Claus Engler

The effect of acetazolamide on passive and active transport of fluorescein across the blood-retina barrier in retinitis pigmentosa complicated by macular oedema

Abstract · Background: The carbonic anhydrase inhibitor acetazolamide (AZM) reduces macular oedema in some patients with retinitis pigmentosa. To better understand the oedema-reducing effect of AZM, the effect of AZM on passive permeability and active transport of fluorescein across the blood-retina barrier was studied in patients with retinitis pigmentosa and varying degrees of macular oedema. · Method: The selection of patients was based on an introductory examination including vitreous fluorometry for qualitative assessment of the vitreous. Macular oedema was graded by fluorescein angiographic leakage. The effect of AZM on the transport properties of the blood-retina barrier was determined by differential spectrofluorometry, in a randomised, double-masked, cross-over study, comprising 2 weeks’ treatment with AZM (500 mg/day) and 2 weeks’ treatment with placebo. The penetration ratio, defined as the ratio between vitreous concentration 3 mm in front of the retina and the plasma integral, was determined for fluorescein and its metabolite fluorescein glucuronide at 30–60 min and at 120 min after fluorescein injection. Passive permeability and unidirectional permeability in the direction vitreous to blood, due to outward active transport of fluorescein, were determined in those cases where the curves for vitreous concentration of fluorescein could be fitted to a mathematical model. Visual acuity was tested by use of ETDRS standard logarithmic charts. · Results: Twenty-two patients volunteered to participate in the study. Signs of significant vitreous detachment/liquefaction caused the exclusion of ten patients after the introductory examination. Nine patients with approximately intact vitreous and varying degrees of oedema completed the cross-over study. AZM treatment was related to a decrease in the penetration ratio of 21% for fluorescein (P=0.01) and of 22% for fluorescein glucuronide (P=0.004). Passive permeability and unidirectional permeability were determined in seven patients. AZM caused a decrease of 27% in the passive permeability of fluorescein (from 1.1×101 nm/s, P=0.031), and a 95% increase in unidirectional permeability of fluorescein (from 1.2×102 nm/s, P=0.047). AZM led to a reduction in the grade of macular oedema as determined by fluorescein angiography in three out of seven patients. Only small improvements (≤5 letters) in visual acuity were noted. · Conclusion: The present study indicates that the oedema-reducing effect of AZM is due to decreased leakage and stimulated active transport across the blood-retina barrier.

Probenecid inhibition of the outward transport of fluorescein across the human blood‐retina barrier

Abstract. The effect of probenecid on the outward transport of fluorescein from vitreous to blood was studied in 13 insulin‐dependent diabetic patients with background retinopathy in a randomised double‐masked placebo controlled cross‐over study. Fluorescein and fluorescein glucuronide were separated in the vitreous and in plasma by differential spectrofluorometry. The data for fluorescein were analysed using a simplified mathematical model of the eye. The inward permeability was estimated from data obtained 1 h after injection and the outward transport from data obtained 7 h after injection. During placebo treatment the mean inward permeability was 3.75 times 10−7 cm/sec and the mean outward permeability was 2.25 times 10−5 cm/sec. During probenecid treatment the mean inward permeability was 3.34 times 10−7 cm/sec and the mean outward permeability was 1.44 times 10−5 cm/sec. Thus, we found no significant change in inward permeability (p = 0.5879), whereas a significant decrease of 36% was found in the outward permeability of fluorescein (p = 0.0171). The demonstration that the outward permeability, which is more than 100‐fold higher than the inward permeability in the healthy eye, is significantly decreased by probenecid, demonstrates that active transport is involved in movement of fluorescein across the blood‐retina barrier from the vitreous to the plasma.

Interferon alpha-2a treatment of patients with subfoveal neovascular macular degeneration. A pilot investigation.

Abstract It has recently been suggested that interferon alpha‐2a has a beneficial effect on exudative age‐related macular degeneration (AMD). So far, results are controversial, and masked, placebo controlled, randomized studies with well‐defined inclusion criteria are required to assess the effect of interferon alpha‐2a. In preparation for such a study we performed a pilot investigation that included 5 patients with subfoveal neovascularizations. All patients received interferon alpha‐2a (Roferon‐A, Hoffmann La‐Roche) 1.5 mio, IU subcutaneously every second day for 8 weeks. Improved visual acuity was subjectively observed by 4 patients and objectively by 3 patients. Two patients showed decreased central visual field defect. Fluorescein angiography and fundus photography showed ambiguous changes. Amsler chart and contrast sensitivity also showed heterogenous results. Even though the treatment with interferon alpha‐2a may show some positive effect, our results are not unequivocal and serve to underline the need for controlled studies before the effect of interferon alpha‐2a on neovascular AMD can be reliably assessed.

Fluorescein transport across the human blood-retina barrier in the direction vitreous to blood. Quantitative assessment in vivo.

Abstract. Inward and outward movement of fluorescein across the human blood‐retina barrier was studied in five healthy volunteers, using a differential spectrofluorometry method that eliminates the contribution of fluorescein glucuronide to the total fluorescence in the vitreous and in plasma. The inward permeability across the blood‐retina barrier, which is presumed to be passive, and the diffusion coefficient in the vitreous for fluorescein was calculated from data obtained 1 h after intravenous injection of fluorescein. The rate of elimination of fluorescein from the vitreous across the blood‐retina barrier was estimated from data obtained 7 to 12 h after injection of fluorescein. The calculations were based upon the free plasma fluorescein decay curve and the preretinal fluorescein gradient in the vitreous. The mean inward permeability of fluorescein was 1.39 times 10−7 cm/sec (range: 0.70‐2.06 times 10−7 cm/sec), whereas the mean outward permeability was 1.51 times 10−5 cm/sec (range: 1.14‐1.73 times 10−5 cm/sec). We have thus found that the movement of fluorescein across the blood‐retina barrier is highly asymmetric, the outward transport being more than 100 times faster than the passive inward leakage. This could indicate the presence of an active pumping mechanism in the blood‐retina barrier, responsible for fluorescein transport in the direction from the vitreous to the blood.

Blood-retina barrier permeability and its relation to the progression of diabetic retinopathy in type 1 diabetics

Blood-retina barrier (BRB) permeability and its relation to the progression of diabetic retinopathy was studied over an 8-year period in 50 insulin-dependent diabetic patients. Initially, the patients underwent an ophthalmological examination, including measurement of best corrected visual acuity, fundus photography and vitreous fluorometry for determination of BRB permeability. After 8 years the patients were reexamined and their retinal status and clinical course were evaluated. We found a positive correlation between a high initial permeability value and an unfavorable clinical course using the parameter photocoagulation. A decrease in follow-up visual acuity was also associated with high initial permeability; however, this correlation was not statistically significant. A significant difference in mean blood pressure was found between values measured in laser-treated patients vs a group that did not undergo such therapy. Thus, in patients showing the same initial retinal morphology, high permeability seems to indicate an unfavorable disease course. The extent to which BRB permeability can be a valuable supplement to fluorescein angiography and three-mirror examination in the clinical decision process needs to be further evaluated.

Blood-retina barrier permeability in diabetes during acute ACE-inhibition

Abstract We assessed the acute effect of ACE‐inhibition (captopril) on blood‐retina barrier (BRB) permeability in 10 hypertensive insulin‐dependent diabetic patients with background retinopathy in a double‐masked placebo controlled cross‐over study. All patients underwent ophthalmological examination, fundus photography, fluorescein angiography, vitreous fluorometry, and continuous blood pressure recording within 3 h of the drug/placebo administration. The decrease in mean arterial blood presure, from placebo treatment 149/92 ± 17/7 to captopril treatment 132/83±14/7 mmHg (mean ± sd), P< 0.01 was not accompanied by a significant decrease in BRB permeability, which was 2.51 (1.24–9.15) with placebo and 3.02 (1.25–13.93) ± 10‐7 cm/s during captopril treatment (geometric mean and range), NS. Our study suggests that abnormal leakage through the BRB in hypertensive insulin‐dependent diabetic patients with background retinopathy is caused predominantly by structural changes in the retinal vessels whereas hydrostatic forces play a minor role.

IFN-α Antibodies in Patients with Age-Related Macular Degeneration Treated with Recombinant Human IFN-α2a

We tested for development of binding and neutralizing antibodies to interferon-α (IFN-α) during IFN-α2a therapy of patients with age-related macular degeneration (AMD) of the eyes. Antibodies were investigated retrospectively in sera of 34 patients treated with 3 × 106 IU IFN-α2a (Roceron-A®, Hoffmann La-Roche, Basel, Switzerland) three times weekly for periods of 8-16 weeks with or without a drug-free 4-12-week intermission. Additionally, 10 patients were investigated prospectively; 7 received 1.5-6 × 106 IU IFN-α2a three times weekly for 12 months, and 3 received placebo. Binding antibodies were tested by molecular size and protein G affinity chromatography using 125I-IFN-α2a. Neutralizing activities were tested by antiviral neutralization bioassay. IgG antibodies were detected in 24 of 34 IFN-α2a-treated patients (71%). Significantly higher anti-IFN-α levels were observed in patients who after discontinuation were readministered IFN-α2a (p < 0.02). Three of the IFN-α2a-treated patients in the prospecti...

Absence of foveal avascular zone demonstrated by laser scanning fluorescein angiography

Abstract We present laser scanning fluorescein angiograms of abnormal foveal capillary patterns in a healthy subject and an insulin‐dependent diabetic patient with mild diabetic retinopathy. In both subjects capillaries were seen to cross the central foveal area where capillaries are usually absent. The flow pattern of the foveal capillaries, which were visualised with the use of a laser scanning ophthalmoscope, was indistinguishable from that of the more peripheral capillaries, indicating that foveal vessels are functionally normal retinal capillaries. The two cases demonstrate that identification of abnormal capillary patterns induced by retinal disease such as diabetic retinopathy is made difficult by the marked interindividual variation in capillary anatomy. In prospective studies, however, the method may be capable of detecting subtle changes in early diabetic retinopathy with a high degree of sensitivity.

Blood-retina barrier permeability is independent of trace substance lipid solubility in retinitis pigmentosa and in the healthy eye

Differential ocular spectrofluorometry was used toassess the passive permeability of the blood-retinabarrier in healthy subjects and in patients withretinitis pigmentosa by determination of the rate ofinward leakage of fluorescein and fluoresceinglucuronide after intravenous injection offluorescein.In five healthy subjects we found permeabilities of1.3 (0.6–2.8) nm/s [log-mean (range)] for fluoresceinand 1.3 (0.6–3.1) nm/s for fluorescein glucuronide.Six patients with retinitis pigmentosa all had amarkedly increased blood-retina barrier leakage, withinward permeabilities of 8.2 (3.4–25) nm/s forfluorescein and 8.2 (5.6–27) nm/s for fluoresceinglucuronide.Since no detectable difference was found between thepermeabilities of the two tracers the passive permeability of the blood-retina barrier appears to beindependent of the 18-fold difference in lipidsolubility between the two tracers, both in retinitispigmentosa and in healthy subjects. Presumably, thestructural substrate for leakage of small hydrophilicmolecules through the blood-retina barrier is awater-filled pore, since diffusion through lipidcellular membranes would favor fluorescein over itsmore water soluble glucuronide.