Biomedical subjects

William H Ridder

Publications and source records attributed to William H Ridder.

5 recordsLinked to original sources

PubMed2005

Short-term effects of artificial tears on visual performance in normal subjects.

PURPOSE: Temporal changes in tear film structure can distort the optical wavefront as it passes through the tear layer and reduce contrast sensitivity. Theoretically, any substance applied to the tear layer that alters its structure could affect contrast sensitivity. The purpose of this study is to investigate how different formulations of carboxymethylcellulose sodium (CMC) applied to the tear layer affect contrast sensitivity over time. Additionally, the visual effect of these drops applied over soft and rigid, gas-permeable contact lenses was also investigated. METHODS: Twenty normal subjects took part in this project. Refresh Celluvisc (Allergan, Irvine, CA, 1.0% high-viscosity CMC) was compared with Refresh Liquigel (Allergan, 1.0% total CMC made by blending 0.35% high-viscosity with 0.65% medium viscosity CMC). Ten of the subjects were habitual soft contact lens wearers and 10 were habitual gas-permeable lens wearers. The stimulus, viewed monocularly, was a stationary, vertically oriented, sine wave grating (14 CPD). A temporal, two-alternative, forced-choice paradigm combined with a self-paced method of limits was used to monitor threshold over time. After baseline data collection, a drop of the artificial tear was applied to the tear layer and the procedure continued for 30 min. This allowed continual tracking of the threshold. Data were collected while viewing the stimulus with the subject's contact lens or with their spectacle prescription. RESULTS: One drop of Liquigel or Celluvisc decreased contrast sensitivity for a 14 CPD sine wave grating (all p values < 0.005). This decrease in contrast sensitivity was observed during spectacle, soft contact lens, and gas-permeable contact lens wear. Soft contact lens wear resulted in a greater decrease in contrast sensitivity than spectacles when Liquigel was applied to the tear layer. None of the other conditions were different between contact lens and spectacle wear. The return to baseline contrast sensitivity was not significantly different between soft or gas-permeable contact lens wear and spectacles for either Liquigel or Celluvisc. In general, Celluvisc had a greater effect on visual performance than Liquigel. CONCLUSIONS: These results suggest that Liquigel and Celluvisc alter the tear layer and affect contrast sensitivity. The results agree with patient observations that Celluvisc causes a moderate amount of blur that gradually subsides. In such patients, the shorter duration of blur with Liquigel (about half that of Celluvisc) may be more acceptable. The technique of blending various viscosity CMC materials while maintaining the total CMC concentration of 1.0% may be beneficial in dry eye therapy without causing excessive blur to patients.

Adult↗

PubMed2005

Effect of artificial tears on visual performance in subjects with dry eye.

PURPOSE: Disruption of the anterior refracting surface of the eye (i.e., the tear layer) reduces visual performance. Tear layer breakup occurs soon after a blink in contact lens wearers and patients with dry eye. This study determined whether artificial tears stabilize the tear film and improve visual performance in contact lens wearers who also exhibit a dry eye. METHODS: Five subjects with mild to moderate dry eye (probably as a result of an evaporative dry eye) during spectacle and contact lens wear were fitted with a Focus Night & Day hydrogel lens for this study. A temporal, two-alternative, forced-choice paradigm was used to measure contrast sensitivity. The stimuli were vertically oriented sine wave gratings (between 0.5 and 14 cpd) presented for 16.67 msec. The stimuli were presented at two different times after blink detection: 2 sec after blink detection (i.e., before tear layer breakup) or 4 sec after tear film breakup. Four conditions were investigated at 4 sec after tear layer breakup: 1) without artificial tears added, 2) with Clerz2 (Alcon, Fort Worth, TX) instilled, 3) with Sensitive Eyes (Bausch & Lomb, Rochester, NY), and 4) with GenTeal (Novartis, Basel, Switzerland) applied. The artificial tears were instilled at 10-min intervals during the data collection. The short-term visual effects of drop instillation were also investigated by continually monitoring contrast sensitivity for a 14-cpd grating after a single-drop administration. RESULTS: High spatial frequency contrast sensitivity and visual acuity were found to be reduced after tear film breakup in the absence of supplementation with artificial tears. For the group data (and four of five subjects), the instillation of Sensitive Eyes improved the contrast sensitivity and visual acuity to the level attained before tear breakup, thus prolonging visual performance. Clerz2 and GenTeal did not produce any enhancement in visual performance. A short-term decrease in contrast sensitivity was also observed with a single administration of Clerz2 and GenTeal. CONCLUSIONS: This study indicates that there was a benefit of Bausch & Lomb Sensitive Eyes tear supplementation on visual performance in subjects with an evaporative dry eye. This may be the result of 1) aqueous supplementation in these subjects and/or 2) the minimal tear layer disruption found with Sensitive Eyes drop administration. The results suggest that practitioners need to identify those patients who can benefit from the use of appropriate artificial tear supplements.

Adult↗

PubMed2004

Methods of visual acuity determination with the spatial frequency sweep visual evoked potential.

PURPOSE: The spatial frequency sweep visual evoked potential (sVEP) is used to rapidly determine visual acuity in children or non-responsive patients. Two techniques have been used to separate signal from noise: (1) the 95% confidence interval for the signal amplitude (95% CI) or (2) the amplitude of a Fourier frequency adjacent to 2x the signal frequency (DFT). The purpose of this study is to determine if there is a significant difference in acuity estimates with these techniques. METHODS: Ten normal subjects (approximately 0.00 logMAR acuity) and 11 patients with decreased visual acuity took part in this project. Stimulus production and data analysis were done with an Enfant 4010 (Neuroscientific Corp). Standard VEP recording techniques were employed. The stimulus was a horizontal-oriented, sine wave grating that swept up the spatial frequency spectrum (contrast 80%, temporal reversal rate 7.5 Hz). Sweeps were repeated until the confidence intervals for the data were no longer decreasing. The Bailey Lovie logMAR chart was used to determine visual acuity. A line was fit to the high spatial frequency data using either the 95% CI or the DFT as the noise estimate. By using these linear equations, acuity estimates were obtained at 0, 1, and 2 microV signal amplitudes. RESULTS: The average logMAR acuity for the subjects with normal acuity was -0.06 +/- 0.070 (SD). The sVEP acuity estimates were 0.08 +/- 0.098, 0.18 +/- 0.092, and 0.33 +/- 0.195 (0, 1, and 2 microV extrapolations) with the 95% CI used as noise and 0.07 +/- 0.100, 0.18 +/- 0.103, and 0.33 +/- 0.202 (0, 1, and 2 microV extrapolations) with the DFT used as noise. By using the average noise from the Fourier frequency as the extrapolation level, the acuity was 0.10 +/- 0.098 logMAR. The average logMAR acuity for the subjects with decreased visual acuity was 0.67 +/- 0.306 (SD). The sVEP acuity estimates were 0.53 +/- 0.175, 0.66 +/- 0.171, and 0.88 +/- 0.295 (0, 1, and 2 microV extrapolations) with the 95% CI used as noise and 0.53 +/- 0.179, 0.65 +/- 0.176, and 0.86 +/- 0.268 (0, 1, and 2 microV extrapolations) with the DFT used as noise. By using the average noise from the Fourier frequency as the extrapolation level, the acuity was 0.57 +/- 0.186 logMAR. No significant difference was found between the two acuity estimate techniques for all of the subjects (repeated measures ANOVA, p = 0.16, F20 = 2.131). The sVEP estimates of acuity to the 0 microV and noise levels were not significantly different from the logMAR acuity (paired t-test, all p values > 0.05). CONCLUSIONS: The results indicate that the sVEP acuity does not depend on the noise estimation technique. In agreement with prior studies, the sVEP acuity underestimates the logMAR acuity in normally sighted individuals by about an octave.

Adolescent↗

PubMed2003

The effect of artificial tears on visual performance in normal subjects wearing contact lenses.

PURPOSE: Disruption of the anterior refracting surface of the eye reduces visual performance. In the case of a contact lens wearer, this surface is the prelens tear film. This study determined whether artificial tears stabilize the tear film in contact lens wearers and maintained optimal visual performance for a prolonged period. METHODS: Five normal subjects all in good general and ocular health and adapted to contact lens wear were fitted with Acuvue lenses. A temporal, two-alternative, forced-choice paradigm was used to measure contrast sensitivity. The stimuli were vertically oriented sine-wave gratings (between 0.5 and 14 cpd) presented for 16.67 ms. The stimuli were presented at two different times after blink detection: 2 s after blink detection (i.e., before tear layer break-up) or 4 s after tear film break-up. Three conditions were investigated at 4 s after tear layer break-up: (1) without artificial tears added, (2) with Clerz2 (Ciba Vision) instilled, and (3) with Sensitive Eyes (Bausch & Lomb) applied. The artificial tears were instilled at 10-min intervals during the experimental run. RESULTS: High spatial frequency contrast sensitivity was found to be reduced after tear film break-up and was not enhanced by either tear solution. CONCLUSIONS: This study indicates that there is no effect of Clerz2 or Sensitive Eyes in maintaining or improving visual performance beyond the normal prelens tear film break-up time in normal subjects wearing Acuvue lenses.

Adult↗

PubMed2002

Contact lens drying and visual performance: the vision cycle with contact lenses.

BACKGROUND AND PURPOSE: The purpose of this study was to measure the effect of precontact lens tear film break-up on visual performance. METHODS: Four asymptomatic soft contact lens wearers had contrast sensitivity measured by a temporal, two-alternative, force choice paradigm combined with a self-paced methods of limits. Stimuli were vertically orientated sine wave gratings (0.5 to 14 cycles per degree [cpd] presented for 16.67 ms. Contrast sensitivity was measured before precontact lens tear break-up by a stimuli presented 2 s after the blink. A post-tear layer break-up measurement taken with the stimuli presented after break-up had been observed by the use of a video camera attached to a Tearscope. RESULTS: Contrast sensitivity was found to be reduced following precontact lens tear film break-up for stimuli of 4, 6, and 10 cpd; the data approached significance at 14 cpd. Further reductions in contrast sensitivity were observed for one subject when measurements were continued for 4 s following break-up. CONCLUSIONS: Contrast sensitivity is significantly reduced for middle to high spatial frequencies when the precontact lens tear film dries and breaks up. The combination of observations of visual performance immediately following the blink (from earlier experiments) and measurements following tear film break-up in this experiment allows description of a "vision cycle" for contact lens wearers in the interval between blinks. It is suggested that break-up of the precontact lens tear film could account for the complaints of intermittent blurred vision in some contact lens wearers and may provide a stimulus to blinking in these individuals.

Blinking↗