Selective fovea-related deprived activation in retinotopic and high-order visual cortex of human amblyopes.

Amblyopia is a visual disorder starting at early childhood and characterized by reduced visual acuity not of optical origin or due to any eye disease. One expression of such an anomalous early visual experience is abnormal foveal vision. In a previous fMRI study, faces that were presented to amblyopic eyes evoked little response compared to houses in high-order visual areas. Patients also demonstrated reduced recognition of facial expression, raising the possibility that these face-selective abnormalities are related to foveal vision deficit. Whether this deficit originates in low-level processing or is mediated by compromised activation in high-order visual areas is unresolved. In the present functional magnetic resonance imaging (fMRI) study, we explored the impact of amblyopia on the representation of object images presented in foveally biased central versus peripheral retinotopic eccentricities through manipulation of object size. Small and large pictures were correlated to visual acuities of 6/6 and 6/60, respectively. In low-level visual areas, the amblyopic eye showed significantly reduced activation for centrally placed, small pictures than the sound eye, while activation to large pictures was only slightly reduced. Similarly, in high-order visual areas, the amblyopic eye showed marked reduction in activation in the fusiform gyrus, with normal activation in the collateral sulcus. The center/periphery size-related amblyopic outcomes of this study support a "bottom-up" nature of the center-periphery effect observed in high-order visual areas. Taken together, these findings point to the regional extent and functional selectivity of fovea-related cortical reorganization that is related to abnormal visual development of one eye.

The outcome of pseudotumor cerebri induced by tetracycline therapy.

OBJECTIVE: To demonstrate the association between tetracycline treatment and pseudotumor cerebri (PTC). METHODS: Consecutive patients from two neuro-ophthalmic referral centers, who developed PTC syndrome post-treatment with tetracycline, were enrolled and followed for a minimum of 2 years after cessation of tetracycline. RESULTS: A total of 243 consecutive patients were diagnosed with PTC; 18 had concurrent history of tetracycline treatment; a third experienced a limited course of illness with no relapses; 12 had a variable course with a prolonged relapsing illness. Mean duration of tetracycline treatment prior to diagnosis was 2.73 months. CONCLUSIONS: Tetracycline, and especially minocycline, is currently considered a cause or a precipitating factor for PTC. Although there is little information on the natural course of tetracycline induced PTC, the present cases demonstrate that drug withdrawal is curative only in some patients.

Area-specific amblyopic effects in human occipitotemporal object representations.

The role of early visual experience in the establishment of human high-order visual areas is poorly understood. Here we investigated this issue using human amblyopia--a developmental visual disorder, which manifests a central vision (acuity) deficit. Previous fMRI studies of amblyopes have described abnormal functional activations in early retinotopic areas. Here we report the surprising finding of a selective object-related abnormality in high-order occipitotemporal cortex. Specifically, we found that face-related cortical areas show a severe disconnection from the amblyopic eye, while building-related regions remain essentially normal. The selectivity of the deficit highlights the differential computations performed in the different object-related areas and is compatible with the suggested association of face regions with analysis of fine detail.

Effect of sub-Tenon's and peribulbar anesthesia on intraocular pressure and ocular pulse amplitude.

PURPOSE: To compare the effect of peribulbar and sub-Tenon's anesthesia on intraocular pressure (IOP) and ocular pulse amplitude (OPA) in the injected eye and the fellow noninjected (control) eye. SETTING: Tel Aviv Medical Center, Tel Aviv, Israel. METHODS: This prospective study measured IOP and OPA at baseline and 1 and 10 minutes after administration of lidocaine anesthesia in 40 consecutive adult patients having elective cataract surgery. RESULTS: The IOP remained stable throughout the study with both modes of anesthesia. One minute after injection of the anesthetic agent, the OPA was significantly decreased in the injected eyes in both the sub-Tenon's (24%; P < .05) and peribulbar (25%; P < .05) groups. The decrease in the OPA in the sub-Tenon's group (14%; P < .05) was detectable after 10 minutes in the control eyes. In the peribulbar anesthesia group, the OPA in the control eyes increased significantly (9%; P < .05) 1 minute after injection of the anesthetic agent, returning to preinjection levels 10 minutes after the injection. CONCLUSIONS: The OPA in the eyes in which lidocaine was injected decreased significantly in both the sub-Tenon's and peribulbar groups. These findings have implications for the management of patients whose ocular circulation may be compromised.

Hyperhomocystinemia in patients with nonarteritic anterior ischemic optic neuropathy, central retinal artery occlusion, and central retinal vein occlusion.

OBJECTIVE: This study aimed to determine the prevalence of hyperhomocystinemia among patients with nonarteritic anterior ischemic optic neuropathy (NAION), central retinal artery occlusion (CRAO), or central retinal vein occlusion (CRVO). DESIGN: Retrospective, case-control study. PARTICIPANTS: The study cohort consisted of 74 consecutive patients with NAION, CRAO, or CRVO who were examined at the Retina or Neuro-ophthalmological Unit of the Tel-Aviv Sourasky Medical Center from 1998 through 1999. The control group consisted of 81 consecutive patients of similar gender and age with no history of these pathologic conditions. MAIN OUTCOME MEASURES: Plasma homocystine levels of all study participants were obtained. RESULTS: Eighteen of 40 patients (45%) with NAION and eight of 13 patients (61.5%) with CRAO had hyperhomocystinemia compared with three of 21 (14.3%) in the CRVO group (P < 0.001) and eight (9.8%) in the control group (P < 0.0001). Hypertension and ischemic heart disease were significantly more prevalent in the NAION patients with elevated plasma homocystine. CONCLUSIONS: Our findings suggest that hyperhomocystinemia is a risk factor for NAION and CRAO.

Clonidine provides an allergy-free alternative in glaucoma patients with proven allergy to apraclonidine.

PURPOSE: The aim of this study was to determine allergic responses to clonidine hydrochloride 0.25% in glaucoma patients with proven allergic reaction to apraclonidine 0.5%. METHODS: Fifteen consecutive glaucoma patients with allergic reaction to apraclonidine were prospectively challenged with clonidine hydrochloride 0.25% and evaluated for recurrence of allergic reactions and efficacy of treatment. Intraocular pressure (IOP), conjunctival hyperemia, blood pressure and resting pulse rate were determined at baseline and after 1, 3, 6 and 12 months. RESULTS: None of the patients developed ocular allergic reaction during 12 months on clonidine therapy. Blood pressure and pulse rate did not change significantly with clonidine treatment. Clonidine caused a significant reduction of IOP from baseline. In one patient, topical clonidine caused fatigue, dizziness and dry mouth. CONCLUSION: Clonidine did not cause allergic reaction in patients with proven allergy to apraclonidine, indicating that there is no cross-reactivity with apraclonidine. Due to the small series, however, we cannot assume that allergy will not occur with clonidine 0.25% given time and a larger number of patients.

Nonadrenergic, noncholinergic relaxation of bovine iris sphincter: role of endogenous nitric oxide.

PURPOSE: To investigate the role of endogenously generated nitric oxide (NO) in the relaxation of bovine iris sphincter. METHODS: Isolated bovine sphincters were mounted on an isometric tension apparatus. Contraction-relaxation response was elicited by electrical field stimulation (ES; 12 Hz, 50-msec duration, 70-80 V). Relaxation was arbitrarily defined as maximal decrease of tension below prestimulation baseline after cessation of ES. We also determined the tissue levels of cyclic guanosine monophosphate (cGMP) by radioimmunoassay. RESULTS: ES produced a biphasic response: contraction followed by relaxation. After cessation of ES, the muscle relaxed to below the initial baseline tension. Tetrodotoxin (TTX) abolished most of the contraction and all the relaxation response. Atropine blocked most of the contraction component, leaving the relaxation component unchanged. Prazosin and bupranolol (alpha1-adrenergic and beta-adrenergic antagonists, respectively) also did not affect the relaxation component of the response. Neither substance P nor its antagonist (N-acetyl-L-tryptophane 3,5-bis (trifluoromethyl)-benzyl ester; ATTB) inhibited or mimicked the response. The nitric oxide synthase (NOS) inhibitors Nomega-nitro-L-arginine methyl ester (L-NAME), Nomega-nitro-L-arginine (L-NNA), and aminoguanidine dose-dependently inhibited the relaxation response by 50% to 70%. The free radical scavenger 2-(4-carboxyphenyl) 4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (carboxy-PTIO) and the guanylyl cyclase inhibitor methylene blue also abrogated 70% and 45% of the relaxation response, respectively. ES caused an increase in muscle cGMP from 2.3+/-0.3 to 3.9+/-0.5 picomoles per muscle. L-NNA or L-NAME significantly decreased the tissue cGMP content (to 1.2+/-0.1 picomoles per muscle) and prevented the increase caused by ES. CONCLUSIONS: The relaxation component of the iris sphincter response to ES is a distinct nonadrenergic, noncholinergic, ES-induced event. Most of the relaxation is mediated by the endogenously generated NO-guanylyl cyclase-cGMP cascade.