Response of the pupil to tropicamide is not a reliable test for Alzheimer disease.

OBJECTIVE: To confirm the putative hypersensitivity of the pupil to a weak mydriatic in persons with Alzheimer dementia. DESIGN: Twenty patients with Alzheimer dementia and 20 control subjects were examined. Automated binocular infrared pupillography was performed in the dark after instillation of 0.01% tropicamide or placebo. Ocular penetration of eye drops was assessed simultaneously using 2% fluorescein sodium as a tracer. SETTING: Rochester, Minn. SUBJECTS: Twenty patients and 20 cognitively normal control subjects from the Alzheimer's Disease Patient Registry of the Mayo Clinic, Rochester, Minn. MAIN OUTCOME MEASURE: Percent change in the diameter of the pupil following topical ocular instillation of a diluted concentration of the mydriatic drug tropicamide and penetration of topically applied fluorescein into the aqueous humor. RESULTS: No statistically significant difference was found between patients with Alzheimer disease and control subjects in either the mydriatic response of the pupil or in the rate of penetration of topically applied fluorescein. CONCLUSION: No evidence of pupillary hypersensitivity to an anticholinergic mydriatic drug was found in patients with Alzheimer disease or any evidence that this putative hypersensitivity could be used as an early, simple diagnostic test for Alzheimer disease.

Flow of aqueous humor in humans [The Friedenwald Lecture].

Based on clinical experiments with fluorophotometry, several observations can be made about aqueous flow through the chambers of the human eye. 1. The rate of flow is 2.75 +/- 0.63 microliters/min in normal subjects, as derived from measurements averaged during normal office hours. The normal range (95%) is 1.8 to 4.3 microliters/min. 2. There is a circadian rhythm of flow, with the highest rates during morning hours, slightly lower rates during afternoon hours, and rates during sleep that are approximately one half of those during the morning. The hormonal basis for this rhythm is unknown, but it is known to be present in both eyes of persons with unilateral Horner's syndrome. 3. A slight decline of the rate occurs after age 10 yr--3.2% per decade. There is no significant difference in aqueous flow between men and women. 4. Of the hundreds of drugs that are used clinically, most are unlikely to have a significant effect on aqueous flow. Exceptions are the beta-adrenergic agonists that, under certain circumstances, are able to increase flow, the corticosteroids that may have a stimulating effect on flow, and three classes of drugs that have therapeutically useful suppressing effects on flow: carbonic-anhydrase inhibitors, beta-adrenergic antagonists, and alpha 2-selective adrenergic agonists. 5. Timolol, which has a remarkably consistent suppressing effect on flow during the day, has no effect on the flow of sleeping subjects. By contrast, acetazolamide and apraclonidine are able to reduce the flow of sleeping subjects. 6. Acute doses of beta-adrenergic antagonists and alpha 2-agonists are not additive, but beta-adrenergic antagonists and carbonic-anhydrase inhibitors are partly additive. 7. The eye adapts partly to the chronic use of timolol and recovers from its effects when it is discontinued. 8. The rate of disappearance of the effect of beta-adrenergic antagonists is longer for the noncardioselective agents, such as timolol and levobunolol, but is relatively short for the cardioselective agent, betaxolol. 9. The rate of aqueous flow is insensitive to moderate changes of intraocular pressure. Clinical studies can provide suggestive leads for more basic investigations or test specific hypotheses. Biochemical, biologic, and pharmacologic approaches in simpler, more controlled experimental conditions are necessary to determine the fundamental processes that bring about aqueous formation in the living eye. The combination of many disciplines (eg, studying molecules, cells, tissues, organs, and the intact living system) has the best chance of furthering our understanding of the aqueous circulation.

Isoproterenol stimulates aqueous flow in humans with Horner's syndrome.

Topical 1 percent isoproterenol in the presence of the phosphodiesterase inhibitor theophylline was tested for its ability to stimulate the rate of aqueous humor flow through the anterior chamber of the normal and the partially adrenergically denervated human eye (Horner's syndrome). Both the affected eye and the unaffected eye were observed to have lower flows at night than during the day. Isoproterenol had no significant effect on flow during the day in normal eyes or in Horner's syndrome, but during sleep this beta-adrenergic agonist increased flow in the normal eye by 34% and in the Horner's eye by 50%. We interpret the results as indicating that beta-adrenergic activity in the human eye can stimulate aqueous formation under some conditions. However, the observed stimulation could have been due to something other than increased beta-adrenergic activity in the ciliary epithelium.

The effect of isoproterenol on aqueous humor formation in humans.

Isoproterenol was applied topically to one eye of each of 20 normal human volunteers. The rate of aqueous humor flow was measured with fluorophotometry. Intraocular pressure fell slightly in the treated eye, but the rate of aqueous humor flow was unaltered. Even when applied to the cornea in high concentrations, this beta-adrenergic agonist appeared to have no measurable effect on the flow of aqueous humor through the anterior chamber in the human eye.

Method of measuring aqueous humor flow and corneal endothelial permeability using a fluorophotometry nomogram.

A new method of measuring aqueous humor flow and corneal endothelial permeability to fluorescein using a fluorophotometry nomogram is described. This method is compared to four other methods, two of which have been described previously. All five methods were carried out simultaneously in a group of 20 normal human subjects. All methods give closely comparable results in most of the eyes tested. A tabular comparison of the results of the nomographic method and the published results of other investigators, which are in good agreement, is given. The relative advantages and disadvantages of the nomographic technique are discussed.

Immediate effect of epinephrine on aqueous formation in the normal human eye as measured by fluorophotometry.

Epinephrine hydrochloride (1%) and an identical-appearing placebo were instilled into the right/left eye pairs (random assignment) of 24 young normal subjects. Aqueous humor flow (measured by fluorophotometry over a 7 hr period), intraocular pressure, and (in 10 subjects) tonographic facility of outflow were measured. The effects of epinephrine were to lower intraocular pressure (2.8 mm Hg +/- 1.9, mean +/- S.D.), raise the facility of outflow (37.4% +/- 21.7), and increase the rate of formation of aqueous humor (18.6% +/- 18.1). By comparing tonographic and fluorophotometric data in the same subjects, it was postulated that epinephrine increases the rate of outflow via the pressure-insensitive (uveoscleral, uveovortex) outflow pathway.

Acute effect of epinephrine on aqueous humor formation in the timolol-treated normal eye as measured by fluorophotometry.

A double-blind, randomized, placebo-control study of the effect of epinephrine on the rate of aqueous formation in eyes pretreated with a beta-adenergic blocking drug was carried out in 25 normal subjects with the use of fluorophotometry. All eyes were pretreated with timolol maleate before epinephrine or placebo was given. The effect of timolol maleate alone was to lower intraocular pressure and to reduce the rate of formation of aqueous humor. In the presence of timolol, aqueous formation was decreased further, approximately 7% more, in the epinephrine treated-eye as compared to the placebo-treated eye. This additional decrease in aqueous formation was statistically significant. No statistically significant difference was found in intraocular pressure or in tonographic C value between the epinephrine-treated and the placebo-treated eye. However, intraocular pressure was so low in both eyes that differences in intraocular pressure were not expected and tonographic tracings were difficult to interpret.

A scanning ocular spectrofluorophotometer.

We describe an instrument called a scanning ocular spectrofluorophotometer (SOSF) that measures fluorescence in a two-dimensional cross-section through the anterior chamber and cornea and provides the ability to change excitation and emission wavelengths rapidly. The output of a xenon arc lamp is filtered by a diffraction grating monochromator which has a bandpass of 4 nm and a range of 400 to 800 nm. Light emitted from the fluorophore is filtered by a variable wavelength interference filter which has a bandpass of approximately 11 nm and a range of 400 to 700 nm. To demonstrate the versatility of the instrument, we measured the spectra of fluorescein, fluorescein glucuronide and rhodamine B in the anterior chambers and corneas of pigmented rabbits after topical administration. We also measured simultaneously and independently the redistribution and disappearance of a mixture of fluorescein-labeled dextran and rhodamine B after intracameral injection. Rhodamine B was very rapidly absorbed by the cornea and lens while fluorescein-dextran was not measurable in the cornea before 4 hr. The SOSF provides a means of carrying out spectrofluorophotometry in the living eye and carrying out kinetic experiments which would otherwise be awkward or impossible.

Intraocular pressure after optic nerve transection.

Intraocular pressure response to systemically administered osmotic agents was studied in albino rabbits with one optic nerve transected and the fellow optic nerve left intact. There eas a significant increase in intraocular pressure of both eyes following water ingestion but no significant difference in the pressure rise of the two eyes. There was a significant decrease in intraocular pressure of both eyes following glycerol ingestion but no significant difference in the pressure fall of two eyes. These results do not support the hypothesis that the optic nerve carries fibers which are part of the control system for intraocular pressure.

Pharmacokinetics of fluorescein in the vitreous.

The pharmacokinetics of fluorescein in the vitreous after intravenous or oral fluorescein administration was studied in normal individuals. Vitreous and free blood fluorescein concentrations were measured over an 8 hr period by fluorophotometry and fluorescence polarization. A computer model was constructed based on the free plasma fluorescein concentrations and conformed closely to the experimental data. The concentration profiles of fluorescein appearance in the vitreous were then examined. The effect of alterations in retinal permeability and free blood fluorescein concentration are also discussed. This article illustrates that an increase in the concentration of fluorescein in the vitreous as measured by fluorophotometry can be caused by factors other than an increase in blood-retinal barrier permeability.

The nocturnal suppression of aqueous humor flow in humans is not blocked by bright light.

Normal human subjects were studied hourly by fluorophotometry to measure the normal circadian rhythm of aqueous humor flow. On a separate day, the subjects slept for approximately 1 hr after lunch; this short nap was not found to have any effect on aqueous flow. On a separate night, the subjects slept under a bright light of 2500 lux; the light was not found to have any effect on flow in the sleeping subjects. Because bright light blocks melatonin release in humans, nocturnal suppression of aqueous flow in humans may not be driven by systemic melatonin release.

Effect of chronic epinephrine on aqueous humor flow during the day and during sleep in normal healthy subjects.

Epinephrine 2% drops were administered to one eye and a placebo to the fellow eye twice a day for 2 weeks in 18 normal human volunteers. The circadian rhythm of aqueous humor flow was measured by fluorophotometry. Epinephrine (compared with placebo) had no measurable effect on the rate of aqueous flow or the circadian rhythm of aqueous humor flow. These results suggest either that topical application of epinephrine cannot achieve a sustained effect on the mechanism of aqueous formation compared with endogenous epinephrine or that circulating epinephrine is not the sole or principal hormonal messenger that mediates the circadian rhythm of aqueous flow in humans. An experiment in which epinephrine was administered systemically might clarify this ambiguity.

Measurement of fluorescein and fluorescein monoglucuronide in the living human eye.

Fluorescein monoglucuronide is a fluorescent metabolite of fluorescein, and is 1/3 to 1/34 as fluorescent as fluorescein, depending on the wavelength of excitation. After systemic administration, fluorescein glucuronide reaches concentrations many times greater than fluorescein. In order to study the effect of fluorescein glucuronide on the measurement of ocular dynamics, we devised a technique to measure fluorescein and fluorescein glucuronide in the anterior segment of the living human eye. Concentrations of each fluorophore were determined by differential spectrofluorophotometry from measurements at excitation wavelengths of 457.9 nm and 488.0 nm. Measurements were made on normal volunteers after oral and intravenous administration of fluorescein. Fluorescein was the dominant fluorophore during the first hour, while fluorescein glucuronide became dominant after 3 hours. By 6 hours there was 10 to 30 times more fluorescein glucuronide than fluorescein in the anterior chamber after oral administration, and three to ten times more after intravenous administration. The blood aqueous diffusion coefficient kd estimated from the apparent concentration of fluorescein measured at 457.9 nm was consistently greater than kd estimated from measurements at 488.0 nm. Estimates of kd, which were made on the basis of concentrations of fluorescein determined from measurements at both wavelengths, were lower than estimates based on measurements at either wavelength. These results indicate that wavelength of excitation may influence the determination of ocular parameters when systemic fluorescein is used. Care must be taken in the interpretation of measurements when metabolites of a fluorophore can interfere with measurement of the fluorophore itself.

A two-dimensional scanning ocular fluorophotometer.

For certain studies of the dynamics of fluorescein in the anterior segment of the eye it would be advantageous to measure fluorescent intensity from several anatomic regions of the cornea and anterior chamber simultaneously or in rapid succession. In the present paper we describe a device called a two-dimensional scanning ocular fluorophotometer that we have designed and built to measure fluorescein concentration in a horizontal section through the cornea and anterior chamber. The 488-nm wavelength beam of an argon laser is mechanically scanned through the target area (70 microW total power at the eye) and fluorescent light is measured with a photon-counting photomultiplier tube. A single anterior-posterior scan requires 100 msec and is divided into 33 sample time periods of 3 msec each. Thirty anterior-posterior scans are made within 3 sec. A two-dimensional array of fluorescein concentration is reconstructed from the data. Concentrations ranging from 3 X 10(-10) gm/ml to 3 X 10(-6) g/ml are measured in a single scan. Examples of scans through the anterior chamber and cornea after topical and systemic administration of fluorescein are presented. These scans illustrate how this instrument can be used to measure two types of regional differences in fluorescein concentration, the "pupillary aqueous bubble" following topical administration and the radial concentration gradient in the cornea following systemic administration.

Effects of timolol, epinephrine, and acetazolamide on aqueous flow during sleep.

The effects of timolol, epinephrine, and acetazolamide on the rate of flow of aqueous humor through the anterior chamber of awake and sleeping human subjects was studied. Timolol reduced the rate in awake subjects but not sleeping subjects. Epinephrine increased the rate in sleeping subjects to a greater extent than in awake subjects. Acetazolamide reduced the rate of flow in awake subjects or epinephrine-stimulated subjects. Acetazolamide reduced the rate of flow slightly below the basal rate observed during sleep, but the reduction was small and not statistically significant. The authors propose that the diurnal fluctuation of the rate of aqueous humor flow in humans is driven by changes in the concentration of endogenous epinephrine available to the ciliary epithelia.

Measurement of aqueous flow in rabbits with corneal and vitreous depots of fluorescent dye.

Using pigmented rabbits, two fluorophotometric methods for measuring aqueous flow were compared. A corneal depot of dye was used to measure aqueous flow in one eye of each rabbit while the vitreous depot method of Johnson and Maurice was used to measure aqueous flow over the same period in the fellow eye. After intravenous administration of acetazolamide or mannitol, during the first hour after drug delivery a decrease in aqueous flow was observed in the eye with the corneal depot of dye that was undetected in the eye with the vitreous depot of dye. In rabbits which were water-loaded by orogastric tube, an increase in aqueous flow was observed by the corneal depot method, while the vitreous depot method indicated a decrease in aqueous flow. The vitreous depot method depends on the assumption that the rate of loss of dye from the vitreous remains stable. It is shown that movement of water into or out of the vitreous can cause large changes in the rate of movement of dye from the vitreous to the anterior chamber and can make interpretation of the vitreous method ambiguous. While the vitreous depot method is probably superior for measuring sustained changes of the rate of aqueous flow over tens of hours or days, it is concluded that it cannot be used for measuring changes over shorter periods.

Aqueous humor flow and flare in patients with myotonic dystrophy.

PURPOSE: Myotonic dystrophy is an autosomal dominant form of muscular dystrophy associated with a mutation that affects a gene on chromosome 19. Extremely low intraocular pressure is one of a constellation of clinical signs that sometimes accompany this disorder. This study was performed to determine if the ocular hypotony can be explained by aqueous humor hyposecretion. METHODS: Seventeen persons with myotonic dystrophy and seventeen age-matched controls were studied. Intraocular pressure, light scattering (flare), fluorescein clearance at various times of day, and the response of the eye to the topical timolol were measured. RESULTS: Intraocular pressure was 40% lower in the persons with myotonic dystrophy (8.4 mm Hg vs 14.0 mm Hg) and flare was 50% higher (55.8 mg/dl albumin equivalent vs 37.1 mg/dl albumin equivalent). Fluorescein clearance in persons with myotonic dystrophy was indistinguishable from normal at all times of day. Myotonic eyes responded normally to topical timolol. The physiological data of this study are most consistent with the conclusion that the rate of aqueous humor flow is reduced approximately 9%, and the rate of inward leakage of light scattering proteins is increased approximately 37% in well-established myotonic dystrophy with ocular hypotony. CONCLUSIONS: The reduced aqueous humor flow alone is insufficient to explain the ocular hypotony. We hypothesize that the hypotony is due primarily to atrophy of the ciliary muscle that increases fluid exchange between the anterior chamber and the anterior uvea with consequent enhancement of uveoscleral outflow.

Measurement of aqueous humor flow by fluorophotometry in the presence of a dilated pupil.

PURPOSE: To determine by means of fluorophotometry whether pharmacologic dilation of the pupil can interfere with the measurement of aqueous flow. METHODS: Ten normal human volunteers underwent dilation with tropicamide, phenylephrine, and a combination of the two drugs. Before and after dilation, the rate of aqueous flow was measured by the rate of disappearance of fluorescein from the cornea and the anterior chamber. RESULTS: Dilation of the pupil with tropicamide alone had no effect on the rate of clearance of fluorescein. Dilation with phenylephrine increased the rate of clearance of fluorescein by 40% and caused a small increase in the variability among subjects. Dilation with a combination of tropicamide and phenylephrine caused clearance of fluorescein at more than double the normal rate and a marked increase in variability among subjects. CONCLUSIONS: When the pupil is dilated sufficiently to permit mixing of aqueous humor in the posterior and anterior chambers, fluorescein can leave the system by a posterior route, and its rate of clearance may not be an accurate measure of the net rate of aqueous humor flow through the anterior chamber.

Effect of thymoxamine on aqueous humor formation in the normal human eye as measured by fluorophotometry.

A double-blind, randomized, placebo-controlled study of the effect of 0.5% topical thymoxamine hydrochloride an alpha-adrenergic antagonist, on the rate of aqueous humor formation in the eyes of 25 normal human subjects was performed with fluorophotometry. The effect of thymoxamine on intraocular pressure and anterior chamber volume was also studied. four of the 25 subjects were used to study the effect of thymoxamine on the permeability to fluorescein of the blood-aqueous barrier. Pupillography was used to confirm that alpha blockade was present in the iris. Thymoxamine-treated eyes had 12% greater aqueous humor flow than placebo-treated eyes, but this difference was not statistically significant. No statistically significant difference was found in the rate of aqueous humor formation, intraocular pressure, anterior chamber volume, or premeability of the blood-aqueous barrier between thymoxamine-treated and placebo-treated eyes. The lack of an effect on the aqueous system could be interpreted as being a result of too low a concentration of thymoxamine in the ciliary body, lack of blockable receptors in the ciliary body, lack of physiologic tone in a blockable receptor system, or lack of a role of such a receptor system in the formation of aqueous humor.

Hypotony and aqueous humor dynamics in myotonic dystrophy.

A group of 26 subjects with myotonic dystrophy were studied with fluorophotometry to evaluate the relationship between aqueous humor dynamics and the hypotony found in this disorder. All 26 received topical fluorescein to determine the anterior chamber elimination coefficient; five received systemic fluorescein to evaluate the integrity of the blood-aqueous barrier. The group has a mean intraocular pressure of 7.1 mm Hg. The rate of clearance of fluorescein from the anterior chamber and the cornea-to-anterior chamber transfer coefficient for fluorescein were normal. An abnormally high level of fluorescence, three times normal, was observed in the anterior chambers of the myotonic subjects after oral administration of fluorescein. This finding could not be attributed to abnormal absorption and elimination of fluorescein or to abnormal plasma binding. This finding indicates that there is a defect in the blood-ocular barrier to fluorescein in myotonic subjects. Thus conclusions regarding aqueous humor flow cannot be made from the rate of clearance of topically applied fluorescein in myotonic subjects, since the clearance due to diffusion may represent a significantly large fraction of the total clearance.