Effect of Healon and Viscoat on outflow facility in human cadaver eyes.

PURPOSE: To compare the acute effects of Healon (sodium hyaluronate) and Viscoat (sodium chondroitin sulfate-sodium hyaluronate) on outflow facility in human cadaver eyes and determine which viscoelastic agent is least likely to cause an intraocular pressure (IOP) spike after cataract surgery. SETTING: The Glaucoma Research Lab, University of Toronto, Ontario, Canada. METHODS: In this prospective paired study, 15 pairs of human cadaver eyes were used. Following the construction of a 3.0 mm scleral tunnel, 0.25 cc of Healon was injected into the anterior chamber of 1 eye and 0.25 cc of Viscoat was injected into the contralateral eye. The viscoelastic agents were removed from both eyes in a standardized fashion and the scleral tunnels closed. The eyes were then perfused at a constant IOP of 8.0 mm Hg, corresponding to 16.0 mm Hg in vivo. Outflow facility (microL/minute [min]/mm Hg) was recorded every 15 minutes for 24 hours using standard methods. RESULTS: Outflow facility in the Viscoat-treated eyes decreased appreciably for the first 3 hours, then recovered somewhat after 12 hours; facility in the Healon-treated eyes showed less of an overall decrease. Over the 24 hour perfusion period, mean outflow facility was 0.037 microL/min/mm Hg +/- 0.015 (SD) in the Viscoat-treated eyes and 0.060 +/- 0.012 microL/min/mm Hg in the Healon-treated eyes. Healon reduced outflow facility significantly less than Viscoat between 3.25 and 10.50 hours postoperatively (P < .05, 2-tailed t test). CONCLUSIONS: Healon reduced outflow facility less than Viscoat between 3.25 and 10.50 hours postoperatively.

Central corneal thickness in low-tension glaucoma.

BACKGROUND: It is possible that the intraocular pressure (IOP) is underestimated in eyes whose central cornea is thinner than normal. The objective of this study was to determine and establish the significance of central corneal thickness in patients with low-tension (normal-tension) glaucoma compared with those with chronic open-angle glaucoma (COAG) or ocular hypertension and healthy eyes. METHODS: The study was carried out from February 1998 to May 1999. Central corneal thickness was measured by ultrasonic pachymetry and IOP was measured by Goldmann applanation tonometry in 25 patients with low-tension glaucoma (untreated IOP less than 21 mm Hg with evidence of optic nerve head damage and corresponding visual field loss on automated perimetry), 80 patients with COAG (untreated IOP 21 mm Hg or greater with evidence of optic nerve head damage and corresponding visual field loss on automated perimetry), 16 patients with ocular hypertension (untreated IOP 21 mm Hg or greater, with normal optic nerve head and no history of glaucoma or elevated IOP, and normal visual field on automated perimetry) and 50 control subjects (untreated IOP less than 21 mm Hg with normal optic nerve head and no history of glaucoma or elevated IOP). Analysis with Pearson's product-moment correlation was performed to determine the correlation of IOP and central corneal thickness, and one-way analysis of variance was used to compare corneal thickness between groups. RESULTS: The central cornea was significantly thinner in the low-tension glaucoma group (mean 513.2 mu [standard deviation (SD) 26.1 mu]) than in the COAG group (mean 548.2 mu [SD 35.0 mu]) and the control group (mean 556.7 mu [SD 35.9 mu]) (p < 0.001). No significant difference in corneal thickness was found between the COAG and control groups. The ocular hypertension group had significantly thicker corneas (mean 597.5 mu [SD 23.6 mu]) than the three other groups (p < 0.001). INTERPRETATION: Patients with low-tension glaucoma may have thinner corneas than patients with COAG and healthy subjects. This results in underestimation of their IOP. Corneal thickness should be taken into account when managing these patients to avoid undertreatment.

Contrast sensitivity in asymmetric glaucoma.

We measured central contrast sensitivity in both eyes of 27 patients with asymmetric glaucomatous visual field loss or optic disc cupping. In 15 patients contrast sensitivity was less in the eye that by perimetry or ophthalmoscopy was the more severely damaged. In 10 patients contrast sensitivity was the same in the two eyes. In two patients, it was impaired more in the eye with the normal visual field. However, the latter two patients had ophthalmoscopic evidence of optic nerve damage (disc hemorrhage or large cup) in the eye with the lower contrast sensitivity, even though the visual field was normal. Asymmetry of contrast sensitivity was not found in normal control subjects. These results suggest that glaucoma does alter central vision, even when visual acuity remains normal and visual field defects are far from fixation. Contrast sensitivity may be impaired by a different mechanism than that which leads to visual dield loss. Although the two types of visual dysfunction often occur together, some patients may have more severe impairment of central vision (as measured by contrast sensitivity testing) in one eye and more severe loss of peripheral vision (as measured by perimetry) in the other eye.

Effect of retrobulbar anesthesia on ocular tension.

To determine the effect of retrobulbar lidocaine, with or without epinephrine, on intraocular pressure, 50 patients admitted to hospital for cataract surgery were selected at random. By applanation tonometry the tension of each eye was measured when the patient was placed on the operating table and 4 minutes after the retrobulbar injection. The decrease in intraocular pressure 4 minutes after the injection was not significant, clinically or statistically, and probably resulted from relaxation of the extraocular muscles.

Baring of a circumlinear vessel in glaucoma.

We independently examined 144 optic disc stereophotographs. Despite a preliminary learning trial, we were able to agree about the presence of a circumlinear vessel in only 73% of eyes and about baring of a vessel, if present, in only 71% of eyes. Bared vessels were present in 73% of 22 glaucomatous eyes, 41% of 71 ocular hypertensive eyes, and 14% of 51 normal eyes. During several years of follow-up of 44 ocular hypertensive eyes with bared circumlinear vessels, visual field defects developed in only three. We conclude that baring of a circumlinear vessel is a difficult sign for trained observers to detect with certainty and, although present frequently in glaucoma, is of low specificity as a sign or predictor of glaucomatous damage.

The early psychophysical disturbances in chronic open-angle glaucoma. A study of visual functions with asymmetric disc cupping.

Fourteen patients with elevated intraocular pressures, normal visual fields, and asymmetry of disc cupping were examined using a number of psychophysical tests. The results suggest that color vision and visually evoked potentials show early disturbances, but a contraction of the visual field is variable.

Visual field defects in low-tension glaucoma. Comparison of defects in low-tension glaucoma and chronic open angle glaucoma.

In a study of the visual fields of 160 eyes with low-tension glaucoma (LTG) and 154 eyes with chronic open angle glaucoma with the same degree of optic nerve change, no differences in the qualitative or quantitative characteristics were found. The field defects in those eyes with LTG in which a major hemodynamic crisis had occurred were not different from those in which no crisis had been documented.

Sources of variability in the results of applanation tonometry.

Sources of variability in measurements of intraocular pressure (IOP) by applanation tonometry were examined with a repeated 3 X 3 Latin square design that allowed independent extraction of variation attributable to nine patients, three observers and the order in which the observers performed the measurements. The observers, who were experienced, did not differ significantly in the general level of the IOP readings they obtained or in the variability of the readings. The effect of order was significant; there was an approximately linear decrease in IOP with successive measurements, though the difference between the first and second readings was the largest. The intrinsic variability of the IOP readings gave approximate 90% tolerance intervals of +/- 4.5 mm Hg for a single reading and +/- 3 mm Hg for the average of two readings. The mean decrement between the first and second IOP readings, 1.0 mm Hg, implies the need for a consistent protocol for successive sessions of applanation tonometry.

Features of the optic disc in preglaucomatous eyes.

Sixteen preglaucomatous eyes in which glaucomatous field defects developed were compared with 38 preglaucomatous eyes matched for age and sex whose fields remained normal. A noticeable enlargement of the cup occurred in 31% of those in which field loss developed. The cups of those in whom visual field defects developed were larger than in the controls, thus suggesting early acquired tissue damage preceding field loss. Field defects developed without noticeable enlargement and with a small initial cup in 12% of those observed, and these would not have been suspected from the initial disc appearance.

The effect of pH and osmolarity on the ability of tolerate artificial tears.

Many patients with keratitis sicca complain that the commercially available artificial tears burn when they are instilled and fail to relieve their distressing symptoms. We examined the effects of altering both the pH and osmolarity of hydroxypropyl methylcellulose tear substitute on the tolerance of 15 patients with varying degrees of keratitis sicca. Approximately equal numbers of patients selected the neutral hypotonic tear preparations and the isotonic or near-isotonic alkaline tear substitutes. The isotonic alkaline tear preparation was preferred by the majority of our patients with moderate or severe dry eyes. A commercially available alkaline tear substitute is needed.

Vitreous and retinal surgery in pseudophakia.

We review scleral buckling and vitrectomy procedures in thirteen pseudophakic eyes. Pre-operative difficulties in visualizing the fundi were few. Despite operative complications due to the implant, 90% of the retinas were reattached. Late complications involving particularly the anterior segment in both the buckling and vitrectomy groups caused the poor visual results.