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Biomedical subjects

L G Carney

Publications and source records attributed to L G Carney.

15 recordsLinked to original sources
PubMed1979

Human tear buffering capacity.

With the use of a closed chamber microelectrode system, we measured the relative buffering capacities of 490 human tear samples from young healthy adults. The buffering capacities of the 457 waking-hour samples did show small but regular oscillations that were similar to those previously reported for blood and tear pH, but only rarely did the buffering capacity of one sample approach double that of another. The buffering capacities of 33 tear samples, associated with periods of prolonged eye closure (sleep), were not significantly different (P less than 0.5) from those of the open eye.

Adult↗
PubMed1979

Bilateral keratoconus posticus circumscriptus: a case report.

The characteristics, clinical appearance, and frequency of the rare corneal condition, keratoconus posticus circumscriptus, are discussed. A bilateral case of this condition, examined by use of techniques not previously employed, is described.

Adult↗
PubMed1979

Vision through an abnormal cornea: a pilot study of the relationship between visual loss from corneal distortion, corneal edema, keratoconus, and some allied corneal pathology.

Visual function was assessed by classic acuity measures as well as contrast thresholds over a wide spatial frequency range for subjects with experimentally induced corneal distortion and induced corneal edema. These results were compared with similar results for patients with uniocular keratoconus, bilateral keratoconus, and allied corneal pathology. Distortion and edema were found to produce characteristically different types of contrast attenuation at threshold (amplitude) and have quite different suprathreshold abnormalities (phase) for objects within the resolution limit and therefore could form the basis of a useful functional classification of the visual degradation from corneal pathology.

Cornea↗
PubMed1979

Tear pH: resistance to change.

While considerable study and clinical speculation has been given to tear pH, almost no attention has been paid to the buffering capacity of this fluid. Responses of tears to an alkaline challenge test as a measure of their buffering capacity are described here for a series of patients. The magnitudes of those resulting shifts, and the probable mechanisms influencing them are commented upon.

Buffers↗
PubMed1979

Oxygen levels beneath the closed eyelid.

The level of oxygen at the anterior corneal surface beneath the closed eyelid is shown to be equivalent to an atmosphere of 7.7% oxygen. This finding is in good agreement with assumptions which have been based on the oxygen level at the palpebral conjunctiva. However, in some instances a significant amount of oxygen is derived not only from the palpebral conjunctiva but also from the atmosphere as a result of an imperfect palpebral aperture seal.

Adult↗
PubMed1978

Corneal topography and monocular diplopia following near work.

Monocular diplopia, reported by a subject following near work, was shown to be caused by changes in the corneal topography. Prior slit lamp biomicroscopy had revealed no corneal abnormality. The degree of corneal distortion and ray tracing calculations confirmed the presence and position of the resultant diplopia.

Adult↗
PubMed1978

Tear pH: how predictable?

While the tear pH of a patient is now known to be continually shifting throughout the waking day, such variations were found to be contained within fairly narrow limits (a range here of about 0.6 of a pH unit). Further, sufficient repetition of these shifts occurred over 10 days observed that patterns distinctive of the individual patient often emerged.

Humans↗
PubMed1977

Comparison of accommodation with rigid and flexible contact lenses.

Measurements were made of the amplitude of accommodation for myopes wearing spectacles, rigid contact lenses, and flexible contact lenses. Both forms of contact lenses placed greater accommodative requirements on the myope than did spectacle correction, but no significant difference was found between the 2 types of contact lenses in this respect.

Accommodation, Ocular↗
PubMed1976

Human tear pH. Diurnal variations.

Using a closed chamber microelectrode system, the tear pH levels of sixteen subjects were monitored throughout the waking extent of five days. In addition to the absolute mean pH differences found among subjects, diurnal patterns of pH change could be identified for the majority. The amplitudes and periods of these cycloid patterns, however, were distinctive to each individual. Also, tear pH levels following periods of prolonged eye closure were found to be notably more acid than those associated with the waking hours.

Adult↗
PubMed1976

Other hydrophilic lens environments: pH.

Although hydrophilic contact lenses are specifically designed for compatibility with the eye environment, i.e., the tears, they will, with the exception of continuous wear types, spend a significant fraction of their daily cycle in other solutions. This investigation explores the pH characteristics of certain of those alternative media.

Contact Lenses, Hydrophilic↗
PubMed1976

The closed eye environement: pH.

Earlier observations showed that unbuffered bathing media held by a closed chamber against the eye would become progressively more acid over a few minutes. Such shifts, however, when examined for the naturally closed eye, even for prolonged periods, were found to be within 1 pH unit of the open-eye measured average.

Adult↗
PubMed1976

Hydrogen ion concentration of human tears: Effects of prolonged eye closure.

Using a closed chamber microelectrode technique, human tear hydrogen ion concentration was measured following periods of eye closure of 6 to 8 hours and then compared with normal open eye findings from the same patients. Closed eye tears were found to be significantly more acid (average age difference = 26 nM/1) and required some 3 to 4 hours to return to average open eye levels. The population rate for this return averaged 6.9 nM/1/hr. This degree of acid shift measured for prolonged eye closure, however, remained, for the average patient, well within comfort limits commonly cited, and appeared insufficient to distrub the water content or optical parameters of hydrophilic polymers in common use today for therapeutic or cosmetic purposes.

Adult↗
PubMed1975

pH profiles: Part I--One pH, or many?

Examples of particular characteristics of tear pH are given for a contact lens patient, both previous to fitting and following.

Adaptation, Physiological↗