Peer-reviewed Articles

Please use the archived list on the right to look at past peer-reviewed articles.

2006

Begley,C. G., Himebaugh,N., Renner,D., Liu,H., Chalmers,R., Simpson,T., Varikooty,J. Tear breakup dynamics: A technique for quantifying tear film instability. Optometry and Vision Science 2006;83,1:15-21. [ Show Abstract ]

PURPOSE: The purpose of this study was to develop a novel, quantitative measurement of tear film breakup dynamics (TBUD) to study the phenomenon of tear breakup in dry eye and control subjects and its impact on dry eye symptoms. METHODS: Ten control and 10 dry eye subjects completed the Dry Eye (DEQ) and other questionnaires. After the instillation of sodium fluorescein, subjects kept the tested eye open for as long as possible, similar to a staring contest, while tear film breakup was videotaped (S-TBUD). The maximum blink interval (MBI) and tear breakup time (TBUT) were measured from digital movies by a masked observer. Individual frames of movies were converted to gray-scale images, maps of relative tear film fluorescence were generated, and the total area of tear breakup (AB) of the exposed cornea was quantified. RESULTS: On average, dry eye subjects demonstrated a higher AB and shorter TBUT and MBI, but only the AB was significantly different (p = 0.023). Subjects most often used the descriptors stinging and burning to describe their sensations during staring trials. The AB showed a high correlation between eyes and with some DEQ symptom measures. CONCLUSIONS: These methods allow objective quantification and tracking of the phenomenon of tear breakup. Our results suggest that tear breakup stresses the corneal surface, resulting in stimulation of underlying nociceptors. The tear film of dry eye subjects was less stable than controls. They had a larger AB measured from the last video frame before MBI (i.e., just before blinking) than did controls. This perhaps reflects adaptation to the repeated stress of tear instability in dry eye.

Dumbleton,K., Keir,N., Moezzi,A., Feng,Y., Jones,L., Fonn,D. Objective and subjective responses in patients refitted to daily-wear silicone hydrogel contact lenses. Optometry and Vision Science 2006;83,10:758-768. [ Show Abstract ]

PURPOSE. Silicone hydrogel (SiH) lenses offer many physiological advantages for daily wear (DW) in addition to the continuous-wear modality for which they were originally developed. The purpose of this study was to investigate the clinical performance and physiological responses in a group of successful long-term wearers of conventional hydrogel lenses when refitted with DW SiH contact lenses. METHODS. Eighty-seven successful soft lens wearers (8.4 ± 4.7 years of prior lens wear) participated in this study. Bulbar and limbal hyperemia were subjectively graded and digitally photographed for subsequent masked objective evaluation. Subjective symptoms were scored using visual analog scales. In addition, refractive error, corneal curvature, and corneal thickness were measured. All subjects were refitted with Focus Night & Day (lotrafilcon A) SiH lenses; however, to reduce the potential for bias, they were informed that they were being randomly assigned to wear either low oxygen permeability (Dk) lenses or high Dk SiH lenses and were "masked" as to their lens assignment. Subjects returned after 1 week, 1 month, and 2 months of DW, at which time all gradings, photographs, and measurements were repeated. End-of-day subjective symptoms were also graded periodically during the study. RESULTS. Ninety-three percent of subjects were successfully refitted. Both objective and subjective evaluations showed that bulbar and limbal hyperemia decreased significantly in all quadrants during the study (p < 0.001), particularly for those subjects with greater baseline hyperemia (p < 0.001). Subjects reported a concurrent reduction in end-of-day dryness and improved end-of-day comfort compared with their habitual lenses (p < 0.001). No significant changes in refractive error, tarsal papillary response, corneal curvature, or corneal thickness were found during the study. CONCLUSIONS. Hyperemia in contact lens wearers may be attributed to a number of factors, including hypoxia. Refitting existing low Dk lens wearers with SiH lenses on a DW basis can result in a decrease in hyperemia, which may be significant for some subjects and also results in improvements in symptoms of dryness and discomfort. © 2006 American Academy of Optometry.

Haque,S., Simpson,T., Jones,L. Corneal and epithelial thickness in keratoconus: A comparison of ultrasonic pachymetry, Orbscan II, and optical coherence tomography. Journal of Refractive Surgery 2006;22,5:486-493. [ Show Abstract ]

PURPOSE: To compare corneal thickness measurements in individuals with keratoconus using optical coherence tomography (OCT), Orbscan II, and ultrasonic pachymetry and to measure epithelial and stromal thickness in these individuals using OCT. METHODS: Twenty individuals with keratoconus and 20 controls (without keratoconus) were enrolled. The Orbscan II was used to locate the steepest area of the cornea, which was taken to represent the cone apex. Each instrument was used to obtain four total corneal thickness measurements-from the cone apex, corneal center, mid-nasal, and mid-temporal cornea. Optical coherence tomography scans were analyzed to provide epithelial and stromal thickness readings. RESULTS: In individuals with keratoconus, mean central corneal thickness (CCT) measured by ultrasonic pachymetry, Orbscan, and OCT was 494.2±50.0 μm, 438.6±47.7 μm, and 433.5±39.7 μm, respectively. The central keratoconic cornea was 57.7 μm thinner than the normal cornea (post-hoc P.05). CONCLUSIONS: Ultrasonic pachymetry produced the highest corneal thickness readings in the center and apex, compared to Orbscan II and OCT. Centrally, the total cornea, epithelium, and stroma were thinner in individuals with keratoconus than in normal individuals.

Lu,F., Simpson,T., Fonn,D., Sorbara,L., Jones,L. Validity of pachymetric measurements by manipulating the acoustic factor of Orbscan II. Eye and Contact Lens 2006;32,2:78-83. [ Show Abstract ]

PURPOSE. To assess the validity of pachymetric measurements by examining the constancy of the acoustic factor (AF) of the Orbscan II (Orbtek, Bausch & Lomb, Rochester, NY) after overnight rigid gas-permeable (RGP) contact lens wear. METHODS. Twenty participants wore CRT (Paragon Vision Sciences, Mesa, AZ) HDS 100 contact lenses on one eye and control lenses on the contralateral eye for one night while sleeping. Another 24 participants wore CRT lenses on both eyes for one night. Central corneal thickness was measured using optical coherence tomography and Orbscan II on the night before lens use, immediately after lens removal on the following morning, and 1, 3, 6, and 12 hours later. By using optical coherence tomography as a reference, the adjusted AF was calculated by using a least squares method over time. RESULTS. The adjusted AF depended on the corneal thickness in normally hydrated corneas. The adjusted AF and the percentage change of the adjusted AF varied before and after overnight lens wear. There was a strong and significant correlation between the corneal swelling and the percentage change of the adjusted AF (all r at least 0.91, P<0.05). CONCLUSIONS. The adjusted AF is a variable, not a constant. The AF is a function of the corneal thickness and its alteration with, for example, corneal swelling. The validity of the adjusted Orbscan II pachymetric measures using a single AF is untenable. © 2006 Lippincott Williams & Wilkins, Inc.

Moezzi,A. M., Fonn,D., Simpson,T. L. Overnight corneal swelling with silicone hydrogel contact lenses with high oxygen transmissibility. Eye and Contact Lens 2006;32,6:277-280. [ Show Abstract ]

PURPOSE. To compare central corneal swelling after 8 hours of sleep in eyes wearing 2 different silicone hydrogel lenses with high oxygen transmissibility. METHODS. Twenty neophyte subjects were randomly assigned to wear a comfilcon A lens (CooperVision Inc) in one eye and a lotrafilcon A lens (CIBA Vision) in the contralateral eye for an 8-hour overnight period. The study was repeated with another 20 neophyte subjects wearing comfilcon A in one eye only and no lens in the contralateral control eye. Central corneal thickness was measured with optical pachometry before lens insertion, immediately after lens removal on waking, at 20 and 40 minutes, 1 hour, 2 hours and 3 hours. RESULTS. There was no significant difference between the amount of overnight central corneal swelling induced by the 2 lenses (4.1% ± 1.9% with comfilcon A vs. 4.0% ± 1.7% with lotrafilcon A; P>0.05). The swelling of the comfilcon A lens-wearing eyes was significantly higher than that found in the non-lens-wearing contralateral eyes (4.5% ± 2.1% vs. 3.0% ± 1.7%; P<0.05). CONCLUSIONS. The same amount of overnight corneal swelling was induced by the 2 study lenses. The higher overnight swelling observed with the comfilcon A lenses compared to the non-lens-wearing eyes is similar to that reported in the literature for studies using lotrafilcon A lenses. © 2006 Lippincott Williams & Wilkins, Inc.

Moezzi,A. M., Sin,S., Simpson,T. L. Novel pachometry calibration. Optometry and Vision Science 2006;83,6:E366-E371. [ Show Abstract ]

PURPOSE: The purpose of this study was to develop a simple method for cross-calibrating instruments that measure corneal thickness. METHODS: Fourteen rigid lenses of different thicknesses were manufactured using a material with refractive index of 1.376. Center thickness of the lenses (CT) was measured using a computerized optical pachometer (OP), two optical coherence tomographers (OCTs), and a confocal microscope (CM). Accuracy of measurements was compared between the four instruments. RESULTS: Before calibrating the machines, there was a significant effect of the measurement device (p < 0.05). The differences between instruments were eliminated (p > 0.05) after applying calibration equations for each device. In addition, after each instrument was calibrated with lenses of 1.376 refractive index, there was no significant difference (p > 0.05) between measured values of lens center thickness by OP, each OCT, CM, and the physical center thickness of the lenses. CONCLUSIONS: Using calibration lenses with the same refractive index as the cornea (1.376) allows rapid and simple calibration of the pachometers so that corneal thickness measurements from different devices can be used interchangeably.

Sin,S., Simpson,T. L. The repeatability of corneal and corneal epithelial thickness measurements using optical coherence tomography. Optometry and Vision Science 2006;83,6:360-365. [ Show Abstract ]

PURPOSE.: The purpose of this study is to examine within and between session repeatability of clinical optical coherence tomography (OCT) imaging for anterior segment morphometry. METHODS.: Images of the corneal apex of each eye in 18 subjects were obtained using a Humphrey Zeiss OCT imager. Subjects viewed a target positioned to ensure that scans were orthogonal to the ocular surface and each image, consisting of 100 adjacent sagittal scans, analyzed using custom software. Repeatability data were analyzed using intraclass correlation coefficients (ICCs), correlation coefficient of concordance (CCC, perfect test-retest agreement ICC or CCC = 1.0), and coefficients of repeatability (COR, 95% confidence interval of test-retest differences). To account for each eye, the multivariate repeatability statistic Iota was estimated. RESULTS.: Mean central corneal and epithelial thickness of 32 eyes (OD and OS combined) is 536 ± 26 μm (standard deviation [SD]) and 52 ± 3 μm (SD) with 5th and 95th percentile thicknesses of 507 and 591 μm for central cornea and 48 and 57 μm for central epithelial. Worst case within session repeatability was defined as repeatability between images with greatest differences in mean thickness within a session. Corneal thickness worst case ICC was 0.95 and COR was ± 9.98 μm. Epithelium worst case ICC was 0.36, CCC was 0.12, and COR was ± 11.11 μm. First image between session corneal thickness had an ICC = 0.98 and a COR = 10.83 μm, whereas epithelium ICC = 0.38, CCC = 0.37, and COR was ± 12.84 μm. When we compared the average of the first three tests with the first three retest images, corneal ICC was 0.98 and COR was ± 10.64 μm and epithelium ICC = 0.73, CCC = 0.72, and COR was ± 6.53 μm. Iota (multivariate repeatability, using eye as a factor) for the cornea was at least 0.96 (worst case) and increased to at least 0.98 when within-session image data were averaged. Iota for epithelium measures ranged from 0.29 when first images were compared with 0.57 when within-session image data were averaged. CONCLUSIONS.: There is very good repeatability of corneal thickness measurement using OCT; even the worst case measurements are similar between sessions. On the other hand, this is not the case for epithelium measurements, and if multiple images within a session are acquired, the worst case results demonstrate how important it is to optimize each OCT scan and also average multiple scans to maximize intersession repeatability. Copyright © 2006 American Academy of Optometry.

Subbaraman,L. N., Bayer,S., Glasier,M. -A, Lorentz,H., Senchyna,M., Jones,L. Rewetting drops containing surface active agents improve the clinical performance of silicone hydrogel contact lenses. Optometry and Vision Science 2006;83,3:143-151. [ Show Abstract ]

PURPOSE: The purpose of this study was to investigate the impact of using a rewetting drop (RWD) containing surface active agents (OPTI-FREE RepleniSH; Alcon, Fort Worth, TX) on the clinical performance and protein deposition when using a continuous-wear (CW) silicone hydrogel (SH) contact lens. METHODS: Subjects wore lotrafilcon A SH lenses on a 30-day CW basis for two consecutive 1-month periods while inserting either 0.9% unpreserved unit-dose saline (control) or multidose OPTI-FREE RepleniSH (test RWD). Subjective comfort and symptoms were assessed after 2 and 4 weeks with each product. After 1 month of wear with each product, lenses were collected and analyzed in the laboratory for total protein, total lysozyme, and percentage of denatured lysozyme. RESULTS: Symptoms of dryness and comfort varied across the day regardless of drop type (p < 0.001) with dryness being maximal on waking, least in the middle of the day, and increased towards the evening. The test RWD provided greater comfort on insertion (p = 0.02), better visual quality (p < 0.01), and less mucous discharge on waking (p = 0.02) than the control product. Lysozyme deposition was significantly reduced after the use of the test RWD as compared to saline (0.73 +/- 0.5 microg/lens vs. 1.14 +/- 0.7 microg/lens; p < 0.001) as was total protein deposition (1.17 +/- 0.7 microg/lens vs. 1.86 +/- 0.8 microg/lens; p < 0.001). Lysozyme denaturation was also reduced with the use of the test RWD compared with the control (76 +/- 10% vs. 85 +/- 7%; p < 0.01). CONCLUSIONS: The use of a RWD containing surface active agents provided greater subjective satisfaction, reduced lysozyme and total protein deposition, and reduced denatured lysozyme than a RWD containing saline alone.

Subbaraman,L. N., Glasier,M. -A, Senchyna,M., Sheardown,H., Jones,L. Kinetics of in vitro lysozyme deposition on silicone hydrogel, PMMA, and FDA groups I, II, and IV contact lens materials. Current eye research 2006;31,10:787-796. [ Show Abstract ]

We sought to compare the kinetics of in vitro lysozyme deposition on silicone hydrogel (SH), polymethyl methacrylate (PMMA), and FDA groups I, II, and IV contact lenses. Lenses were incubated in 125I-labeled lysozyme for time periods ranging from 1 hr to 28 days, and radioactive counts were determined. SH lenses and PMMA deposited less lysozyme than conventional hydrogel lenses (p < 0.05). Lysozyme accumulation on group IV lenses reached a maximum on the seventh day and then plateaued, whereas on groups I, II, and SH lenses, deposition continued to increase across all time periods, reiterating that kinetics of lysozyme deposition is highly material dependent.

Teichroeb,J. H., Forrest,J. A., Ngai,V., Jones,L. W. Anomalous thermal denaturing of proteins adsorbed to nanoparticles. European Physical Journal E 2006;21,1:19-24. [ Show Abstract ]

We have used localized surface plasmon resonance (LSPR) to monitor the structural changes that accompany thermal denaturing of bovine serum albumin (BSA) adsorbed onto gold nanospheres of size 5nm-60nm. The effect of the protein on the LSPR was monitored by visible extinction spectroscopy. The position of the resonance is affected by the conformation of the adsorbed protein layer, and as such can be used as a very sensitive probe of thermal denaturing that is specific to the adsorbed protein. The results are compared to detailed calculations and show that full calculations can lead to significant increases in knowledge where gold nanospheres are used as biosensors. Thermal denaturing on spheres with diameter > 20 nm show strong similarity to bulk calorimetric studies of BSA in solution. BSA adsorbed on nanospheres with d ≤ 15nm shows a qualitative difference in behavior, suggesting a sensitivity of denaturing characteristics on local surface curvature. This may have important implications for other protein-nanoparticle interactions. © EDP Sciences, Società Italiana di Fisica and Springer-Verlag 2006.