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RESUMEN

The Keeler Tearscope Plus was invented by the author as a multi-use instrument for the non-invasive examination of the tear film, its appearance, volume, stability and, its effect on the ocular and contact lens surface. Its use is maximised by following a step-by-step approach described which is based on simple clinical principles of tear film stability.

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The aims of the current investigation were to: (1) characterize (structure, volume, and stability) the preocular tear film of contact lens wearers and nonwearers and (2) test for any difference between contact lens wearers and nonwearers and between symptomatic and asymptomatic subjects. The tear film structure and stability were tested using the Tearscope in conjunction with the biomicroscope observation system. The tear prism height, which is indicative of the tear volume, was measured with the slitlamp. The study was carried out on 239 subjects (478 eyes) who attended our clinic for contact lens fitting. Of these, 184 were habitual daily soft contact lens wearers who had not been wearing contact lenses for at least 24 h; the other 55 were noncontact lens wearers. The results obtained showed that: (1) the stability of the tear film was correlated for two eyes of the same subject; (2) the structure, volume, and stability of the preocular tear film were similar for both groups; (3) no difference in tear film stability was found between asymptomatic and symptomatic contact lens wearers, but a significant difference was found between asymptomatic and symptomatic noncontact tact wearers; and (4) the stability of the tear film was influenced by the nature of the lipid layer present at the surface of the aqueous layer; the greatest stability was achieved when the lipid layer was thick and homogeneous (amorphous pattern).

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The surface of hydrophilic contact lenses is intrinsically hydrophobic. Biocompatibility requires the contact lens surface to be coated with a lipoproteinic biofilm produced by the ocular secretion. For daily disposable modality of wear it is essential that biocompatibility, clinically represented by good in vivo wettability and subjective acceptance, is achieved as quickly as possible following insertion, as the process needs to be repeated daily. It has been hypothesised that non-ionic materials will not achieve biocompatibility as rapidly as ionic materials owing to the latter's ability to attract high levels of adsorbed proteins. The current investigation was a double-masked crossover study that evaluated, over 1 week of wear, a new non-ionic material (Nelfilcon A) and a current ionic material (Etafilcon A) under daily disposable modality. The results obtained showed that overall, both contact lens materials achieved good in vivo tear stability over the first 30 min of wear and good subjective acceptance that remained stable over the period of wear. The results obtained demonstrate that a non-ionic material can achieve rapid biocompatibility and subjective acceptance in a similar manner to an ionic material.

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This investigation monitored the response of established contact lens wearers using contact lenses made from Filcon 4a 77% water-content material in three different thicknesses (0.08, 0.10 and 0.12 mm) over a 6-hour period of wear under adverse environmental conditions. The results obtained showed the following. (1) In accordance with previous studies carried out with lenses of similar water content, the present lenses produced corneal desiccation staining under the challenging conditions of use. However, the staining produced was similar for all three lens thicknesses tested. (2) Corneal desiccation staining was present despite the good and stable fitting characteristics observed during the study, confirming that mechanical trauma is not a necessary cause for soft-lens-induced desiccation staining. (3) Corneal desiccation staining was associated with a rapidly destabilizing pre-lens tear film (PLTF) and a thinning lipid layer. The initial break-up of the PLTF and corneal staining were recorded with a higher incidence in the vertical quadrants than in the horizontal quadrants. The PLTF is thinnest and most unstable at the tear prism margin border, hence least efficacious at preventing evaporation. Corneal desiccation staining may be due, at least partly, to excessive evaporation at the contact lens front surface.

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The in vivo wettability of soft contact lenses worn by a group of 10 subjects was monitored over a 24-hour period including 8 hours closed eye. Two types of lenses were tested: Igel 67 (Prima) and Bausch & Lomb 70. They were each worn once in both eyes by all the subjects. The in vivo wettability of the lenses tested was evaluated by measuring the pre-lens non-invasive break-up-time (NIBUT) and assessing the nature of the pre-lens tear film structure. The results obtained showed good wettability throughout the study and no difference between the two materials tested, but a significant difference between open and closed eye wear. The tear film was far more stable (p less than 0.01) immediately upon waking (mean NIBUT 21.2 s) than during open eye wear (mean NIBUT 11.2 s). Also at waking the pre-lens lipid layer was thicker than during open eye wear and the lens surface had a greater mucous coating. The presence of a more stable pre-lens tear film at waking was associated with a different tear film structure. We believe these differences in pre-lens tear film structure are responsible for the greater stability recorded.

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Polarised light biomicroscopy was used to examine the normal pre-corneal tear film in 21 eyes of 12 pekingese dogs. The purpose of the study was to examine the influence of excessive exophthalmos on the pre-corneal tear film in the dog. The majority of the animals were found to have high levels of ocular surface contamination by particulate material and plaques of viscous mucus. Other abnormalities included surface lipid with an abnormal granular (three dogs) or 'curdled' (two dogs) appearance; excessive thinning of the lipid layer of the tear film; and the presence of dark globular structures in two dogs, which were presumed to be abnormal meibomian lipid. Break up of the tear film was observed in one dog. Grossly, a thread of viscous mucus was frequently observed along the margin of the lower eyelid. It is postulated that this thread forms because of the excessively exophthalmic conformation of the breed, which prevents the normal access of effete mucus and entrapped debris to the lower conjunctival fornix. The combination of the above factors in the pekingese is suggested as the mechanism whereby the tear film has a reduced stability, thus enhancing the risk from factors more usually considered to initiate corneal ulceration in the breed. The possible adverse effects of lid splitting for the mass removal of distichiae in exophthalmic dogs is discussed.

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Polarised light biomicroscopy was used to assess the behaviour and interactions of two polymer-containing preparations of artificial tears, and two lipid-containing ointments, with the normal and abnormal pre-corneal tear film. The preparations were used topically in six normal dogs, and three dogs with keratoconjunctivitis sicca. A transient morphological alteration of the surface lipid layer of the tear film was commonly observed after the use of polymer solutions. The ointments spread as a continuous or semi-continuous layer over the normal, or polymer-supplemented, aqueous tears. Further applications of artificial tears produced only a temporary disruption of this layer. In dogs with keratoconjunctivitis sicca, thickening of the lipid layer of the tear film was observed for over 20 hours after the administration of ointment. These observations are discussed in relation to the prospects for the improved medical treatment of keratoconjunctivitis sicca by the use of polymer-containing solutions and ointments in combination.

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