Why the eye becomes dry: a cornea and lacrimal gland feedback model.

PURPOSE: Many explanations have been offered for why a large segment of the population develops dry eye. The purpose of this paper is to describe a new unifying theory of dry eye that incorporates all of these causes. METHODS: Data from the Department of Ophthalmology, University of Iowa Hospitals and Clinics was analyzed from 520 patients with dry eye, blepharitis and other conditions to assess the relationship between dry eye and blepharitis. This data was reviewed in terms of the relationship between dry eye, menopause, and aging. Also examined in detail were many of the proposed causes for dry eye in the literature. RESULTS: A close relationship between corneal damage and lacrimal gland function is hypothesized. Not only does decreased lacrimal gland output damage the ocular surface, but also damage to the corneal surface creates a negative feedback loop and damage to the lacrimal gland. There are probably several mechanisms by which this feedback occurs. One mechanism results from interruption or damage to the sensory corneal nerves. Damage to the nerves within the lacrimal gland may be another mechanism. Alteration of growth factor levels in the lacrimal gland, which occurs following corneal damage, represents another possible mechanism. Contact lenses and corneal refractive surgery are additional elements that may create negative feedback to the lacrimal gland. CONCLUSION: The ocular surface and the lacrimal gland functions as a tightly integrated unit. Dry eye conditions damage the ocular surface and this in turn leads to further damage to the lacrimal gland.

Confirmation of confocal microscopy diagnosis of Acanthamoeba keratitis using polymerase chain reaction analysis.

BACKGROUND: Acanthamoeba keratitis has commonly been identified with in vivo confocal microscopy and confirmed with histologic examination of an epithelial biopsy specimen. OBJECTIVE: To determine if Acanthamoeba keratitis can be verified using polymerase chain reaction (PCR) of epithelial biopsy specimens. METHODS: Epithelial specimens from patients with suspected Acanthamoeba keratitis by confocal microscopy were tested for Acanthamoeba with PCR of Acanthamoeba ribosomal DNA. RESULTS: Twenty-four of 31 patients with evidence of Acanthamoeba keratitis were positive for Acanthamoeba on PCR analysis using 3 sets of primers. In 22 cases, the sequence obtained closely matched Acanthamoeba castellanii. CONCLUSIONS: This study demonstrates that PCR analysis of epithelial biopsy specimens can provide definitive verification of the confocal microscopic and histologic identification of Acanthamoeba organisms associated with keratitis. Acanthamoeba keratitis is probably quite common, especially in contact lens wearers, although more than half of the patients in this study did not wear contact lenses.

Cytologic changes in the conjunctiva mimicking malignancy after topical mitomycin C chemotherapy.

PURPOSE: To describe the epithelial changes observed in the conjunctiva secondary to the use of topical mitomycin C (MMC) for treatment of primary acquired melanosis with atypia. DESIGN: Retrospective comparative case series. PARTICIPANTS AND CONTROLS: Conjunctival biopsy specimens (18) were taken during the follow-up of ten patients treated with MMC drops (0.02% or 0.04%) during 14 or 21 days for primary acquired melanosis with atypia. An equal number of age- and sex-matched patients with normal conjunctival biopsy findings were included for control. Conjunctival biopsy specimens from patients treated with MMC were compared with the morphologic changes already described in the urothelium following the use of the same chemotherapeutic agent. METHODS: Hematoxylin and eosin-stained biopsy samples were evaluated for recurrent neoplasm and chemotherapeutic effect in the epithelium using the following criteria: nuclear enlargement, nuclear hyperchromasia, smudging of the chromatin, presence of nucleoli, cytoplasmic eosinophilia, and individual cell necrosis. MAIN OUTCOME MEASURES: The presence or absence of morphologic changes in the conjunctival epithelium related to the use of MMC. RESULTS: Morphologic features consistent with chemotherapy effect were seen in the biopsy specimens of nine patients. Nuclear enlargement and chromatin smudging-hyperchromasia localized in the superficial layers of the epithelium were the main features observed (9 patients). Cytoplasmic eosinophilia, single cell necrosis, and occasionally subepithelial chronic inflammation were also seen. CONCLUSIONS: Secondary changes with the topical use of MMC are seen in the conjunctival epithelium and are similar to the changes described in the urothelium. These changes are important to recognize and to differentiate from recurrent neoplasm. The localization of the described features in the superficial layers of the conjunctival epithelium is the key feature in the differential diagnosis.

New technique for the cytologic identification of presumed Acanthamoeba from corneal epithelial scrapings.

PURPOSE: To describe a cytologic technique for the rapid identification of presumed Acanthamoeba organisms from corneal epithelial scrapings. METHODS: After administering topical anesthesia, we removed the affected corneal epithelium with a scalpel blade. The tip of the blade, containing the scrapings, was washed off into a cuvette with a solution of an alcohol-based fixative for cytology specimens. The blade was immersed in the cuvette and agitated to ensure that the sample was collected. The specimen was fixed for at least 10 minutes and processed by cytospin centrifugation. RESULT: Seventy-five patient samples have been studied with this technique, with excellent preservation of the organism. CONCLUSIONS: The organism preservation with this technique is superior to that of conventional smears and permits confirmatory organism identification by immunohistochemistry.

Exclusion of AR-CHED from the chromosome 20 region containing the PPMD and AD-CHED loci.

Congenital hereditary endothelial dystrophy (CHED) is a disorder of the corneal endothelium and has been recognized to segregate in families with both autosomal dominant (AD) and autosomal recessive (AR) modes of transmission. AD-CHED has been previously linked to the pericentric region of chromosome 20. Posterior polymorphous dystrophy (PPMD), a corneal endothelial disorder showing phenotypic overlap with CHED, has also been previously genetically mapped to this region. The genetic interval containing AD-CHED is within the larger genetic interval containing the PPMD locus. This study sought to determine whether AR-CHED segregating in a consanguineous Saudi Arabian pedigree is linked to the previously mapped and overlapping loci for AD-CHED and PPMD on the pericentric region of chromosome 20. Forty members of a consanguineous Saudi Arabian pedigree segregating AR-CHED were ascertained. Short tandem-repeat polymorphic markers from the 20 cM interval on chromosome 20 containing both the PPMD and AD-CHED loci were used to genotype these individuals. LOD score analysis of the genotype data with the MENDEL software package utilizing a model of autosomal recessive inheritance with complete penetrance showed exclusion of CHED from the entire PPMD/AD-CHED interval by utilizing overlapping intervals of LOD scores of at least -2. The results obtained demonstrate that AR-CHED is not allelic to either AD-CHED or PPMD, although it has been proposed that AD-CHED may be allelic to PPMD. Thus, there are at least two genes responsible for CHED and PPMD.

An epidemic of presumed Acanthamoeba keratitis that followed regional flooding. Results of a case-control investigation.

OBJECTIVES: To investigate an outbreak of presumed Acanthamoeba keratitis (AK), to identify risk factors associated with its development, and to characterize the changing epidemiology of AK. METHODS: We performed a pairwise-matched case-control study involving 31 patients who were diagnosed as having AK between July 1993 and December 1994. Risk factors were identified using conditional logistic regression analysis. To investigate the impact of regional flooding, we stratified counties within Iowa by whether their water facilities were affected and then calculated population-based estimates of the incidence of AK. RESULTS: During the study, 43 presumed incident cases of AK were diagnosed; 31 were included in the case-control study. Cases were diagnosed based on the clinical presentation of keratitis, positive tandem scanning confocal microscopy examination results, and confirmatory cytopathologic findings. There were no positive culture specimens. On average, cases had symptoms for 8 weeks before diagnosis, most notably photophobia (94%), red eyes (94%), and pain (80%). Contact lens use (odds ratio [OR] = 44.16; P = .02) and fishing (OR = 22.62; P = .04) were independent predictors of the development of AK. The presence of a humidifier in the home (OR = 0.08; P = .03) and having household water that originated from a private well instead of the municipal water supply (OR = 0.12; P = .08) were protective. Twenty-nine of 30 cases resided in counties in which the water supplies were affected by flooding as determined by the Department of Natural Resources, Des Moines, Iowa. The incidence of AK in these counties was more than 10 times higher than that in the unaffected counties (relative risk = 10.83, 95% confidence interval, 1.48-79.49; P < .003). CONCLUSIONS: We describe an epidemic of keratitis that, based on clinicopathologic and epidemiological evidence, is consistent with AK. As in previous outbreaks of culture-proven AK, contact lens use was the major risk factor. Both the results of the case-control study and the population-based incidence estimates suggest that the recent outbreak may be caused, in part, by the effects of regional flooding. However, because the outbreak also coincided with a change in diagnostic techniques, we cannot eliminate recognition bias as the reason for the apparently changing epidemiology.

Corneal thickness in Fuchs' dystrophy with and without epithelial oedema.

PURPOSE: To investigate whether the occurrence of epithelial oedema in Fuchs' endothelial dystrophy is associated with a particular corneal thickness or the extent of central corneal guttae. METHODS: Sixty-seven patients, aged 52-90 years, presenting in our clinic with Fuchs' dystrophy were divided on the basis of the presence or absence of epithelial oedema as determined by slit lamp examination. After exclusion of extreme cases, the 56 cases without oedema were compared with the 10 cases with oedema with respect to corneal thickness, measured by ultrasound pachymetry and corneal guttae diameter, obtained from the slit lamp examination. RESULTS: Mean corneal thickness was significantly higher (p = 0.002) in the oedematous group (mean = 0.682 mm) than in the group without epithelial oedema (mean = 0.624 mm). A corneal thickness greater than 0.650 mm was associated with a greater than 85% probability of oedema occurrence. Corneal guttae diameter did not differ significantly (p = 0.941) between the two groups and was not significantly correlated with corneal thickness (p = 0.269). CONCLUSION: There is a demonstrable association between epithelial oedema and the measured thickness of the cornea.

Menopause and tear function: the influence of prolactin and sex hormones on human tear production.

PURPOSE: The onset of dry eye is very common during menopause and may result from the loss of hormonal support. The purpose of this study was to assess the effect that changes in sex hormone and prolactin levels have on tear function in premenopausal and menopausal woman. METHODS: Women between the ages of 30 and 60 were solicited to participate in a study concerning menopause and tear function. One-hundred and ten women were given tear function tests (osmolarity, tear volume, tear flow, Schirmer's test) and serum levels were measured for total testosterone, estradiol, prolactin, and follicle stimulating hormone. RESULTS: For all women on hormone replacement therapy, we found a strong negative correlation between serum prolactin level and tear function. For women in menopause, total testosterone correlated positively with tear function, whereas for premenopausal women there was a negative correlation between total testosterone and tear function. Serum estradiol levels correlated positively with tear function for women 30-39 years of age, whereas for menopausal women the correlation was negative. CONCLUSIONS: This is the first demonstration in humans that tear production is correlated with serum prolactin and sex hormone levels prior to and during the menopause.

Correlation between surface water contamination with amoeba and the onset of symptoms and diagnosis of amoeba-like keratitis.

AIM: A seasonal variation was noted in the incidence of amoeba-like keratitis in Iowa. The level of contamination of amoeba in surface water has been found previously to vary on a monthly basis for Tulsa, Oklahoma, a region with a similar climate. It was hypothesised that this seasonal variation in amoeba-like keratitis correlated with the concentration of amoeba in surface water. METHODS: The monthly variation in the onset of symptoms was determined and date of diagnosis in 137 cases of amoeba-like keratitis, in Iowa, from January 1993 to the end of December 1996. RESULTS: Over a 4 year period a significant variation was found, on a monthly basis, in the onset of symptoms as reported by the patient. There were two peak periods per year when the onset of symptoms was most frequent: June and November. This corresponded closely with the concentration of amoeba in the ground water reported for a similar region in the mid-west (Tulsa, Oklahoma). A yearly increase was found in the number of cases diagnosed from January 1993 to the end of December 1996. CONCLUSIONS: This study supports the hypothesis that the concentration of amoeba in surface water may influence the rate of an amoeba-like keratitis infection.

Coexistent Acanthamoeba keratitis and herpetic keratitis.

OBJECTIVE: To describe a series of patients with proved herpes simplex virus keratitis (herpetic keratitis) who also had documented Acanthamoeba keratitis. METHODS: Herpetic keratitis was documented with viral cultures, immunologic stains, or histopathologic examination for multinucleated giant cells in the corneal epithelium. Acanthamoeba organisms were identified using confocal microscopy and epithelial biopsy with hematoxylin-eosin staining. Biopsy of the stroma and epithelium was used to identify Acanthamoeba organisms in 1 case. RESULTS: Cultures for herpes simplex virus were positive in 6 of the 9 cases. Immunologic stains were positive in an additional 2 cases, and in 1 case multinucleated giant cells were present in the epithelium consistent with the diagnosis of herpes simplex virus keratitis. Tandem scanning confocal microscopic findings were positive for Acanthamoeba in 8 of the 9 cases, and all of them demonstrated Acanthamoeba organisms in epithelial scrape biopsy specimens. In 1 case, which was not evaluated with confocal microscopy, Acanthamoeba was detected using a stromal and epithelial biopsy. Two of the 9 patients had a history of contact lens use. CONCLUSION: Acanthamoeba keratitis may be present as a secondary or opportunistic infection in patients with herpetic keratitis.

Assessment of the tear film with tandem scanning confocal microscopy.

PURPOSE: To evaluate the confocal microscopic appearance of the tear film by correlating the interference pattern created by the lipid surface with physiologic measurements of tear function and with clinic diagnosis. METHODS: A series of 53 patients was examined with a battery of tests to evaluate the tear film and with confocal microscopy to evaluate the interference pattern created by the lipid surface of the tear film. Assessment of the tear-film appearance involved five nonparametric scales: degree of debris in the tear film, variability of the interference pattern over time, linearity of the interference pattern, number of dry spots seen, and relative thickness of the lipid layer. For 10 other subjects, the confocal appearance of the tear film and evaporation from the ocular surface was tested for before and after meibomian gland expression. RESULTS: The confocal appearance correlated with multiple physiologic variables and clinical diagnosis. Patients with seborrheic meiboman gland dysfunction had a thicker lipid layer, greater variability, and more debris than did patients with obstructive meibomiam gland dysfunction. After meibomian gland expression, lipid thickness and linearity increased, whereas pattern variability and evaporation decreased significantly. The mean reduction in evaporation was 48%. CONCLUSIONS: Confocal microscopy can be used to examine the tear film, and its appearance correlates significantly with physiologic variables in normal-individuals and in disease states. The confocal appearance of the lipid interference patterns and evaporation from the ocular surface are altered after lipid expression from meibomian glands.

Adherence of Pseudomonas aeruginosa to shed rabbit corneal epithelial cells after overnight wear of contact lenses.

PURPOSE: Previous studies have shown that contact lens oxygen transmissibility correlates with binding of Pseudomonas aeruginosa to the rabbit cornea after overnight lens wear. Studies of human lens wear stratified by oxygen transmissibility will be required to validate these animal results. In humans, bacterial binding to shed cells obtained through corneal irrigation cytology may provide an indirect measure of in vitro binding. The purpose of this study was to establish the relationship between binding to shed cells and to the residual corneal surface in an animal model of lens wear prior to initiation of human studies. METHODS: The test contact lenses used were: rigid lens A (Dk/L = 10 x 10(-9) [cm/ sec][mL O2/mL mmHg]); rigid lens B (Dk/L = 97); soft lens A (Dk/L = 9); soft lens B (Dk/L = 20); and, soft lens C (Dk/L = 39). There were six rabbits in each group, except for the soft lens C group, which had seven rabbits. After overnight lens wear, the corneal surface was irrigated with a corneal irrigation chamber to collect surface cells before exposure to a bacterial suspension (1 x 10(7) CFU/mL) for 30 minutes. The number of bacteria adherent to the residual corneal surface was then assessed by CFU determination. Cells collected from the corneal surface (9 mL) were incubated with 1 mL bacterial suspension containing 10(8) (CFU/mL) for 30 minutes. The number of bacteria adherent to shed cells was assessed by staining with acridine orange and direct counting by epifluorescence microscopy. RESULTS: The differences in the number of bacteria adhering to shed epithelial cells between the treated and the control eyes were 2.90 +/- 1.20 and 0.23 +/- 0.41 for rigid lenses A and B, respectively, and 5.97 +/- 1.54, 3.67 +/- 2.32, and 0.90 +/- 1.45 (bacterial/cell) for soft lenses A, B, and C, respectively. Overnight contact lens wear induced a significant increase in bacterial binding to shed corneal epithelial cells for rigid lens A and for soft lenses A and B. There were significant differences among lens groups (P = 0.00017, ANOVA), with significant differences between rigid lenses A and B, soft lenses A and C, and soft lenses B and C. The binding of bacteria to shed cells was significantly correlated with the binding of bacteria to the residual corneal surface, both confirming and extending previous results (R = 0.78, P < 0.001). CONCLUSION: These results demonstrate a positive correlation between P. aeruginosa adherence to shed corneal cells and to the residual corneal surface in the rabbit eye following contact lens wear. In light of the results from prior animal studies, examination of the behavior of P. aeruginosa binding to exfoliated cells appears to be a promising and valid method for future assessment of similar lens-induced increases in bacterial binding in prospective human clinical studies.

Evaluation of infectious crystalline keratitis with confocal microscopy in a case series.

We sought to determine whether there are unique findings in infections crystalline keratitis (ICK) examined by confocal microscopy and if confocal microscopy is predictive for bacteriology in ICK. A retrospective review of consecutive patients with a presumed diagnosis of ICK by slit-lamp examination was performed. These patients were then examined with confocal microscope and cultured. Sixteen patients were identified by biomicroscopy. Average age was 71 years; 12 of 16 patients were women; 10 of 16 had prior penetrating keratoplasty; and 12 of 16 were taking topical steroids. Confocal microscopy revealed a variable appearance to the crystals in the corneal stroma. Eight of 16 patients had distinct needle-like deposits at varying depths in the stroma, and eight had amorphous deposits grouped at different levels of the stroma. The results of confocal microscopic examination resembled the reported histopathology with clusters of deposits, but its current resolution does not allow identification of bacterial morphology. There was no correlation of morphology with culture results. Organisms were recovered in 12 of 16 patients by culture. In 10 of 16 patients, the infection was successfully treated with topical antibiotics, usually cefazolin. Crystal morphology of ICK can be observed by confocal microscopy. No pathognomonic, single pattern for this disease is seen with the confocal microscope. The latter may be an aid in determining the clinical response to treatment.

Diagnosis of Aspergillus keratitis in vivo with confocal microscopy.

Confocal microscopy provides a new, noninvasive way of imaging the human cornea in vivo. One of its most important clinical uses is the diagnosis and management of infectious keratitis. The authors used tandem scanning confocal microscopy to image the corneas in two culture-proven cases of Aspergillus keratitis. Fungal hyphae were imaged as high-contrast filaments 6 microns in diameter from 60 to 400 microns in length. Confocal microscopy may be a fast and safe diagnostic tool in determining the presence of fungal hyphae in vivo within the human cornea.

Tear film changes associated with normal aging.

We examined a group of normal subjects to evaluate the tear film function by measuring reflex tear capacity using the Schirmer test without anesthetic, steady state tear flow using fluorophotometry, meibomian gland function based on gland drop-out, expressible lipid volume and viscosity, tear loss from evaporation, and tear osmolarity. We found the average tear flow to be 0.19 +/- 0.19 microliters/min, lower than previously measured. The average tear volume was also correspondingly less, 2.74 +/- 2.0 microliters. We found there was a decline associated with advancing age for all parameters except the decay constant and lipid volume. The highest correlations with aging were tear volume (-0.64), Schirmer test (-0.63), and tear osmolarity (0.59). Our results indicate that there is a decline in tear film function throughout life and that tear flow is considerably less than previously estimated.

Tear flow and evaporation in patients with and without dry eye.

PURPOSE: To evaluate the steady-state tear flow and evaporation from the ocular surface of patients with and without dry eye. METHODS: Two groups of patients, 21 with dry eye and 34 without dry eye, with similar age distributions were selected by criteria based on tear osmolarity, Schirmer test, meibomian gland loss, and dry eye symptoms and were compared for tear flow, tear volume, percent turnover, and surface evaporation. RESULTS: Tear flow averaged 0.10 +/- 0.08 microliters/minute in patients with dry eye versus 0.15 +/- 0.12 microliters/minute in patients without dry eye (P = 0.002). Tear volume averaged 2.13+/- 1.3 microliters in patients with dry eye versus 2.23 +/- 2.5 microliters in patients without dry eye (P = not significant) and tear turnover averaged 5.3 +/- 2.9% in patients with dry eye versus 8.2 +/- 4.3% in patients without dry eye (P = 0.019). Evaporation averaged 25 +/- 35 X 10(-7) g/cm(2)/second in patients with dry eye versus 13 +/- 6 X 10(-7) g/cm(2)/second in patients without dry eye (P = 0.003). CONCLUSIONS: Measured tear flow was significantly lower than previously determined in patients with and without dry eye. Evaporation was increased in patients with dry eye and accounted for the majority of the tear loss in patients with dry eye. Normal tear osmolarity can be maintained, even with low tear flow, if evaporation is kept within the normal range.

Model for ocular tear film function.

Blepharitis patients have a number of disturbances in their tear film associated with meibomian gland dysfunction that affect evaporation and tear osmolarity. We tested a series of 156 consecutive patients, with a presumed diagnosis of blepharitis, dry eye, or allergic disease, and a series of 72 normals. We compared their tear film characteristics using tear osmolarity, tear volume, tear production (fluorophotometric and Schirmer test), tear turnover (decay constant), tear evaporation, and meibomian gland function evaluated by gland drop-out, expressed lipid viscosity, and volume. Of the 156 patients tested, we found 37 had dry eye, 10 had only allergic disease, 73 had meibomian gland dysfunction and dry eye, and 36 had only meibomian gland dysfunction. We created a model of the relative influence some of these factors had on each other using their correlation coefficients. The highest correlations for osmolarity were Schirmer test (-0.44), lipid volume low (-0.44), lipid viscosity high (0.39), gland drop-out (0.39), and tear evaporation (0.36). With regression analysis we accounted for 47% of the total variation in osmolarity, but only 17% of the variation in tear evaporation. We also present our classification system for blepharitis and dry eye patients based on our measurable physiologic parameters.

Outbreak of keratitis presumed to be caused by Acanthamoeba.

PURPOSE: A sharp increase of Acanthamoeba keratitis from two cases per year to 30 cases per year at our institution prompted this study to determine whether there was a change in the clinical characteristics, basic epidemiology, and outcome of this disease. METHODS: We reviewed all cases of Acanthamoeba keratitis diagnosed at the University of Iowa Hospitals and Clinics from mid-1993 through 1994. RESULTS: We screened 217 patients with keratitis by tandem scanning confocal microscopy and suspected Acanthamoeba in 51 patients. Diagnosis was confirmed by cytology in 43 patients (48 eyes). There were no positive cultures. Patients examined within four weeks of onset of symptoms were younger (mean age, 32.6 +/- 15.4 years) and wore contact lenses (11 of 18 patients), and infrequently herpes simplex keratitis (four of 18 patients) was diagnosed. Patients examined after four weeks were older (mean age, 54.0 +/- 19.5 years), infrequently wore contact lenses (six of 25 patients), and often had herpes simplex keratitis (12 of 25 patients). CONCLUSIONS: Corneal examination with tandem scanning confocal microscopy was associated with a marked increase in the detection of Acanthamoeba, strongly suggesting that the disease is more prevalent than suspected. Acanthamoeba may account for many cases of clinically presumed herpes simplex keratitis, the leading cause of corneal blindness in the United States. Acanthamoeba should be considered in the differential diagnosis of any unexplained keratitis, even those of short duration.

A study of aqueous humor dynamics in keratoconus.

Clinical observations suggest that patients with keratoconus have lower intraocular pressures, on average, than normal subjects. Our purpose was to determine whether differences in aqueous production and outflow facility could account for differences in intraocular pressure between a group of patients with keratoconus and a group of normal, age-matched control subjects. Aqueous humor dynamics were determined by the use of fluorophotometry in one eye of seven patients with keratoconus and ten age-matched normal subjects. Intraocular pressure was measured by applanation tonometry. Keratoconus patients had a statistically significant lower mean intraocular pressure than normal control subjects (11.3 +/- 1.6 mmHg vs. 16.6 +/- 2.8 mmHg, P = 0.0004). The difference in mean intraocular pressure remained significant even after correcting for possible errors in applanation tonometry due to thin corneal stroma. There was no difference in mean aqueous humor flow rates in the keratoconus patients as compared to controls (2.29 +/- 0.53 microliter min-1, P = 0.73). The mean apparent outflow facility was 0.21 +/- 0.07 microliter min-1 mmHg-1 for keratoconus patients compared to 0.14 +/- 0.03 microliter min-1 for controls (P = 0.02). Lower mean intraocular pressure in keratoconus patients appears to be due to increased outflow facility as compared to normal subjects.