Physical properties of stimulated and unstimulated tears.

It has long been assumed that unstimulated tears are more thoroughly equilibrated with epithelial secretions than stimulated tears, since they are in contact with tarsal, bulbar and corneal surfaces for longer. It was also believed from results with model solutions that soluble mucin is responsible for the observed surface tension and viscosity of tears. If longer contact means more mucin is dissolved in the aqueous tears, then the surface activity (surface tension lowered by mucin) and viscosity (raised by mucin) of tears should therefore be enhanced in unstimulated over stimulated tears. Pools of stimulated and minimally-stimulated tears were collected from a group of healthy adult volunteers by glass capillary. Viscosities were measured in the Contraves Low Shear 30 rheometer over the range of shear rates 0-130 sec-1. Surface tension was measured in the collection capillaries by a micro-technique, before and after refrigerated storage. Both surface tension and viscosity were determined for a variety of tear proteins and mucins. No significant difference was found between the viscosity/shear rate plots of stimulated and unstimulated tear samples. The viscosities of solutions of individual tear proteins were low, except for the combination of lysozyme and secretory IgA. Surface tensions were also similar in both cases, and unchanged by storage at room temperature or refrigeration, indicating no significant loss of surface-active material by adsorption on the capillary walls. Results with model mucin solutions gave a variety of results indicating either little surface activity or losses due to wall adsorption. Tear proteins, individually or in combination, did not lower surface tension to the level of tears. Tear viscosity seems not to depend on the level of dissolved mucins. This suggests either that a constant level of these is picked up even by short-term contact with ocular surfaces, or that viscosity arises from currently unknown materials which vary little with tear flow rate. This type of shear-dependent viscosity is most easily simulated in model solutions with polyionic linear macromolecules, including mucins. The contribution of individual proteins to overall viscosity is small, but combinations including lysozyme show tear-like characteristics, and may indicate that proteins whose concentration is relatively independent of tear flow rate combine with other tear components (possibly including mucins or lipids) to produce their full effect on tear viscosity. The surface tension results suggest that mucins are not of primary importance. Theories of tear film structure and performance need revision.

National survey of corneal abrasion treatment.

PURPOSE: To survey the different methods used in the management of corneal abrasions (including iatrongenic cases) nationally. METHOD: A questionnaire survey of all 162 ophthalmic units in the UK was carried out in 1997. RESULTS: The response rate was 134 of 162 (83%). The majority of units do not have an established policy for the treatment of corneal abrasions. Topical antibiotic alone and antibiotic together with a cycloplegic are the commonest immediate treatments, whilst the most common treatment course is topical antibiotic. Padding and patient follow-up is practised some of the time by most units and all of the time by the remaining minority. Use of a soft bandage contact lens is uncommon. There is no statistically significant difference (p > 0.05) between the policy-holders and non-policy-holders in their use of the various topical regimes, padding and soft bandage contact lens. CONCLUSION: The traditional trio of topical antibiotic, cycloplegic and padding is still the mainstay of corneal abrasion treatment amongst units nation-wide. However, there is a lack of reproducible scientific evidence to support this treatment. Larger randomised trials looking at the efficacy of the different treatment options are needed.

Recurrent papilloedema and early onset optic atrophy in Behçet's syndrome.

Two patients with Behçet's syndrome and intracranial hypertension are reported. One developed a recurrence of papilloedema while receiving treatment but eventually made a full recovery, whereas the other developed optic atrophy within three months of onset despite treatment.