Biomedical subjects

C M Schnider

Publications and source records attributed to C M Schnider.

10 recordsLinked to original sources

PubMed1998

Effect of patient personality profile and verbal presentation on successful rigid contact lens adaptation, satisfaction and compliance.

BACKGROUND: Rigid gas permeable (RGP) lenses have numerous benefits, including quality of vision, ocular health, and reduction of myopic progression in young people. Nevertheless, RGP lens use is not increasing in the United States. It is possible that certain patient personality characteristics and/or how a practitioner presents RGP lenses to a new patient may affect satisfaction and success. The purpose of this study was to evaluate the effect of individual patient's personality and the practitioner's method of presenting RGP lenses to new patients on their ability to adapt to these lenses. METHODS: Forty-nine subjects, all noncontact lens wearers, were entered into this 1-month study, which was conducted at both the University of Missouri-St. Louis School of Optometry and the Pacific University College of Optometry. All subjects initially completed standardized questionnaires pertaining to locus of control, openness to new experiences, and motivation/expectations. After diagnostic fitting with a RGP lens material, the subjects were placed into one of the following three groups: (1) Fear-Arousing Non-Enthused; (2) Neutral Content Non-Enthused; or (3) Neutral Content Enthused. They observed one of three video presentations on RGP lens wear. Subjects submitted daily questionnaires providing their evaluation of such factors as comfort, wearing time, and handling. RESULTS: The results showed that there was a significant difference (chi(2) = 6.99; p < 0.05) among the different groups in the number of dropouts: 6/19 with the Fear-Arousing Non-Enthused group, 2/17 with the Neutral Content Non-Enthused group, and 0/13 with the Neutral Content Enthused group. There was also a significant difference (ANOVA F = 4.1, p < 0.05) among the groups on compliance, with the Neutral Content Enthused group demonstrating greater compliance. In terms of satisfaction, there was no significant difference among presentation groups. CONCLUSION: It was concluded that the method of presentation is important for successful RGP contact lens wear. If presented with genuine interest and a positive and realistic attitude, patients are more likely to succeed in RGP lens wear during the initial critical period.

Adaptation, Physiological↗

PubMed1997

Effect of lens design on peripheral corneal desiccation.

BACKGROUND: Management of peripheral corneal desiccation (PCD; also known as 3 and 9 o'clock staining) has challenged rigid-lens fitters since the early days of corneal contact lenses. This study investigated effects of changing diameter and edge lift on severity of staining in two groups of rigid extended wear patients: stainers and nonstainers. METHODS: Five different lens designs, representing three diameters (9.0, 9.6, and 10.2 mm) and three edge lifts (low, moderate, and high), were worn by 12 subjects who exhibited significant levels of PCO (stainers) and a matched group that had shown no significant staining (nonstainers) after a period of wear with the same standard tricurve design. RESULTS: The study demonstrated that larger lens diameters (10.2 and 9.6 mm) and moderate-edge lifts outperformed the small-diameter (9.0 mm) and low-edge lift designs. However, these effects were demonstrated in the group of stainers only. Significant lens performance variables affecting the degree of staining in known stainers included low-vertical centration, narrow or shallow edges observed with fluorescein, erratic or insufficient lens movement, and smaller lens diameters. CONCLUSIONS: In patients who demonstrate a significant amount of peripheral corneal desiccation with rigid lenses, careful attention should be paid to the peripheral lens design. Larger lenses are preferred, as long as a moderately wide tear reservoir can be maintained under the lens edge.

Adult↗

PubMed1996

Effect of patient and lens performance characteristics on peripheral corneal desiccation.

BACKGROUND: The problem of 3 and 9 o'clock staining has been a challenge to rigid lens fitters since the early days of corneal lenses. METHODS: To investigate the features of peripheral corneal desiccation (PCD) in a rigid lens extended wear (RGP EW) population, a study was conducted using 12 subjects known to exhibit significant levels of PCD ("stainers"), and a matched group of individuals who had not shown significant staining with the same lens design ("non-stainers"). Analyses of factors which may be of use in predicting which patients will have problems with PCD were performed to identify differences between groups. RESULTS: Pre-fitting variables that were associated with the tendency for staining included higher levels of conjunctival hyperemia, a longer inter-blink interval, and poorer tear quality (higher levels of tear lipid and debris in the tear film). Variables associated with lens fitting that were predictive of staining susceptibility included poorer lens surface wetting, faster front surface drying time, an increased ratio of blink interval to lens drying time, inferior lens centration, and more variable or erratic lens movement during the blink cycle. CONCLUSIONS: These data suggest the presence of an underlying ocular surface disorder in patients prone to PCD. It is recommended that all patients be monitored for staining on daily wear prior to commencing an extended wear regimen, and that patients displaying clinically significant levels of corneal staining not proceed to extended wear.

Adult↗

PubMed1994

Extended-wear RGP contact lenses: a viable alternative to refractive surgery.

The rigid gas-permeable (RGP) extended-wear lens offers a unique alternative to the hydrogel extended-wear lens as well as to refractive surgery. In suitable patients it can provide almost maintenance-free visual correction for a wide variety of refractive errors. With prudent patient selection, use of high-permeability RGP materials, sound lens design and fitting principles, and conservative follow-up procedures, RGP extended-wear lenses can have success rates exceeding those of either hydrogel extended-wear lenses or refractive surgery, with fewer complications. The complications that do occur are often predictable after a short period of daily wear, and the remainder can often be managed with small changes to lens design.

Contact Lenses, Extended-Wear↗

PubMed1993

CCLRU standards for success of daily and extended wear contact lenses.

Success in contact lens wear is often judged on the basis of patient "survival" rather than the achievement of satisfactory performance based on specific criteria. In 1971, Sarver and Harris defined a series of standards for successful polymethyl methacrylate (PMMA) lens wear which incorporated criteria for wearing time, comfort, vision, ocular tissue changes, and patient appearance. In this paper we propose a revision of these criteria based on current understanding of the ocular response to contact lens wear. These revised CCLRU (Cornea and Contact Lens Research Unit) standards for success are intended as realistic performance objectives, and can be applied in clinical trials to evaluate and compare the clinical performance of present and future rigid and soft contact lenses, worn for daily and extended wear.

Contact Lenses↗

PubMed1993

A comparison between nomogram vs. trial fitting of rigid gas permeable contact lenses.

To determine the differences between prescribing a trial fitted vs. nomogram (System 10) selected rigid gas permeable contact lens, 42 subjects were fit with one lens design on one eye and the other lens design on the opposite eye. Subjective responses for comfort and vision, objective signs of central corneal clouding, conjunctival injection, post keratometry readings, 3-9 staining, over-refraction, post refraction and lens position were ranked and assigned to success levels for each eye. Subjects were evaluated at 1 week, 1 month, and 3 months. The first fit success rates were 92 percent for the trial fit and 86 percent for the nomogram fit. The trial fit lens attained significantly better outcomes in individual categories of comfort and over-refraction. It was noted that the lens diameters differed significantly and a large percentage of both types of lenses benefited from a slight blend and edge modification. Although trial fitting remains the method of highest success, nomogram fitting (using System 10) appears consistent enough to consider it an option for certain practice situations.

Adolescent↗

PubMed1989

Guide to the clinical assessment of on-eye wettability of rigid gas permeable lenses.

The number of rigid gas permeable (RGP) contact lens materials is increasing rapidly. One of the most critical issues for acceptance of new materials is lens wettability. This paper describes techniques for assessing lens wetting characteristics while the lenses are worn on the eye, and relates each observation to the lens material properties or patient tear characteristics. This method of lens wetting assessment is intended to aid the practitioner in determining the optimal lens material for a patient, based upon assessment of the interactions inherent in the lens-eye system.

Blinking↗

PubMed1987

Normative data and control studies of flash VEP's for comparison to a clinical population.

The effects of aging, interocular comparisons, pupil dilation, iris pigmentation, and simulated cataracts on bright flash visual evoked potentials (VEP's) of normal observers were studied to assess the flash VEP as a potential predictor of postsurgical visual function in cataract patients. Seventy-six observers (from 20 to 80 years old) were tested for age differences in flash VEP's. Implicit time measures for transient responses increased significantly as a function of age, but neither transient nor steady-state response amplitudes were altered significantly. Moreover, no significant changes in VEP's occurred as a function of interocular comparisons, pupil dilation, or differences in iris pigmentation of normal observers. Simulation of cataracts with 14 observers did not affect implicit time measures, but did change response amplitudes significantly. Therefore, implicit time measures of cataract patients should be compared either to those of normal age-matched controls or, in the case of a unilateral problem, to the normal fellow eye. Delayed implicit time measures, after the appropriate comparison, suggest optic nerve/pathway dysfunction. However, comparisons of amplitude measures require compensation for opacity density.

Adult↗

PubMed1985

Orthoptic effects on accommodation and related visual functions in an adult alternating esotrope.

Orthoptic therapy was instituted in an adult, alternating esotrope with asthenopia who exhibited inaccurate static accommodative responses with adequate, clinically determined, accommodative facility. During and following therapy the patient showed considerable improvement in accommodative accuracy and related visual functions, such as contrast sensitivity, in the absence of any change in strabismic deviation. This case provides the first laboratory documentation of orthoptic effects on accommodation in an adult strabismic.

Accommodation, Ocular↗

PubMed1984

Accommodation dynamics in divergence excess exotropia.

Objective recording of accommodation dynamics was performed in four patients with divergence excess exotropia (two true and two simulated) and in three visually normal control subjects. The accommodative peak velocity/amplitude relationship was normal in the exotropic patients and in the control subjects. Latency for decreasing accommodation was increased significantly, and overshoot frequency was decreased, in the divergence excess exotropes of the true variety, thus demonstrating slightly slowed accommodation dynamics in this diagnostic group. These subtle deviations in response dynamics reflect central rather than peripheral mechanisms.

Accommodation, Ocular↗