Ocular fluorophotometric analysis

Fluorophotometric determination of aqueous humor flow rates in red-tailed hawks (Buteo jamaicensis)

OBJECTIVE

To determine aqueous humor flow rate (AHFR) in an avian species by use of anterior segment fluorophotometry.

ANIMALS

9 healthy red-tailed hawks (Buteo jamaicensis; 4 males and 5 females) that ranged from 8 months to 8 years of age.

PROCEDURES

A protocol was developed for fluorophotometric determination of AHFR. Topical administration of 10% fluorescein was used to load the corneas, and corneal and aqueous humor fluorescein concentrations were measured approximately 5, 6.5, and 8 hours later. Concentration-versus-time plots were generated, and slopes and cornea-to-aqueous humor concentration ratios from these plots were used to manually calculate flow rates.

RESULTS

Mean ± SD AHFRs for the right eye, left eye, and both eyes were 3.17 ± 1.36 μL/min (range, 1.67 to 6.21 μL/min), 2.86 ± 0.88 μL/min (range, 2.04 to 4.30 μL/min), and 2.90 ± 0.90 μL/min (range, 1.67 to 4.42 μL/min), respectively. The AHFRs were similar for right and left eyes. These flow rates represented a mean aqueous humor transfer coefficient of 0.0082/min, which is similar to that of mammalian species.

CONCLUSIONS AND CLINICAL RELEVANCE

The AHFR in red-tailed hawks was similar to that of most mammalian species, and the fractional egress was almost identical to that of other species. This information will allow a greater understanding of aqueous humor flow in avian eyes, which is crucial when evaluating diseases that affect avian eyes as well as medications that alter aqueous humor flow.

Bioavailability of fluorescein from a new drug delivery system in human eyes

AIM

To assess the ocular bioavailability of fluorescein from a novel drug delivery system compared with one single preservative free eye drop.

METHODS

Part A: In a randomised study 10 volunteers applied the lyophilisate to one eye and a conventional fluorescein eye drop to the fellow eye. Fluorophotometry was performed before and every 2 minutes up to 30 minutes after application in the cornea and anterior chamber. Part B: Another 10 volunteers applied each form of the application. Fluorophotometry was performed before, +2 minutes, and at +8, +10, +12 hours. The dose corresponding to a single fluorescein dose of the lyophilisate was 68 l microg fluorescein SE 0.17%.

RESULTS

Part A: During the first 30 minutes after administration of the preservative free eye drop of 40 microg the corneal and anterior chamber concentration means were up to 16 times higher in eyes treated with the lyophilisate. Part B: 8-12 hours after application the mean fluorescein concentration in the cornea of the lyophilisate group was two times higher than at baseline. Eyes treated with eye drops had baseline values at +8, +10 and +12 hours.

CONCLUSION

A significantly better bioavailability was achieved in human eyes by using lyophilisate compared with the same dose from a conventional eye drop. Lyophilisates are a favourable alternative to conventional eye drops since they have no preservatives, higher long term stability, no pH adjustment, and easy handling.

Early retinal and renal abnormalities in diabetes

The integrity of the blood-retinal and blood-glomerular vascular barriers were investigated simultaneously in diabetic individuals to determine whether or not the early forms of diabetic retinopathy and nephropathy are temporally related. The blood-retinal barrier was assessed by the technique of vitreous fluorophotometry. Twenty-four hour urinary excretion of albumin was determined by radioimmunoassay before fluorescein measurement. Posterior vitreous fluorescein leakage was greater in the study cohort than in the control population after diabetes had been present 11-20 years (p < 0.05) and 21 years or more (p < 0.01). Albumin excretion was also increased in the diabetic subjects (p < 0.001) and correlated to duration of diabetes (r = 0.51, p < 0.005). Hypertension raised midvitreous fluorescein levels (p < 0.05), but it had no effect on posterior vitreous values. Hypertension was an independent predictive factor for urinary albumin excretion (p < 0.05). Partial correlation analysis showed that vitreous fluorescence and urinary protein were not significantly correlated when controlled for duration of diabetes and for age. Early proteinuria did not predict retinal vascular leakage, nor did increased fluorescein leakage predict renal decompensation in the diabetic subjects. The data suggest that during the early stages of retinal and renal abnormalities associated with insulin-dependent diabetes, the eye and kidney follow different temporal courses to abnormal function.