J.A. van Best

Corneal epithelial permeability after instillation of ophthalmic solutions containing local anaesthetics and preservatives

The effect of the local anaesthetics oxybuprocaine (OBu) and tetracaine (Tetra) and the preservatives chlorhexidine (CH) and benzalkonium chloride (BAK) on corneal epithelial permeability was studied by fluorophotometry in normal human eyes. Five instillations of one drop ophthalmic solution of the compounds were administered to one eye at 2-minute intervals; a control solution was instilled into the fellow eye. The increase in corneal epithelial permeability, expressed as the permeability ratio between the treated and control eye, was not significant after instillation of the anaesthetics. The preservatives and the combination OBu + CH increased corneal epithelial permeability significantly (P less than 0.05). OBu + BAK and Tetra + BAK increased permeability to a far greater extent (P less than 0.005).

A Simple Method for Determination of Corneal Epithelial Permeability in Humans

A simple method for the determination of human corneal epithelial permeability to fluorescein is presented. The method consists of applying a 1% sodium fluorescein solution to the cornea for 8 minutes by means of an eye bath, rinsing the eye, and measuring corneal fluorescence by fluorophotometry. The permeability value is calculated from the corneal fluorescein concentration immediately after the bathing period. Mean permeability value determined in 86 eyes of 46 volunteers aged 15 to 67 years (mean 30.9 years) was 0.038 nm/s +/- 0.017 SD. No significant correlation with age was found (corr. coeff. = 0.17, P = 0.28). The reproducibility was within 10%.

In vivo Assessment of Lens Transmission for Blue-Green Light by Autofluorescence Measurement

A simple quantitative and reproducible method for evaluating lens transmission (lambda = 490 and 530 nm) is described. It is based on the measurement of autofluorescence in the anterior and the posterior part of the lens by means of a fluorophotometer, assuming an about equal fluorescence quantum efficiency in both parts. Consequently any difference in fluorescence between both parts can be attributed to a loss of exciting and fluorescent light in the lens. For both wavelengths, the average lens transmission is determined by this method in a normal population as a function of age.

Corneal transmission in whole human eyes

The transmission of blue-green argon laser light (lambda = 488 nm and lambda = 514.5 nm) through clear healthy corneae was measured by means of a photodiode implanted into whole human donor eyes. The mean corneal transmission in seven eyes (donor age: 32-84 y) was 93.2 +/- 3.2% S.D., range 87-98%. The time between death and measurement ranged from 3.5 to 16 hr. These results indicate that hardly any correction for light loss in a healthy cornea is required in fluorophotometric results obtained with the use of fluorescein (lambda max.exc. = 489 nm, lambda max.em. = 514 nm).

Blood aqueous barrier permeability versus age by fluorophotometry

Values of the diffusion coefficient into the anterior chamber and the blood aqueous barrier permeability as a function of age were determined by fluorophotometry in 58 healthy volunteers. The diffusion coefficient was calculated from aqueous fluorescein concentration and the time integral of non-protein bound fluorescein concentration in plasma. Blood-aqueous barrier permeability was calculated using diffusion coefficient values, the area of fluorescein inflow into the anterior chamber and anterior chamber volume. Values for diffusion coefficient as well as permeability were found to be independent of age between 13 y and 72 y (lin. corr. coeff. 0.2, p = 0.11) mean values were 4.7 .10(-4) min-1 +/- 1.5. 10(-4) SD and 15.4 nm/s +/- 4.8 SD, respectively. The difference between permeability values calculated from fluorophotometric scans at 30, 55 and 65 mins. after fluorescein injection was less than 5% and the 7 months reproducibility was within 15%. There was no significant correlation between simultaneously measured values of blood-retinal and blood-aqueous barrier permeability (lin. corr. coeff. 0.13, p = 0.4).

Corneal epithelial permeability and daily contact lens wear as determined by fluorophotometry

The condition of the corneal epithelium of 57 non-, 18 soft-, 29 gas-permeable- and 26 hard contact lens-wearing eyes was investigated by fluorophotometric determination of the corneal epithelial permeability. The mean permeability values for non-, soft-, gas-permeable- and hard contact lens-wearing eyes were 0.040 nm/s +/- 0.017 SD, 0.024 nm/s +/- 0.009 SD, 0.028 nm/s +/- 0.017 SD and 0.044 nm/s +/- 0.020 SD, respectively. The mean permeability values for soft and gas-permeable contact lens-wearing eyes were significantly lower than that for non contact lens-wearing eyes (-40%, p less than 0.001 and -30%, p less than 0.005); no significant difference was found between the mean values for hard and non contact lens-wearing eyes (p = 0.38).

Determination of basal tear turnover in insulin-dependent diabetes mellitus patients by fluorophotometry

The tear turnover was determined by fluorophotometry in 25 insulin-dependent diabetes mellitus (IDDM) patients without retinopathy and 29 IDDM patients with (pre-)proliferative retinopathy. The results were compared with those in 34 healthy controls, to investigate the lacrimal gland function in diabetic patients. The tear turnover was calculated from the decay of the relative tear fluorescein concentration values measured after instillation of one μL of fluorescein.The tear turnover values in both patient groups did not correlate significantly with age or diabetes duration (linear correlation coefficients: r < 0.3). The tear turnover values in patients both without retinoplathy and with (pre-)proliferative retinopathy did not differ significantly from those in healthy controls (mean ± SD in %/min: 13.7 ± 4.5, 14.7 ± 5.8 and 15.5 ± 5.1, respectively; P > 0.16). The tear turnover was significantly decreased in eyes having a BUT shorter than 10 seconds compared with eyes having a BUT longer than 10 seconds (P < 0.05). The tear turnover values correlated significantly with the HbA1c and Schirmer-test values in patients with (pre-)proliferative retinopathy (r = 0.7 and r = 0.4, respectively; P < 0.02) and with the blood glucose values in patients without retinopathy (r = 0.41, P = 0.04).Since the tear turnover was not significantly decreased in IDDM patients in comparison with healthy controls the corneal disorders which are more frequently seen in these patients than in a healthy population may not be attributed to a decrease in tear production.

Effects of microwave-induced hyperthermia on the anterior segment of healthy rabbit eyes

Hyperthermia was induced in nine healthy rabbit eyes by means of a microwave 2450 MHz stripline applicator. The anterior segment of each eye was heated to a fixed temperature of between 42° C and 46° C for 30 min. The temperature distribution in the eye was calculated using a thermal model and the actual boundary temperatures and microwave intensity were measured. The effects of treatment were evaluated by daily macroscopic examination, fluorescein angiography and fluorophotometry, as well as by histology. Histological examination of changes induced by this hyperthermic delivery system revealed a sharp transition at 44°–45° C from no permanent damage to the anterior chamber at lower temperatures to serious damage such as local necrosis, pigment disruption and local cataract at high temperatures. A sharp transition in the same temperature range was observed in vivo in the fluorescein leakage of the iris vessels by comparative fluorescein angiography and by anterior segment fluorophotometry.

Plasma fluorescein decay determination during fluorophotometry

Two useful methods for determination of the decay curve of non-protein bound fluorescein (NPBF) in plasma up to 1 hour after intravenous fluorescein injection are described and evaluated. The course of NPBF is approximated in method 1 by a sum of two exponential decay functions and in method 2 by a power of time function. The parameters in these functions are calculated with the use of concentration values measured in two blood samples taken at about 5 min. and 60 min. after injection. Calculations in method 1 include the amount of fluorescein injected.The accuracy of each method was evaluated in 7 volunteers by measuring NPBF concentration in 15–28 blood samples taken after fluorescein injection at intervals of 5 min. or less. The mean relative deviation between calculated and measured concentration values amounted to 9.2% + 4.3 SD and 12.7% ± 4.5 SD for method 1 and 2, respectively.The time integral of NPBF concentration in plasma up to one hour after injection was calculated according to the results of both methods and compared with integral values obtained by linear interpolation between concentration values measured in the 15–28 plasma samples. The mean relative deviation for the 7 volunteers amounted at 15 min. to 2.8% and 17% and at 60 min. to 11% and 18% for method 1 and 2, respectively.The maximal difference between the blood-retinal barrier permeability value for NPBF calculated with and without taking glucuronation into account was estimated to be 20% for an average glucuronation percentage of 70% or less.

The effect of therapeutic ultrasound on the average of multiple intraocular pressures throughout the day in therapy-resistant glaucoma

The effect of therapeutic ultrasound was evaluated in 17 patients with therapy-resistant glaucoma by comparing average intraocular pressure (IOP) curves measured before and 3–4 months after insonification. The insonification regimen was standardized; the medication was identical during both pressure curve measurements. The average IOP decrease was 44% ± 24 SD (range, 73% decrease to 6% increase). In 82% of the patients the IOP decrease was more than 34%. There was no correlation between the percentage of IOP decrease and the average IOP before insonification (correlation coefficient, 0.21;P = 0.41).