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Biomedical subjects

M G Harris

Publications and source records attributed to M G Harris.

At least 109 records · Page 6Linked to original sources
PubMed1981

Base curve measurements of soft contact lenses.

Efforts to fit and duplicate soft contact lenses depend to a certain extent upon the practitioner's ability to determine the base curve (posterior apical radius) of the lenses accurately. In the study, three devices were used to measure the base curve of seven different manufacturers' soft lenses. Each manufacturer provided six to ten -3.00-D lenses in factory-sealed vials. Each vial was masked and coded so that measurements could be taken in a masked fashion. A different investigator used each of the different devices. Each investigator took 10 base curve measurements on each lens in a random fashion. The lens vials were not unmasked until the end of the study, at which time the data were analyzed and the results compared. Not only did we determine the reliability of the three devices, but we also tried to determine the reliability of the labeled posterior apical radius of the lenses. The Hydrovue Analyzer had the best reliability (sigma = +/- 0.09 mm), followed by the Neitz Softmeter (sigma = +/- 0.13) and the Rehder gauge (sigma = 0.30). With the latter two devices, the variability increased as lens center thickness decreased. Spin-cast lenses showed better lens label repeatability than lathe-cut lenses.

Contact Lenses, Hydrophilic↗
PubMed1981

Refitting.

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Contact Lenses↗
PubMed1980

Corneal edema with hydrogel lenses and eye closure: effects of lens thickness.

Subjects wore hydrogel lenses of two different thicknesses (0.07 mm and 0.18 mm) on one eye and no lens on the other eye during 3-hour periods of eye closure. They developed more corneal edema (12.7%) with the thicker lenses than with the thinner lenses (7.9%) and more corneal edema with the thinner lenses than with no lens (0.9%). The results suggest that hydrogel lens thickness would have to be less than 20 nm to reduce corneal edema to levels that develop when the eyes are closed without a contact lens.

Adult↗
PubMed1980

Patient response to hydrogel contact lenses: a comparative study.

Eleven subject (22 eyes) wore the best fitting lenses of each of four different types of hydrogel contact lenses (Bausch and Lomb Soflens contact lenses, Hydrocurve HCII contact lenses, AOSOFT-TM/Aquaflex hydrophilic contact lenses, and Alcon Tresoft contact lenses) in a random order for 2-3 week periods so that their short-term responses to the lenses could be evaluated and compared. None of the subjects had any contraindications to hydrogel lens wear. All the lenses centered well with proper movement. Using a double masked procedures, we evaluated each patient's response to each lens type according to the standard of success of Sarver, Harris and Polse. Approximately 63% to 72% of the patients were successful with each lens type. We found no statistically significant differences in the patients' responses to the different lens types, even though individual differences were found. The majority of our subjects were successful with several or all of the lens types evaluated.

Adult↗
PubMed1979

Residual astigmatism and visual acuity with hydrogel contact lenses: a comparative study.

Residual astigmatism, visual acuity, and transferred corneal toricity were measured in a double masked fashion on 24 randomly selected patients fitted with Buasch and Lomb Soflens contact lenses, the Hydrocurve II contact lenses, and the AOSoftTM hydrophillic contact lenses. None of the subjects had any contraindications to hydrogel lens wear. All three lens types produced a small but similar reduction in refractive astigmatism. However, because of residual astigmatism, fewer eyes achieved 20/20 or better visual acuity with each of the hydrogel lens types than with the best spectacle correction. Corneal toricity was found to be transferred to the front surface of all three lens types. Our findings indicate that generally these three types of hydrogel lenses result in similar residual astigmatism, visual acuity and transferred corneal toricity. However, individual differences may occur. Therefore, the choice of lens type should be based on the individual patient's response to various lens types.

Adult↗
PubMed1979

Dear Milt.

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Contact Lenses, Hydrophilic↗
PubMed1978

Apparent foveofugal drift of counterphase gratings.

Counterphase gratings, and several other stimuli which consist of equal components of motion in both directions, appeared to drift foveofugally, rather than foveopetally, when presented to the retinal periphery. This 'foveofugal drift effect' was demonstrated by descriptive and nulling techniques and its magnitude was shown to vary across subjects. The effect was fairly brief under continuous fixation. Several lines of evidence suggested that eye movements were not responsible for the effect. The phenomenon implies a directional asymmetry in the human visual system which may be related to our consistent exposure to expanding patterns of visual flow.

Differential Threshold↗
PubMed1978

Stability of back-toric prism-ballast hydrogel contact lenses.

We fitted each of 20 eyes with 3 different Hydrocurve contact lenses: (1) spherical with prism ballast, (2) back-toric without prism ballast, and (3) back-toric with prism ballast. We monitored the stability of the lenses. The prism-ballast lenses were generally stable on corneas with zero to 3.5 DK of with-the-rule toricity; the back-toric nonprism lenses were not stable.

Adult↗
PubMed1978

Light transmission of hydrogel contact lenses.

The visible-light transmission of various Bausch & Lomb Soflens contact lenses and HydrocurveTM contact lenses was measured with a Perkin-Elmer model 202 UV spectrophotometer. The light transmission for both types of lenses ranged from 96-99%, and was almost constant over the visible spectrum. Neither the power, the thickness, nor the posterior apical radius of the lenses had a significant effect on the amount of light they transmitted.

Contact Lenses, Hydrophilic↗
PubMed1978

Corneal effects of high plus hydrogel lenses.

Five aphakic patients and five phakic patients were fitted with high plus Bausch & Lomb Soflenses. We evaluated corneal edema, staining, vertical striae, and corneal thickness before and after a 5-hr wearing period. The high plus lenses produced average corneal-thickness changes of 9.6% and 7.1% for the phakic and aphakic groups, respectively. Biomicroscope examination showed moderate amounts of vertical striae, epithelial staining, and corneal edema for both groups. The amounts of edema, staining, and striae were higher than when regular and thin minus lenses were worn. It is likely that the thickness of the high plus lenses reduces the oxygen supply to the corneal epithelium, causing relatively marked edema.

Adult↗
PubMed1977

The effect of peripherally fenestrated contact lenses on corneal edema.

To determine the effect of peripherally fenestrated contact lenses on central corneal edema, 6 subjects (12 eyes) wore steeply fitted lenses of identical dimensions but with various numbers of 0.1-mm diameter peripheral fenestrations for 3-hr periods. At the end of the wearing periods, thickening, steepening, and central clouding of the cornea were generally reduced as the number of fenestrations was increased. However, 20 fenestrations were required before the edema was reduced to a clinically acceptable level.

Adult↗
PubMed1977

Results with the Bausch and Lomb F3 series Soflens contact lens.

We wanted to determine whether the Bausch and Lomb F3 series Soflens contact lens increases the number of patients who can successfully wear Soflenses. Thirty-two patients (64 eyes) who could not successfully wear 12.5-mm-diameter B, F, J, or N series Soflenses were fitted with the 13.6-mm-diameter F3 series lenses. For 40 of the 64 eyes, the F3 series lenses were successfully worn. Use of this lens series clearly increased the number of patients who could be fitted with Bausch and Lomb Soflens contact lenses. For many patients, this flatter, larger lens centered better and improved vision and comfort compared with the best-fitting Soflens of the 12.5-mm-diameter series.

Adult↗
PubMed1977

Patient responses to gas-permeable hard (Polycon) contact lenses.

Forty-six patients who were unable to wear polymethylmethacrylate (PMMA) contact lenses, owing mainly to corneal edema and associated symptoms, were fitted with gas-permeable hard Polycon lenses of the same dimensions. Thirty-one patients (67%) wore the POLYCON lenses successfully. Thirteen (28%) did not, because of discomfort. For 2 patients, the results were unknown. None of the 46 patients exhibited observable edema with the POLYCON lenses. For a group of 5 patients (10 eyes), mean corneal thickness change after 8 hr of lens wear was insignificant. Oxygen transmissibility of these lenses is approximately 5.0 X 10(-11) (cm2 X ml O2)/(sec X ml X mm Hg), a value less than that for hydrogel lenses which produce more edema. It is predicted that gas-permeable hard lenses will eventually replace PMMA lenses.

Adolescent↗
PubMed1977

Patient responses to 13.6-mm diameter Bausch & Lomb thin Soflens contact lenses.

Responses were obtained from 12 subjects (24 eyes) who wore 2 types of 13.6-mm diameter Bausch & Lomb Soflens contact lenses-thin F 3 lenses and conventional-thickness F3 lenses. These responses were also compared with those of patients who had worn thin F lenses that were 12.5 mm in diameter. Fewer patients experienced discomfort or corneal changes with the thin F3 lenses than with the conventional ones. Lens diameter was also an important factor in improving the patients' responses. Only 35% of a different sample of 23 patients who had been fitted with 12.5-mm diameter thin F lenses had been able to wear them successfully, compared with 75% of those wearing the 13.6-mm diameter thin F3 lenses, even though the mean corneal thickening caused by the smaller lenses did not differ significantly from that caused by the smaller lenses did not differ significantly from that caused by the thin F3 lenses. Thin hydrogel lenses with diameters larger than 13.6 mm thus might produce an even better overall patient response while still causing minimal corneal edema.

Adult↗
PubMed1977

Patient response to thin hydrogel contact lenses.

This study was designed to evaluate the patient response to experimental Bausch & Lomb thin F series SOFLENSES. The center thickness of these lenses was 0.04-0.06mm compared to 0.14-0.16 mm for the conventional F series lenses. Eight of the twenty-three subjects fitted (35% of the patients, 39% of the eyes) were successful by the standard of Sarver, Harris and Polse. The principal reason for failure was discomfort, which was often associated with poor centration and arcuate staining. Neither vertical corneal striae nor significant corneal thickening were observed during the eight hour wearing periods. Lens handling was a major problem. During the eight weeks of the study 35% of lenses used were torn. Our results indicate that even though thin F series SOFLENSES cause less corneal edema than conventional F series SOFLENSES, the overall patient response to these thin lenses is less favorable than the response to conventional SOFLENSES. Further research with thin hydrogel lenses is needed to determine if the patient response can be improved by altering such lens parameters as diameter and/or curvature.

Adult↗
PubMed1976

Rotation of lathe-cut hydrogel lenses on the eye.

The rotation lathe-cut HydroCurveTM gel contact lens was measured on six eyes to evaluate the parameters that influence lens rotation and to determine if this lens could be used to correct astigmatism. Of the 72 observations made, 73.6% showed some lens rotation, and 33.4% of the sample rotated more than 5 degrees per 10 blinks. Of the observations in which rotation was noted, 88.7% were encyclorotation. These results are similar to those found for spin-cast hydrogel lenses. None of the lens parameters evaluated seemed to be related to lens rotation, whereas the eye parameters studied were. Lenses were more likely to rotate on eyes with smaller corneal diameters, smaller palpebral apertures, and corneal curvatures steeper than 4 3.00 DK (X2, N =72, p less than 0.05). Our findings indicate that some method of lens stabilization will be needed before lathe-cut hydrogel lenses can be used to effectively correct astigmatism.

Adult↗