Richard M. Hill

Selective Sensitivity to Direction of Movement in Ganglion Cells of the Rabbit Retina

Among the ganglion cells in the rabbits retina there is a class that responds to movement of a stimulus in one direction, and does not respond to movement in the opposite direction. The same directional selectivity holds over the whole receptive field of one such cell, but the selected direction differs in different cells. The discharge is almost uninfluenced by the intensity of the stimulus spot, and the response occurs for the same direction of movement when a black spot is substituted for a light spot.

Initial Clinical Experience With the Ahmed Glaucoma Valve Implant

PURPOSE We studied the Ahmed Glaucoma Valve implant, an aqueous shunting device that has a unidirectional valve mechanism designed to prevent postoperative hypotony in eyes with intractable glaucoma. METHODS In this multicenter, prospective clinical trial, we studied 60 eyes (60 patients) with increased intraocular pressure or glaucoma that had not responded to medical treatment, laser photocoagulation, or previous glaucoma surgery, in which the Ahmed Glaucoma Valve implant was placed to decrease intraocular pressure. RESULTS Success was defined as intraocular pressure less than 22 mm Hg and greater than 4 mm Hg for two months or longer, intraocular pressure that was lowered by at least 20% from preoperative values (in eyes with preoperative intraocular pressures less than 22 mm Hg), and no additional glaucoma surgery or visually devastating complications. Cumulative probability of success at 12 months was 78%. Eight (13%) of 60 eyes had intraocular pressure less than 5 mm Hg the first postoperative day. Two other eyes had shallow anterior chambers, which required anterior chamber reformation. The major complications associated with the use of the valve were serous choroidal detachments in 13 eyes (22%), blockage of the tube in six eyes (10%), malposition of the tube in four eyes (7%), a suprachoroidal hemorrhage in one eye (2%), and corneal graft rejections in three (19%) of 16 eyes with corneal grafts. CONCLUSIONS Although the 12-month success with the Ahmed Glaucoma Valve implant is similar to that reported for other drainage devices, the complications associated with overfiltration in the immediate postoperative period appear to be less frequent than with other valved drainage devices. Randomized, prospective studies to compare the Ahmed Glaucoma Valve implant with other drainage devices are needed to make clinical comparisons of the different devices.

The thickness of the tear film

Measurements of the thickness of the pre-corneal tear film, pre-lens tear film, post-lens tear film, and the lipid layer on the surface of the tear film are summarized. Spatial and temporal variations in tear film thickness are described. Theoretical predictions of tear film thickness are discussed. Mechanisms involved in the upward drift of the tear film after a blink, and in the formation of dry spots, are considered.

Follow-up of the original cohort with the Ahmed glaucoma valve implant

PURPOSE To study the long-term results of the Ahmed glaucoma valve implant in patients with complicated glaucoma in whom short-term results have been reported. METHODS In this multicenter study, we analyzed the long-term outcome of a cohort of 60 eyes from 60 patients in whom the Ahmed glaucoma valve was implanted. Failure was characterized by at least one of the following: intraocular pressure greater than 21 mm Hg at both of the last two visits less than 6 mm Hg at both of the last two visits, loss of light perception, additional glaucoma surgery, devastating complications, and removal or replacement of the Ahmed glaucoma valve implant. Devastating complications included chronic hypotony, retinal detachment, malignant glaucoma, endophthalmitis, and phthisis bulbi; we also report results that add corneal complications (corneal decompensation or edema, corneal graft failure) as defining a devastating complication. RESULTS The mean follow-up time for the 60 eyes was 30.5 months (range, 2.1 to 63.5). When corneal complications were included in the definition of failure, 26 eyes (43%) were considered failures. Cumulative probabilities of success at 1, 2, 3, and 4 years were 76%, 68%, 54%, and 45%, respectively. When corneal complications were excluded from the definition of failure, 13 eyes (21.5%) were considered failures. Cumulative probabilities of success at 1, 2, 3, and 4 years were 87%, 82%, 76%, and 76%, respectively. Most of the failures after 12 months of postoperative follow-up were because of corneal complications. CONCLUSIONS The long-term performance of the Ahmed glaucoma valve implant is comparable to other drainage devices. More than 12 months after the implantation of the Ahmed glaucoma valve implant, the most frequent adverse outcome was corneal decompensation or corneal graft failure. These corneal problems may be secondary to the type of eyes that have drainage devices or to the drainage device itself. Further investigation is needed to identify the reasons that corneal problems follow drainage device implantation.

Original ArticlesFollow-up of the original cohort with the Ahmed glaucoma valve implant1☆

PURPOSE To study the long-term results of the Ahmed glaucoma valve implant in patients with complicated glaucoma in whom short-term results have been reported. METHODS In this multicenter study, we analyzed the long-term outcome of a cohort of 60 eyes from 60 patients in whom the Ahmed glaucoma valve was implanted. Failure was characterized by at least one of the following: intraocular pressure greater than 21 mm Hg at both of the last two visits less than 6 mm Hg at both of the last two visits, loss of light perception, additional glaucoma surgery, devastating complications, and removal or replacement of the Ahmed glaucoma valve implant. Devastating complications included chronic hypotony, retinal detachment, malignant glaucoma, endophthalmitis, and phthisis bulbi; we also report results that add corneal complications (corneal decompensation or edema, corneal graft failure) as defining a devastating complication. RESULTS The mean follow-up time for the 60 eyes was 30.5 months (range, 2.1 to 63.5). When corneal complications were included in the definition of failure, 26 eyes (43%) were considered failures. Cumulative probabilities of success at 1, 2, 3, and 4 years were 76%, 68%, 54%, and 45%, respectively. When corneal complications were excluded from the definition of failure, 13 eyes (21.5%) were considered failures. Cumulative probabilities of success at 1, 2, 3, and 4 years were 87%, 82%, 76%, and 76%, respectively. Most of the failures after 12 months of postoperative follow-up were because of corneal complications. CONCLUSIONS The long-term performance of the Ahmed glaucoma valve implant is comparable to other drainage devices. More than 12 months after the implantation of the Ahmed glaucoma valve implant, the most frequent adverse outcome was corneal decompensation or corneal graft failure. These corneal problems may be secondary to the type of eyes that have drainage devices or to the drainage device itself. Further investigation is needed to identify the reasons that corneal problems follow drainage device implantation.

THE NATURE OF NORMAL BLINKING PATTERNS

The blinking patterns of 20 normal subjects were examined under controlled experimental conditions. While the mean blink rate was 12.55 blinks/min, there were marked variations between individuals. As well, each subject displayed a characteristic pattern of blinking, mixing inter‐blink periods of shorter and longer durations in a regular fashion.

Oxygen Uptake from a Reservoir of Limited Volume by the Human Cornea in vivo

Oxygen flux across the anterior surface of the human cornea from a closed reservoir of air-saturated, physiological, isotonic saline was measured in vivo as a function of time. The rate of oxygen consumption calculated from this flux compares favorably with estimates given in the literalure, which were based on studies in which the microrespirometer technique of Warburg was used.

Human basic tear fluid osmolality. I. Importance of sample collection strategy.

Abstract. Osmolalities of 200 human tear prism fluid samples collected from two subjects were determined from their melting‐point temperatures with the Clifton Nanoliter Osmometer by calibration with 200 standard solution samples (290 mOsm/kg). Comparisons were made between tear fluid osmolalities obtained using a single‐sample simultaneous‐recalibration method: 1) for tear samples collected using finely‐drawn microcapillaries without biomicroscopy, vs secondly with biomicroscopic observation by illumination of only the sampling area on the inferior tear prism, the two collections separated by an interval of 10 min; and 2) for samples collected without biomicroscopy before, vs after a 10‐min interval. Tear fluid collection using a biomicroscope resulted in values that were significantly lower than those collected without (overall mean = 299.5 and 306.6 mOsm/kg, respectively; p <0.0001). The difference (7.1 mOsm/kg) may have resulted from mechanical, photic, and/or psychogenic reflex stimulation due to biomicroscopy, as the 10‐min interval had no osmotic effect on samples collected without biomicroscopy. Based on these results from two subjects, we suggest that relatively rapid, repetitive collections of human tear prism fluid can be made without significantly disturbing the osmotic outcome. However, physiological representation of basic human tear fluid is more accurate by avoidance of reflex‐inducing collection methods that were formerly considered unobtrusive. Basic human tear prism fluid is more hypertonic, by at least 7 mOsm/kg, than generally realized.

SENSITIVITY THRESHOLD OF THE LOWER LID MARGIN IN THE COURSE OF ADAPTATION TO CONTACT LENSES

ABSTRACT The time course for change of touch threshold across the lower lid margin was determined throughout the adaptation periods of four patients (eight lids). The greatest changes, up to two log10 units, took place within seven and 14 days, the primary impact point being the most rapid to adjust. Lower lid margin sensitivity previous to adaptation approached and sometimes exceeded central corneal sensitivity of the same eye.

Unit responses of the rabbit lateral geniculate nucleus to monochromatic light on the retina.

Seven unique wavelength responses, two inhibitory and five excitatory, with sensitivity maxima from 435 to 635 millimicrons, have been recorded from light-adapted, non-albino rabbits. Several combinations, usually one excitatory with one inhibitory response, often having characteristics suggesting mutual antagonism between them, were observed from single lateral geniculate cells.