Alteration of the blood-retinal barrier by dipyridamole.
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Blood Physiological Phenomena↗
Biomedical subjects
J R Howard-Williams
Publications and source records attributed to J R Howard-Williams.
Quantifying early diabetic retinopathy.
A precise and accurate method of numerically quantifying diabetic retinopathy, on standardised retinal colour photographs, has been developed which allows small changes and trends to be monitored. Colour slides are projected onto a screen and features noted on an acetate sheet which provides a permanent record. Sector analysis showed microaneurysms and haemorrhages to occur most often at the temporal-to-macula area, exudates at the macula and cotton wool spots on the nasal side of the retina. Seventy percent of microaneurysms appeared in the previous year, irrespective of the severity of the retinopathy. In proportion to their usual relative prevalences, after normalisation of distribution, the various features can be combined to provide a single value, the Retinopathy Index. This provides an overall assessment of retinopathy which is suitable for comparing the progress of mild retinopathy in prospective studies.
Aneurysm↗
Flash and pattern electroretinograms in normal and laser-induced glaucomatous primate eyes.
Experimental glaucoma was produced in one eye of five cynomolgus monkeys with the argon laser delivering 100-200 50-mu spots at 1200-1500 mW power and 0.5 sec to 360 degrees of the mid-trabecular meshwork. Monocular electroretinograms (ERGs) were recorded prior to and 2, 3, and 4 mo following the laser treatment. In the laser-treated (glaucoma) eyes, normal flash ERGs were observed using 1-Hz stimulation; however, pattern ERGs (PERGs) elicited using steady-state counterphase modulation of a 0.51 cpd square wave grating showed statistically significant reductions of amplitude. Only small reductions of PERG amplitude were seen with a 1.25 cpd grating. In three animals, abnormalities of the PERG occurred prior to clinically significant cupping of the optic nervehead. Moreover, reductions of PERG amplitude were progressive and associated with the magnitude of cupping of the optic nervehead and elevation of intraocular pressure. PERG amplitude did not change following acute reductions in intraocular pressure in the glaucoma eyes. Several control experiments were conducted to insure that results were not due to alterations in pupil size, refractive state, or accommodation in the glaucoma eyes. The authors believe they now have a monkey model for the electrophysiologic study of glaucoma.
Animals↗
Pharmacological testing in the laser-induced monkey glaucoma model.
Glaucoma was induced in cynomolgus monkeys by photocoagulating the trabecular meshwork with the argon laser. Repeat treatments were often necessary and wide intraocular pressure fluctuations were characteristic. Baseline intraocular pressure was measured with a calibrated pneumatonometer hourly for six hours. On a succeeding day a baseline measurement was made, 50 microliter of the drug to be tested applied, and six hourly measurements of intraocular pressure repeated. The effects on intraocular pressure of timolol, epinephrine, pilocarpine, vanadate, prostaglandin F2 alpha (PGF2 alpha), forskolin, and corynanthine were tested in at least eight eyes. Significant (p less than 0.05) reductions of intraocular pressure were produced by 0.5% timolol, 2% epinephrine, 4% pilocarpine, 1% vanadate, 500 micrograms of PGF2 alpha and 1% forskolin. Five per cent corynanthine produced no significant lowering of intraocular pressure. Tonography revealed an increased outflow facility associated with the reduction of intraocular pressure 2 hours after the administration of 4% pilocarpine. This glaucoma animal model may be useful in investigating agents that lower intraocular pressure by a variety of mechanisms.
Administration, Topical↗