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Ohio Lions Eye Research Foundation THE RELATION OF TEAR FILM THINNING TO THE THICKNESS AND DISTRIBUTION OF THE LIPID LAYER Principal Investigator: P. Ewen King-Smith Co-investigators: Jason J. Nichols, Kelly K. Nichols, Barbara A. Fink College of Optometry, The Ohio State University Progress Report Lipid thickness measurements. This work has been performed by Erich Hinel, a graduate student in the College, with advice from Drs. Jason and Kelly Nichols and the Principal Investigator. The aim of the studies was to investigate the relationship between the thinning rate of the tear film between blinks and the thickness of the superficial lipid layer. This layer retards evaporation, which makes a major contribution to tear film thinning. We believe that the thinning of the tear film between blinks, as studied in our experiments, ultimately can cause "tear film breakup" which in turn can cause the ocular surface damage in dry eye conditions; thus we are interested in tear thinning rate because of its clinical implications. An improved method of measuring lipid layer thick was developed and applied, based on measuring the absolute value of the reflectance of the lipid layer as a function of wavelength. A preliminary report of this study "Measurement of the Thickness of the Lipid Layer of the Tear Film Using Reflection Spectra" was made at the 2008 Annual Meeting of ARVO – the Association for Research in Vision and Ophthalmology. Principal findings were:
A manuscript describing these results is currently in preparation. Lipid interferometer development. The measurements described above are based on the assumption that the lipid layer has a uniform thickness within the measurement spot on the tear film (nominally 33 micrometers in diameter, but probably larger on account of aberrations, diffraction and any defocus). Recent evidence indicates that this is not true. It is therefore important to obtain high resolution images of the lipid layer, so that estimates of the spatial variability of the lipid layer within our measurement spot can be made. This new high resolution lipid imaging system, which is supported by the 2007 Ohio Lions Eye Research Foundation grant, is currently being developed. This is a complicated system with 4 optical channels – one of which is used for imaging the lipid layer, two being used for eye alignment, and one being used to monitor the light output from the stroboscopic source. It is intended that all these channels will be imaged on a single video camera (so that, for example, the eye alignment can be checked for any image of the lipid layer). I have recently submitted a grant application to NIH for which the Lions funds have contributed importantly as a seed grant. Presentations Satiani N, Green-Church K, Nichols JJ, King-Smith PE, Nichols KK (2007). Omega 3 fatty acids and dry eye: clinical, interferometric and proteomic considerations. American Academy of Optometry Annual Meeting. Nichols JJ, Hinel E and King-Smith PE (2008) . Lipid Layer Thickness and Tear Film Thinning Before and After Application of a Lipid Emulsion Drop. ARVO annual meeting. King-Smith PE, Hinel E and Nichols JJ (2008) . Measurement of the Thickness of the Lipid Layer of the Tear Film Using Reflection Spectra. ARVO annual meeting. Publications Heryudono, A; Braun, R J; Driscoll, T A; Maki, K L; Cook, L P; King-Smith, P E (2007) Single equation model for the tear film in a blink cycle: realistic lid motion. Mathematical medicine and biology : a journal of the IMA vol. 24, no. 4 347-77. Nichols, JJ, Sinnott, LT, King-Smith, PE, Hidenobu, N, and Sadayasu, T (2008). Hydrogel contact lens binding induced by contact lens rewetting drops. Optom Vis Sci 85, 236-240. Maki KL, Braun RJ, Driscoll TA and King-Smith PE. (2008) A Model of Reflex Tearing Using an Overset Grid Method. Math Med Biol, in press. King-Smith PE, Fink BA, Nichols JJ, Nichols KK and Braun RJ. (2008) Contributions of Evaporation and Other Mechanisms to Tear Film Thinning and Break-Up. Optom Vis Sci, in press Wu D, Boyer KL, Nichols JJ and King-Smith, PE. (2008) Texture based prelens tear film segmentation in interferometry images. Machine Vision and Applications Journal, in press Low Vision Rehabilitation: The Next Important Questions Mark Bullimore, MCOptom, PhD, FAAO Layperson Abstract Low vision is defined as a permanent visual impairment that is not correctable with spectacles, contact lenses, or surgical intervention and that interferes with normal everyday function (Leat et al., 1999). The number of patients with low vision is increasing dramatically as the population ages. Low vision patients are usually prescribed magnifiers, and less often telescopes and more sophisticated devices, and receive limited training in their use. This proposal will compare various approaches to improving the visual performance, and thus the quality of life, in low vision patients. The approaches to be compared are:
Influence of Blur Adaptation on Visual Acuity Vidhya Subramanian Progress report of 2007-08 fellowship-related activities Blur, especially from uncorrected or under-corrected refractive error such as myopia (nearsightedness), is an obvious cause for degraded quality of vision. However, interestingly, a number of studies have shown that the response of the visual system to blur is not static. Adaptation to blur can result in an improvement in visual performance following prolonged periods without refractive correction or with induced refractive blur. These studies have significant clinical implications as blur adaptation possibly may be a way to enhance visual sensitivity in individuals with sub-optimal results following refractive surgery procedures such as LASIK. Also, there have been speculations that if blur adaptation can produce an improvement in vision, perhaps part-time spectacle wear or partial correction may be adequate when correcting patients with myopia. However, differences between the methodologies used and the visual outcome measures obtained across these studies make it difficult to draw firm conclusions about the role of blur adaptation in the management of myopia. In the protocol, for which I had received the 2007-08 fellowship, I had proposed to explore the temporal aspects of blur adaptation. In this study we have tried to assess the influence of two factors on the visual acuity measurements: initial adaptation time and acuity presentation duration. A new rapid, randomized computer-based letter presentation technique, which we had developed, was employed to control for the practice effects and letter viewing time. In this procedure individual letters were presented in a random order, thereby the possibility of perceptual learning to occur is minimal. The study has been successfully completed and below is the brief report.The study was carried on 10 individuals with normal vision (emmetropes) between 18 and 35 years of age following a screening procedure to determine eligibility for participation. To examined the induction of blur adaptation three initial blur exposure durations were employed – 15min, 5min and 1min, with a natural scene as the adapting target. Also the influence of two durations of test target presentation (1.5min and 10min presentations) on blur adaptation was assessed. There was also a condition for measuring visual acuity without any influence of blur adaptation, which served as a comparison for the post-adaptation values. Hence each subject was tested on eight different conditions, one condition per day. During all the eight conditions, a myopic defocus of +1.00D was used. The data was analyzed using the with-in subject repeated measures. The results show that there was no statistically significant influence (p=0.64) of any of the four initial adaptation durations (0min, 1min, 5min and 15min) on the post adaptation visual acuity measure. However, acuity was better (mean = 0.30 logMAR) with 10min acuity presentation times compared to 1.5min presentation times (mean = 0.40 logMAR; p = 0.002). Hence, this result indicates that the test presentation duration had a significant influence on the visual acuity measure. So these results possibly indicate that although blur adaptation might bring about an improvement in visual sensitivity, its enhancement effects might be specific to the test visual target and might not be transferable to normal "out of laboratory" viewing conditions. As the visual acuity outcome is independent of the initial adaptation period, it indicates the possibility of blur adaptation being feature-specific. Presentation that has resulted from the funding: Subramanian, V. and Mutti, D.O. (2008). "Temporal Characteristics of Blur Adaptation." Abstract to be presented at the 2008 meeting of the American Academy of Optometry. I would like to take this opportunity to thank the Ohio Lions Eye Research Foundation for selecting me to receive the fellowship for 2007-08.
Abstract of the work that has been accepted to be presented as a paper at the 2008 meeting of the American Academy of Optometry TEMPORAL CHARACTERISTICS OF BLUR ADAPTATION Vidhya Subramanian, Donald O Mutti College of Optometry, The Ohio State University Purpose: Visual acuity in the presence of blur has been demonstrated to be dynamic; there is an improvement in visual acuity following prolonged periods of uncorrected or induced refractive blur (Mon-Williams et al., 1998). However the influences of the initial blur exposure duration and the test stimuli presentation time on these adaptation effects is less well known. In this study we assess the temporal aspects of blur adaptation by measuring visual acuity following varying initial adaptation and test presentation durations. Methods: Computer-based visual acuity, using Bailey-Lovie optotypes, was measured in 10 emmetropic subjects after adaptation to a natural scene whose amplitude spectrum had a slope of -1.0. All measurements were made monocularly in the right eye. Each subject was exposed to eight different conditions. The eight conditions included 4 initial blur exposure periods of 0min, 1min, 5min and 15min and two visual acuity presentation times of 1.5min (1 sec per letter) and 10 min (21 sec per letter). Myopic defocus of 1D was used during both the initial adaptation period and test stimuli presentations. Results: Repeated measures (within-subjects effects) analysis was performed. The four initial adaptation durations did not show any statistically significant effect on post adaptation visual acuity measure for either of the test presentation times (p = 0.64). However, there was a statistically significant effect of test presentation duration. Acuity was better (mean = 0.30 logMAR) with 10min acuity presentation times compared to 1.5min presentation times (mean = 0.40 logMAR; p = 0.002). Conclusions: Visual acuity was independent of the initial adaptation time, possibly indicating that blur adaptation has a feature-specificity; viewing a blurred generic scene did not improve optotype acuity. However exposures of at least 21 seconds to the letter to be identified resulted in enhanced visual acuity. Such feature specificity might make blur adaptation of limited value in dynamic viewing conditions.Functional Significance of Lacritin, A Novel Tear Film Glycoprotein, In Contact Lens- Related Dry Eye and Meibum and Tear Film Secretion Principal Investigator: Jason J. Nichols, OD, MPH, PhD, FAAO †Co-Investigator: Gordon Laurie, PhD ‡Lacritin is a recently identified glycoprotein associated with the tear film and ocular surface. Initial evidence suggests that it is a prosecretory mitogen, with possible involvement in regulation of lacrimal gland secretion. It has also recently been found in the meibomian gland secretion proteome, and although its functional significance there is unknown, it may play a role in regulation of meibomian gland lipid secretion. The purpose of this proposed work is to test the hypotheses that 1) lacritin expression is reduced in both the tear film and meibum of individuals with contact lens dry eye, and 2) this reduction in lacritin expression in the tears and meibum is associated with a reduced secretion of the tear film and lipid. |
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