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Although the hydrogel contact lenses have been commercially available for over a decade, reports on pnmate controlled studies of the ultrastructural response to such lenses are sparse.' There is an abundance of physiological and pathological evidence of individual variations in response as seen in the human at clinical levels of observations.2The present study was designed to examine the comeal epithelial stress effects of different thicknesses of soft lenses over various time periods and to study this on the primate eye by means of the electron microscope. Furthermore, the contact lens oxygen gas flow was measured by calculation and the lens pressure effects correlated with degrees of anoxia.The results will be compared with the recent study in the same laboratory of Bergmanson and Chu.3 They studied primates wearing hard non-permeable corneal lenses (PMMA) for 2 to 24 hours, and their results indicated epithelial loss, atrophy and oedema.

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SUMMARY Vertical corneal striae distributed across the posterior cornea are one of the objective signs of clinically unacceptable corneal swelling (>6%) resulting from contact lens wear. This study reports that corneal striae are repeatable both in configuration and location with different levels of hypoxia. In most instances entoptic phenomena result from the presence of these lines. The results suggest that the healthy, avascular, transparent cornea has certain localised areas in its anatomical structure which may give rise to bundles of collagen fibres being made visible objectively and subjectively during conditions of corneal swelling.Corneal striae is a term used to describe lines seen in the corneal stroma of varied appearance, aetiology, and pathology. Deep striae have been seen as a result of trauma (penetrating wounds),' after intraocular operations (striate keratitis),' in degenerative changes of collagen such as keratoconus,' in diabetes,' and in idiopathic6 corneal conditions. It is a well known clinical observation that vertical striate lines distributed across the posterior cornea are caused by corneal oedema accompanying hydrogel (soft) lens wear.7" The vertical or near-vertical striate lines, indicating the presence of 4 to 6% or more of corneal oedema,' are reversible on removal of the lens.' Striate keratopathy accompanies stromal swelling of about 7 to 10% or more, and appears as deep folds in the endothelial mosaic/Descemet's membrane area.7' The stromal lines can best be viewed against the dark background of the pupil with high light intensity from the slit-lamp biomicroscope by using direct focal illumination.""'The reproducibility and entoptic phenomena of corneal striae were first noted by Johnson (reported by Johnson and Ruben") while investigating stromal oedema induced by soft gel lens wear.'2 The striae were induced by thick hydrogel lenses in normal adult corneae following three hours of wear in both the open and closed eye conditions. Photographic records were made of the appearance of the striae by retroillumination, and the similarity to the entoptic phenomena as recorded in a drawing by the indi- intrasubject repeatability of striae with large intersubject variability of corneal striate lines. In this paper we describe the repeatability and entoptic phenomena of corneal striae following contact lens wear and provide additional clues to its aetiology. Material and methods SUBJECTSThe study involved 11 volunteers with an age range of 23 to 36 years, consisting of nine males and two females. A second group of subjects seen after an interval of one year comprised five females and two males, with an age range of 21 to 30 years. All were free of any eye pathology and none had previously worn contact lenses.To verify the first series of observations a second group of subjects similar to the first were studied. The experiment was to ascertain a qualitative finding and not measure in any degree the striae.The illustrations (Figs. 1 and 2) are selected from those taken from one subject. C...

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