The tear film is important both as a lubricating and protective layer and because it provides the outer, optically-smooth, refracting surface of the cornea. The tear film has a thickness of about 6 ,um and appears to be able to maintain its integrity during long periods between the respreading and replenishing action of the blink, by two means: I. The corneal epithelium holds the tear film on its surface, probably aided by mucus from conjunctival cells, which encourages spreading of the film (Lemp, Holly, Iwata, and Dohlman, 1970) purpose (Brown, Foster, Norton, and Richards, I964). Since BZA is a surface-active agent (and indeed may owe its antibacterial activity at least in part to this detergent property), the present experiments were undertaken to examine its effect on the stability of the tear film in rabbit and man. A significant hastening effect of BZA on corneal drying was observed in both species. Methods and results RABBITDutch rabbits were anaesthetized with halothane (3 per cent) in nitrous oxide-oxygen (3:i). The animals to be tested were placed in front of a small fan to hasten drying of the comea, and any tendency of the eyelids to droop was overcome by clipping back the fur on to the top of Address for reprints: Dr W. S. Wilson, Department of Pharmacology, University of Glasgow, Glasgow G12 8QQ the skull. The eyes were equally illuminated by similar 6o watt lamps placed on each side of the animal.Saline (3 drops of o-9 per cent) was applied to both eyes at zero time; the excess fluid was removed from the conjunctival sac by means of paper tissue without allowing the eyelids to blink. The time taken for the development of a dry spot on each cornea was measured and this was taken as the zero-time control value. The tear film was immediately restored by blinking the eyelids tlhree times. BZA solution (3 drops of o-oooi per cent w/v in o09 per cent saline) was then applied, the excess fluid removed as before, and the time for the appearance of a dry spot measured again. This procedure was repeated for successive threefold increases in concentration of BZA. Finally, the cornea was irrigated with saline, and the eyelids repeatedly blinked during a period of about IO minutes, after which another control determination was made 'end control'.These experiments were so straightforward that they were mainly carried out by one person. Since the possibility of observer bias existed, a second series of experiments was conducted in which an entirely impartial observer judged the times of dry spot appearance; another observer administered the eyedrops and operated the stop-clocks.The statistical significance of the results was evaluated using the paired Student's t test.The dry area usually appeared first as a well-defined pit or spot about i mm in diameter. If drying had been allowed to continue, other spots would soon have appeared, enlarged, and coalesced until the entire cornea eventually would have appeared dry and dull. Occasionally, the cornea would dry more uniformly, changing gradually from the norma...
SUMMARY The results of a randomised, prospective, multicentre trial of the management of primary open angle glaucoma are presented at up to five years' follow up. Previously undiagnosed cases were selected with intraocular pressure of 26 mmHg or more on two occasions together with field loss characteristic of glaucoma. Analysis was performed on one eye selected at random from each of 99 patients. Conventional medical treatment followed in unsuccessful cases by trabeculectomy (group A) was compared with trabeculectomy at diagnosis followed when necessary by supplementary medical therapy (group B). The life expectancy of these glaucoma patients was found to be similar to that for the local population matched for age and sex. In group A after four years trabeculectomy had been performed in 53% of eyes because medical management had failed to control the disease. The rate of operation was lower in those patients with intraocular pressure less than 31 mmHg and mild relative field loss (17% at three years) than in those with intraocular pressure greater than 30 mmHg and dense scotomas (75% at three years). Early surgery provided much more stable control with fewer changes in treatment than in group A. The group mean intraocular pressure after trabeculectomy was 15*0 mmHg irrespective of the time of operation, and this was significantly lower than the intraocular pressure in those cases thought to be controlled on medical therapy alone at the end of the first year . Early operation provided significantly better protection of visual field, and the extra loss of visual field with delayed operation occurred in the preoperative period. Changes in visual fields were not related to the use of miotics. There was no significant difference in the final visual acuity in the two groups, but six cases in group A lost central fixation because of progressive loss of visual field, and there were no such cases in group B. Cataract occurred in approximately 10% of cases in both groups, but in group A this happened with only half the number of operations and at a shorter postoperative follow-up than in group B. It appears that in cases of primary open angle glaucoma of this severity the risk of delaying operation are significantly greater than those of performing trabeculectomy as the primary treatment.
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