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Biomedical subjects

M M Bibby

Publications and source records attributed to M M Bibby.

10 recordsLinked to original sources
PubMed1985

Determination of the effective diameter for the calculation of equivalent thickness of soft contact lenses.

This study determines the effective diameter of soft contact lenses for the calculation of their equivalent thickness by relating the physiological response to the wear of prescription and calibration (constant thickness) lenses in a group of subjects. First a relationship is derived between corneal swelling response and thickness of the calibration lenses. Then, by relating the swelling response obtained with the prescription lens to this relationship, it is possible to determine the equivalent thickness of the prescription lens. After determining the geometry of the prescription lenses it is possible to calculate by an iterative integration technique the diameter of the prescription lens to be used in the determination of equivalent thickness. This diameter is found to differ between plus and minus prescription lenses. The integration diameter for all lens powers was found to be 6.7 mm.

Adult↗
PubMed1983

A model to explain the effect of soft lens design specifications on movement.

A model is presented which explains the movement of a contact lens in terms of its primary design specifications. The model is supported by clinical evidence. The interrelation between lens thickness, sagittal depth, and diameter is explained. The model explains why fewer base curves are needed as lens thickness is reduced.

Contact Lenses, Hydrophilic↗
PubMed1983

Validation of a model describing soft lens movement as a function of lens specification.

The authors fitted 12 subjects with 30% water-content, soft contact lenses. The sagittal depth of the lenses was varied in five steps while diameter was held constant. In a second study, diameter was varied from 12 to 14 mm in five steps. Regression analysis was used to analyze the data. Lens movement can be decreased by increasing lens thickness, reducing lens diameter, or flattening the base curve of the lens.

Contact Lenses, Hydrophilic↗
PubMed1982

Lid interaction and toric soft lens axis location.

A group of 15 subjects were fitted with truncated toric soft lenses varying in cylinder power from 1 to 4 D, in 1 D steps, with axes 90 and 180 degrees. After 30 min of wear, the location of the truncation was measured from a slitlamp photograph and calculated from a spherocylindrical over-refraction. Blink-initiated rotation of the lenses was measured by slitlamp photography. Comparison of the location of the truncation of lenses with cylinder at axes 90 and 180 degrees showed no significant difference using matched pair analysis, nor was cylinder power found to effect truncation location. However, analysis of the incidence of acceptable location (truncation within 25 degrees of the horizontal) showed significantly more acceptable locations for those toric lenses with the cylinder at axis 90 degrees (against-the-rule). A significant product moment correlation between the amount of mislocation of the axis and blink-initiated rotation was found. A high correlation was found between axis location measured from photographs and that calculated from over-refraction. However, because of the large variance of the differences between the two values, over-refraction is not considered to be a clinically acceptable method of determining toric lens axis location. The significance of the results of this study are discussed with respect to toric lens design.

Astigmatism↗
PubMed1981

Temporal sequence study of the factors affecting corneal edema associated with soft contact lens wear.

The contribution of various factors to the edema associated with soft contact lens wear is considered. Time of wear, individual patient response level, baseline thickness of the cornea, and base curve radius of the contact lens are found by multiple regression analysis to be the most significant contributors to edema. The small but significant contribution of contact lens base curve to edema suggests that some oxygen is supplied to the cornea via a tear pump mechanism.

Contact Lenses, Hydrophilic↗
PubMed1980

Movement and rotation of soft contact lenses. Effect of fit and lens design.

Control of the movement of a contact lens on the eye is of particular importance in the case of a toric lens fitted on a toroidal cornea. Lens rotation was measured on 13 eyes fitted with each of three types of spherical contact lenses, regular, prism ballasted-truncated, and truncated only. Edge lift was varied in three steps, and lenses fitted flat and steep were tested for the amount of blink-associated rotation. Rotation can be reduced by decreasing the radius of the base curve or providing truncation and/or prism ballast.

Contact Lenses, Hydrophilic↗
PubMed1979

Factors affecting peripheral curve design.

Factors associated with edge clearance in the contact lens-corneal relationship are peripheral curve radius and width, lens diameter, and corneal shape. The effect of each parameter is quantified, permitting an examination of current design practices. Recommendations are that minor adjustments be made by changing radius, that major adjustments be made by changing width, and that the peripheral curve radius should be steepened as the diameter increases.

Contact Lenses↗
PubMed1979

Sagittal depth considerations in the selection of the base curve radius of a soft contact lens.

Examination of the relationship between the sagittal depth of the cornea and the sagittal depth of an optimally fitting soft contact lens reveals that base curves are not always well chosen. The author reports a new system for selecting the number, range, and distribution of base curve radii such that the range of saggital depths clinically encountered is covered evenly. The saggital increment between adjacent base curves is then 0.1 mm.

Contact Lenses, Hydrophilic↗
PubMed1978

Evaluation and control of Durasoft lens rotation.

Fifteen subjects forming three groups of refractive astigmats (astigmation less than 1.00 D., astigmatism greater than or equal to 1.00 D and less than 2.00 D, and astigmatism greater than or equal to 2.00 D) were fitted with spherical DuraSoft lenses. Rotation was assessed from slit-lamp photographs taken after 30 min and after 4 hr of lens wear. The results show that incorporating either a prism or a single truncation alone into a spherical DuraSoft lens suffices as a method of stabilization, stabilization being effectively achieved with this lens in subjects with refractive astigmatism less than 2.00 D.

Astigmatism↗