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Biomedical subjects

M G Harris

Publications and source records attributed to M G Harris.

At least 19 recordsLinked to original sources
PubMed1992

Human sensitivity to expanding and rotating motion: effects of complementary masking and directional structure.

A comparison of sensitivity to expanding, rotating, translating and random motion suggests the existence of specialised mechanism for the detection of expansion and rotation. Complementary masking shows that the detection of expansion is unaffected by the presence of rotation, and vice versa. These results are interpreted in terms of a Relative Motion System, which combines the outputs of localised motion detectors in a variety of ways, and which functions to analyse complex image motion into simpler, more useful, components.

Female↗
PubMed1992

Task and visual performance with contact lenses and spectacles.

Previous studies found task and vision performance differences between presbyopic contact lens corrections and distant contact lenses combined with reading spectacles. The present study was designed to compare task and vision performance with single vision contact lenses and spectacles. Eighteen soft (SCL) and seventeen rigid gas permeable (RGP) successful contact lens wearers were examined and fitted with CR-39 spectacles (SPEX) which corrected their distance vision. Their occupational task performance and visual acuity (high contrast, low contrast, low contrast with glare) were measured while they wore their contact lenses and spectacles. The tasks included putting pointers in straws, filing cards in a box, counting letters on a photograph of a VDT screen, and a distance/near fixation task. Visual acuity scores were lower with SCL than with SPEX. Low contrast visual acuity with glare was reduced by 1.36 letters on a 5-letter row (p less than 0.05) for SCL compared to SPEX. No statistically significant differences in performance times were measured between contact lenses and spectacles. None of the error performance differences were statistically significant; however, more errors were made on each occupational task with soft contact lenses compared to spectacles. The findings suggest nearly equivalent task and visual performance with properly prescribed RGP contact lenses and spectacles, and minimal performance decrements with SCL compared to spectacles.

Adult↗
PubMed1992

Vision and task performance with monovision and diffractive bifocal contact lenses.

We measured vision and task performance on 26 presbyopes, ages 46 to 65 years, fitted with diffractive bifocal contact lenses (BFCL) and monovision contact lenses (MVCL). Distance contact lenses combined with reading spectacles (DCL) served as the control condition. Twenty subjects completed the 6-week study. All subjects wore BFCL and MVCL daily for a period of 3 weeks each. Performance times for three near tasks were 6 to 8% longer with BFCL compared with DCL and 2 to 6% longer for MVCL compared with DCL. There were significant reductions in distance visual acuity with BFCL (0.4 to 1.5 Snellen lines) and MVCL (0.5 to 0.8 Snellen lines) compared to DCL. At the conclusion of the study, given a choice between BFCL and MVCL, 2 of the 20 subjects chose to continue wearing BFCL, whereas 18 of the 20 subjects chose MVCL. Our results show greater visual compromise and decreased task performance with BFCL and MVCL compared to DCL and greater patient preference for MVCL.

Aged↗
PubMed1992

Retention of patient records.

Patient records are essential to provide patients with appropriate health care and to preserve patients' rights. Patient records are also vital to help practitioners defend lawsuits. Therefore, practitioners must maintain patient records in good order for as long as possible. This paper discusses the clinical and legal issues involved in record retention, including the relevant state regulations and record requirements in other health care fields, to provide guidelines for retention of optometric patient records. Based on the statutes of limitations, common practice and sound medical and legal advice, optometric patient records should be retained for a minimum of 10 years after the patient was last seen. Ideally, patient records should be retained forever.

Humans↗
PubMed1991

Task and visual performance with concentric bifocal contact lenses.

We evaluated the effects of concentric simultaneous vision bifocal contact lenses on task performance, visual acuity, and stereopsis. Forty extensively screened presbyopes were fitted with CIBA Spectrum center-near bifocal contact lenses (BCL) and with distant contact lenses combined with reading spectacles (DCL) which served as the control. Thirty-two subjects completed the 8-week study. At dispensing and after 8 weeks of regular BCL wear, performance times with BCL were significantly greater than with DCL for all three near tasks. BCL generally resulted in more errors per trial. Visual acuities with BCL were reduced significantly by 0.8 to 1.4 acuity lines compared to DCL. Stereopsis was reduced significantly by 32 to 36 sec arc with BCL compared to DCL at both measurement sessions. It is likely that the decreased task performance with the simultaneous vision BCL is caused by the decreased visual acuity with these lenses. Nonetheless, 27 patients (58.7% of those selected to be fitted; 67.5% of those who were fitted) chose to wear the BCL on a regular basis at the study conclusion. Thus, even though BCL reduced task and visual performance, thoroughly screened and properly fitted presbyopic patients can become satisfied BCL wearers. However, the reduced task and visual performance with BCL should be considered when evaluating prospective BCL candidates.

Adult↗
PubMed1991

Haemodynamic adjustments to mental stress in normotensives and subjects with mildly elevated blood pressure.

Cardiac output, heart rate, stroke volume, pre-ejection period, total peripheral resistance, systolic and diastolic blood pressure, and oxygen consumption were monitored or derived in young men with mildly elevated casual blood pressures and unambiguously normotensive control subjects before, during, and after exposure to a mental arithmetic stress. Measurements were also taken while subjects underwent graded dynamic exercise. This permitted cardiac output-oxygen consumption regression equations to be calculated and, as a consequence, cardiac output during mental stress to be represented as additional cardiac output. Systolic and diastolic blood pressure were higher during all phases of the study in the mildly elevated blood pressure group. An overall groups effect during the mental stress phase of the experiment was observed for cardiac output and pre-ejection period, and the effect for stroke volume was close to significance. Significant Groups X Periods interactions were found for cardiac output and additional cardiac output, and the heart rate effect was nearly significant. Post-hoc comparisons here indicated that, in the main, group differences in these cardiac variables were more evident during the mental arithmetic stress than during the pre- and post-task baseline periods. Total peripheral resistance did not differ reliably between groups and the cardiac effects were specific to the mental stress phase of the study.

Adult↗
PubMed1991

Informed consent for extended-wear patients.

Because of the risk of complication posed by extended-wear lenses, contact lens practitioners must comply with the requirements of informed consent, which obligate the optometrist to communicate these risks to patients. Documentation of informed consent can be obtained by using printed agreements that describe the risks of wear, instructions for lens care, wearing schedules, and required follow-up evaluations. In determining wearing schedules for patients, optometrists should not recommend more than 7 days (ie, 6 nights) of continuous wear without demonstrable benefit to the patient, and informed consent requirements should be complied with and adequate documentation retained whenever extended periods of wear are contemplated. For wearers of disposable lenses, informed consent is necessary because practitioners are not able to inspect lenses prior to wear. Patients must be advised to remove lenses if pain, redness, reduced acuity, discharge, or photophobia result and to return for examination when these symptoms occur. Documentation of this warning and of other aspects of disposable lens wear may be provided by a printed agreement.

Consumer Product Safety↗
PubMed1991

Failure to advise.

A recent Massachusetts case expands the concept of medical malpractice and the legal requirements of health care practitioners to their patients. Doctors can be found liable for negligence if they fail to advise patients to return for follow-up evaluations or treatment when symptoms persist or become worse. The legal theories involved and their implications are discussed.

Follow-Up Studies↗
PubMed1991

Patient response to concentric bifocal contact lenses.

We evaluated the visual results and success rate with a center-near concentric simultaneous vision bifocal contact lens. Forty subjects (screened from 175 presbyopic applicants) entered the study and were fitted with the CIBA Spectrum bifocal lenses (BCL) and also with single vision distance contact lenses combined with reading glasses (DCL). Visual acuity and stereoacuity measurements were made at dispensing and after 8 weeks of regular bifocal contact lens wear. At both times, visual acuity measurements with BCL were significantly reduced by 1-1.5 lines compared to DCL. Stereoacuity was reduced by 32-36" with BCL compared to DCL. Thirty-two patients completed the study and 27 chose to continue wearing BCL after completion of the study. None of the subjects had adverse corneal findings or problems of discomfort. The primary reason for BCL discontinuation was blurred vision. The data was retrospectively analyzed to identify risk factors for discontinuance--none were significant.

Adult↗
PubMed1991

Clinical application of the oxygen transmissibility of powered contact lenses.

Stipulation of the oxygen transmissibility (Dk/L) of a contact lens based upon oxygen permeability (Dk) and nominal lens thickness (L) can be misleading since center thickness, average thickness, and hence Dk/L of a contact lens vary with lens power. While earlier confusion regarding determination of Dk has now been resolved, this data has yet to be fully incorporated into a clinically applicable model. We developed a graphical solution describing variations in Dk/L with power for a representative sample of currently available hydrogel and rigid contact lenses. The Dk/L is found to be optimal for lenses of low minus power (approximately -2.50 D). The model presented here will assist practitioners in assessing the potential oxygen performance of different lens designs with respect to a given power. We advocate that lens manufacturers print the average Dk/L on lens packaging, according to the model described in this paper, along with the parameters that are usually stated.

Contact Lenses, Hydrophilic↗
PubMed1990

The temporal range of motion sensing and motion perception.

Apparent motion (AM) was studied using the missing-fundamental square-wave grating, displaced discretely over time. At inter-stimulus intervals (ISIs) greater than about 40 msec, AM was seen in the direction of displacement of the visible features of the pattern, while at shorter ISIs AM was seen in the reversed direction, following the displacement of the third harmonic spatial frequency component. This confirms (a) that the "long-range", feature-based process can bridge much greater time-gaps than the "short-range" motion sensors and (b) that the missing-fundamental pattern is a particularly useful tool for teasing the two processes apart.

Humans↗
PubMed1990

The pH of aerosol saline solution.

We evaluated the pH of eight brands of aerosol saline solution to determine if there is a change in pH during the normal usage of an aerosol canister. The pH measurements were taken over a period of 14 to 24 days with a Corning model 10 pH meter (accuracy +/- 0.05 pH units). The saline was expelled and measured daily in 15-ml increments, the approximate volume used each day by soft lens wearers. We found no significant change in pH within each brand evaluated over the test period. However, there was a statistically significant difference in the median pH of the buffered and the unbuffered aerosol saline solutions. The mean pH of the buffered aerosol saline solutions, which averaged 7.30 pH units, was within the ocular comfort range. The mean pH of the unbuffered aerosol saline solutions, which averaged 5.79 pH units, was outside the ocular comfort range. This indicates that all aerosol saline solutions should be buffered.

Aerosols↗
PubMed1990

In-office microwave disinfection of soft contact lenses.

We evaluated the effectiveness of an in-office microwave disinfection procedure which allowed for the disinfection of up to 40 soft contact lenses at one time. Ciba AOSept cases filled with sterile unpreserved saline were contaminated with one of six FDA test challenge microorganisms at a concentration of approximately 10(3) colony forming units per milliliter (CFU/ml). Twenty cases were placed on the rotating plate of a standard 2450 MHz 650 W microwave oven in a 10-cm diameter circle. The cases were exposed to high intensity microwave irradiation for periods of 0 to 15 min. None of the 6 microorganisms evaluated survived 2 min or longer of microwave exposure. Our findings indicated that microwave irradiation can be a convenient, rapid, and effective method of disinfecting a number of soft contact lenses at one time and thus adaptable as an in-office soft contact lens disinfection procedure.

Bacteria↗
PubMed1990

In vivo dehydration of disposable (Acuvue) contact lenses.

The in vivo dehydration of the Acuvue disposable contact lens was measured in six subjects using a contact lens refractometer. On average, the lenses dehydrated 6.2 +/- 1.9% after 20 min and 10.2 +/- 3.9% after 6 h of wear. The magnitude of dehydration is greater than has been reported for other hydrogel lens types of similar water content. This information may assist practitioners in the interpretation of clinical signs pertaining to lens behavior and associated patient symptoms.

Adult↗
PubMed1990

Professional liability and the Federal Tort Claims Act.

Professional liability claims against military optometrists must be brought in federal court under the Federal Tort Claims Act, which establishes rules of procedure that are somewhat different from those found in malpractice claims against private sector optometrists. Despite these differences, cases litigated against military optometrists may potentially be used as precedents to be applied to cases involving private practitioners. Recent decisions of the federal courts have in fact set such precedents, in cases alleging misdiagnosis of ocular disease, failure to refer for medical treatment, and failure to warn of the significance of symptoms.

Diagnostic Errors↗
PubMed1990

Legal consequences of the FDA's 7-day extended wear letter.

The U.S. Food and Drug Administration (FDA) recently sent contact lens practitioners a letter advising them that the FDA had asked manufacturers to indicate a maximum recommended wearing time of 7 days for cosmetic extended wear soft contact lenses. This paper discusses the authority of the FDA and the legal consequences of the FDA's "7-day Letter." Congress has authorized the FDA to enact rules, guidelines and recommendations. The 7-day letter does not appear to be any of the above. However, it does have a significant effect on contact lens practitioners' professional responsibilities and legal obligations because the letter has led to changes in product labeling and the standard of care for extended wear patients. Practitioners would be wise to give careful consideration to any deviation from the FDA's recommendation and the provisions of the product labeling. As any deviation will likely impose greater legal responsibility on the practitioner, the special circumstances that justify the deviation should be thoroughly documented in an informed consent agreement.

Contact Lenses, Extended-Wear↗