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Biomedical subjects

P Erickson

Publications and source records attributed to P Erickson.

At least 55 records · Page 3Linked to original sources
PubMed1990

Effects of intraocular lens position errors on postoperative refractive error.

Previous theoretical attempts to predict the refractive effects of intraocular lens (IOL) misalignment have resulted in conflicting information. Discrepancies in both the potential magnitude and direction of the refractive changes exist in the literature. This paper provides a detailed description of the mathematical framework required to achieve a valid predictive model and a quantitative analysis of the effects of IOL positional errors. The effects of misalignment are shown to influence the spherical refractive component primarily. Astigmatism related to oblique incidence is generally small. Movement of the IOL away from the retina produces myopia, while movement toward the retina produces hyperopia. It is likely that longitudinal IOL positional errors are a principal component of postoperative refractive errors. Alignment errors, on the other hand, must have generally minor effects on refraction.

Astigmatism↗
PubMed1990

Visual function with presbyopic contact lens correction.

All forms of ophthalmic correction for presbyopia require compromises in viewing flexibility and visual function. The unique effects on vision of contact lenses used in managing presbyopia are especially intriguing and potentially problematic. Bifocal contact lenses produce unique changes in the nature and quality of the retinal image. In monovision (MV) correction, anisometropia is intentionally created by fitting one eye to see clearly at optical infinity and the other eye to see clearly at the near working distance. Our review of the literature indicates that most visual functions are affected by these departures from the conventional optical correction strategies used on nonpresbyopes. Sensory functions such as contrast sensitivity and stereoacuity are affected most, whereas motor functions such as convergence and accommodation are not noticeably impaired. MV appears to produce a more widely acceptable visual compromise than currently available bifocal contact lenses for most patients.

Adaptation, Ocular↗
PubMed1990

Monovision.

Monovision has been a controversial contact lens correction modality for over 30 years. This paper addresses the major issues and concerns and considers them in the light of patient safety, visual efficiency and practitioner liability.

Adaptation, Ocular↗
PubMed1990

A new macula lens.

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Equipment Design↗
PubMed1989

Regional and physical mapping studies characterizing the Greig polysyndactyly 3;7 chromosome translocation, t(3;7)(p21.1;p13).

The Greig polysyndactyly-craniofacial anomalies syndrome is an autosomal dominant disorder involving a gene(s) located in band 7p13. We have isolated and characterized a reciprocal 3;7 chromosome translocation that resulted in the syndrome. We have identified two closely linked (0 cM) conserved DNA sequences (P137/p944B) that flank the translocation breakpoint. A pulsed-filed analysis combined with available genetic linkage information demonstrates that the disorder is linked (2 cM) to the T-gamma receptor locus, lending considerable support to the hypothesis that the mouse mutant extra-toes is the counterpart of the Greig syndrome. We have found no evidence that physically links the EGF receptor to the P137/p944B region, again compatible with mouse linkage relationships. The isolation of the der(3) chromosome from the 3;7 translocation has allowed us to regionally localize probes within the 3p21.1 band. For three probes commonly used in heterozygosity experiments with human cancers involving chromosome 3, we have determined that the order from centromere to telomere is D3S3, D3S2, and DNF15S2. Our pulsed-field studies also demonstrate the utility of band density differences combined with partial digests in evaluating linkage relationships. The P137/p944B probes should be useful in examining other hereditary disorders with phenotypic similarities to the Greig syndrome.

Animals↗
PubMed1989

Using composite health status measures to assess the nation's health.

Research in progress at the National Center for Health Statistics for evaluating the usefulness of composite measures of health status for assessing the nation's health is described. Three measures suitable for use in the general population, the Health Insurance Experiment-Functional Limitations (HIE-FL), the Health Utility Index (HUI), and the Quality of Well-being (QWB) scale, have been mapped to data collected in the 1980 National Health Interview Survey (NHIS). Analysis using current algorithms for making composite function status measures according to the QWB methods suggests that traditional single indicators of health tend to overestimate the level of health by about 10%. When symptoms and problems are added to the composite function score, the overestimate as measured by the single indicator is at least 50%. The authors are continuing to validate these algorithms, to develop similar ones for the HIE-FL and HUI, and to extend the analysis to data collected in 1977, 1979, and 1984. Current results indicate that to realize fully the benefits of composite measures, well-established, valid, and reliable measures of health-related quality of life should be included as part of the regular NHIS data collection procedures.

Activities of Daily Living↗
PubMed1989

Factors influencing vision with rigid gas permeable alternating bifocals.

This study assessed the fitting and visual performance of a rigid, gas permeable (RGP), monocentric, alternating bifocal. Fourteen presbyopic eyes each wore 24 different lenses consisting of all combinations of 2 diameters, 2 segment heights, 2 prism ballasts, and 3 fitting relations. The influence of parameter selection on visual performance and the usefulness of clinical measurements in predicting visual performance were determined statistically by multivariate logistic regression. Our results showed that prism, segment height, and the fitting relation can influence distance and near visual performance. Lens movement, postblink segment positioning, and return time were the most useful measured predictors of visual performance.

Aged↗
PubMed1989

Nursing is at war!

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Conflict, Psychological↗
PubMed1989

Effects of interocular blur suppression ability on monovision task performance.

Suppression of anisometropic blur induced by monovision contact lenses was examined in 18 presbyopic subjects. Suppression ability was quantified by reducing the contrast of a bright test target, viewed by subjects wearing a monovision correction, until the blurred image was suppressed. Subjective success with monovision was evaluated using a patient survey and no correlation to blur suppression ability was found. Objective success was evaluated in terms of performance at three near work tasks, each requiring a different level of stereoscopic localization. A significant correlation was found between card filing performance (requiring a moderate level of stereopsis) and blur suppression ability. Correcting either the dominant or non-dominant eye for near in the monovision correction did not significantly affect blur suppression ability. There was no evidence for adaptation to monovision in terms of increasing blur suppression ability over time.

Adult↗
PubMed1988

Stereopsis in presbyopes wearing monovision and simultaneous vision bifocal contact lenses.

One of the advantages suggested for contact lens bifocals over monovision treatment of presbyopia is that there may be less impairment of binocular function. We evaluated nearpoint stereoposis on the Titmus stereotest for 10 presbyopic patients. Testing was done under five conditions; monovision and binocular correction with each of four marketed simultaneous bifocal contact lenses. Simultaneous vision bifocals tested produced at least as much reduction in stereopsis as monovision compared to baseline spectacle correction. Repeat testing of bifocal stereopsis with best near over-refraction suggested that a substantial portion of the stereo reduction could be attributed to insufficient effective adds with the bifocal contacts.

Contact Lenses↗
PubMed1988

Patterns of binocular suppression and accommodation in monovision.

The binocular depth of focus of monovision wearers was compared to the sum of the two monocularly determined depths of focus. Observers fell into three groups based upon ocular sighting dominance. Complete binocular summation of the monocular depths of focus was observed in subjects without a preferred fixating eye. Subjects who preferred to fixate with one eye had difficulty suppressing blur of that eye while the binocular target was within the depth of focus of the nonpreferred eye. A third group showed partial summation of the two monocular depths of focus. Similar patterns of accommodative response, measured objectively with the SRI optometer, were observed in subjects wearing monovision corrections. Accommodative response to sinusoidal variations in blur was controlled primarily by the dominant sighting eye. These results demonstrate the effectiveness of interocular suppression of anisometropic blur in monovision correction and the influence of ocular dominance upon this suppression process.

Accommodation, Ocular↗
PubMed1988

Optical design considerations for contact lens bifocals.

Primary concerns for designing conventional bifocal contact lens optics involve placement of sufficient representation of distance and near optical powers before the pupil and minimizing the presence of secondary images. Geometrical models and lens measurements are used to establish guidelines for predicting bifocal contact lens performance. Proportional optical zone representation, image jump, and power distribution are presented for the most commonly employed bifocal zone configurations. Adequate zone representation and effective lens power are shown to be quite sensitive to variation in pupil size and position. Strategies for optimizing lens performance in view of these effects are discussed.

Contact Lenses↗
PubMed1988

Potential range of clear vision in monovision.

A possible limitation for monovision contact lens treatment of presbyopia is that an intermediate correction cannot be incorporated into the prescription without compromising distance or near vision. A simple model using a standard prescription strategy for the add and a conservative estimate for the static depth of focus of the eye was used to predict the range of clear vision with monovision lenses. For adds up to 2D, little compromise in visual acuity was predicted for any gaze position.

Accommodation, Ocular↗