of Corneal Response to the Wear of Low Water Content Soft Lenses

Corneal edema was induced by a 2-h closed-eye wear of a thick hydrogel contact lens. Corneal edema production and edema recovery responses were measured in the central and mid-peripheral (3 mm inferior) cornea of 10 younger (20.4 +/- 2.0 years) and 10 older (69.0 +/- 3.4 years) subjects using optical pachometry. The amount of edema produced was not significantly different between the two corneal locations nor between the two age groups. The edema recovery rates of the central and mid-peripheral cornea were not significantly different in either the younger or older group. The edema recovery rates at both corneal positions were significantly faster in the younger group than in the older group. The results of this study suggest that the mechanisms that control edema production and recovery in the inferior mid-peripheral cornea are similar to those previously described in central and temporal mid-peripheral locations. Ageing appears to influence the edema production and recovery mechanisms of both the central and mid-peripheral cornea in similar ways.

Section: Discussionsupporting

confidence: 93%

mentioning

confidence: 99%

The effect of age on the edema response of the central and mid‐peripheral cornea

Siu

Herse

1993

“…A low positive correlation between changes of central corneal thickness and curvature was reported by El Hage & Beaulne (1975). In accordance with other studies (Bailey & Carney 1972;Carney 1975b: Lowther & Tomlinson 1979, the curvature changes in our group of hydrophilic lens wearers were not readily explained by neither a corneal swelling nor a moulding effect. This has commonly been ascribed to the flexibility of the lens material and to an evenly distributed corneal swelling during hydrophilic lens wear (Carney 1975a;Mandell 1975).…”

Section: Discussion'supporting

confidence: 92%

“…The hydrophilic lens group showed a small, initial mean corneal flattening followed by a significant steepening. Both the pattern and the magnitude of these changes were in accordance with pretiiously reported findings (Barnett & Rengstorff 1977;Bradley & Schoessler 1979;Grosvenor 1975;Lowther & Tomlinson 1979). A low positive correlation between changes of central corneal thickness and curvature was reported by El Hage & Beaulne (1975).…”

Section: Discussion'supporting

confidence: 90%

Variations of Central Corneal Curvature During the First Year of Contact Lens Wear

Høvding

1983

During hard, hydrophilic and silicone lens wear the variations of central corneal curvature in the 2 eyes of each individual were significantly correlated. Mean changes of principal radii of curvature were small in each lens group (-0.075-+0.068 mm). Hydrophilic lens wearers showed an initial mean flattening of corneal curvature, followed by a significant steepening. Hard lens wearers apparently showed the opposite sequence of mean changes. Silicone lens wearers showed a significant mean corneal flattening. Central corneal asphericity was reduced during hard lens wear. Considerable individual curvature changes occurred (-0.35-+0.30 mm), but none of these necessitated lens refitting. Changes of the central corneal thickness and curvature during hard lens wear were apparently inversely correlated, the ratio between the changes being about -0.08:1. Hard and silicone lenses probably exerted a mechanical moulding effect. The exact aetiology of curvature changes in hydrophilic lens wearers remains obscure. Corneal curvature changes appear less reliable than corneal oedema in the detection of lens-induced impairment.

“…Pachometry studies of topographical corneal swelling with hydrogel contact lenses (El Hage & Leach 1975;Sanders et al 1975;Lowther & Tomlinson 1979; Schwartz & Tomlinson 1979; Hirji &-Larke 1979) have generally supported this conclusion. However, most studies have limited their measurements to the mid-periphery of the cornea (approximately 4 mm from the central cornea).…”

mentioning

confidence: 96%

Topographical corneal oedema

Holden

McNally

Mertz

et al. 1985

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.