Photic resetting of the human circadian pacemaker in the absence of conscious vision.

Ocular light exposure patterns are the primary stimuli for entraining the human circadian system to the local 24-h day. Many totally blind persons cannot use these stimuli and, therefore, have circadian rhythms that are not entrained. However, a few otherwise totally blind persons retain the ability to suppress plasma melatonin concentrations after ocular light exposure, probably using a neural pathway that includes the site of the human circadian pacemaker, suggesting that light information is reaching this site. To test definitively whether ocular light exposure could affect the circadian pacemaker of some blind persons and whether melatonin suppression in response to bright light correlates with light-induced phase shifts of thecircadian system, the authorsperformed experiments with 5 totally blind volunteers using a protocol known to induce phase shifts of the circadian pacemaker in sighted individuals. In the 2 blind individuals who maintained light-induced melatonin suppression, the circadian system was shifted by appropriately timed bright-light stimuli. These data demonstrate that light can affect the circadian pacemaker of some totally blind individuals--either by altering the phase of the circadian pacemaker or by affecting its amplitude. They are consistent with data from animal studies demonstrating that there are different neural pathways and retinal cells that relay photic information to the brain: one for conscious light perception and the other for non-image-forming functions.

Nonglaucomatous cupping of the optic disc.

Optic disc cupping is a consequence of myriad disorders. The anatomy and vasculature of the disc provide great insight into why, how, and when ODC occurs in various conditions. Approaches to distinguish glaucomatous from nonglaucomatous causes of ODC should rely on patient history, visual fields assessment, and funduscopic findings, as described. Cupping can be seen with neurological processes, including benign tumors, that are treatable. The clinician must remain vigilant to detect uncommon but potentially threatening forms of nonglaucomatous optic disc cupping.

Acute idiopathic blind spot enlargement syndrome: a review of 27 new cases.

OBJECTIVE: To describe the clinical findings in patients with acute idiopathic blind spot enlargement (AIBSE). METHODS: Medical record review of 27 patients with AIBSE (without sufficient optic nerve head swelling to cause blind spot enlargement) seen in 2 academic neuro-ophthalmology units. RESULTS: All patients were women aged between 19 and 53 years. Twenty-three patients reported positive visual phenomena. Visual acuity was normal in 16 patients. All patients had enlarged blind spots of variable size and density. Dyschromatopsia and afferent pupil defects were prevalent. Ophthalmoscopic features included uveitis, mild optic nerve swelling, granularity of macular pigment, subretinal white dots, and peripapillary pigment disturbances. Twelve of the 13 patients who underwent fluorescein angiography had optic disc staining and 5 had retinal pigment epithelial lesions with late staining. Full-field electroretinogram results were normal in 8 of 9 patients, although focal electroretinogram results were abnormal in 8 of 9 patients. Photopsia always decreased but visual fields did not improve. Six patients experienced recurrence. CONCLUSIONS: The clinical features of AIBSE include photopsia, visual field defects, abnormal findings from fundoscopic and fluorescein angiography, and abnormal results of focal electroretinography. The disease affects the peripapillary retina and may cause an afferent pupillary defect. The striking predilection for the peripapillary retina suggests a local etiologic factor and distinguishes AIBSE from the multiple evanescent white dot syndrome. Unlike patients with multiple evanescent white dot syndrome, recovery of visual field did not occur in patients with AIBSE.

Concordance of bilateral temporal artery biopsy in giant cell arteritis.

OBJECTIVE: To determine whether the diagnostic sensitivity of bilateral temporal artery biopsy is superior to that of unilateral biopsy in cases of suspected temporal arteritis. MATERIALS AND METHODS: A retrospective analysis of the results of 60 bilateral temporal artery biopsies examined in an ophthalmic pathology laboratory. RESULTS: The histopathologic diagnosis in 13% of the biopsy pairs was discordant. There was a 5% chance of obtaining a positive biopsy result on the side opposite an initially negative biopsy result. CONCLUSIONS: Bilateral temporal artery biopsy is 5% more likely than unilateral biopsy to detect the characteristic histopathologic findings in patients with temporal arteritis.

Multi-electrode stimulation and recording in the isolated retina.

As part of an exploration of the feasibility of an epi-retinal prosthesis, we developed an experimental method to electrically stimulate and record from retinal neurons using a micro-fabricated multi-electrode array. An isolated retina is placed on an array of 10 microm diameter disk electrodes with the ganglion cell side of the retina facing the electrode surfaces. The retina is bathed in oxygenated Ames' medium and warmed in order to sustain it in vitro for the duration of an experiment, typically 4-9 h. To reduce stimulus artifacts, the electrodes are grouped into two clusters - one used for stimulation and the other for recording--spaced several hundred microns apart, and electrodes are insulated with both silicon nitride and a 10 microm thick layer of polyimide. Stimuli are delivered to the array using an optically isolated current source stimulator, and the resulting responses recorded with an eight channel nerve response amplifier. Stimulation and recording are performed under computer control. A variety of physiologic measurements is described in order to illustrate the strengths and drawbacks of this method.

Neuroophthalmological complications of ocular surgery.

Visual dysfunction, including visual loss and diplopia, may occur in association with ocular surgery. Strabismus may be the most common abnormal eye movement seen as a complication of local anesthesia. Local anesthesia also may cause direct and indirect traumatic optic neuropathy. Vitrectomy is associated with visual-field loss from direct manipulation of the nerve fiber layer during suctioning of the vitreous or by direct compression of intraocular gas. Trabeculectomy may be complicated by visual-field loss. Patients may be at higher risk if their eye is hypotonous after surgery, but the duration or severity of hypotony that places the eye at risk is unknown. The only neuroophthalmic complication directly related to cataract surgery itself is AION. Complications of ONSD include motility disorders, pupillary dysfunction, and vascular compromise. Neuroophthalmic complications are uncommon after blepharoplasty. They include ocular motility disorders, transient pupil dilation, and vision loss.

Ocular myasthenia gravis: predictive value of single-fiber electromyography.

Extraocular muscle weakness is the most common presenting sign of myasthenia gravis (MG). More than half of patients presenting with symptoms isolated to these muscles (OMG) develop generalized myasthenia gravis (GMG) over the course of their illness. No clinical, laboratory, or electrophysiological features are recognized that identify these high-risk patients. We have therefore assessed the ability of single-fiber electromyography (SFEMG) to predict the development of GMG in patients presenting with OMG. Thirty-nine consecutive patients presenting with OMG underwent SFEMG of the extensor digitorum communis muscle as well as a battery of other laboratory and imaging studies at the time of diagnosis. All patients were followed prospectively for a minimum of 24 months or until they developed GMG. Two patients were excluded, leaving 37 for assessment. Twenty remained with pure OMG for the entire follow-up period (mean, 55 months). Twenty-six of the 37 had abnormal SFEMG studies at presentation. Eleven of these remained with OMG and 15 developed GMG. Fifty-eight percent of patients with an abnormal SFEMG developed GMG, whereas 82% of those with a normal study remained with OMG. Thus, a normal SFEMG was associated with MG remaining restricted to the extraocular muscles. (P = 0.036, Fisher's exact test), but an abnormal SFEMG was not predictive of subsequent development of GMG.

Visual discrimination after anterior temporal lobectomy in humans.

OBJECTIVE: To determine whether right anterior temporal lobectomy (RTL) results in perceptual deficits, and whether the perception of particular stimulus features (i.e., shape, motion, color) is affected differentially. BACKGROUND: RTL results in abnormal visual discrimination, recognition, and recall of pictorial material that cannot be easily specified verbally, such as designs and faces. It is unclear whether stimuli must be conceptually meaningful to elicit perceptual deficits. METHODS: Tests were constructed to assess a wide spectrum of basic visual discrimination abilities with simple, meaningless stimuli. The performance of nine patients who underwent left temporal lobectomy (LTL) and nine patients who underwent RTL were compared with that of normal control individuals. The mean excision size along lateral cortex was 3.7 cm for the LTL group and 5.6 cm for the RTL group; mean mesial excision size was 5.2 cm for LTL and 4.6 cm for RTL. RESULTS: Basic visual discrimination capacities were demonstrated to be essentially intact after LTL and RTL, except for a mild loss of blue color discrimination after RTL. CONCLUSIONS: There is little evidence that RTL produces perceptual impairments limited to the domain of pattern perception, or generalizable to nonmeaningful stimuli. The perceptual loss after RTL may be largely restricted to extraction of meaning, and related to the disruption of the circuits that connect the outcome of visual analysis to previously stored semantic information.

The diagnostic challenge of occult large vessel ischemia of the retina and choroid.

Vascular occlusions of the retina and choroid can cause severe visual loss. These occlusions can occur as a result of systemic disease or after surgery. In most cases, the retinal appearance provides evidence of ischemia as the cause of visual loss. On occasion, however, clinical examination shows no objective signs of vascular occlusion, and this can lead the clinician to suspect optic nerve pathology as the cause of visual loss. This paper outlines some of the diagnostic criteria, clinical findings, and ancillary studies that can be used to differentiate between occult occlusion of the retina or choroid and optic nerve disease.

Nonphotic entrainment of the human circadian pacemaker.

In organisms as diverse as single-celled algae and humans, light is the primary stimulus mediating entrainment of the circadian biological clock. Reports that some totally blind individuals appear entrained to the 24-h day have suggested that nonphotic stimuli may also be effective circadian synchronizers in humans, although the nonphotic stimuli are probably comparatively weak synchronizers, because the circadian rhythms of many totally blind individuals "free run" even when they maintain a 24-h activity-rest schedule. To investigate entrainment by nonphotic synchronizers, we studied the endogenous circadian melatonin and core body temperature rhythms of 15 totally blind subjects who lacked conscious light perception and exhibited no suppression of plasma melatonin in response to ocular bright-light exposure. Nine of these fifteen blind individuals were able to maintain synchronization to the 24-h day, albeit often at an atypical phase angle of entrainment. Nonphotic stimuli also synchronized the endogenous circadian rhythms of a totally blind individual to a non-24-h schedule while living in constant near darkness. We conclude that nonphotic stimuli can entrain the human circadian pacemaker in some individuals lacking ocular circadian photoreception.

Does optic disc appearance distinguish ischemic optic neuropathy from optic neuritis?

OBJECTIVE: To determine whether characteristics of optic nerve swelling assist in distinguishing between optic neuritis and anterior ischemic optic neuropathy. METHOD: Optic nerve stereophotograph review by masked observers. RESULTS: Altitudinal swelling, pallor, arterial attenuation, and hemorrhage are found more commonly in anterior ischemic optic neuropathy than in optic neuritis. CONCLUSION: Optic disc appearance does help to distinguish anterior ischemic optic neuropathy from optic neuritis, although there are overlapping features.

Neural network differentiation of optic neuritis and anterior ischaemic optic neuropathy.

AIMS: The efficacy of an artificial intelligence technique, neural network analysis, was examined in differentiating two optic neuropathies with overlapping clinical profiles-idiopathic optic neuritis (ON) and non-arteritic anterior ischaemic optic neuropathy (AION). METHODS: A neural network was trained with data from 116 patients with 'gold standard' diagnoses of ON or AION. It was then tested with data from 128 patients with presumed ON or AION, and the correlation of the network's diagnosis with that of expert clinicians tabulated. RESULTS: The network agreed with the clinicians on 97.8% (88 of 90) of the patients with presumed ON and 94.7% (36 of 38) of the patients with presumed AION. Youth, female sex, better initial acuity, a central scotoma, subsequent improvement in acuity, or progressive disease biased the network towards a diagnosis of ON, while advanced age, male sex, presence of hypertension, poor initial acuity, an altitudinal field defect, disc oedema, or less improvement in acuity biased the network towards a diagnosis of AION. CONCLUSION: Neural network analysis is a useful technique for classification of optic neuropathies, particularly where there is overlap of clinical findings.

Recurrent chiasmal apoplexy due to cavernous malformation.

We report a case of chiasmal apoplexy due to a cavernous malformation (CM). Surgery was delayed because of the patient's advanced pregnancy, and nearly complete recovery of vision occurred spontaneously. Recurrent hemorrhage prompted surgical extirpation. The patient was left with a residual deficit. The literature pertaining to chiasmal apoplexy and CMs is reviewed. Nearly half of the reported cases of chiasmal CM had recurrent hemorrhages. The co-occurrence of hemorrhage from CM and pregnancy is too rare to merit any conclusions about cause and effect.