Postlens tear film morphology, lens movement and symptoms in hydrogel lens wearers Simon A. Little* and Adrian S. Bruce Centre for Eye Research, School of Optometry, Queensland University of Technology, GPO Box 2434, Brisbane 4001, Australia (Received 30 April 1993, in revised form 4 August 1993) Postlens tear film morphology, iens movement and symptoms were assessed in 100 subjects wearing hydrogel contact lenses on a daiiy wear schedule. Postlens tear film appearance in specular reflection was categorized as amorphous, coloured, striated or dynamic (variable with biinicing), and subjects' symptoms were assessed using a questionnaire. Non-amorphous appearances were present in 25% of subjects and occurred approximateiy equally with HEMA, Acuvue. igei 55 and other lens typies. Patterned appearances were found to be associated with reduced lens movement (Kruskal-Wallis ANOVA, P < 0.001). The most common symptom (dryness) was not significantly related to postlens tear film appearance. Postlens tear fiim morphology was shown to be a determinant of iens movement, but may be unrelated to common symptoms. On application of a contact lens to the eye, the precorneal tear film is divided into two new and different tear layers'. The new tear layers, the pre- and postlens tear films, must perform the normal functions ofthe precorneal tear film, as well as any new tear fiilm functions arising with contact lens wear. Probably the most important functions of the prelens tear film are in forming the anterior optical surface and pro- viding lubrication for stable, comfortable vision. Irregularity of the prelens tear film may produce scattering of incident light^, along with a reduction in the quality of vision\ In addition, comfort may be reduced by prelens lipid layer instability"*, and associated lens surface drying^^. Other benefits of prelens tear film integrity are the prevention of lens dehydration^" facilitation of lens surface rehydration^ and resistance to deposit formation'^*". The functions of the postlens tear film are less clearly established than those of the prelens tear film. Never- theless, many potential roles ofthe postlens tear film have been put forward. A model for some ofthe possible functions ofthe prelens and postlens tear films is presented in Figure 1. Postlens tear film viscosity has been proposed as a determinant of force required for lens movement'". Also, coloured or patterned appearances of the postlens tear film observed in specular reflection have been associated with minimal lens movement" and implicated in the mechanism of hydrogel lens binding'''. However, these studies can not be considered conclusive as small numbers of subjects were involved. Several authors have speculated that more efficient postlens tear exchange may increase expulsion of debris and metabolic *MBCO ^ '^. Josephson and Caffery have also suggested that greater postlens tear exchange may reduce the incidence of infiltrative keratitis in daily wear'^ In hydrogel lens wear the supply of nutrients'^ and epidermal growth factor (EGF)''' from the tear film to the corneal epithelium may be reduced^". Also, a reduction in blink-induced shear forces at the corneal epithelium may result in diminished epithelial exfoliation^' "^. Bacteria may adhere more readily to older epithelial cells^^ " which may facilitate the development of infectious keratitis following Prelens tear film 1. Optical {vision) 2. Lubrication (comfort) 3. Maintain lens hydration 4. Role in deposit formation Contact Lens Postlens tear film 1. Lubrication (lens movement) 2. Comfort 3. Epithelial hydration {staining) 4. Debris removal 5. Anti-microbial 6. Epiihelial nutrition 7. Promote epithelial exfoliation Figure 1 Theoretical model of some possible roles of the prelens and postiens tear films in hydrogel lens wear © 1994 Butterworth-Heinemann for British Coilege of Optometrists 0275-5408/94/010065-05 Ophthal. Physiol. Opt.. 1994. Vol. 14, January 65