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Biomedical subjects

Kenneth A Polse

Publications and source records attributed to Kenneth A Polse.

8 recordsLinked to original sources
PubMed2006

Scalloped channels enhance tear mixing under hydrogel contact lenses.

PURPOSE: Tear exchange under a soft contact lens is directly related to the amount of lateral and transverse lens motion. Hydrodynamic modeling suggests that channels placed on the back surface of a soft lens will reduce fluid resistance and increase transverse lens movement. This study measured the effect of posterior lens surface scalloped channels on tear exchange. METHODS: Tear exchange in the postlens tear film (PoLTF) was estimated using a fluorometer to measure the exponential depletion of high-MW fluorescein under the lens expressed as the time to deplete 95% of dye (T95). A total of 32 subjects wore two pairs of identical lenses except that the experimental lens had 12 scalloped channels placed radially in the midperiphery of the posterior lens surface, whereas lenses without channels served as controls. RESULTS: The mean +/- standard error T95 values for the channel lenses was 28 +/- 2 minutes compared with 32 +/- 2 minutes for the control lenses (p = 0.107). There was a marginally significant difference in T95 between two lens groups in Asian eyes (p = 0.054). CONCLUSION: Placing scallop-shaped channels on high-H2O content soft lenses improved the postlens tear pumping in Asian eyes.

Adolescent↗
PubMed2005

Morphometry of cells and guttae in subjects with normal or guttate endothelium with a contour detection algorithm.

PURPOSE: To develop a semiautomatic method to analyze morphology of cells and guttae in corneal endothelium. METHODS: Specular endothelial pictures from 42 and 21 subjects with healthy and guttate corneas, respectively, were analyzed independently by two observers with cell contour-extracting routines. One observer also analyzed healthy endothelia with the Corner method (Bambi). Differences between observers and between methods in mean cell area (MCA), coefficient of variation (CV), and percentage of cells with five, six, or seven sides were tested for significance with paired t tests. The Contour analysis of pictures with guttae included their mean area. RESULTS: There were no significant differences in MCA, CV, or the percentage of cells with five, six, or seven sides between the measurements obtained on repeated analysis by the same observer or on a second analysis performed by a different observer with the Contour method. However, the differences between the Contour and Bambi methods were statistically significant for MCA (337.5 +/- 37.7 vs. 327.7 +/- 36.5), CV (0.32 +/- 0.05 vs. 0.30 +/- 0.05), and percentage of cells with six and seven sides, but not for the percentage of five-sided cells. In subjects with guttata, the MCA was 561 +/- 170 microm, and the mean area of guttae was 1,538 +/- 849 microm. CONCLUSIONS: This detection algorithm is repeatable and reproducible, and it generates a cell border overlay useful in analyzing the morphology of cells and guttae. The analysis of corneal guttae could become a useful follow-up procedure to discriminate between patients with corneal guttata and Fuchs dystrophy.

Adult↗
PubMed2003

Soft contact lens extended wear affects corneal epithelial permeability: hypoxic or mechanical etiology?

Contact lens extended wear increases the permeability of epithelium to sodium fluorescein (P(dc)). The exact mechanism is not known. However, changes in P(dc) likely result from either corneal hypoxia or mechanical trauma, or both. We explored the effects of one-night continuous wear with either high- or low-Dk/t soft lenses on P(dc). The results show that corneal epithelial barrier function decreases significantly with both lens groups. We also observed that Asian eyes had higher P(dc) after overnight wear compared to non-Asian and that for both Asian and non-Asian eyes, the elimination of corneal hypoxia did not prevent changes in epithelial permeability.

Journal Article↗
PubMed2003

The effects of ocular and lens parameters on the postlens tear thickness.

PURPOSE: To assess the effects of soft contact lens base curve radius (BCR), sex, ethnicity, central corneal curvatures, and vertical palpebral aperture size (PAS) on the postlens tear thickness (PLTT). METHODS: The PLTT was measured using optical pachometry on 114 experienced lens wearers who were fitted with lathe-cut soft lenses (Alden 47, polymacon, 35.5% H2O, -2.00 diopter, and 14.0 mm). Each subject was randomly allocated to one lens group receiving a BCR of 7.9, 8.3, or 8.7 mm. Pachometry measurements were taken at 30 min after lens insertion. Vertical PAS and keratometry readings were measured for 94 of the 114 subjects. RESULTS: The mean (95% confidence interval) PLTT was 15.7 microm (13.2-18.0 microm), 12.8 microm (10.9-14.7 microm), and 12.1 microm (10.2-14.0 microm) for the 7.9-mm, 8.3-mm, and 8.7-mm BCR groups, respectively. The differences in PLTT among the three BCR groups was significant (analysis of variance F-test; P=0.039). Post hoc testing using the Tukey honestly significant difference statistic showed that only the two extreme BCR groups (7.9 mm and 8.7 mm) were significantly different. Sex had no effect on the PLTT; however, the PLTT was significantly thinner for the Asian compared with non-Asian eyes (P=0.0001). The Asian PLTT did not vary with different soft lens BCRs. The non-Asian PLTT was thicker with lenses of the steep BCR compared with the flat BCR. CONCLUSION: These results show that the base curve radius of a soft contact lens and several ocular characteristics can affect the thickness of the postlens tear film.

Adult↗
PubMed2003

Fenestrations enhance tear mixing under silicone-hydrogel contact lenses.

PURPOSE: Extended wear of conventional hydrogel soft contact lenses (SCLs) is associated with adverse ocular responses. Some of these ocular events are thought to result from inadequate tear mixing in the postlens tear film (PoLTF). Therefore, strategies to increase tear mixing may improve the safety of extended-wear SCLs. Recently, it has been suggested that placing fenestrations in soft lenses increases tear mixing. In the present study, hydrodynamic modeling and tear-mixing measurements were used to explore the effects of fenestrations on tear exchange under an SCL. METHODS: Tear mixing, expressed as the time to deplete 95% of fluorescent dye from the PoTLF (T(95)), was measured in 20 subjects fitted with two pairs of silicone hydrogel SCLs. The lenses were identical except that one pair was fenestrated (F) with 40 holes each 100 microm in diameter. The effect of fenestrations on improving tear mixing is explained and enhancement of tear mixing is predicted, with the use of hydrodynamic modeling. RESULTS: T(95) estimates were significantly lower (P < 0.001) in the F (mean T(95) = 18.3 minutes) lenses compared with the standard unfenestrated (S-uF) (mean T(95) = 22.6 minutes) lenses (DeltaT(95) = 4.3 minutes, 95% CI = 2.5-6.2) and were in general agreement with the proposed mixing model. Optimization of tear mixing can be achieved by selectively placing fenestrations in the pooling regions before the thinnest regions. The model predictions were sensitive to the distribution of tear-film thickness under the lens. CONCLUSIONS: Fenestrations improve tear-mixing efficiency. Accurate prediction of the effects of lens parameters on tear mixing, however, demands quantitative measurement of the postlens distribution of tear-film thickness.

Adolescent↗
PubMed2002

Black-line formation and the "perched" human tear film.

Introduction. McDonald and Brubaker(1) observed that after instillation of fluorescein, dark lines appear near the upper and lower lid margins of the human eye immediately following a blink. Methods. This paper numerically models the dynamic black-line formation under the lubrication approximation at low Reynolds number, including gravity and surface tension forces. Results. The hydrodynamic model predicts that menisci at the lid margins draw liquid from the tear film, resulting in local thinning close to the lids (i.e., black lines) due to capillary suction. Once the film thins locally, resistance to further thinning increases. No vertical gravity-induced drainage occurs between blinks, and the tear film is trapped in its initially deposited state or "perched" between the two black lines. Conclusions. We demonstrate quantitatively that due to rapid formation of black lines, the tear film is trapped for extended periods. Lid action is therefore required to disturb the perched tear film.

Adult↗
PubMed2002

Impact of rigid gas-permeable contact lens extended wear on corneal epithelial barrier function.

PURPOSE: To measure the effect of hypoxia and eye closure on epithelial permeability to fluorescein (P(dc)) during rigid lens extended wear (EW). METHODS: Central corneal thickness (CT) and P(dc) were measured in 42 subjects with an optical pachometer and automated scanning fluorophotometer, respectively. All subjects had been successfully wearing rigid gas-permeable (RGP) lenses on a 6-night EW regimen, and each individual was randomized to wear either medium- or high-oxygen-permeable (Dk) RGP lenses (two types of siloxane-fluorocarbon polymer lenses with Dk of 49 and 92). CT and P(dc) measurements were performed at an afternoon visit (baseline) and were repeated in the morning after 8 hours of overnight wear. Subjects slept with a patch over the right eye. The patch was not removed until immediately before the morning measurement. RESULTS: The mean overnight swelling response for subjects in the medium-Dk group was greater than that in the high-Dk group. Results of a paired t-test indicate that the eye wearing the medium-Dk lens with a patch overnight had a significant increase in epithelial permeability. Results of mixed-effect models suggest that eye closure and lens-induced hypoxia are significant factors in altering P(dc). CONCLUSIONS: The results indicate that corneal epithelial permeability increases with hypoxic dose and that epithelial barrier function is impaired by overnight rigid lens wear.

Adult↗