Jonathan D. Nussdorf

Vitreous concentration of topically applied brimonidine tartrate 0.2

OBJECTIVE To determine the vitreous concentration of brimonidine after topical administration of Alphagan. DESIGN Prospective observational case series. PARTICIPANTS Eighteen patients scheduled for elective pars plana vitrectomy. METHODS Brimonidine tartrate, 0.2%, was topically administered twice or three times daily for 4 to 14 days preoperatively in 13 patients. Four patients served as controls, without application of brimonidine. A dry, undiluted vitrectomy specimen obtained intraoperatively was collected, frozen, and sent to an independent bioanalytical facility for quantitative determination of vitreous concentration of brimonidine using gas chromatography/mass spectrometry. MAIN OUTCOME MEASURES The concentration of brimonidine in human vitreous. RESULTS All patients treated with brimonidine measured above the lower limit of quantitation with a mean vitreous concentration of 185 +/- 500 nM. All patients not treated with brimonidine measured at or below the lower limit of quantitation of 0.05 nM. There was a trend toward higher concentration in patients who were either aphakic or pseudophakic compared with those that were phakic. CONCLUSIONS Topically applied brimonidine results in vitreous levels at or above 2 nM, the concentration shown to activate alpha(2)-receptors.

Binocular function in early glaucoma

PurposeThis study investigated whether certain binocular mechanisms are disrupted in early glaucoma. MethodsGlaucoma patients, suspects, and normals were tested on a battery of psychophysical tests consisting of flicker sensitivity (5 and 34 Hz), temporal cut-off frequency (CFF), contrast sensitivity (Pelli-Robson chart), and stereoacuity. Monocular channels were evaluated with tests of monocular flicker performance and spatial contrast sensitivity. Binocular summation on spatial and temporal tests was used to reflect integrity of binocular neural interactions. Stereoacuity was taken as a measure of performance of disparity processing mechanisms. ResultsThe groups differed in terms of binocular flicker sensitivity at both temporal rates, binocular and monocular peak contrast sensitivity, and stereoacuity. Binocular summation of both spatial and temporal sensitivity was normal. The glaucoma suspect group was distinguishable from the age-matched normal group on binocular contrast sensitivity and stereoacuity. ConclusionsThe binocular mechanisms that mediate stereoacuity appear to be heavily disrupted, whereas the binocular mechanisms that mediate central neural interaction of monocular inputs are normal. Although monocular spatiotemporal abilities are disrupted, the binocular processes combine the monocular input normally. In addition, our results suggest a benefit of binocular testing for routine assessment of glaucoma patients. The profound disruption of stereoacuity appears to result from disorder in the spatial sampling array at the ganglion-cell level similar to the disorder reported in the normal periphery and the central retina of strabismic amblyopes. These and previous findings were reviewed to evaluate the supposition of preferential M-pathway disruption in early glaucoma. Such a model can not be reconciled with the present findings. We conclude that measurements of temporal modulation sensitivity fit well with such a model, but that the current evidence of spatiotemporal contrast sensitivity disruption is less supportive of such a model.

Spectral sensitivity of the electroretinogram b-wave in dark-adapted goldfish

The action spectrum of the ERG b-wave was measured under dark-adapted conditions in intact goldfish (Carassius auratus). It is substantially broader than the absorption spectrum of goldfish rod porphyropsin. Neither prolonged dark adaptation nor removal of possible efferent neural activity affected its shape. Moreover, a 682-nm background did not produce a selective loss of sensitivity to long wavelengths. The results imply that the spectral sensitivity of the b-wave in dark-adapted goldfish reflects the influence of at least two photoreceptor types which act as a single univariant mechanism near absolute threshold.

Inferior Oblique Overaction in Infantile Esotropia: Fundus Extorsion as a Predictive Sign

BACKGROUND Inferior oblique overaction develops in 72% of patients with infantile esotropia but generally is not recognized until the patient is between 2 and 4 years of age. METHODS While undergoing bilateral medial rectus recessions, photographs were taken of the posterior pole of 27 eyes in 14 patients with infantile esotropia and graded for the presence or absence of torsion by a masked observer. Follow up ranged from 10 months to 6 years. RESULTS Oblique muscle overaction developed in 15 of the 27 eyes. Of these 15, six demonstrated fundus torsion in infancy, before the oblique dysfunction was recognized clinically. CONCLUSION The presence of abnormal fundus torsion can serve as a marker for patients with infantile esotropia who ultimately will develop overt oblique muscle dysfunction.

APB selectively reduces visual responses in goldfish to high spatiotemporal frequencies

Visual responses of goldfish to rotating square-wave gratings were recorded before and after intraocular injection of 2-amino-4-phosphonobutyric acid (APB). High doses of APB reduced the rate of optokinetic nystagmus (OKN) to a relatively high spatial frequency grating moving at a high temporal frequency. Responses to a low spatial frequency grating were not altered, nor were responses to the higher spatial frequency when it rotated slowly. The effects of APB were transient and lasted no longer than 3 d. We conclude that APB reduces OKN to high spatiotemporal frequencies in goldfish.

Responsivity and absolute sensitivity of retinal ganglion cells in goldfish of different sizes, when measured under “psychophysical” conditions

Retinal neurogenesis occurs in adult goldfish, and more rods are added to the retina than any other class of cell as the fish grows. To determine whether the disproportionate addition of rods affects the responsivity and sensitivity of dark adapted retinal ganglion cells, we recorded activity from optic tract fibers in goldfish of different sizes. Experimental conditions were as similar as possible to those used in a separate study in which psychophysical absolute thresholds were measured: large, dim, monochromatic spots 1 sec in duration were projected close to the right eye of alert, self-respiring goldfish. A total of 214 fibers were recorded in small (5.0-5.7 cm), medium (9.5-11.0 cm) and large (13.0-20.0 cm) fish. Neither maintained activity (mean and variance of the discharge rate in darkness) nor responsivity (quantum-to-spike ratios) nor absolute threshold (quantal irradiance required to produce a difference of 1 spike/trial from spontaneous rates) varied reliably with size of fish. However, some Off cells were more active in the dark than On and On/Off cells; these had low QSRs and absolute thresholds, and were found in all sizes of fish. Fifty percent (50%) of Off cells (compared to 8% of On cells) had thresholds comparable to or lower than psychophysical threshold, and Off cell thresholds (but not On cell thresholds) tended to be lower in larger fish. Because psychophysical threshold is closely related to the planimetric density of rods in goldfish, the similarity between Off cell threshold and psychophysical threshold suggests that Off cells may be influenced relatively more than On cells by the addition of new rods to the retina.

Anisocoria associated with the medical treatment of irritable bowel syndrome

A case of anisocoria associated with oral pharmacologic treatment of irritable bowel syndrome is reported. A 26-year-old woman developed sudden onset of anisocoria and compromised accommodation that lasted 2 days after the use of oral scopolamine methylbromide for treatment of irritable bowel syndrome. The anisocoria and compromised accommodation occurred after contamination of the ocular surface after administration of scopolamine methylbromide and resolved within 1 week without further contamination. Oral preparations used for the pharmacologic treatment of irritable bowel syndrome can cause anisocoria due to anticholinergic pharmacologic blockade of the iris sphincter muscle.