James LaMotte

Fluorophotometric measurement of human tear turnover rate

Measurement of tear turnover rate using an automated scanning fluorophotometer (FluorotronR) was compared to Schirmer test results without anesthesia in young adults with no known ocular disorder. After the instillation of fluorescein, tear film fluorescence, expressed as fluorescein concentration equivalent, decreased exponentially in a linear fashion with time. The mean tear turnover rate was 30% per minute. Contact lens wearers had higher mean tear turnover rates when compared with non-contact lens wearers, but differences were not statistically significant. Half of tested eyes demonstrated total wetting of Schirmer Tear Test StripsR. Higher mean tear turnover rates were associated with complete wetting of the Schirmer test strips. There was no significant correlation between Schirmer paper wetting of less than 30 mm and fluorescein turnover rate.

Contrast Sensitivity and Tear Layer Aberrometry in Dry Eye Patients

Purpose. Dry eye disease is a common condition that affects millions of people world wide. The common findings of dry eye disease are blurred vision and tear film instability. The purpose of this study was to determine if long-term use of artificial tears altered visual disturbances and tear film instability of dry eye patients. Methods. Contrast sensitivity and optical aberrations were measured in 22 dry eye and 10 normal patients before and after daily use of artificial tears. The contrast sensitivity and optical aberrations were measured in response to the administration of a single drop of artificial tear placed in the eye. Results. The short-term effect (i.e., a few minutes) of a single drop of artificial tear placed in the eye was a decrease in contrast sensitivity and an increase in optical aberrations. Long-term daily use of the artificial tears (i.e., up to 2 weeks) resulted in less of a short-term effect in dry eye patients. No long-term effect was observed for normal subjects. Both contrast sensitivity loss and optical aberrations decreased by 35% per week of artificial tear use for the dry eye patients suggesting that the changes in contrast sensitivity were the result of optical aberrations. Conclusions. The results suggest that the changes in contrast sensitivity with artificial tear administration were the result of optical aberrations. It appears that long-term use of artificial tears may normalize the tear layer of dry eye disease patients.

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 subjects 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.

Effect of aftermarket automobile window tinting films on driver vision.

This study was conducted to determine the level of automobile window tint that causes a significant reduction of vision for automobile drivers. Contrast sensitivity was measured on 20 participants, of whom 10 were age 20 to 29 years and 10 were age 60 to 69 years, through a stock automobile window (control) and two windows darkened with plastic film. For the younger drivers, a car window with 37% transmittance did not significantly reduce contrast sensitivity, but a darker tint of 18% transmittance reduced contrast sensitivity at higher spatial frequencies. For the older drivers, a tint of 37% transmittance significantly reduced mid-to- high spatial frequency contrast sensitivity. The typical state standard (no tint with less than 35% transmittance) would thus seem to be appropriate for younger drivers; however, further examination of the standard may be necessary in regard to older drivers. Actual or potential applications of this research include guidelines and regulations regarding tinting of automobile windows.

A review of the potential to restore vision with stem cells

Vision research involving stem cells is a rapidly evolving field. Animal experiments have shown that in response to environmental cues, stem cells can repopulate damaged retinas, regrow neuronal axons, repair higher cortical pathways, and restore pupil reflexes, light responses and basic pattern recognition.

The power output of laser pointers : Do they exceed federal standards?

Background. Concern about the safety of laser pointers has increased as these devices have become readily available to the public, which includes children who may use them improperly. According to federal (Food and Drug Administration) standards, laser pointers are class 3a devices, and power output cannot exceed 5.0 mW. Methods. We tested a sample consisting of 29 red diode laser pointers obtained from various sources that were equipped with fresh batteries. Power output was measured with an optical power meter with the sensor 5.0 cm from the laser. The laser was turned on for 60 s and a reading was taken every 10 s. This procedure was repeated five times for every laser. Results. The power output of unaltered lasers ranged from 0.7 mW to a high of 3.9 mW. Alterations to some of the lasers increased the output slightly above 5.0 mW. Conclusions. When the laser pointers in our sample were used as packaged, they did not exceed the federal standards of 5.0 mW.

Emerging options for the management of age-related macular degeneration with stem cells

Age-related macular degeneration (AMD) is a devastating retinal disease that occurs in later life as the retinal pigment epithelium (RPE) cells die, with subsequent photoreceptor degeneration. In the past, RPE transplant surgeries gave evidence that AMD was potentially treatable, but it involved limited amounts of ocular tissue, and the complication rate was high. Then, stem cell transplants offered an unlimited supply of retinal precursors for endogenous repair and exogenous cell replacement. Debate continues as to which type of stem cell is most appropriate for treating AMD. The prospects include adult-derived progenitor stem cells (including progenitor cells from ocular tissues), hematopoietic stem cells, embryonic stem cells, and induced pluripotent stem cells. Now the therapy is expanding into phase I human trials. This review examines the collective research contributions toward a clinical model of AMD management with stem cells.

Absorption of ammonia by high water content hydrogel lenses: an inexpensive method of analysis.

Few studies have been done on the absorption and release of chemical vapors by high water content hydrogel lenses. In this study we investigated the absorption of ammonia vapors by this type of contact lens (CL). Ten high water content hydrogel lenses were exposed to vapor generated in a cuvette by 1 drop of aqueous ammonia. The contact lens was transferred to a 0.9% saline solution containing a colorometric indicator for ammonia and the amount of ammonia released into the saline was measured. We found that significant quantities of ammonia were absorbed into the lenses and the relation between average concentration of ammonia vapor and amount absorbed per contact lens was nearly linear from 50 parts per million (ppm) to 250 ppm ammonia vapor. For concentrations greater than 250 ppm there appears to be a saturation effect. Our findings indicate that high water contact lenses will absorb ammonia and release it into a solution similar to tears.