Interaural time sensitivity in the inferior colliculus of the albino cat.

Anatomical studies of the Creel albino cat have demonstrated a pronounced atrophy of cells in the medial superior olive, a structure thought to be important for the detection of interaural time differences (ITDs). We looked for physiological abnormalities in the binaural interaction of cells in three albino cats by recording from single cells in the central nucleus of the inferior colliculus to ITDs of tones and noise. We found that the sensitivity to ITDs of tones and noise was somewhat diminished in the albino cats as compared to normally pigmented cats, though this deficit was only evident when a population of cells was examined.

Influence of palpebral aperture height on tear pump efficiency.

Oxygen uptake rates were measured on 6 human corneas fitted with a standardized rigid contact lens in order to determine the relation between vertical palpebral aperture height and exchange efficiency of tears in such systems. The contribution provided by tear exchange to the oxygen available to the cornea was isolated through the use of lenses of negligible transmissivity (PMMA). Measurements of corneal oxygen uptake were made on the normal open eye, after 5 min of static (with no blinking) open eye contact lens wear, and after 5 min of dynamic (with blinking every 5 s) contact lens wear.

Visual performance in high myopia.

The visual performances of eight low myopic subjects (-2 D to -7 D) and eight high myopic subjects (greater than -7 D) with normal visual acuities were analyzed by contrast sensitivity testing with both spectacle and contact lens corrections to determine if any differences in function exist between those groups. Statistically significant (p = 0.0382) contrast sensitivity losses, particularly at the higher spatial frequencies, were found for the high myopic subjects when corrected with spectacles.

Corneal oxygenation: blink frequency as a variable in rigid contact lens wear.

Using a micropolarographic system, we measured the responses of six human corneas to nine oxygen exposure conditions: to air (continuous open-eye) with no contact lens in place, and to eight interblink intervals (1, 2, 3, 4, 5, 6, 7, and 300 s durations) with an oxygen impermeable lens in place. The corneal oxygen uptake rates immediately following each of those conditions were direct indices of tear bulk-flow exchange under a rigid contact lens as an oxygen route. Greatest efficiencies in reducing corneal oxygen demand were associated with the two highest blink frequencies examined (namely, for interblink intervals of 2 s or less).

Tear buffering in contact lens wearers.

The buffering capacity of tears collected from contact lens wearers was compared to that from non-contact lens wearers. Three groups of subjects were investigated: 6 subjects not wearing contact lenses, 3 subjects wearing rigid contact lenses, and 3 subjects wearing hydrogel contact lenses. Each of the 12 subjects provided, on 6 separate occasions, 100 microliters of tears.

Is the quality of vision with contact lenses adequate? Not only adequate but often superior.

Two factors govern the quality of vision with contact lenses (CLs): the fit and movement of the lens and the adequacy of its optics. Studies have not demonstrated any inherent inadequacies in material or design parameters that might account for visual difficulties in lens wearers. To the contrary, thickness, water content, and fit can be varied within clinically acceptable ranges without compromising vision.

Visual performance with aspheric rigid contact lenses.

Single vision aspheric contact lens designs may be able to enhance visual performance by controlling spherical aberration. In this study, we have compared the visual performance provided by two front surface aspheric rigid contact lenses with that of a spherical rigid contact lens and spectacle correction. These 4 corrections were worn by ten subjects while visual acuity was determined as a function of aperture size.

Extended contact lens wear in the developing cynomolgus monkey eye. Recovery from adverse responses.

Soft extended wear contact lenses were designed for and fitted to 12 eyes of 11 infant semiwild cynomolgus monkeys. The lenses were satisfactorily worn over observation periods of up to 465 days, the longest continuous period of lens wear being 69 days. However, some of the corneas were subject to a pattern of complications analogous to that in human contact lens wear.

Responses of low-frequency cells in the inferior colliculus to interaural time differences of clicks: excitatory and inhibitory components.

1. We studied extracellular responses of low-frequency cells in the central nucleus of the inferior colliculus (ICC) to interaural time differences (ITDs) of clicks and compared their responses to ITDs of noise and tones. Most cells that displayed sensitivity to ITDs of clicks responded cyclically as a function of ITD with central peaks and troughs at the same ITDs as in response to noise.

Buffering in human tears: pH responses to acid and base challenge.

The buffering capacity of tears collected from six young, healthy subjects was assessed using a microtitration technique. Each subject provided, on six separate occasions, about 100 microliter of tears, collected in small amounts and with minimal mechanical stimulation over several hours. The pH of the total stirred pool of tears from each subject was determined at the outset.

The radiation impedance of the external ear of cat: measurements and applications.

The configuration of external ears varies dramatically among mammalian species. In order to relate these structural differences to acoustic performance, it is useful to determine the "output" (radiation) impedance of the external ear. Measurements were made of the radiation impedance ZE of the cat external ear looking out from the location of the tympanic membrane.

Temporal coding of resonances by low-frequency auditory nerve fibers: single-fiber responses and a population model.

1. We recorded responses of low-frequency auditory nerve fibers (characteristic frequency (CF) less than 3 kHz) in the cat to resonant stimuli with varied natural frequencies, damping coefficients, and sound pressure levels. Responses to resonances were synchronized to frequencies lying between the peak frequency of the stimulus spectrum and a frequency near the fiber's CF.

Time course of corneal oxygen uptake during contact lens wear.

We used a polarographic oxygen sensor to measure corneal oxygen uptake rates of 16 subjects during daily wear of soft contact lenses. The subjects reported for examinations on nine occasions over a 30-week lens wearing period. Corneal oxygen uptake rates were measured immediately after lens removal and at 11 additional times over the following 60 minutes.

Effect of hydrogel lens wear on contrast sensitivity.

Conflicting reports on the adequacy of the visual performance provided by hydrogel contact lenses continue to appear in the literature. We conducted a study to determine the effect on visual performance, as assessed by contrast sensitivity measurements, of (1) lens wear of optimally fitting 38% water content lenses and (2) altered lens parameters, including fitting characteristics, of 38% and 67% water content lenses. During normal wear of lenses, neither the lenses themselves nor any contact lens-induced corneal changes produced measurable visual losses.

Corneal oxygen availability during contact lens wear: a comparison of methodologies.

Three distinct methodologies have been used to assess corneal oxygen supply during contact lens wear--oxygen transmissibility (Dk/L), equivalent oxygen percentage (EOP), and corneal swelling. To examine the interelation among these methodologies, we measured the EOP and the amount of corneal swelling in response to a set of contact lenses of a range of Dk/L values on 10 subjects. We also measured the corneal swelling response after exposure to gas mixtures of 0.

Critical oxygen requirements to avoid oedema of the central and peripheral cornea.

A randomized double-masked experiment was performed to compare the critical oxygen concentrations required to avoid corneal thickening at the central and peripheral cornea. Pachometry was performed on 10 subjects before and after 3 h of corneal exposure to the following gasmixtures: 0.00, 1.

Effects of interaural time delays of noise stimuli on low-frequency cells in the cat's inferior colliculus. III. Evidence for cross-correlation.

1. We tested the coincidence, or cross-correlation, model of Jeffress, which proposes a neuronal mechanism for sensitivity to interaural time differences (ITDs) in low-frequency cells in the central nucleus of the inferior colliculus (ICC) of the cat. Different tokens of Gaussian noise stimuli were delivered to the two ears.

Dehydration of hydrogel lenses during overnight wear.

We studied the extent of dehydration of hydrogel lenses during overnight wear. Seven subjects used a hand refractometer to measure the water content of five different lenses (Hydron zero-6 (nominal water content 38.6%), -0.

Patient compliance and its influence on contact lens wearing problems.

One hundred consecutively presenting patients, fifty from each of two contact lens clinics, were questioned about the procedures encountered in care and maintenance of their contact lenses and asked to demonstrate their use of those procedures. Their clinic records were then analyzed for the occurrence of signs and symptoms that were related potentially to noncompliance with instructions and procedures, and that could not be otherwise explained. Only 26% of patients were fully complaint.

A temporal analysis of auditory-nerve fiber responses to spoken stop consonant-vowel syllables.

Auditory-nerve fiber spike trains were recorded in response to spoken English stop consonant-vowel syllables, both voiced (/b,d,g/) and unvoiced (/p,t,k/), in the initial position of syllables with the vowels /i,a,u/. Temporal properties of the neural responses and stimulus spectra are displayed in a spectrographic format. The responses were categorized in terms of the fibers' characteristic frequencies (CF) and spontaneous rates (SR).

The effects of fenestrating soft contact lenses on corneal swelling: a re-examination.

Previous studies have suggested that central corneal oedema during hydrogel lens wear can be reduced by placing peripheral fenestrations in the lens. In this study, optical pachometry was used to monitor central and peripheral corneal swelling in response to a peripherally fenestrated hydrogel lens. The experiment was conducted in a double-masked, randomized manner on 10 unadapted subjects.

Use of tear enzyme activities to assess the corneal response to contact lens wear.

A non-invasive biochemical method for assessing the effects of contact lens wear on the in vivo corneal epithelium is described. A fluorometric technique is used to measure the activities of lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) in human tear fluid. In view of the corneal epithelial origin of these enzymes, changes in their activity can indicate the severity of environmental stresses on the corneal epithelium.

Human tear enzyme changes as indicators of the corneal response to anterior hypoxia.

A non-invasive biochemical technique for quantifying the effects of anterior corneal hypoxia on the in vivo corneal epithelium of the human eye is described. Following short-term exposure of the cornea to low atmospheric oxygen pressures, lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) activities in tears are altered so that the tear LDH/MDH ratio is elevated. The degree of elevation of the ratio and its timing are related to the severity of hypoxia.

The contact lens environment: tear proteins in perspective.

Tear protein deposition on contact lenses can lead to interruption or even cessation of lens wear. Yet, there are positive roles that tear proteins play in the maintenance of ocular integrity, with and without contact lenses present. One of these roles, that of tear buffering, is explored here.

Meridional variations of corneal shape.

The corneal shape of 196 eyes was determined by photokeratoscopy and subsequent fitting of a conicoid equation to four individual corneal meridians. This conicoid was found in almost all instances to be ellipsoidal, with the asphericity not varying between meridians. The corneal radius of curvature did vary as expected between meridians.