Jaap A. van Best

Topical timolol with and without benzalkonium chloride: epithelial permeability and autofluorescence of the cornea in glaucoma

Epithelial permeability and autofluorescence of the cornea were determined by fluorophotometry in 21 patients with open-angle glaucoma or ocular hypertension using timolol medication with the preservative benzalkonium chloride (BAC) and 2 weeks after changing to timolol medication without BAC. The investigation was performed to determine whether removal of BAC would reduce toxic effects on the cornea and complaints of sensations of burning or dry eye. Corneal epithelial permeability decreased significantly after changing medication (mean decrease per patient 27%, P=0.025). Corneal autofluorescence increased significantly after changing medication suggesting an alteration in corneal metabolism (mean increase per patient 6%, P = 0.003). Timolol without BAC was found to be as effective as timolol with BAC in reducing intraocular pressure (P=0.4). Removal of BAC from timolol resulted in an improvement of corneal epithelial barrier function and in a reduction of complaints. The improvement was found to be proportional to the duration of the preceding BAC-containing therapy.

Light transmission of the cornea in whole human eyes

The transmission of the cornea for light in the wavelength range 450-1000 nm was measured in steps of 50 nm by means of a photodiode implanted into the anterior chamber of whole human donor eyes. In the range from 450 nm up to 600 nm the percentage transmission was found to increase with wavelength from 80% up to 94%. In the range from 60 nm up to 1000 nm the percentage transmission was between 95% and 98%. The corneal transmission for donors younger than 45 yr (n = 3, 22-43 yr) did not differ significantly from that of donors older than 45 yr (n = 5, 67-87 yr) at any wavelength.

Analysis of tear fluid proteins in insulin-dependent diabetes mellitus

Abstract. Secretory immunoglobulin A, lactoferrin, lysozyme and tear specific pre‐albumin were analyzed in stimulated tear fluid of 25 diabetic patients without retinopathy and in 29 diabetic patients with (pre‐) proliferative retinopathy using high performance liquid chromatography. Results were compared to those obtained in 26 healthy controls to determine the effect of diabetes mellitus on the exocrine function of the main lacrimal gland. Sodium dodecyl sulfate polyacrylamide gel electrophoresis onto minigels was performed on 20 tear samples for verification of high performance liquid chromatography fractions recorded. The mean total protein values in tear fluid (Bradford assay) of diabetics without retinopathy, with retinopathy and healthy controls did not differ significantly (mean in mg/ml ± sd: 6.4 ± 2.2, 5.9 ± 2.0 and 5.7 ± 1.7, respectively; Mann‐Whitney: p>0.2). High performance liquid chromatography showed an increased secretory immunoglobulin A and decreased peak 5 OD280 (+56% and ‐38%, respectively; p< 0.02) in patients without retinopathy, whereas in patients with retinopathy lysozyme was increased (+27%; p< 0.01) and tear specific pre‐albumin and peak 5 OD280 decreased (‐24% and ‐42%, respectively; p< 0.04), when compared to healthy controls. These inconsistent differences do not uniformly suggest an exocrine dysfunction of the main lacrimal gland in diabetic patients.

Measurement of basal tear turnover using a standardized protocol

Abstract• Background: The aim of this study was to compare basal tear turnover values of healthy volunteers in different countries.• Methods: Healthy volunteers aged between 20 and 70 years were selected in three European cities. Basal tear turnover values were calculated according to a standardized protocol from the decay of the fluorescein concentration in tears after instillation of 1-μl drop of fluorescein in the conjunctival sac. Fluorescein concentration was measured with identical commercial fluorophotometers. A monoexponential decay of fluorescein was assumed to represent basal tear flow. • Results: The mean tear turnover values were 13.1%/ min ± 4.6 SD (n=4), 16.0%/ min ± 5.2 SD (n=24) and 17.5%/ min ± 3.4 SD (n = 20) in Clermont-Ferrand (France), Leiden (The Netherlands) and Madrid (Spain), respectively. The differences between the values were not significant (Mann-Whitney test P > 0.09).• Conclusions: The tear turnover in the different cities was similar. The methods used were simple and the software easy to use.

Corneal autofluorescence in diabetic and penetrating keratoplasty patients as measured by fluorophotometry.

At first it was verified that the major part of the fluorophotometer signal obtained when measuring corneal autofluorescence originated from fluorescence and not from scatter of excitation light at the corneal surface. The minimum percentage of the signal which can be attributed to fluorescence was determined using a fluorescence blocking filter placed in the excitation and fluorescence light path, respectively. The minimum percentages in two healthy controls, two diabetic patients and two patients after penetrating keratoplasty ranged from 75% to 93% (mean 84%). Then the corneal autofluorescence was determined in 22 healthy controls, 18 non-insulin-dependent diabetes mellitus (NIDDM). 23 insulin-dependent diabetes mellitus (IDDM) and 21 penetrating keratoplasty patients in order to detect a possible difference in autofluorescence as a result of diabetes or penetrating keratoplasty. The means of the corneal peak autofluorescence values in the NIDDM, IDDM and penetrating keratoplasty patient groups were significantly higher than that in the healthy control group (mean values in ng equivalent fluorescin ml-1: 18.0 +/- 4.2 S.D., 20.6 +/- 5.1 S.D., 17.9 +/- 5.5 S.D. and 13.7 +/- 3.7 S.D., respectively; P less than 0.01). The mean values in the NIDDM and IDDM patients did not differ significantly (P = 0.09). The autofluorescence values were independent of age in all four groups (linear correlation coefficient: r less than 0.47). The corneal peak autofluorescence was linearly correlated with the diabetes duration in the NIDDM and IDDM patients [r = 0.6, P = 0.02; increase: 0.36 ng equiv. fluorescein ml-1 yr diabetes-1]. Our results show that corneal autofluorescence is an easily obtained parameter which can be of assistance in evaluating corneal metabolism.

Tumor destruction by intermediate level hyperthermia

The tumoricidal effect of hyperthermia was studied in Greenes amelanotic hamster melanoma transplanted into the anterior chamber of rabbit eyes. To achieve optimal depth penetration, hyperthermia was induced with near infrared light of 820-870 nm, during 15 minutes, at a beam diameter of 2.5-6.0 mm resulting in an intermediate level hyperthermia of 45-60 degrees C. At 45 degrees C no tumor destruction occurred, at 50 degrees C the effect varied from no destruction to total thickness tumor destruction. At 55-60 degrees C total tumor destruction with additional lens damage occurred. In comparison photocoagulation with white light revealed only necrosis up to half the tumor thickness.

Effects of aldose reductase inhibition with tolrestat on diabetic retinopathy in a six months double blind trial.

To study the effects of the new aldose reductase inhibitor tolrestat on diabetic retinopathy, 31 diabetic patients with various degrees of retinopathy were randomly assigned to either tolrestat (200 mg once daily) or placebo treatment for six months. Separate morphological features of diabetic retinopathy were assessed by fundus photography and fluorescein angiography before and at the end of the study. The results showed some amelioration of clinical signs of diabetic retinopathy during aldose reductase treatment. Hard exudates, intraretinal hemorrhages and focal fluorescein leakage increased on average in the placebo and decreased in the tolrestat group. The difference was statistically significant for focal fluorescein leakage only. The permeability of the blood retinal barrier was determined by vitreous fluorophotometry before and at the end of the study. No change in permeability values was found.

Function and morphology of the retinal pigment epithelium after light-induced damage.

The purpose of this study was to determine the threshold energy for light‐induced functional damage of the retinal pigment epithelium at various wavelengths. Retinas of 58 pigmented and 21 albino rabbits were exposed to low intensity broadband blue light (400–520 nm), yellow light (510–740 nm), and narrowband blue light (408, 417, 439, 455, 485, 501 nm, respectively; Δλ = 10–13 nm). The intensity values were 50, 280, and 5 mW · cm−2, respectively, and the illumination time was 0.5 up to 5 h. The cumulative dose of light energy was calculated from these data (J · cm−2). The blood‐retinal barrier dysfunction was evaluated in vivo using fluorophotometry to measure the leakage of fluorescein into the vitreous after intravenous injection and in vitro using light and electron microscopy after an in vivo intraarterial injection of horseradish peroxidase (HRP). The threshold energy for fluorescein leakage was 50 J · cm−2 for blue light and 1,600 J · cm−2 for yellow light. After broadband blue light exposure, the HRP reaction product was seen in the cytoplasm of the retinal pigment epithelium (RPE) cells and in the subretinal space but only if fluorescein leakage had been observed. Threshold energy and fluorescein leakage as a function of light energy were similar for albino and pigmented rabbits (P > 0.5). Only after yellow light exposure in excess of 3,700 J · cm−2 was fluorescein leakage found. In that case complete disruption of the RPE was seen, but no HRP was observed in the RPE cytoplasm. Of the narrow‐band blue light exposures, only that at λ = 418 nm caused a significant increase in fluorescein leakage; the threshold energy was 18 J · cm.−2. Blue light was found to be at least 30 times more efficient than yellow light in causing dysfunction of the blood‐retinal barrier. The most efficient wavelength was 418 nm, corresponding with the absorption spectrum of cytochrome c oxidase. Melanin seemed to play no role. The presence or absence of melanin in the RPE appeared to have no influence on the threshold energy. Microsc Res Tech 36:77–88, 1997.

Decreased Basal Tear Turnover in Patients With Untreated Primary Open-Angle Glaucoma

PURPOSE To detect whether untreated primary open-angle glaucoma or ocular hypertension is associated with an impaired basal tear turnover. METHODS Basal tear turnover was determined by fluorophotometry in 18 patients with newly detected, untreated primary open-angle glaucoma and 29 patients with untreated ocular hypertension. The results were compared with those of 27 age-matched control subjects. RESULTS The basal tear turnover in glaucoma patients (mean +/- S.D., 11.4 +/- 3.1%/min) was 22% lower than in patients with ocular hypertension (14.7 +/- 3.0%/min; P = .0007) and 27% lower than in control subjects (15.7 +/- 5.3%/min; P = .001). Tear turnover of patients with ocular hypertension did not differ significantly from that of control subjects (P = .4). The basal tear turnover values were found to decrease with increasing vertical or horizontal cup/disk ratios (P = .004 and P = .008, respectively). CONCLUSIONS Primary open-angle glaucoma, but not ocular hypertension, was found to be associated with an impaired basal tear turnover. Dry eye complaints may originate from decreased basal tear turnover as a result of glaucoma drug therapy as well as from primary open-angle glaucoma itself.

Spectral sensitivity of the blood-retinal barrier at the pigment epithelium for blue light in the 400-500 nm range.

To specify the spectral sensitivity of the retinal pigment epithelium (RPE) for blue light damage, pigmented rabbits were exposed to light of 408, 418, 439, 455, 485, and 500 nm (half-peak bandwidth approximately 12 nm). The range of radiant exposure was 15–275 J cm−2 (1.7–19 mW cm−2 for 0.5–5 h). Vitreous fluorophotometry was used to functionally evaluate the blood-retinal barrier at the RPE in vivo, and electron microscopy to visualize RPE ultrastructure in vitro. A significant increase in permeability of the blood-retinal barrier was seen only after exposure to light of 418 nm. Radiant exposure at threshold for permeability increase was 18 J cm−2. Electron microscopy of the RPE demonstrated dispersion and clumping of melanin granules. The results suggest that the RPE is most sensitive to light in the range 412–425 nm, possibly due to damage-mediating chromophores such as cytochromec oxidase and lipofuscin.