Characterization of alpha(1)-adrenoceptor subtypes in the eye

β-Adrenoreceptors as Therapeutic Targets for Ocular Tumors and Other Eye Diseases-Historical Aspects and Nowadays Understanding

β-adrenoreceptors (ARs) are members of the superfamily of G-protein-coupled receptors (GPCRs), and are activated by catecholamines, such as epinephrine and norepinephrine. Three subtypes of β-ARs (β₁, β₂, and β₃) have been identified with different distributions among ocular tissues. Importantly, β-ARs are an established target in the treatment of glaucoma. Moreover, β-adrenergic signaling has been associated with the development and progression of various tumor types. Hence, β-ARs are a potential therapeutic target for ocular neoplasms, such as ocular hemangioma and uveal melanoma. This review aims to discuss the expression and function of individual β-AR subtypes in ocular structures, as well as their role in the treatment of ocular diseases, including ocular tumors.

Impact of intraoperative floppy IRIS syndrome in cataract surgery by phacoemulsification: Analysis of 622 cases

BACKGROUND

Small pupil syndromes, including IFIS, increase the risk of complications during cataract surgery if proper surgical planning is not performed. Tamsulosin is associated with a very significant increase in the risk of IFIS, due to the prolonged inactivation of alpha-1 adrenergic receptors in the smooth muscle fiber of the iris.

MATERIAL AND METHODS

Single-center prospective observational study, carried out at the Hospital de l'Esperança - Parc de Salut Mar.

RESULTS

622 eyes of 502 patients were included, of which 337 (62%) were women. The mean age of the sample is 74.8 years. 61 cases of IFIS (11%) were observed, of which 13 received treatment with Tamsulosin and 1 with Doxazosin. 23 cases of IFIS were observed in female patients. The female:male ratio was approximately 1:3. 19 cases (3%) of severe IFIS were observed, of which 6 received treatment with alpha-antagonists, with no statistically significant correlation. The mean surgical time was 13.80 min (Standard Deviation - SD: 4.01 min) in patients without IFIS and 16.93 min (SD: 4.32 min) in patients with IFIS. The relationship between the duration of the surgical procedure in minutes and the presence of IFIS was statistically significant, applying a 'two-tailed' or bilateral t-Student test with a p value of 0.01.

CONCLUSION

Regardless of the degree of severity, the diagnosis of IFIS lengthens the surgical time in cataract surgery. This represents yet another piece of evidence that supports the use of less selective alpha-1 adrenergic antagonist treatments than Tamsulosin or the performance of cataract surgery before starting these treatments.

Increased Choroidal Blood Perfusion Can Inhibit Form Deprivation Myopia in Guinea Pigs

Purpose

In guinea pigs, choroidal thickness (ChT) and choroidal blood perfusion (ChBP) simultaneously decrease in experimental myopia, and both increase during recovery. However, the causal relationship between ChBP and myopia requires further investigation. In this study, we examined the changes of ChBP with three different antimyopia treatments. We also actively increased ChBP to examine the direct effect on myopia development in guinea pigs.

Methods

Experiment 1: Guinea pigs wore occluders on the right eye for two weeks to induce form-deprivation myopia (FDM). Simultaneously they received daily antimyopia treatments: peribulbar injections of atropine or apomorphine or exposure to intense light. Experiment 2: The vasodilator prazosin was injected daily into the form-deprivation eyes to increase ChBP during the two-week induction of FDM. Other FDM animals received appropriate control treatments. Changes in refraction, axial length, ChBP, ChT, and hypoxia-labeled pimonidazole adducts in the sclera were measured.

Results

The antimyopia treatments atropine, apomorphine, and intense light all significantly inhibited myopia development and the decrease in ChBP. The treatments also reduced scleral hypoxia, as indicated by the decrease in hypoxic signals. Furthermore, actively increasing ChBP with prazosin inhibited the progression of myopia, as well as the increase in axial length and scleral hypoxia.

Conclusions

Our data strongly indicate that increased ChBP attenuates scleral hypoxia, and thereby inhibits the development of myopia. Thus ChBP may be a promising target for myopia retardation. As such, it can serve as an immediate predictor of myopia development as well as a long-term marker of it.

Improvement in Near Vision Following Silodosin Treatment in Patients With Lower Urinary Tract Symptoms

PURPOSE

The objective of this study was to investigate the change in near visual function after the administration of oral silodosin to patients with lower urinary tract symptoms (LUTS).

METHODS

This prospective study included treatment-naive patients who were scheduled to start treatment with silodosin for LUTS. A comprehensive ophthalmological evaluation including the near vision and the automated pupillometry was performed at baseline and after 3 months of silodosin treatment. For subjective assessment of near visual ability and satisfaction, a Near Activity Visual Questionnaire-10 (NAVQ-10) was also used at the same time (higher scores indicating worse quality).

RESULTS

Of 23 patients enrolled in this study, 15 continued with silodosin (8 mg once daily) treatment for 3 months and completed a follow-up evaluation. The mean age of participants was 60.4±8.4 years. Distant visual acuity and spherical error were unchanged after silodosin treatment. However, near vision acuity (logMAR) was improved after treatment (right, 0.47±0.36 vs. 0.38±0.39, P=0.018; left, 0.41±0.37 vs. 0.31±0.34, P=0.068; both, 0.27±0.26 vs. 0.21±0.27, P=0.043). Pupil size under room light decreased significantly in both eyes (right, 3.77±0.60 vs. 3.16±0.58, P=0.001; left, 3.72±0.80 vs. 3.21±0.75, P=0.002). The Rasch scale at NAVQ-10 improved from 54.7±9.9 to 48.5±11.2 (P=0.004).

CONCLUSION

This preliminary study demonstrated that highly selective alpha-1A adrenergic receptor antagonists such as silodosin improve near visual acuity and quality in patients with LUTS/benign prostatic hyperplasia. Decrease in pupil size caused by inhibition of adrenergic alpha 1 mediated contraction of iris dilator muscle is a possible mechanism underlying improved near vision.

The Role of Adrenoceptors in the Retina

The retina is a part of the central nervous system, a thin multilayer with neuronal lamination, responsible for detecting, preprocessing, and sending visual information to the brain. Many retinal diseases are characterized by hemodynamic perturbations and neurodegeneration leading to vision loss and reduced quality of life. Since catecholamines and respective bindings sites have been characterized in the retina, we systematically reviewed the literature with regard to retinal expression, distribution and function of alpha₁ (α₁)-, alpha₂ (α₂)-, and beta (β)-adrenoceptors (ARs). Moreover, we discuss the role of the individual adrenoceptors as targets for the treatment of retinal diseases.

Functional-Optical Coherence Tomography: A Non-invasive Approach to Assess the Sympathetic Nervous System and Intrinsic Vascular Regulation

Sympathetic nervous system dysregulation and vascular impairment in neuronal tissue beds are hallmarks of prominent cardiorespiratory diseases. However, an accurate and convenient method of assessing SNA and local vascular regulation is lacking, hindering routine clinical and research assessments. To address this, we investigated whether spectral domain optical coherence tomography (OCT), that allows investigation of retina and choroid vascular responsiveness, reflects sympathetic activity in order to develop a quick, easy and non-invasive sympathetic index. Here, we compare choroid and retina vascular perfusion density (VPD) acquired with OCT and heart rate variability (HRV) to microneurography. We recruited 6 healthy males (26 ± 3 years) and 5 healthy females (23 ± 1 year) and instrumented them for respiratory parameters, ECG, blood pressure and muscle sympathetic nerve microneurography. Choroid VPD decreases with the cold pressor test, inhaled hypoxia and breath-hold, and increases with hyperoxia and hyperpnea suggesting that sympathetic activity dominates choroid responses. In contrast, retina VPD was unaffected by the cold pressor test, increased with hypoxia and breath hold and decreases with hyperoxia and hyperpnea, suggesting metabolic vascular regulation dominates the retina. With regards to integrated muscle sympathetic nerve activity, HRV had low predictive power whereas choroid VPD was strongly (inversely) correlated with integrated muscle sympathetic nerve activity (R = -0.76; p < 0.0001). These data suggest that Functional-OCT may provide a novel approach to assess sympathetic activity and intrinsic vascular responsiveness (i.e., autoregulation). Given that sympathetic nervous system activity is the main determinant of autonomic function, sympathetic excitation is associated with severe cardiovascular/cardiorespiratory diseases and autoregulation is critical for brain health, we suggest that the use of our new Functional-OCT technique will be of broad interest to clinicians and researchers.

Modulation of α-adrenoceptor signalling protects photoreceptors after retinal detachment by inhibiting oxidative stress and inflammation

BACKGROUND AND PURPOSE

Currently available treatments do not halt progression of photoreceptor death and subsequent visual impairment related to retinal detachment (RD) which is observed in various retinal disorders. This study investigated the neuroprotective effects of two adrenoceptor ligands, the α₁ -adrenoceptor antagonist doxazosin and the α₂ -adrenoceptor agonist guanabenz, against photoreceptor cell death in RD.

EXPERIMENTAL APPROACH

We used a model of experimental RD in Brown-Norway rats induced by subretinal injection of sodium hyaluronate. Oxidative stress biomarkers and cytokine production were quantified with elisa. Protein expression levels and immunofluorescent labelling were determined in rats with RD and controls for mechanistic elucidation. The effects of systemic (i.p.) administration of doxazosin or guanabenz on photoreceptor apoptosis, retinal histology and electroretinography were evaluated in rats with RD and compared to the effects in vehicle controls.

KEY RESULTS

Photoreceptors were the major source of RD-induced ROS overproduction in the rat retina through the regulation of NADPH oxidase. Systemic administration of doxazosin or guanabenz decreased the RD-induced production of ROS and proinflammatory cytokines, including IL-1β and the chemokine CCL2, and suppressed retinal gliosis, resulting in attenuation of photoreceptor death and preservation of retinal structures and functions in RD.

CONCLUSIONS AND IMPLICATIONS

Our findings point to α-adrenoceptors as novel therapeutic targets to provide photoreceptor protection and suggest that both doxazosin and guanabenz, two FDA-approved drugs, could be further explored to treat retinal diseases.

Floppy iris syndrome and cataract surgery

PURPOSE OF REVIEW

Intraoperative floppy iris syndrome (IFIS) occurs in 2% of cataract surgeries and is associated with an increased risk of surgical complications. These complications can be avoided when high-risk patients are identified by preoperative screening and appropriate measures are used intraoperatively. The purpose of this article is to review emerging risk factors for IFIS and to summarize management strategies used in IFIS.

RECENT FINDINGS

Although α1-antagonists in general, and tamsulosin (Flomax, Jalyn) in particular, have long been associated with IFIS, recent studies have more firmly demonstrated the elevated risk of IFIS attributed to tamsulosin. This resulted in a revision of the American Society of Cataract and Refractive Surgery/American Academy of Ophthalmology guidelines on IFIS. Our understanding of additional medications and medical conditions involved in IFIS is also evolving, including an appreciation that women are also susceptible to IFIS. New modifications of techniques used in the intraoperative management of IFIS are also discussed.

SUMMARY

Preoperative screening should include both men and women. Current or prior use of α1-antagonists and antipsychotics should be documented, along with hypertension. Surgeons should be prepared to employ a range of perioperative interventions in a graded response to IFIS of different severities.

Anterior segment morphologic changes related to α-1 adrenergic receptor antagonists use

PURPOSE

To investigate possible changes in anterior segment parameters with the Pentacam in patients taking tamsulosin or doxazosin for benign prostatic hyperplasia.

METHODS

This prospective, cross-sectional study was conducted at Necip Fazil City Hospital, Kahramanmaras, Turkey. Patients included in the study were grouped as follows: 29 patients treated with tamsulosin (group 1), 27 patients treated with doxazosin (group 2), and 40 untreated controls (group 3). Right eyes of each patient were included in the study. All patients underwent examination with the Pentacam under standard dim light conditions and with undilated pupils. Anterior chamber depth (ACD), anterior chamber volume (ACV), anterior chamber angle (ACA) width, central corneal thickness (CCT), corneal volume (CV), and pupil diameter (PD) were recorded.

RESULTS

Mean duration of treatments was 2.7 ± 1.2 (1-5) and 2.4 ± 0.9 (1-5) years in groups 1 and 2 (p = 0.276). The ACD, ACV, ACA width, and PD were statistically significantly decreased in groups 1 and 2 when compared to group 3 (p&lt;0.05). There were no statistically significant differences among the groups in mean values of CCT and CV.

CONCLUSIONS

In this study, decreased ACD, ACV, ACA width, and PD values were detected in tamsulosin and doxazosin groups when compared to controls. These findings should be considered during anterior segment examinations and surgeries.

The Effect of Systemic Tamsulosin Hydrochloride on Choroidal Thickness Measured by Enhanced Depth Imaging Spectral Domain Optical Coherence Tomography

BACKGROUND

To evaluate the effects of selective α1A-adrenoceptor antagonist tamsulosin hydrochloride on choroidal thickness using enhanced depth imaging spectral-domain optical coherence tomography (EDI-OCT).

METHODS

This is a prospective observational study including 29 eyes of 29 patients with newly diagnosed benign prostatic hyperplasia. Choroidal thickness and retrobulbar ocular blood flow measurements were performed at baseline and after 3 months of treatment. Results were analyzed by the masked observer.

RESULTS

The mean subfoveal choroidal thickness (275.8-291.9 µm) and thicknesses 750 µm nasal (257.9-270.4 µm) and 750 µm temporal (262.4-277.0 µm) to the fovea were significantly increased after 3 months of treatment (p < 0.001). No statistically significant change was found in retrobulbar ocular blood flow.

CONCLUSIONS

Tamsulosin causes a significant increase in EDI-OCT-based choroidal thickness measurements. This increase might be associated with choroidal vasodilation in consequence of blockade of sympathetic α1A-adrenoceptors, which is critical for the maintenance of vascular tone and resistance in the choroidal vascular architecture. This should be kept in mind when choroidal disease and its response to treatment are followed by EDI-OCT imaging.

Stimulation of adrenergic β-receptors enhances mydriasis in a porcine eye model

PURPOSE

To compare the mydriatic effect of intracamerally injected isoprenaline plus phenylephrine to phenylephrine alone and to epinephrine in a porcine eye model, aiming to eventually find the best combination of adrenergic substances for surgical mydriasis in humans.

METHODS

In this study, we used 89 intact eyes from newly slaughtered pigs, pretreated with 2.0 mg of intracameral acetylcholine. After waiting 60 seconds for miosis to develop, 0.15 ml 0.3% isoprenaline and 0.15 ml 3.0% phenylephrine were injected sequentially with a 90-second interval in 21 eyes. In another 22 eyes, the same substances were given in the reverse order. In 20 eyes, 0.15 ml of 0.025% epinephrine was injected, and as a negative control 0.15 ml of balanced salt solution was injected in 26 eyes. The pupils were filmed during the treatments, and the mean pupil diameters were measured every 15 seconds from the video recordings.

RESULTS

Phenylephrine injected after isoprenaline had a larger mydriatic effect than epinephrine (p < 0.01). Without isoprenaline pretreatment, the mydriatic effect of phenylephrine was significantly smaller than that of epinephrine (p < 0.05). Isoprenaline also exhibited a small mydriatic effect of its own.

CONCLUSIONS

The β-receptor stimulator isoprenaline enhances the mydriatic effect of intracameral phenylephrine, indicating a role for the β-receptor in the mydriatic response. Mydriasis mediated by β-receptors may explain why nonspecific adrenergic stimulators such as epinine and epinephrine can have larger mydriatic effects than the specific α(1)-receptor stimulator phenylephrine.

Intraoperative floppy iris syndrome (IFIS): a practical approach to medical and surgical considerations in cataract extractions

Intraoperative floppy iris syndrome (IFIS) during cataract surgery is characterized by iris fluttering, iris prolapse towards the incisions, and a progressive pupillary constriction leading to high rates of complications. The syndrome has been reported following the treatment of benign prostatic hyperplasia with α-1(a) adrenergic receptor inhibitors, especially tamsulosin. The present paper describes the syndrome and discusses its pharmacological background. Several techniques to prevent and to deal with the syndrome are presented.

Topical mydriatics affect light-evoked retinal responses in anesthetized mice

PURPOSE

To characterize effects of the muscarinic antagonist atropine (A) and the alpha-adrenergic agonist, phenylephrine (P), on mydriasis and light-evoked signaling in mice anesthetized by ketamine and xylazine (K+X).

METHODS

Pupillary areas of anesthetized C57BL/6 mice were measured, with or without topical application of A or A+P. Dark-adapted ERGs were recorded from 2- to 4-month-old C57BL/6 and 7.5-month-old albino hrhoG/hrhoG mice after application of A or P singly or in combination, before or after induction of K+X anesthesia. Effects of GABA were tested in the hrhoG/hrhoG mice.

RESULTS

K+X anesthesia resulted in maximum mydriasis that was not enhanced by A or A+P. Dark-adapted b-wave amplitudes (-1.3 log sc td s) after K+X anesthesia were similar with or without A or P. A+P in the presence of K+X produced a slow growth in b-wave amplitude, reaching a plateau of twofold enhancement in 1 hour. Recordings of responses to varying flash energies revealed that the effects of A+P were on the maximum amplitude of the a- and b-waves and not on their sensitivity. Scotopic threshold responses were augmented as well. In photoreceptor-degenerated mice (hrhoG/hrhoG), an electronegative ERG wave recorded with K+X+A, was converted to a gamma-aminobutyric acid (GABA)-sensitive response with two electropositive components with A+P after K+X.

CONCLUSIONS

Topical administration of A and P together, but not separately, in the presence of K+X, leads to a slow, dramatic enhancement of a- and b-waves by an unknown mechanism independent of pupil dilation.

The Effects of Systemic Alpha-1 Adrenergic Antagonists on Pupil Diameter in Rats

PURPOSE

To investigate the effects of alpha-1 adrenergic blockers on pupil diameter (PD) in rats.

METHODS

Four groups, with 10 rats each, were designed to receive terazosin, tamsulosin, doxazosin, and no medication. Dilated pupil diameter (PD) measurements were performed 24 hr before, 24 hr after, and 30 days after the initiation of medication, and after 30 days of washout. The intergroup and intragroup differences in PD were evaluated using one-way ANOVA and Wilcoxon signed rank test, respectively.

RESULTS

In day 1, PD decreased in both eyes significantly only in tamsulosin and doxazosin groups, but these effects became insignificant at 30 days of treatment (p > 0.05). The control group showed no significant difference in PD (p > 0.05). PD values returned to baseline after the washout period in all groups.

CONCLUSIONS

A significant reduction in PD occurred in two of the three groups with alpha-1 adrenergic blockers (tamsulosin and doxazosin), but this effect was not sustained at 30 days. Further functional and structural studies of the iris are needed to determine the clinical significance of these findings.

Iris morphologic changes related to alpha(1)-adrenergic receptor antagonists implications for intraoperative floppy iris syndrome

PURPOSE

To identify iris structural alterations associated with intraoperative floppy iris syndrome (IFIS) in patients using systemic alpha(1)-adrenergic receptor antagonists (alpha-1ARA).

DESIGN

Cross-sectional study.

PARTICIPANTS AND CONTROLS

Twenty-nine patients with current or past treatment with any systemic alpha-1ARA and 22 untreated controls.

METHODS

Consecutive eligible patients underwent slit-lamp-adapted optical coherence tomography in a masked fashion under standardized lighting conditions.

MAIN OUTCOME MEASURES

Iris thickness at the dilator muscle region (DMR; measured at half of the distance between the scleral spur and the pupillary margin) and at the sphincter muscle region (SMR; 0.75 mm from the pupillary margin), the ratio between the DMR/SMR (to compensate for possible intersubject variability), and pupillary diameter.

RESULTS

Most treated patients were on tamsulosin (27/29). Mean age was similar in study and control groups (70.6+/-7.6 vs 67.1+/-9.1 years; P = 0.061). Photopic pupil diameter was reduced in the study group (2.06+/-0.5 vs 2.5+/-0.6 mm; P = 0.001). The SMR was similar between groups (P = 0.53). Significantly lower values were found in treated subjects for the DMR and the DMR/SMR ratio (P<0.001). These differences remained significant after adjusting for pupil diameter (P<0.001). Multiple regression analysis showed that a longer duration of alpha-1ARA treatment correlated to a reduced DMR/SMR ratio (P = 0.001; r = 0.47). Age and eye color were not significant in this model.

CONCLUSIONS

Patients using systemic alpha-1ARA have significantly lower values of DMR thickness and DMR/SMR ratio and smaller pupil diameter when compared with age-matched controls. These differences seem to be related to the duration of drug exposure and provide evidence of structural alterations to the iris dilator muscle from this class of agents in IFIS.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Adrenergic Receptors in the Ptotic Human Eyelid: Correlation With Phenylephrine Testing and Surgical Success in Ptosis Repair

PURPOSE

To investigate the relationship between adrenergic receptors in Müller muscle and response to phenylephrine testing in patients undergoing ptosis surgery. This study also compares outcomes of Fasanella and Putterman approaches to posterior ptosis repair.

METHODS

Prospective analysis of 71 patients undergoing posterior ptosis surgery. Eyelid height was measured before and after phenylephrine. Müller muscle was examined for alpha-1D, alpha-2C, beta-1, and beta-2 receptors. Specimens were graded on receptor staining intensity. Patients were seen 1 week and 6 weeks following surgery. Surgical outcomes were scored on a scale of 1 (most favorable) to 3 (least favorable).

RESULTS

Adrenergic receptors were found in decreasing order: alpha-1D, beta-1, alpha-2C, and beta-2. Receptor grade significantly predicted eyelid height for alpha-2C receptors (p = .03). Mean outcome scores for 36 Putterman (1.10) and 35 Fasanella (1.27) procedures were not significantly different.

CONCLUSIONS

Alpha 1D, alpha-2C, and beta-2 receptors are documented within human Müller muscle. Human eyelid elevation response to phenylephrine is inversely related to the amount of alpha-2C receptor staining in Müller muscle. Fasanella and Putterman procedures have equal outcomes, independent of adrenergic receptors.

Prospective Multicenter Evaluation of Cataract Surgery in Patients Taking Tamsulosin (Flomax)

PURPOSE

Intraoperative floppy iris syndrome (IFIS) caused by systemic alpha-blockers has been associated with an increased risk of cataract surgical complications when the surgeon was unaware of the medication history and did not anticipate its occurrence. This study was undertaken to evaluate the surgical outcomes and rate of complications when the ophthalmologist knew the patient was taking tamsulosin (Flomax, Boehringer-Ingelheim Pharmaceuticals, Ridgefield, CT) and used 1 of several strategies to manage IFIS.

DESIGN

Prospective multicenter nonrandomized observational series.

PARTICIPANTS

A total of 167 consecutive eyes in 135 patients taking tamsulosin and undergoing cataract surgery.

METHODS

Phacoemulsification was performed in conjunction with at least 1 of 4 different IFIS management strategies, namely, topical atropine preoperatively, iris retractors, pupil expansion ring, or use of viscoadaptive ophthalmic viscosurgical device with reduced fluidic parameters.

MAIN OUTCOME MEASURES

Severity of IFIS, incidence of operative or postoperative complications, and final visual acuity.

RESULTS

The IFIS severity was rated as mild in 17%, moderate in 30%, and severe in 43% of the study eyes. No IFIS was noted in 10% of the eyes. The rate of posterior capsule rupture and vitreous loss was 0.6% (1/167; 95% confidence interval, 0%-1.8%). Ninety-five percent of eyes achieved a best-corrected visual acuity of at least 20/40.

CONCLUSION

When experienced surgeons could anticipate IFIS and employ compensatory surgical techniques, the complication rate from cataract surgery was low and the visual outcomes were excellent in eyes of patients with a history of tamsulosin use.

The effects of two systemic α1-adrenergic blockers on pupil diameter: a prospective randomized single-blind study

Our aim was to investigate the effects of two alpha(1)-adrenergic blockers-tamsulosin and alfuzosin-on pupil diameter (PD). In this prospective randomized single-blind clinical trial, 64 patients with benign prostatic hyperplasia received treatment with either tamsulosin or alfuzosin. The same ophthalmologist, masked to the given medication, evaluated patients prior to, 4 weeks after and 6 months after the start of the medication (day 0, day 28 and month 6). Best corrected visual acuity and PD under mesopic, scotopic, and dilated conditions were measured. t-test, ANOVA, and Dunnett's multiple comparison post-test were used for statistical analysis. With tamsulosin treatment, both mesopic and scotopic PD decreased, respectively, from 3.9 +/- 0.7 and 5.7 +/- 0.6 mm at day 0 to 3.6 +/- 0.9 and 5.5 +/- 0.8 mm at day 28, and 3.6 +/- 0.7 and 5.4 +/- 0.7 mm at month 6 (ANOVA; P = 0.021 and = 0.040, respectively). However, the difference in dilated PD was not significant (day 0 7.8 +/- 0.6 mm, day 28 7.7 +/- 0.7 mm, and month 6 7.6 +/- 0.6 mm, P = 0.379). In the alfuzosin group, PD did not differ significantly from the baseline except for the scotopic measurements, which decreased from 5.6 +/- 0.6 mm at day 0 to 5.5 +/- 0.6 mm at day 28 and 5.2 +/- 0.8 mm at month 6 (P = 0.004). Compared to baseline values, small but statistically significant decreases were detected in mesopic and scotopic illumination in patients treated with tamsulosin and in scotopic PD in patients treated with alfuzosin. The clinical significance of these differences needs further evaluation.

Choroidal detachment following the use of tamsulosin (Flomax)

PURPOSE

To report choroidal detachment following tamsulosin (Flomax, an alpha(1A)-adrenoceptor antagonist) treatment of benign prostatic hyperplasia (BPH).

DESIGN

Case report.

METHODS

Chart review, serial examination.

RESULTS

A 65-year-old man underwent uncomplicated cataract extraction and placement of a posterior chamber intraocular lens. The patient subsequently developed three separate episodes of choroidal detachments in the operated eye. Each episode was preceded by treatment with an alpha(1)-adrenoceptor antagonist.

CONCLUSIONS

Tamsulosin may cause adverse ocular effects including recurrent choroidal detachments. alpha(1A) is the dominant alpha-adrenoceptor in the rabbit choroid, and the mechanism for choroidal detachment in this patient could include some effect of antagonists like tamsulosin on these receptors.

Incidence of intraoperative floppy iris syndrome in patients on either systemic or topical alpha(1)-adrenoceptor antagonist

PURPOSE

To evaluate the incidence of Intraoperative Floppy Iris syndrome (IFIS) in relation to the usage of alpha(1)-adrenoceptor antagonists.

DESIGN

Prospective, interventional case series.

METHODS

In 2,643 consecutive eyes of 1,968 patients undergoing cataract surgery, occurrence of IFIS and use of alpha(1) antagonists were recorded.

RESULTS

IFIS was observed in 29 eyes (1.1%) of 25 male patients, all of whom were receiving alpha(1) antagonists. In those receiving systemic tamsulosin, alpha(1A) selective antagonist, IFIS developed in 25 (43.1%) of 58 eyes. In those receiving systemic naftopidil, alpha(1A) and alpha(1D) antagonists, IFIS was found in 4 (19.0%) of 21 eyes. There was no case of IFIS in patients who received other systemic alpha(1) antagonists and in eyes treated with bunazosin eyedrops, a nonselective alpha(1) antagonist.

CONCLUSIONS

IFIS occurred in 1.1% of cases treated with systemic alpha(1A)-adrenoceptor antagonists for benign prostatic hypertrophy. Topical nonselective alpha(1) antagonist did not induce IFIS.

α1-Adrenergic Receptor Antagonists and the Iris: New Mechanistic Insights into Floppy Iris Syndrome

Understanding the role of adrenergic receptors in iris biology has gained widespread interest due to the recently described intraoperative floppy iris syndrome sometimes encountered during cataract surgery. alpha(1)AR-mediated iris dilator smooth muscle contraction occurs via alpha(1a)ARs whereas alpha(1b)ARs mediate iris arteriolar contraction. Because alpha(1)AR antagonists are first-line therapy for benign prostatic hyperplasia and lower urinary tract symptoms, more elderly patients requiring cataract surgery now receive these drugs. After reviewing intraoperative floppy iris syndrome, strengths/weaknesses of supporting data, and reviewing iris biology, a case is made that rather than being drug specific (alpha(1)AR antagonists), intraoperative floppy iris syndrome may represent the "tip of the iceberg." Relaxed iris dilator muscle resistant to adrenergic agonists should be expected with clinical drugs shown to relax the iris dilator (e.g., antagonists at alpha(1)AR, endothelin-A, angiotensin receptors, nitric oxide donors such as nitrates), and/or diseases associated with endothelial dysregulation (e.g., congestive heart failure, diabetes, hypertension). Rather than a rare, unexpected, unpredictable syndrome due to one drug, a careful medical history should elucidate intraoperative floppy iris syndrome predisposition. Just as anticoagulants are discontinued prior to elective surgery, conservative management of elderly patients suggests discontinuation of drugs that relax iris dilator muscle, in consultation with the patient's primary physician, should be considered prior to cataract surgery.

In vivo studies on the effects of α1-adrenoceptor antagonists on pupil diameter and urethral tone in rabbits

Alpha1-adrenoceptors mediate contraction of iris dilator smooth muscle and hence pupil dilatation. We compared the ability of i.v. bolus injections of alfuzosin, doxazosin, naftopidil, prazosin, tamsulosin and terazosin to antagonise phenylephrine-induced mydriasis relative to their potency for inhibiting phenylephrine-induced elevations of intraurethral pressure (IUP) in rabbits. Moreover, we compared the ability of these drugs to induce miosis in conscious rabbits in the absence of phenylephrine. All antagonists inhibited the effects of phenylephrine on pupil size and IUP, and the ratio of the respective ED50 values was close to unity in all cases. The doses required to induce statistically significant miosis in the absence of phenylephrine were 30- to 100-fold higher than those inhibiting phenylephrine-induced mydriasis for all antagonists, except for naftopidil. Moreover, the miotic effects of all alpha1-adrenoceptor antagonists were fully reversible within 8 h. We conclude that alfuzosin, doxazosin, naftopidil, prazosin, tamsulosin and terazosin inhibit phenylephrine-induced mydriasis in the same dose range as they inhibit elevations in IUP. Higher doses of all antagonists are required to induce miosis in the absence of an exogenous agonist, and such miosis is always reversible within hours.

Intraoperative floppy iris syndrome associated with tamsulosin

PURPOSE

To assess the incidence and possible causative factors of a newly recognized syndrome, the intraoperative floppy iris (IFIS).

SETTING

Clinical practices in Los Altos and San Rafael, California, USA.

METHODS

A retrospective chart review of consecutive cataract surgeries performed in a 2-surgeon practice over a 12-month period (706 eyes; 511 patients) was used to assess the percentage of cataract patients on systemic sympathetic alpha-1 antagonist medications as well as the percentage of patients who manifested the IFIS. A separate prospective study of 900 consecutive cases (741 patients) performed by another surgeon was used to determine the incidence of IFIS and the percentage of these patients who were taking alpha-1 antagonist medications.

RESULTS

Three percent (16/511) of the patients in the retrospective study, representing 3.0% (25/706) of the total eyes, were taking tamsulosin (Flomax) for benign prostatic hypertrophy. The overall prevalence of IFIS was 2.0% (10/511 patients). The syndrome was noted intraoperatively in 63.0% (10/16) of the tamsulosin patients but in none of the 11 patients on other systemic alpha-1 blockers. In the prospective study of 900 consecutive cataract surgeries, the prevalence of IFIS was 2.2% (16/741 patients). Ninety-four percent (15/16) of the IFIS patients were taking or had taken systemic tamsulosin. Twenty-six patients (36 eyes) in the 2 studies had IFIS associated with systemic tamsulosin. Sphincterotomies and mechanical pupil stretching were ineffective in maintaining adequate pupil dilation in this surgical population.

CONCLUSION

Intraoperative floppy iris syndrome occurred in approximately 2% of a cataract surgery population and appeared to be caused by tamsulosin, a systemic sympathetic alpha-1A antagonist medication that is the most frequently prescribed medication for benign prostatic hypertrophy.

The autonomic control of accommodation and implications for human myopia development: a review

Prolonged nearwork has long been associated with myopia development, however, there is no well described linking mechanism. One theory suggests that if accommodation accuracy during nearwork is not maintained, the defocused retinal image leads to myopia development. Here we review the findings of research aimed at determining whether the autonomic inputs to the ciliary smooth muscle are involved in this type of environmental myopia. We examine whether an autonomic imbalance could be a precursor to axial elongation and the resulting myopia. Accommodation responses, such as tonic accommodation and nearwork-induced accommodative adaptation, as a function of refractive error, are described in relation to an autonomic imbalance model. The collective results of this research point to anomalous accommodation responses, possibly as a result of underlying anomalous autonomic input to the ciliary muscle, being involved in myopia development and progression.

Functional characterization of alpha-adrenoceptors mediating pupillary dilation in rats

Previously, we reported that the alpha(1A)-adrenoceptor, but not the alpha(1D)-adrenoceptor, mediates pupillary dilation elicited by sympathetic nerve stimulation in rats. This study was undertaken to further characterize the alpha-adrenoceptor subtypes mediating pupillary dilation in response to both neural and agonist activation. Pupillary dilator response curves were generated by intravenous injection of norepinephrine in pentobarbital-anesthetized rats. Involvement of alpha(1)-adrenoceptors was established as mydriatic responses were inhibited by systemic administration of nonselective alpha-adrenoceptor antagonists, phentolamine (0.3-3 mg/kg) and phenoxybenzamine (0.03-0.3 mg/kg), as well as by the selective alpha(1)-adrenoceptor antagonist, prazosin (0.3 mg/kg). The alpha(2)-adrenoceptor antagonist, rauwolscine (0.5 mg/kg), was without antagonistic effects. alpha(1A)-Adrenoceptor selective antagonists, 2-([2,6-dimethoxyphenoxyethyl]aminomethyl)-1,4-benzodioxane (WB-4101; 0.1-1 mg/kg) and 5-methylurapidil (0.1-1 mg/kg), the alpha(1B)-adrenoceptor selective antagonist, 4-amino-2-[4-[1-(benzyloxycarbonyl)-2(S)- [[(1,1-dimethylethyl)amino]carbonyl]-piperazinyl]-6,7-dimethoxyquinazoline (L-765314; 0.3-1 mg/kg), as well as the alpha(1D)-adrenoceptor selective antagonist, 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY-7378; 1 mg/kg), were used to delineate the adrenoceptor subtypes involved. Mydriatic responses to norepinephrine were significantly antagonized by intravenous administration of both WB-4101 and 5-methylurapidil, but neither by L-765314 nor by BMY-7378. L-765314 (0.3-3 mg/kg, i.v.) was also ineffective in inhibiting the mydriasis evoked by cervical sympathetic nerve stimulation. These results suggest that alpha(1B)-adrenoceptors do not mediate sympathetic mydriasis in rats, and that the alpha(1A)-adrenoceptor is the exclusive subtype mediating mydriatic responses in this species.

Study of the mechanisms involved in the bradykinin-induced contraction of the pig iris sphincter muscle in vitro

This study was designed to investigate the mechanisms by which bradykinin induces contraction of the pig iris sphincter muscle in vitro. Addition of bradykinin, Lys-bradykinin and Met-Lys-bradykinin to the pig iris sphincter resulted in a graded contraction with a mean EC(50s) of 21, 11 and 5 nM, respectively. The bradykinin B(1) receptor agonist des-Arg(9)-bradykinin only caused a slight contraction, measured 6 h after the tissue was set up. The B(2) receptor antagonists FR 173657 ((E)-3-(6-acetamido-3-pyridyl)-N [N-2-4-dichloro-3-[(2-methyl-8-quinolinyl) oxymethyl] phenyl]-N-methylamino-carbonyl-ethyl] acrylamide) and Hoe 140 (D-Arg(0)-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin produced a graded shift to the right associated with marked inhibition of the bradykinin-induced contraction. Atropine, guanethidine or tetrodotoxin significantly reduced the bradykinin-induced contraction. Dazoxiben, an inhibitor of thromboxane A(2), and MK-571 (3-(3-(2-(7-chloro-2-quinolinyl) ethenyl) phenyl ((3-dimethyl amino-3oxo-propyl) thio) methyl) propanoic acid, a leukotriene D(4) receptor-selective antagonist, also caused inhibition of the bradykinin-mediated contraction. Cyclooxygenase-1 and -2 inhibitors, indomethacin, ibuprofen, valeryl salicylate and NS 398 (N-[2-(cyclohexyloxy)-4-nitrophenyl]methanosulfonamide) all significantly inhibited the bradykinin-mediated contraction without affecting the carbachol-induced contraction of the pig iris sphincter. Taken together, these results indicate that the bradykinin-mediated contraction of the pig iris sphincter muscle seems to be mediated primarily by the activation of the B(2) receptor release of acetylcholine, noradrenaline and both cyclooxygenase-1 and -2 metabolites besides the release of leukotriene D(4) and tromboxane A(2) from the arachidonic acid pathway.

alpha(1A)-adrenoceptors mediate sympathetically evoked pupillary dilation in rats

Evidence suggests that in some species (cats, rabbits, and possibly humans) alpha-adrenoceptors in the iris dilator muscle are "atypical" in that they cannot be readily classified by conventional criteria. This study was undertaken in an attempt to characterize the alpha-adrenoceptor subtype(s) mediating sympathetically elicited mydriasis in rats. Frequency-response pupillary dilator curves were generated by stimulation of the preganglionic cervical sympathetic nerve (1-32 Hz) in pentobarbital-anesthetized rats. Evoked responses were inhibited by systemic administration of nonselective alpha-adrenergic antagonists, phentolamine (0.3-10 mg/kg) and phenoxybenzamine (0.03-1 mg/kg). The selective alpha(1)-adrenergic antagonist, prazosin (0.01-1 mg/kg), also was effective, although alpha(2)-adrenergic antagonism with rauwolscine (0.1-1 mg/kg) was not. alpha(1A)-Adrenoceptor-selective antagonists, 2-([2,6-dimethoxyphenoxyethyl]aminomethyl)-1,4-benzodioxane (WB-4101; 0.1-1 mg/kg) and 5-methylurapidil (0.1-1 mg/kg), as well as the alpha(1D)-adrenoceptor-selective antagonist 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY-7378; 1-3 mg/kg), were used to determine the subtype(s) involved. Evoked mydriasis was significantly antagonized by both WB-4101 and 5-methylurapidil but not by BMY-7378. These results suggest that, unlike some other species, adrenoceptors in the rat iris dilator mediating neurogenic mydriasis are "typical" and, in addition, can be characterized as being primarily of the alpha(1A)-adrenoceptor subtype.