Fungal Keratitis: A Six-Year Review at a Tertiary Referral Centre.

Background This review reports the epidemiology, laboratory results, treatment regimens and costs of fungal keratitis at a tertiary referral center in Lucerne, Switzerland. Patients and Methods Culture-proven fungal infections between January 2010 and December 2015 were reviewed retrospectively. Results Seventeen patients with a mean age of 52 years were identified. Contact lens wear was the most important risk factor (n = 11) (65 % of all cases), with filamentous fungi being identified as the most common fungus type (n = 10) (91 % of all cases of contact lens-associated fungal keratitis). All non-contact lens-associated fungal infections (n = 6) (35 % of all cases) were related to Candida spp. Six patients (35 %) were treated on an outpatient basis; 11 cases (65 %) required hospitalisation. Systemic voriconazole was the treatment regimen prescribed most often (n = 12) (71 %), followed by topical natamycin 5 % (n = 11) (65 %). Corneal crosslinking and penetrating keratoplasty were required in 4 cases each (24 %). One case ended up in enucleation (6 %). Average costs per case were EUR 15 952 for hospitalised patients if surgical intervention was required, and EUR 7415 if no intervention was performed. Average costs for outpatients were EUR 7079. In a majority of cases, visual acuity could be improved (n = 9) (53 %) or preserved (n = 2) (12 %). Conclusion Despite the relatively low incidence of culture-proven keratitis (17 cases in 6 years), a clear pattern with regard to risk factors and fungus species was noted. In the absence of a gold standard for the treatment of fungal keratitis, the combination of systemic voriconazole and topical natamycin seems to be one of the most commonly used antifungal treatment regimens. The costs of outpatient versus inpatient non-surgical treatment were approximately the same.

Treatment options for demodex blepharitis: patient choice and efficacy.

BACKGROUND: Demodex mites are microscopic parasites that live around hair follicles or sebaceous glands and may cause chronic blepharitis. The aim of this outcome analysis was to assess the efficacy and patient preferences with regard to the currently recommended treatment options. METHODS: All patients with microscopic evidence for Demodex blepharitis were informed about the currently published treatments and instructed about daily lid hygiene. Additional topical treatment options included tea tree oil (TTO) 5%, a cleansing foam containing 0.02% TTO (Naviblef®), and metronidazole 2% ointment. Systemic treatment options included oral ivermectin 6 mg on day 1 and 14 and metronidazole 500 mg twice daily for 10 days. All patients were reviewed after 2 months for symptoms and for a mite count on 10 epilated lashes. RESULTS: Ninety-four of 96 patients with Demodex blepharitis opted for an additional treatment. The mean mite count after 2 months of treatment were 13.3 with 5% TTO (n=6), 12.0 with 0.02% TTO (n=38), 9.4 with metronidazole ointment (n=5), 12.8 with ivermectin (n=27) and 22.0 with oral metronidazole (n=5). CONCLUSION: While there are several published treatment options available, none of these options seem to be clearly effective in Demodex blepharitis.

Central corneal regularization--optimization of uncorrected visual acuity in keratoconus patients.

BACKGROUND: Combined excimer laser correction and corneal cross-linking is a promising concept in treating keratoconus patients. Central corneal regularization represents advanced topography-guided custom ablation for ectatic corneas, aiming at correcting irregular astigmatism and at increasing the optical regularity of the corneal surface. PATIENTS AND METHODS: In a prospective single centre study, 10 keratoconus patients underwent combined treatment with corneal cross-linking and central corneal regularization by an iRES-Laser. Uncorrected visual acuity at 1 and 3 months postoperatively represented the primary endpoint. RESULTS: Mean preoperative uncorrected decimal visual acuity was 0.15 (± 0.28 standard deviation). Mean postoperative visual acuity was 0.28 (± 0.47) at one month and 0.24 (± 0.25) at three months, respectively. CONCLUSIONS: Combined corneal cross-linking and central corneal regularization treatment has the potential to achieve a clinically significant improvement of uncorrected visual acuity.

A fluorophotometric comparison of anterior chamber riboflavin delivery via corneal application and fornix instillation.

INTRODUCTION AND OBJECTIVES: We investigated whether riboflavin self-administration by patients could be a feasible option for corneal cross-linking, given the considerable resources required to impregnate the cornea with riboflavin. We analysed whether administering riboflavin in the inferior fornix (the site of self-administration) results in non-inferior riboflavin concentrations as when applied directly on the cornea (the site of administration by medical personnel). PATIENTS AND METHODS: We conducted a prospective study to evaluate riboflavin concentrations at six time-points (baseline, 5, 15, 30, 45 and 60min) in 18 healthy volunteers for each of two application sites: cornea and fornix. Anterior chamber riboflavin (Peschke® TE 0.25%) concentrations were measured by fluorophotometry (Fluorotron™ Master FM-2). RESULTS: For the two application sites cornea and fornix, participants did not differ in terms of age and sex. At baseline, the autofluorescence in the anterior chamber was 16.7ng/mL (SD 5.5) and 14.6ng/mL (SD 4.6) (P=.221). After 30min, anterior chamber fluorescein concentrations had risen to 55.1ng/mL (SD 25.5) and 46.1ng/mL (SD 25.1) (P=.293) without a further relevant increase by 60min. CONCLUSIONS: This study found that applying riboflavin drops in the inferior fornix was non-inferior to applying it directly to the cornea, based on fluorophotometric measurements of anterior chamber riboflavin concentrations. This suggests that self-application of riboflavin is feasible in terms of corneal riboflavin impregnation.

Corneal cross-linking as supplementary treatment option in melting keratitis: a case series.

BACKGROUND: Corneal melting represents a serious condition that can result in corneal perforation and loss of vision. Treatment options include topical and systemic immunosuppression, cyanoacrylate gluing, and emergency keratoplasty, depending on the underlying disease and the stage of corneal melt. Recently, corneal cross-linking (CXL) has emerged as an additional treatment option. The present study evaluates whether CXL induces a clinical improvement in melting keratitis not responding to conventional treatment. HISTORY AND SIGNS: Six patients undergoing CXL for corneal melting of variable origin (including bacterial, fungal and Acanthamoeba keratitis) were reviewed retrospectively. THERAPY AND OUTCOME: Treatment parameters included riboflavin application following UV irradiation with a wavelength of 370 nm and an irradiance of 3 mW/cm2 for 30 minutes. Four patients with corneal melting due to contact lens-related infectious keratitis showed healing without any need for further interventions up to date. In two patients, CXL stabilized the melting cornea and facilitated additional surgical procedures. CONCLUSIONS: By stabilizing corneal collagen fibres, CXL seems to represent an effective option to re-establish corneal integrity in the event of pending perforations. In established perforations, CXL facilitates further emergency procedures by stiffening the tissue.

[Safety of treatment with tacrolimus ointment for anterior segment inflammatory diseases]. / Sicherheit der Behandlung entzündlicher Vorderabschnittserkrankungen mit Tacrolimus-Salbe.

BACKGROUND: The off-label use of topical tacrolimus (Protopic) for inflammatory external eye diseases is gaining popularity. However, there are no reports on the safety profile of this new treatment option. PATIENTS AND METHODS: We treated six patients with different inflammatory eye diseases with topical tacrolimus (Protopic 0.03 %) as off-label use in addition to the conventional anti-inflammatory treatment. Patients were interviewed for side effects and serum drug concentrations were measured under steady state conditions one hour after topical application of tacrolimus ointment. RESULTS: Two patients reported a slight burning sensation immediately after application, in one patient we found a slight worsening of the dry eye problems. No patient abandoned the treatment due to side effects. Serum drug concentrations remained below the analytical threshold in all cases (< 1.5 ng/ml). CONCLUSIONS: Tacrolimus for the topical treatment of anterior segment inflammatory eye diseases is well tolerated without detectable systemic drug resorption.

In vivo confocal microscopy of keratic precipitates in fuchs heterochromic uveitis syndrome.

BACKGROUND: In vivo confocal microscopy (IVCM) enables large-field in vivo examination of the corneal endothelium and corneal precipitates. Keratic precipitates (KP) are prominent features of Fuchs Heterochromic uveitis syndrome (FHUS). The aim of this study was to investigate the effect of KP on the corneal endothelium. PATIENTS AND METHODS: Eight patients with clinically diagnosed FHUS and KP between July 2007 and May 2008 underwent slit lamp examination and IVCM. KP (shape, area), endothelial cell count and percentage of hexagonal cells were measured and compared with an age-matched control group and with not affected healthy contralateral eyes. RESULTS: The age of participants ranged between 26 and 67 years. KP had a diameter ranging between 37 to 217 microm (mean 137 microm) with an average area of KP of 5630 microm (2). The mean endothelial cell count in the study group was 2541 +/- 299 cells/mm (2), 2722 +/- 312 cells/mm (2) in the control group (p = 0,18) and 2397 +/- 192 cells/mm (2) in not affected contralateral eyes (p = 0.17). The percentage of hexagonal cells was 59.1 % in FHUS study group and 69.1 % in the control group (p = 0.0002) and 68.6 % in not affected contralateral eyes (p = 0.0495). CONCLUSIONS: KP in FHUS cause a focal damage of endothelial cells reflected in a decreased percentage of healthy hexagonal cells. The degree of endothelial cell damage seems to be low as it does not lead to a significant reduction in the endothelial cell count.

The impact of infectious ocular emergencies on hospital resources.

BACKGROUND: Infectious ocular emergencies cannot be pre-planned, need a more labour-intensive treatment and are often associated with prolonged hospitalisation. The aim of this study is to assess the impact of infectious ocular emergencies on hospital resources and identify changing trends over the last 10 years. PATIENTS AND METHODS: In a retrospective chart review 13,587 inpatient records from 1998 to 2007 were analyzed for the reason for emergency hospitalization, treatment data, length of hospitalizations and economical impact. RESULTS: 341 cases of severe infectious ocular emergencies with the need for emergency hospitalization were identified. The annual incidence of such emergencies increased continuously and has more than doubled during the last 10 years (51 vs. 24 annual cases). Within the same period the average hospitalization time of all non-infectious patients decreased from 5.41 to 4.95 days while inpatient stay due to infectious ocular emergencies decreased from 10.13 to 8.18 days. The average nursing effort was 4.26 hours per day in the infectious group, while electively admitted patients had an average requirement for nursing time of only 2.92 hours per day. CONCLUSION: The increase in infectious-related hospitalizations, their unpredictability and the need for a more intensive treatment regime have an increasing impact on hospital resources.

Predictability of microkeratome-dependent flap thickness for DSAEK.

BACKGROUND: The recommended thickness of the graft lamella in Descemet's stripping automated endothelial keratoplasty (DSAEK) is 120 - 180 microm. To adjust for the large variation in central corneal thickness (CCT) of eye bank donor corneas, microkeratome plates of different heights are available. The aim of this study was to evaluate the lamella thickness predictability of different keratome plates in a clinical routine setting. METHODS: In a prospective study of 60 consecutive DSAEK procedures, CCT was measured with a 50 MHz ultrasound pachymeter after meticulous epithelium removal immediately before and after lamella creation. Selected plate thickness was 300, 350, or 400 micro, respectively. Cutting depth was calculated by subtracting the remaining CCT of the deep lamella after the cut from the initial CCT before the cut. RESULTS: The mean (+/- SD) cutting depth was 320 +/- 45 microm with the Amadeus 350 keratome, 317 +/- 48 microm with the Moria 300 keratome, 388 +/- 58 microm with the Moria 350 keratome and 467 +/- 94 microm with the Moria 400 keratome. Neither the duration nor the type of donor preservation had an effect on the accuracy of the cutting depth. CONCLUSION: The mean cutting depth for the DSAEK keratomes is more accurate than the cutting depth of the same keratome heads designed for LASIK. This might be due to the fact that DSAEK lamellas were cut after complete epithelial removal. Despite the accurate mean cutting accuracy, there is a substantial variation between individual cuts which have to be taken into consideration.

Comparison of dynamic contour tonometry with Goldmann applanation tonometry following Descemet's stripping automated endothelial keratoplasty (DSAEK).

BACKGROUND: Intraocular pressure (IOP) measurements using Goldmann applanation tonometry (GAT) are influenced by central corneal thickness (CCT) whereas dynamic contour tonometry (DCT) allows for IOP measurements independent of CCT. After Descemet's stripping automated endothelial keratoplasty (DSAEK) the CCT is, compared to healthy eyes, increased. The objective of this prospective study was to compare IOP measurements obtained by DCT and GAT in patients after a DSAEK procedure. PATIENTS AND METHODS: DCT and GAT were performed 3 and/or 6 months after DSAEK. Comparison of means was performed using the Wilcoxon signed-ranks test. RESULTS: In total, 50 IOP measurements on 33 eyes were obtained. Mean CCT was 621 (+/- 60) microm. Overall correlation between GAT and DCT was good, however, in some patients a remarkable difference between pressure readings of up to 10.8 mmHg was observed. Mean IOP readings obtained by DCT were significantly higher (20.9 +/- 5.9 mmHg) than those obtained by GAT (19.1 +/- 6.5 mmHg; p = 0.0002). However, the difference between GAT and DCT readings was not influenced by the thickness of the transplanted lamella. DISCUSSION: The well-known difference in mean pressure readings between DCT and GAT was not affected by the increase in CCT following DSAEK. IOP readings with the GAT seem not to be influenced by the increase in CCT. Because of the remarkable differences in individual pairs of IOP measurements, both GAT and DCT should be used after DSAEK.

The disc damage likelihood scale (DDLS): interobserver agreement of a new grading system to assess glaucomatous optic disc damage.

BACKGROUND: The disc damage likelihood scale (DDLS) is a new grading system to estimate the amount of optic disc damage in glaucoma patients. The objective of this study was to assess the interobserver agreement of the DDLS and the cup/disc ratio. PATIENTS AND METHODS: The reproducibility of the DDLS and the cup/disc ratio was measured by two masked observers (one glaucoma specialist and one of two resident physicians in their first 6 months of training) staging 42 eyes of 25 patients with glaucoma or ocular hypertension. Disc size, cup/disc ratio and DDLS were documented and the Cohen's kappa was calculated as a measure for interobserver agreement. RESULTS: The interobserver agreement for the cup/disc ratio was good (Cohen's kappa 0.803). For the DDLS, the interobserver agreement was even better (Cohen's kappa 0.902). DISCUSSION: Unlike the cup/disc ratio, which focuses on the excavation, the DDLS is based directly on the thickness of the neuroretinal rim and takes into account the optic disc size. Therefore, the DDLS estimates the glaucomatous damage of the optic disc more precisely than the currently used method. Although this new grading system is more complicated to use in clinical practice, the interobserver agreement for the DDLS in our study setting was very good.

Corneal calcification following intensified treatment with sodium hyaluronate artificial tears.

AIM: To report a potential adverse effect of intensified treatment with sodium hyaluronate artificial tears. METHODS: Five cases of deep calcium deposition in the cornea associated with ocular surface disease and frequent use of hyaluronic acid artificial tears are described. All patients used one formulation of phosphate buffered hyaluronate eye drops when rapid calcification developed. All eyes required corneal graft surgery for visual rehabilitation. Specimens at keratoplasty were available for light microscopy and investigation by dispersive x ray analysis. The phosphate concentration in the medication used for topical treatment was measured and compared to alternative hyaluronate preparations. RESULTS: Light microscopy showed dense mineralisation of the entire stroma. The crystalline deposits consisted of hydroxyapatite, Ca5(PO4)3OH. A 50-fold higher concentration of phosphate was measured in the sodium hyaluronate eye drops used for treatment (50.9 mmol/l) when compared with normal serum. The other hyaluronate formulations showed phosphate concentrations from <0.1 mmol/l to 10.9 mmol/l. CONCLUSIONS: The hyaluronate artificial tear formulation "Hylo-Comod" favours the formation of insoluble crystalline calcium phosphate deposits in presence of epithelial keratopathy. This is because of its high phosphate concentration and typically frequent instillation. Manufacturers and prescribers should be aware that topical preparations may contain considerable amounts of phosphate which may lead to sight threatening corneal complications.

Influence of format on in vitro penetration of antibody fragments through porcine cornea.

AIM: Antibody fragments, appropriately formulated, can penetrate through the ocular surface and thus have potential as therapeutic agents. The aim was to investigate the influence of protein fragment format on the kinetics and extent of ocular penetration in vitro. METHODS: Immunoglobulin single chain variable domain fragments of a murine monoclonal antibody with specificity for rat CD4 were engineered with a 20 or 11 amino acid linker by assembly polymerase chain reaction, expressed in Escherichia coli and purified by chromatography. Fab fragments of the parental antibody were prepared by papain digestion. Antibody fragments were formulated with a penetration and a viscosity enhancer and were applied to the surface of perfused pig corneas for up to 10 hours in vitro. Penetration was quantified by flow cytometry on rat thymocytes. RESULTS: 20-mer antibody fragments formed natural monomers and dimers following purification that could be separately isolated, while 11-mer fragments were dimeric. All formats of fragment (20-mer monomers and dimers, 11-mer dimers, Fab) showed penetration through the pig cornea after 6 hours of intermittent topical administration. CONCLUSION: Antibody fragments of different shapes and sizes can penetrate the cornea after topical administration, thereby increasing the potential of this class of proteins for topical ophthalmic use.

[Complications of Descemet Stripping Automated Endothelial Keratoplasty (DSAEK)]. / Komplikationen der Descemet Stripping Automatisierten Endothelkeratoplastik (DSAEK).

BACKGROUND: Lamellar keratoplasties, e.g. Descemet's stripping automated endothelial keratoplasty (DSAEK) and Descemet membrane endothelial keratoplasty (DMEK) are considered the procedures of choice for corneal endothelial diseases. In comparison to penetrating keratoplasty (PK) they are associated with faster visual rehabilitation, a lower risk of complications and a decreased necessity for follow-up visits, which reduces the burden on quality of life in elderly patients. In order to advise patients regarding the indications for surgery and to facilitate the follow-up management, it is important to know the most important complications associated with these keratoplasty techniques. RESULTS AND DISCUSSION: The most important preoperative complication is a delayed indication for the operation. In contrast to PK, DSAEK and DMEK surgery should be provided at an earlier stage of disease as chronic edema alters the stroma and reduces the speed of visual recovery. The most important complications during or early after surgery are detached lamellae, pupillary blocks with increased pressure or air bubbles in the vitreous cavity in patients with previous vitrectomy. The main long-term complications include chronic increased intraocular pressure and immune-mediated graft rejections in DSAEK patients after reducing or stopping topical corticosteroid therapy. This article describes the potential complications of endothelial keratoplasty and provides a detailed explanation of strategies to avoid these complications.

Ocular pulse amplitude as a diagnostic adjunct in giant cell arteritis.

BACKGROUND: To develop an algorithm based on the ocular pulse amplitude (OPA) to predict the probability of a positive temporal artery biopsy (TAB) result in the acute phase of suspected giant cell arteritis (GCA). METHODS: Unilateral TAB was performed and ipsilateral OPA measurements were taken by Dynamic Contour Tonometry. Among the clinical signs and laboratory findings tested in univariate analyses, OPA, Erythrocyte Sedimentation Rate (ESR) and thrombocyte count showed a strong association with a positive TAB result. Algorithm parameters were categorized into three groups (OPA >3.5, 2.5-3.5, and <2.5 mm Hg; ESR <25, 25-60, and >60 mm/h; thrombocyte count <250'000, 250'000-500'000, and >500'000/µl). Score values (0, 1, and 2) were attributed to each group, resulting in a total score range from 0 to 6. A univariate logistic regression analysis using the GCA diagnosis as the dependent and the total score as the independent variate was fitted and probability estimates were calculated. RESULTS: Thirty-one patients with suspected GCA undergoing TAB during an eighteen-month observation period were enrolled. Twenty patients showed histologically proven GCA. Four patients had score values ≤2, fourteen between 3 and 4, and thirteen of ≥5. The corresponding estimated probabilities of GCA were<7, 52.6, and >95%. CONCLUSION: The present study confirms previous findings of reduced OPA levels, elevated ESR, and elevated thrombocyte counts in GCA. It indicates that a sum score based on OPA, ESR, and thrombocyte count can be helpful in predicting TAB results, especially at the upper and the lower end of the sum score range.

Blood flow velocity measured using the Retinal Function Imager predicts successful ranibizumab treatment in neovascular age-related macular degeneration: early prospective cohort study.

PURPOSE: Anti-VEGF treatment has a potent vasoconstrictive effect. Early changes of retinal blood flow velocity (RBFV) measured using the Retinal Function Imager (RFI) combined with indicators of vascular status may help in predicting the visual outcome 1 month post injection in patients with neovascular age-related macular degeneration (nvAMD) under ranibizumab treatment. To develop a simple prediction model based on the change in RBFV 3 days post injection and indicators of a patient's vascular status to assess the probability of a successful visual outcome 1 month post injection. METHODS: RBFV measured using RFI were prospectively collected pre-injection and 3 days post injection in 18 eyes of 15 patients. Indicators of vascular status (history of hypertension, diabetes mellitus without retinal affection, and smoking) were assessed by medical history. By univariate analyses, parameters associated with visual outcome were weighted (-1 to 6 points). A multivariate logistic regression model with the categorized visual outcome parameter (≥0 letters gained after 1 month) as the dependent variate and the sum score as the independent variate (continuous scale) was used to estimate the score value-specific probabilities of letters gained ≥0 1 month post injection. RESULTS: The indicators of vascular status negatively influenced the likelihood of a letter gain ≥0 whereas an increase in the arterial RBFV strongly increased it. The area under the receiver operating characteristics curve for these parameters investigated was 0.71 (95% CI: 0.43-1.00). CONCLUSION: Changes in the arterial RBFV following 3 days after ranibizumab injection combined with three indicators of the vascular status identified nvAMD patients with favorable visual outcome accurately.

Activation of endothelial L-arginine pathway in resistance arteries. Effect of age and hypertension.

In conduit arteries, nitric oxide is formed from L-arginine in the endothelium and released after stimulation with acetylcholine. The contribution of the L-arginine pathway and the effects of age and hypertension on endothelium-dependent vascular regulation were studied, using a video dimension analyzer, in pressurized and perfused mesenteric resistance arteries of 8- and 16-20-week-old Wistar-Kyoto and spontaneously hypertensive rats. Norepinephrine and phenylephrine caused contractions, which were similarly augmented after removal of the endothelium. NG-Monomethyl-L-arginine, an inhibitor of nitric oxide formation, augmented the contraction, but less than endothelial removal. Acetylcholine caused endothelium-dependent relaxations that were much more pronounced with intraluminal than with extraluminal application. NG-Monomethyl-L-arginine, methylene blue, and hemoglobin only partially inhibited the response. With aging, the endothelium-dependent inhibition of the response to norepinephrine decreased in Wistar-Kyoto rats; in spontaneously hypertensive rats this inhibition was smaller as compared with age-matched Wistar-Kyoto rats. In Wistar-Kyoto rats, the difference between intraluminal and extraluminal activation became more pronounced in adult rats. In the adult but not the young spontaneously hypertensive rats, the response to intraluminal but not extraluminal acetylcholine was reduced as compared with Wistar-Kyoto rats. Thus, in mesenteric resistance arteries of the rat, nitric oxide is released from L-arginine under basal conditions and after stimulation with acetylcholine but only in part accounts for endothelium-dependent responses. With aging and hypertension, the inhibitory effects of the endothelium against norepinephrine-induced contractions decrease. In hypertension, the intraluminal but not extraluminal activation of the release of endothelium-derived relaxing factors is impaired.

Intraluminal pressure modulates vascular contractility of perfused mesenteric resistance arteries. Altered response in hypertension.

Intraluminal pressure may affect vascular contractility in both normotension and hypertension. To test this hypothesis, we studied mesenteric resistance arteries from normotensive humans as well as normotensive (WKY) and spontaneously hypertensive (SHR) rats (internal diameter 214 +/- 27, 201 +/- 6, and 172 +/- 6 microns, mean +/- SEM at 10 mm Hg). Vessels were mounted on glass cannulas and perfused in organ chambers filled with buffer solution at intraluminal pressures of 10 to 120 mm Hg; vasomotion was measured using a video dimension analyzer. Under baseline conditions (10 mm Hg), wall thickness was 36 +/- 4 microns in humans, 32 +/- 4 microns in WKY, and 47 +/- 2 microns in SHR (P less than .001). With increasing pressure, the diameter of human vessels increased up to 25 mm Hg and remained constant at higher pressures. In contrast, resistance arteries of normotensive and hypertensive rats exhibited an almost linear increase in diameter over the whole pressure range. In SHR, the pressure-diameter relationship was much flatter than that of WKY, indicating reduced compliance. In human arteries, the contraction to KCl was maximal at 25 mm Hg and averaged 40 +/- 6%. Both above and below 25 mm Hg, the response declined to a minimum of 17 +/- 2% at 120 mm Hg (P less than .01). Similar results were obtained in WKY rats. In contrast, the contractile response in SHR remained maximal over the entire pressure range studied (65 +/- 5%).(ABSTRACT TRUNCATED AT 250 WORDS)