Corneal autofluorescence in choroidal melanoma or in choroidal naevus.

AIMS: To investigate whether corneal autofluorescence is different in patients with choroidal melanoma or choroidal naevus. METHODS: Corneal autofluorescence was determined by fluorophotometry in both eyes of 32 patients with a unilateral choroidal melanoma, 32 patients with a unilateral choroidal naevus, and 32 age matched healthy controls. The corneal autofluorescence ratio between affected and contralateral eyes of patients or between randomly selected eyes of healthy controls was calculated. RESULTS: Mean corneal autofluorescence ratio of patients with a choroidal melanoma was significantly higher than that of healthy controls (mean ratio: 1.09 (SD 0.15) and 1.00 (0.09), respectively, ANOVA p=0.014), and than that of patients with choroidal naevus (mean ratio 0.96 (0.09), p<0.001). Mean ratios of patients with choroidal naevus and healthy controls were not significantly different (p=0.27). CONCLUSIONS: Corneal autofluorescence ratio of patients with a unilateral choroidal melanoma is increased. This is probably due to an increased flow of glucose through the impaired blood-aqueous barrier in the affected eye, resulting in additional glycation of corneal proteins and hence in increased autofluorescence. The corneal autofluorescence is not increased in patients with a choroidal naevus, because the blood-aqueous barrier is not impaired in the affected eye in these patients. Measurement of corneal autofluorescence is simple, fast, and non-invasive, and might be helpful to distinguish between patients with choroidal melanoma and those with choroidal naevus.

Reflex lacrimation in patients with glaucoma and healthy control subjects by fluorophotometry.

PURPOSE: Steady state tear turnover (TTO), defined as TTO under normal physiological conditions, is significantly lower in patients with untreated glaucoma than in healthy control subjects. To obtain more information on the effect of glaucoma on lacrimation, a method for quantification of reflex lacrimation was developed and applied to patients with glaucoma or ocular hypertension and healthy control subjects. METHODS: After instillation of 2 microl of fluorescein (2%), the decay of fluorescein concentration in tears was measured by fluorophotometry over 10 minutes to determine steady state TTO. Then, reflex lacrimation was induced by stimulating the trigeminal nerve with ethanol vapor via the nostrils. Thereafter, the decay of fluorescein and corresponding steady state TTO were determined again. An index of reflex lacrimation, defined as the percentage decrease in fluorescein concentration as a result of stimulation, was calculated by forward and backward extrapolation of the steady state decay of the fluorescein concentration in tears, relative to the time of stimulation. RESULTS: The index of reflex lacrimation was determined in 16 patients with newly discovered but not yet treated glaucoma, 16 patients with untreated ocular hypertension, and 16 healthy control subjects. The values did not differ between groups (mean +/- SD, 67.0%+/-17.7%, 63.5%+/-21.3%, and 70.4%+/-19.6%, respectively; ANOVA, P>0.25). Surprisingly, the steady state TTO after stimulation was lower than that before stimulation in each group (ratio, 0.62+/-0.46; paired t-test, P<0.04). CONCLUSIONS: The method developed is appropriate for the quantification of reflex lacrimation. Reflex lacrimation is not influenced significantly by glaucoma or ocular hypertension. The decreased steady state TTO after reflex stimulation may be caused by exhaustion of the lacrimal glands after excessive reflex lacrimation, indicating that normal lacrimation probably also contains reflex tears.

Autofluorescence distribution along the corneal axis in diabetic and healthy humans.

Corneal autofluorescence, as measured with a commercial scanning fluorophotometer (lambda(exc): 415-491 nm; lambda(em): 515-630 nm), is increased in patients with diabetes mellitus. However, such fluorophotometers register an average fluorescence signal over all corneal layers as a consequence of their limited axial resolution of 0.5 mm. In order to determine the location of the fluorophores responsible for the increased corneal autofluorescence measured in diabetics, an attempt was made to measure in vivo the distribution of autofluorescence along the optical axis of the cornea with a modified slitlamp. Fluorescence excitation and emission filters identical to those of the scanning fluorophotometer were fitted to a slitlamp equipped with a slow scan CCD camera. Corneal autofluorescence intensity profiles were obtained with the slitlamp in five patients with severe diabetic retinopathy and compared to those of age-matched healthy controls. Corneal autofluorescence was also measured with the scanning fluorophotometer for comparison. The resolution of the CCD camera for measurement of fluorescence along the corneal axis was 0.1 mm. The corneal autofluorescence intensity of the patients and the healthy controls gradually decreased by about the same amount from the endothelium to the epithelium (57% mm(-1)+/-6 s.d. and 52% mm(-1)+/-5 s.d., respectively). The area under the fluorescence intensity curve was significantly greater for the patients than for the healthy controls (factor 2.4+/-1.0 s.d., P<0.001) and was proportional to the corneal fluorescence measured with the scanning fluorophotometer (r=0.92, P<0.001). The results show that (1) the distribution of autofluorescence along the corneal axis can be measured in vivo in humans, (2) the fluorophores involved are distributed throughout the cornea, and (3) the relative distribution of fluorescence is similar in diabetic patients and healthy controls.

Autofluorescence of the diabetic and healthy human cornea in vivo at different excitation wavelengths.

Corneal autofluorescence is higher in diabetes mellitus patients with retinopathy than in healthy subjects. In this study, the excitation spectra of corneal autofluorescence of diabetic patients and healthy controls in the range 365 nm-480 nm were compared in an attempt to identify the fluorophores responsible for corneal autofluorescence in health and disease (diabetes). Spectral measurements (from one eye) were recorded from five patients with proliferative diabetic retinopathy and five age-matched healthy controls, using a modified commercial scanning fluorophotometer with a mercury arc or a tungsten halogen lamp as excitation light source in combination with interference filters (excitation wavelengths: 365, 405, 420, 430, 436, 440, 450, 470 and 480 nm; bandwidth: 10 nm). Fluorescence emission was measured in the range 532 nm-630 nm. The sensitivity of the modified fluorophotometer was calibrated by using the excitation spectrum of fluorescein as a reference. The corneal excitation efficiency of the diabetic patients was higher than that of the healthy controls at each wavelength investigated (Mann-Witney test P<0.0005). The ratio between the mean values of both groups was equal for each excitation wavelength (mean ratio 1.9+/-0.12s.d.,P>0. 2), suggesting that the excitation spectra were equal. This indicates that the same fluorophores are responsible for the corneal autofluorescence in both groups. The shapes of the excitation spectra suggest the involvement of flavins, NAD(P)H, and at least one other, as yet unidentified, fluorophore.

Lens transmission by fluorophotometry after brachytherapy and thermotherapy of choroidal melanoma.

We studied the effect of transpupillary thermotherapy (TTT) by a diode laser at 810 nm combined with episcleral ruthenium-106 plaque treatment (106Ru) on lens transparency in patients with choroidal melanoma. Lens transmission of blue-green light was measured by fluorophotometry in 17 patients treated with 106Ru treatment and TTT (measured 0.36 years after treatment), 12 patients treated with 106Ru alone (measured 19 years after treatment) and 25 age-matched healthy controls. Differences in lens transmission were not significant between treated and untreated fellow eyes (p > 0.15) nor between patient and control eyes (p > 0.25). TTT of choroidal melanoma combined with 106Ru plaque irradiation did not have a significant effect on the lens transparency up to 6 years after treatment.

The effect of 1% apraclonidine on intraocular pressure after cataract surgery.

BACKGROUND AND OBJECTIVE: To measure the effect of 1% apraclonidine hydrochloride eyedrops on intraocular pressure (IOP) after cataract surgery. The effects of two different dosage regimens, once before surgery or once before and after surgery, were studied. PATIENTS AND METHODS: Patients scheduled for extracapsular cataract extraction and artificial lens implantation were randomly assigned to three groups: group A had a placebo treatment (n = 18), group B had one drop of 1% apraclonidine 1 hour before surgery (n = 16), and group C had one drop of 1% apraclonidine 1 hour before surgery and 1 drop at the end of surgery (n = 17). Two percent hydroxy-propyl-methyl-cellulose was used as the viscoelastic substance. The preoperative IOP and the IOP 6 hours postoperatively in each patient were compared. The paired Student's t test was used to compare IOP before and after surgery. The study design was a randomly assigned, double-masked controlled clinical trial. RESULTS: In group A (placebo) and group B (apraclonidine before surgery), there was a significant increase in IOP (mean IOP increase 11.2 +/- 9.9 mm Hg SD, range -4 to 32, P = .00017, and 9.4 +/- 7.4 mm Hg SD, range -3 to 24, P = .00014, respectively). In group C (apraclonidine 1 hour before and immediately after surgery), the increase in IOP was not significant (mean IOP increase 5.1 +/- 11.5 mm Hg SD, range -10 to 28, P = .084). A postoperative IOP of more than 40 mm Hg applanation tension was reached by two patients in group A, one patient in group B, and two patients in group C. CONCLUSION: Although 1% apraclonidine eye-drops instilled 1 hour before and immediately after extracapsular cataract extraction with artificial lens implantation may help prevent a statistically significant increase in IOP after the operation, 2 of the 17 patients still had IOPs greater than 40 mm Hg 6 hours postoperatively. Apraclonidine applied only before surgery did not prevent a statistically significant increase in IOP.

Long term follow-up of lenticular autofluorescence and transmittance in healthy volunteers.

This study was undertaken to assess long term changes in the lenticular autofluorescence and transmittance of healthy volunteers. Both eyes of 15 healthy volunteers aged 8 to 62 years were examined by slit-lamp examination and fluorophotometric measurements of lenticular autofluorescence (lambdaexc=415 nm-490 nm, lambdaem= 510 nm-550 nm) and transmittance (lambda=415 nm-550 nm) in 1983 and 1996. The changes in lenticular autofluorescence and transmittance between 1983 and 1996 were determined and compared with those calculated on the basis of age-dependence curves of a group of 56 healthy volunteers measured in 1983. These curves were obtained by approximation of the values of the 56 healthy volunteers by a linear, polynomial or exponential function of age, respectively. A mean yearly increase of lenticular autofluorescence of 8.69 ng . equivalent fluorescein . ml-1 . year-1 was observed in the 15 volunteers between 1983 and 1996 and this increase was significantly larger than that calculated on the basis of the three age-dependence curves in 1983 (6.36, 6.47 and 6.53 ng . equivalent fluorescein . ml-1 . year-1, P=0.0026, 0.0037 and 0.0044, respectively). The transmittance showed a mean yearly decrease of 0.508% . year-1 which was significantly larger than calculated on the basis of the three age-dependence curves in 1983 (0.153, 0.220 and 0.183% . year-1, P=0. 0033, 0.012 and 0.0059, respectively). One volunteer, i.e. the individual with the highest lenticular autofluorescence and lowest transmittance in 1983, had developed cataract in 1996. These measurements demonstrate for the first time, quantitative changes in lenticular autofluorescence and transmittance in a long term follow up. The at least 35% larger increase of autofluorescence and 130% larger decrease in transmittance in the follow-up group between 1983 and 1996 in comparison with the values based on age-dependent curves in 1983 could be caused by the increased solar UV radiation in The Netherlands during that period of time.

Evaluation of diabetic retinopathy by fluorophotometry. European concerted action on ocular fluorometry.

BACKGROUND: Fluorophotometric variables (permeability of the blood-retinal barrier (BRB) and blood-aqueous barrier (BAB), corneal autofluorescence, and lenticular light transmittance) are reported to correlate with the severity of diabetic retinopathy. This preliminary multicenter study was performed to measure these variables simultaneously in patients with type 2 diabetes mellitus and to assess which of these variables could be of help in evaluating diabetic retinopathy. METHODS: Eighty-two patients with type 2 diabetes and diabetic retinopathy were recruited in seven European university clinics. Each patient was investigated three times, at intervals of about one year. The investigations included fluorophotometric determination of corneal autofluorescence, lenticular light transmittance, and permeability of the BRB and BAB. Retinopathy was classified into four grades, using a simplified evaluation system based on the Modified Airlie House retinopathy classification and applied to color fundus slides of standard fields 1 and 2. RESULTS: Multiregression analyses revealed that only corneal autofluorescence and BRB permeability were correlated with the severity of diabetic retinopathy (P < 0.05). Corneal autofluorescence and BRB permeability as single variables were found to be indicative of severe nonproliferative retinopathy and proliferative retinopathy (sensitivity 100% and 86%, respectively, and specificity 65% and 85%, respectively). Combination of both variables increased specificity to 92%. CONCLUSIONS: This preliminary multicenter study shows that fluorophotometric variables can be measured simultaneously and reliably in patients with diabetes and that corneal autofluorescence and BRB permeability (individually or in combination) could be of help in detecting severe non-proliferative retinopathy and proliferative retinopathy.

Simple, low-cost, portable corneal fluorometer for detection of the level of diabetic retinopathy.

A simple, low-cost, portable instrument for measurement of the autofluorescence of the human cornea is presented. Corneal autofluorescence has proved to be strongly correlated with the grade of retinopathy in diabetic patients. It is therefore a reliable parameter for detection of different levels of diabetic retinopathy, thus permitting timely intervention by ophthalmologists. The instrument contains custom optics and electronics and exhibits excellent linearity and repeatability both in vitro and in vivo. Preliminary tests on volunteers show promise for its use in clinical practice.

Permeability of the blood-retinal barrier in healthy humans. European Concerted Action on Ocular Fluorometry.

BACKGROUND: The aim of this study was to compare the inward permeability of the blood-retinal barrier in healthy subjects from six European cities. METHODS: Seventy-two healthy subjects (age 20-70 years) were selected. At 30 min and 60 min after fluorescein injection, fluorescein mass in vitreous was calculated from the concentrations measured along the optical axis of the eye. Non-protein-bound fluorescein (NPBF) concentrations were measured in plasma prepared from blood samples taken 7, 15 and 55 min after injection. Blood-retinal barrier permeability (PBRB) was calculated from the vitreous fluorescein mass and the time integral of NPBF and was corrected for the autofluorescence of ocular tissue and for lenticular light transmittance. RESULTS: Mean PBRB values +/- SD (nm.s-1) were 2.07 +/- 0.54 (Coimbra), 2.01 +/- 0.43 (Frankfurt), 2.24 +/- 0.50 (Ghent), 2.37 +/- 0.56 (Herlev), 1.89 +/- 0.44 (Leiden) and 1.74 +/- 0.38 (Porto). Differences between centers were not significant (P > 0.35). Measurements were reproducible and independent of the time after fluorescein injection (P > 0.50). A PBRB higher than 3.16 nm.s-1 or a value which had increased by 32% was considered abnormal (P < 0.05). CONCLUSION: PBRB values were similar in all centers. The results demonstrate that this is a highly sensitive and reliable method for measuring the permeability of the blood-retinal barrier.

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; deltalambda = 10-13 nm). The intensity values were 50, 280, and 5 mW x 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 x 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 x cm (-2) for blue light and 1,600 J x 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 x 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 lambda = 418 nm caused a significant increase in fluorescein leakage; the threshold energy was 18 J x 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.

Permeability of blood-tear barrier to fluorescein and albumin after application of platelet-activating factor to the eye of the guinea pig.

One of the inflammatory responses of the eye to local application of platelet-activating factor (PAF) is oedema of the conjunctiva, caused by extravasation of plasma. Aim of the study was to investigate if fluorescein would leak from the blood into the tears together with plasma protein after application of PAF to the eye. Fluorescein was given intraperitoneally 30 min prior to application of 25 microl of 0.1% solution of PAF. Thirty min after PAF the tear film was collected by washing the surface of the eye with 25 microl of phosphate buffered saline (PBS). Fluorescein in eye washings and in plasma was measured by fluorophotometry and albumin by immunodiffusion. Both fluorescein and albumin appeared in a related fashion in tears, being absent in washings of placebo-treated control eyes. Extravasation of fluorescein can be used as a measure for plasma leakage in the conjunctiva with the advantage over the Evans Blue method that the former is a non-invasive method.

Long term changes in human corneal endothelium following toxic endothelial cell destruction: a specular microscopic and fluorophotometric study.

AIMS: To investigate the long term relation between corneal thickness, endothelial morphometric variables, and endothelial permeability in patients with endothelial cell counts under 900 cells/mm2 as a result of endothelial cell destruction after cataract surgery. METHODS: Eighteen patients developed the so called toxic endothelial cell destruction (TECD) syndrome following routine cataract surgery because of the intracameral injection of a toxic detergent residue. Ten patients with a mean (SEM) initial cell loss of 72% (2%) were followed for 4 years. Data were obtained at 6 months and 4 years postoperatively and compared between TECD eyes and contralateral control eyes. RESULTS: Mean (SEM) endothelial cell density of the TECD eyes increased from 642 (41) cells/mm2 to 849 (50) cells/mm2 at 4 years postoperatively (p = 0.005). There was no difference in coefficient of variation or percentage hexagonals between 6 months and 4 years postoperatively. Mean (SD) corneal thickness of the TECD eyes and control eyes was similar, 0.51 (0.02) mm and 0.49 (0.01) mm, respectively (p = 0.65). Mean (SD) endothelial permeability was also similar for TECD eyes and control eyes (4.3 (0.9) x 10(-4) cm/min and 4.4 (0.6) x 10(-4) cm/min, respectively (p = 0.57). There was no correlation between endothelial cell density, coefficient of variation, or percentage of hexagonal cells and endothelial permeability in the TECD eyes. In three patients a permanent corneal decompensation occurred. CONCLUSIONS: Four years after TECD corneal endothelial wound healing is stable and the barrier function has been restored.

Corneal endothelial permeability and aqueous humor flow using a standard protocol.

BACKGROUND: The study was carried out to compare corneal endothelial permeability and aqueous flow values of healthy volunteers measured in different countries with identical fluorophotometers using a standardized protocol. METHOD: Healthy volunteers aged between 20 and 70 years were studied in five European cities. Fluorescence scans of the anterior segment of both eyes were made using a commercial fluorophotometer. Beginning 4 h after instillation of four drops of fluorescein 10%, 12 scans of the anterior segment of each eye were performed in 2 h. The values of corneal endothelial permeability and aqueous flow were calculated with standardized software from the decay of the fluorescein concentration in the cornea and anterior chamber. RESULTS: The mean permeability values (x 10(-4) cm.min-1) +/- SD were 3.7 +/- 1.6 (n = 19; Coimbra, Portugal), 4.3 +/- 1.1 (n = 19; Frankfurt, Germany), 3.9 +/- 0.9 (n = 19; Leiden, The Netherlands) and 5.4 +/- 1.2 (n = 10; Milan, Italy). The values were not significantly different (ANOVA, P > 0.3), except those in Milan. The mean flow values (microliters.min-1) +/- SD were 2.3 +/- 0.9 (n = 17; Coimbra), 1.9 +/- 0.7 (n = 10; Cologne, Germany), 2.6 +/- 1.2 (n = 19; Frankfurt), 2.0 +/- 0.6 (n = 19; Leiden) and 1.7 +/- 0.8 (n = 10; Milan). The values were not significantly different (Kruskal-Wallis test, P > 0.1). CONCLUSIONS: Permeability and flow values in the different cities had similar values and standard deviations. The Concerted Action demonstrated the usefulness of a standardized protocol.

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.

Is glaucoma associated with an increased risk of cataract?

AIMS: The risk of developing cataract in patients with untreated glaucoma or with ocular hypertension was evaluated by comparing the values of lenticular autofluorescence and light transmission in 16 patients with primary open angle glaucoma and 22 patients with ocular hypertension with those of 24 healthy controls. METHODS: Increase of lenticular autofluorescence and decrease of transmission values in comparison with controls were considered to be precursors of cataract. The values of both variables were determined by fluorophotometry. Each value was normalised for age by dividing it by the value for a healthy control of the same age. RESULTS: The mean age normalised autofluorescence and transmission values of all patients did not differ significantly from those of the controls (difference < 5%; p = 0.6 and p = 0.2, respectively). Also the mean age normalised autofluorescence and transmission values between glaucoma and ocular hypertension patients did not differ significantly (p = 0.8 and p = 0.9, respectively). CONCLUSION: The study indicates that untreated primary open angle glaucoma or untreated ocular hypertension do not seem to increase significantly the risk of developing cataract.

Effect of timolol with and without preservative on the basal tear turnover in glaucoma.

AIMS: The purpose of this study was to assess whether the preservative benzalkonium chloride (BAC 0.01%) present in timolol induced a decrease in basal tear turnover and a deterioration of precorneal tear film in patients with glaucoma and ocular hypertension using topical timolol. METHODS: The basal tear turnover of 20 patients with open angle glaucoma or ocular hypertension was measured by computerised objective fluorophotometry when using topical timolol preserved with BAC and 2 weeks after changing to topical timolol containing no preservative. Evaluation of the precorneal tear film was done by measuring the break up time (BUT) before and 2 weeks after changing medication. RESULTS: The tear turnover of the patients before the change was 32% lower than that of healthy controls (mean tear turnover values (SD) (%/min): 10.7 (3.0) and 15.6 (5.4), respectively, p < 0.0001). A mean increase of 28% (47%) in the individual tear turnover values was found after the change to the preservative-free timolol (p = 0.04). The BUT values before the change of medication did not differ significantly from those after the change (p = 0.5) but both values were significantly lower than the values of healthy controls (p = 0.009 and p = 0.003, respectively). CONCLUSION: Preservative-free timolol solution has a favourable effect on the tear turnover of patients with glaucoma and ocular hypertension in comparison with timolol containing BAC. The integrity of the precorneal tear film persisted to be affected when using timolol without BAC. Timolol without preservative can be recommended in those patients who have keratoconjunctivitis sicca or a borderline tear production since BAC may exacerbate a dry eye state.

Corneal epithelial permeability during extended wear of disposable contact lenses versus daily wear of soft contact lenses.

AIMS: The corneal epithelial permeability during extended wear of disposable contact lenses was compared with that during daily wear of soft contact lenses. The study was performed to verify whether the extended wear of disposable contact lenses would result in a higher permeability value than the daily wear of soft contact lenses. A higher permeability makes the cornea more vulnerable for bacterial infections and thus could explain the higher incidence of bacterial keratitis found in extended wear of disposable contact lenses in comparison with the daily wear of soft contact lenses. METHOD: The corneal epithelial permeability was determined by fluorophotometry in 33 healthy volunteers after the wear of soft, daily wear contact lenses for at least 6 months. Thereafter the determination was repeated in each volunteer after extended wear of disposable contact lenses for 1 month. The permeability in 34 healthy non-contact lens wearing volunteers was determined as a control. The permeability value was calculated from the amount of fluorescein that passed into the cornea after application by means of an eyebath. RESULTS: The mean permeability values after daily and extended wear were 0.032 nm/s and 0.031 nm/s, respectively. The values were not significantly different (Wilcoxon paired test p > 0.5). The mean permeability for the non-contact lens wearing controls was 0.042 nm/s. CONCLUSION: The results do not sustain the explanation that a difference in permeability value is the main cause of the increased incidence of keratitis during extended wear of disposable contact lenses in comparison with daily wear.