Browsing by Author "Marsack, Jason D."
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Item Change in visual acuity is well correlated with change in image-quality metrics for both normal and keratoconic wavefront errors(Journal of Vision, 2013-11) Ravikumar, Ayeswarya; Marsack, Jason D.; Bedell, Harold E.; Shi, Yue; Applegate, Raymond A.We determined the degree to which change in visual acuity (VA) correlates with change in optical quality using image-quality (IQ) metrics for both normal and keratoconic wavefront errors (WFEs). VA was recorded for five normal subjects reading simulated, logMAR acuity charts generated from the scaled WFEs of 15 normal and seven keratoconic eyes. We examined the correlations over a large range of acuity loss (up to 11 lines) and a smaller, more clinically relevant range (up to four lines). Nine IQ metrics were well correlated for both ranges. Over the smaller range of primary interest, eight were also accurate and precise in estimating the variations in logMAR acuity in both normal and keratoconic WFEs. The accuracy for these eight best metrics in estimating the mean change in logMAR acuity ranged between ±0.0065 to ±0.017 logMAR (all less than one letter), and the precision ranged between ±0.10 to ±0.14 logMAR (all less than seven letters).Item Characterizing Corneal Biomechanical Properties Using Dynamic Optical Coherence Elastography(2016-08) Vantipalli, Srilatha; Frishman, Laura J.; Twa, Michael D.; Burns, Alan R.; Marsack, Jason D.; Larin, Kirill V.; Miller, William L.Purpose: Optical coherence elastography (OCE) quantifies the tissue’s biomechanical properties through mechanical loading and imaging the tissue response using optical coherence tomography (OCT). Current techniques evaluating corneal stiffness do not account for the influence of key physiological factors on the measured corneal biomechanical properties and either require contact, or create global deformations masking the localized variations: the hallmark of corneal ectasias, e.g., keratoconus. To implement OCE in the cornea, we developed a micro air-pulse stimulator that provides non-contact, dynamic, spatially localized, tissue stimulation. This dissertation determines a) the acute effects of tissue hydration and UV riboflavin cross-linking (CXL) treatment on the corneal ultrastructure, and evaluates the corneal biomechanical properties determined using OCE due to the effect of b) hydration and CXL treatment, c) deep stromal cross-linking treatments and d) in vivo application. Methods: a) Ex vivo de-epithelialized rabbit corneas (n=11) were cross-linked instilling 0.1% riboflavin solution for 30min across the whole cornea and UV irradiation (365nm, 3mW/cm2) to only the temporal half-region for 30min while instilling riboflavin and processed for light and transmission electron microscopy. Corneal thickness and collagen fibril separation computed as the average radial inter-fibrillar distance from the sampled fibril cross-sectional electron micrographs were recorded. b) OCE imaging was performed using phase-sensitive OCT imaging to quantify the tissue deformation dynamics resulting from a spatially discrete, low-force air-pulse (150μm spot size; 0.8ms duration; <10Pa (<0.08mmHg)). The time-dependent surface deformation is characterized by a viscoelastic tissue recovery response, quantified by an exponential decay constant—relaxation rate (RR). Higher RR is consistent with increased stiffness. Hydration influence was determined (n=10) instilling 0.9% saline every 5min for 60min and 20% dextran for another 60min. Measurements were made every 20min to determine central corneal thickness (CCT) and RR. Hydration and CXL effects were determined by obtaining OCE measurements on cross-linked corneas using isotonic (n=6) and hypertonic (n=7) riboflavin. c) OCE measurements were performed (n=10) at: the de-epithelialized stromal surface, 2/3rd corneal depth post-trephination, and after deep stromal cross-linking treatment. Rose bengal green light cross-linking (RGX) using 0.1% rose bengal solution for 20min (n=5) and 10min green light irradiation (565nm, 0.25W/cm2) and CXL treatment (n=5) was performed in the deep stroma. d) In vivo OCE was performed on anesthetized Dutch belted rabbits (n=20) recording within-session (IOP: 10, 20, 30, 40mmHg) and between sessions RR measurements before and after animal re-positioning (10mmHg). Results: a) Corneal thickness decreased significantly (−56%) after CXL treatment. Anterior collagen fibril spacing decreased significantly in the paired CXL treated region (−23%) showing that acute CXL treatment-induced changes are not only tonicity-driven. b) Corneal thickness was positively correlated (R2=0.9) with stiffness. CXL treatment using isotonic riboflavin (CCT: −1%) produced stiffer corneas (higher RR: +10%). However, CXL treatment using hypertonic riboflavin (reduced CCT: −31%) produced a tonicity-driven stiffness decrease that offset the expected stiffer material properties due to CXL treatment, resulting in no significant change in corneal material properties (RR: +6%). c) Deep stromal RGX (RR: +22%) and CXL (RR: +44%) treatments showed significantly stiffer corneas. d) In vivo RR showed excellent measurement precision for within and between session measures. Conclusion: OCE is a promising technique to quantify the corneal biomechanical properties while preserving the intact corneal shape and structure. We demonstrate the influence of hydration, and the modifications due to cross-linking treatments on the corneal ultrastructure and biomechanical properties using OCE methods. The observed excellent measurement precision is critical for in vivo application of OCE in clinical settings. Further development and future application of OCE to derive corneal material properties will allow us to quantify the magnitude of ectatic diseases, the effectiveness of CXL treatment and follow changes over time.Item Clinical Applications and Advancements in the Understanding of Visual Image Quality Metrics(2019-12) Hastings, Gareth Dudley; Applegate, Raymond A.; Marsack, Jason D.; Coates, Daniel R.; Thibos, Larry N.PURPOSE To use the visual image quality metric VSX (the visual Strehl ratio) to optimize objective refraction and to evaluate ophthalmic corrections across modalities (spectacles, conventional and wavefront-guided scleral lenses). In doing so, to identify aspects of VSX that could be evolved towards improving its application to real world conditions as well as to individual eyes. METHODS Five experiments are described. (1) The sphere, cylinder, and axis spectacle corrections that objectively optimized VSX for 40 eyes (20 subjects) were compared with subjective refraction. Visual acuity and short-term preference with the two corrections were also compared. (2) Sphere, cylinder, and axis best-corrected normative values of VSX were determined using the same objective optimization method for 146 eyes (146 subjects) ranging from 20 to 80 years at fixed 7, 6, 5, 4, and 3 mm pupil sizes. (3) VSX as well as higher order root mean square (HORMS) wavefront error, visual acuity, and letter contrast sensitivity, were used to evaluate eyes with corneal ectasia corrected by conventional and wavefront-guided scleral lenses. In the final two experiments, the neural weighting component of VSX was (4) evolved to a model that respects the effects of retinal illuminance and age and (5) personalized using measured neural contrast sensitivity functions (measured using a custom orientation-specific Maxwellian-view laser interferometer) of individual eyes (both typical and those with keratoconus). RESULTS (1) For 36 myopic eyes, the VSX correction provided (statistically and clinically) equivalent visual acuity to subjective refraction and was preferred by 72% of eyes over subjective refraction. In four habitually undercorrected hyperopic eyes, the VSX correction was substantially more positive in power than subjective refraction and was not preferred. (2) Normative best-corrected values of VSX as a function of age and fixed pupil size were published. (3) While aberrations (HORMS), visual acuity, and letter contrast sensitivity reached typical levels for most eyes with ectasia when wearing wavefront-guided scleral lenses, these eyes did not reach the normative values of VSX. While the magnitude of higher-order aberrations was within typical levels, the distribution of residual aberration terms was markedly different. Secondary astigmatism was frequently elevated in these corrected ectatic eyes and is particularly devastating to visual image quality. (4) Best-corrected VSX calculated using the model of neural contrast sensitivity that accounted for both retinal illuminance and age, tracked changes in best-corrected visual acuity as a function of age (from literature) better than using a model that only accounted for retinal illuminance and better than using no neural weighting factor. (5) Measured neural contrast sensitivity functions of typical eyes did not substantially differ from that defined by the model. Eyes with keratoconus showed rotationally-asymmetric sensitivities that were comparable at some orientations to typical eyes in milder stages of disease but decreased (especially at higher spatial frequencies and at particular orientations) as disease severity worsened. Personalizing the neural weighting component of VSX did not make a clinical difference to the optimal sphere, cylinder, and axis correction. Measured neural contrast sensitivity functions of eyes with keratoconus apodize (remove the tails / feet of) the PSF more substantially than the photopic function of typical eyes, which over-estimates the detrimental effects of highly-aberrated optics. CONCLUSIONS The visual image quality metric VSX objectively identified spectacle corrections that were clinically equivalent to subjective refraction for myopic eyes and served as a method of evaluating corrections across modalities that is more robust than residual diopters (over-refraction) and RMS wavefront error. Because measurement of orientation-specific neural contrast sensitivity is time-consuming and the gains over the model (that defines neural contrast sensitivity as a function of retinal illuminance and age) were not clinically significant, it is recommended that the model be incorporated into calculation of the metric.Item Comparison of Toric Orthokeratology and Soft Toric Multifocal Contact Lenses in Managing the Astigmatic Myope(2022-05-11) Tomiyama, Erin S.; Richdale, Kathryn L.; Berntsen, David A.; Marsack, Jason D.; Zadnik, KarlaPurpose: Myopia management is an important intervention to reduce the risk of vision threatening ocular disease. Contact lens treatments for patients with astigmatism include toric orthokeratology (TOK) and soft toric multifocal (STM) lenses. The purpose of this study was to quantify visual performance and the potential for myopia management efficacy with TOK and STM in moderate to high astigmatic patients. Methods: Thirty adults, age 18-39 years, with myopia (plano to -5.00 D) and refractive astigmatism (-1.25 to -3.50 D) were recruited to complete this five-visit crossover study. Subjects wore both TOK and STM lenses in random order for 10±2 days each. After lens wear, visual performance and acceptance was measured with logMAR visual acuity and patient-reported outcome surveys. Peripheral refraction and wavefront aberrometry were measured to determine the lens’ potential impact for myopia management. Results: Adults, who are critical users, preferred STM for cost when forced to choose between the two corrections. Compared to baseline, TOK induced a myopic shift in defocus (M) at all retinal locations except 20 degrees nasal (all p<0.03), but STM only induced a myopic shift at 20 degrees temporal (p<0.03). TOK resulted in more myopic defocus than STM at all locations (all p<0.05) except 20 degrees nasal and temporal in the left eye. Higher-order root mean square wavefront error (5 mm pupil diameter) was significantly increased with TOK (0.64±0.22 µm) and STM (0.48±0.11 µm) from baseline (0.24±0.08 µm, both p < 0.001), and TOK was elevated compared to STM (p = 0.026). Conclusion: TOK induced greater peripheral myopic defocus and higher-order aberrations, which may indicate improved efficacy for myopia management. Adult astigmats preferred the vision with TOK over STM.Item Evaluation of an Objective Visual Image Quality-Based Method to Identify Spectacle Corrections for Individuals with Keratoconus(2019-12) Bell, Elizabeth Shumard; Marsack, Jason D.; Applegate, Raymond A.; Anderson, Heather A.Purpose: Clinical best practice recommends providing every contact lens patient with a pair of spectacles for times when contact lenses cannot be worn. Individuals with keratoconus are often thought of as poor candidates for spectacle correction (with many not receiving a spectacle prescription at all) due to a lack of efficacy of spectacles with this disease. It is our conviction that while spectacles will never be the primary correction modality for the majority of individuals with keratoconus, they may be made more efficacious by evolving the method by which the spectacle prescription is identified. Therefore, this work is designed to examine a novel method by which spectacle prescriptions are identified for individuals with keratoconus. In arriving at a sphero-cylindrical correction for an eye with keratoconus, this alternate method is objective in nature and leverages 1) a quantitative measure of the optical performance of the eye; 2) an approximation of the neural performance of the visual system; and 3) an objective method to search the refractive space in the phoropter. Methods: This work was conducted in two parts. First, a direct comparison was made between this objective method of identifying a spectacle prescription, which is based on visual image quality, and subjective refraction, which is the current clinical standard of care for most patients. Both the objectively and subjectively derived corrections were tested on subjects using standard sphero-cylindrical trial lenses. These particular methods were chosen based on previous work that had shown a visual image quality based objective refraction to be predictive of visual acuity in typical subjects.1,2 The subjective refraction was determined using current best clinical practices (refraction with a phoropter, adjusting step size based on visual acuity, using a Jackson cross cylinder to determine cylinder axis and power when appropriate) beginning from an autorefractor measurement when possible. To assess the relative performance of the two methods of identifying refraction, visual acuity and subjective preference were assessed under varied viewing conditions. Second, having examined the performance of both objective and subjective refractions on individuals with keratoconus, and with an eye towards clinical translation of this method, the performance of the objective sphero-cylindrical refraction was modeled in the presence of a dynamically changing pupil diameter, which would naturally occur under real world lighting conditions. Results were compared to values measured on 100 typical eyes recorded as part of the TINCO study for comparison to a control group. The goal of this second phase of the work was to quantify the predicted change in visual image quality as measured by the visual Strehl ratio (VSX) as the dynamic pupil varied behind a static correction. Results: Data from the first part of this study found that a wavefront-derived objective sphero-cylindrical refraction optimized for the VSX provided equivalent quantitative levels of high contrast visual acuity (HCVA) as a subjective refraction. This is in agreement with previous work on typical eyes.3 However, when asked to identify which form of correction they preferred, individuals chose the objective refraction 76% of the time over a subjective refraction. Having demonstrated a baseline level of utility in the objective method, the second part of the study demonstrated that when applying a correction that was optimized for a 4mm pupil to the same eye when the pupil increased in diameter to 5mm, visual image quality (quantified as logVSX) was reduced by 13.9% for keratoconic wavefronts compared to a 1.8% decrease for a typical eye. Conclusions: In aggregate, the two experiments show the promise of the objective method in identifying a correction that is preferred by the individual, while identifying challenges (a potential variation in visual image quality) associated with the wear of spectacles under real-world conditions. Future work could focus on determining the role adaptation plays in perceived visual preference, determining the optimal phoropter search space and development of a method to increase the speed of calculation necessary to identify the objective refraction.Item Objective Measurement of Spectacle Wear Time with a Temperature Sensor Data Logger(2017-05) Lentsch, Matthew; Anderson, Heather A.; Marsack, Jason D.; Das, Vallabh E.Purpose: Many practitioners and researchers desire to objectively quantify spectacle wear time. The purpose of this study was to evaluate the Smartbutton Data Logger Temperature Recorder for monitoring spectacle wear. Methods: Fifty adults (32 female, 18 male) wore a thermosensor on their spectacles for 2 weeks for each of 2 mount types while keeping wear diaries. Temperatures during reported spectacle wear (ON) were compared to temperatures during non-wear (OFF). The success of two methods to approximate wear time was evaluated by percent error with respect to subject reported wear time. The first filtered temperatures, defining wear time from temperature ranges determined from group or individual mean temperatures calculated during subject-reported ON times. The second utilized examiners interpreting temperature versus time plots to identify spectacle wear. Results: Group mean ON (31.8 ± 0.6 ⁰C) and OFF (24.7 ± 1.5 ⁰C) temperatures differed significantly (p<0.001), female ON temperatures averaged 1⁰C higher than males (p=0.04), and there was no significant difference in temperature between mounts (p=0.18) by repeated measures ANOVA. Median percent error and first and third quartiles (Q1, Q3) of each approximation technique was: group mean filtering = 8% (Q1 3%, Q3 18%), individual mean filtering = 7% (Q1 4%, Q3 19%), examiner 1 = 6% (Q1 2%, Q3 14%), examiner 2 = 7% (Q1 3%, Q3 12%). Evaluation of the most detailed diaries (8 subjects) revealed that brief wear intervals and leaving spectacles in a warm, parked car resulted in higher percent error in approximating wear time. Conclusions: The SmartButton is a promising device to monitor spectacle compliance in patients with all approximation methods evaluated providing less than 10% median percent error in wear time.Item Optical and Visual Performance in Typically-sighted and Highly Aberrated Eyes(2021-08) RIJAL, SUJATA; Marsack, Jason D.; Coates, Daniel R.; Cheng, Han; Vera-Diaz, Fuensanta A.Purpose: This dissertation explores the manner in which typically-sighted individuals and individuals with keratoconus perform simulated, clinical and real-world visual tasks under varying levels uncorrected optical aberration. Methods: Study 1 tested the viability of a common (rather than an eye-specific) decentration rule for placement of wavefront-guided optics in a wavefront-guided scleral lens. Study 2 quantified threshold word acuity with and without accompanying flanking words at high (100%) and low (25%) contrast over 5 stimulus durations for habitually corrected individuals with keratoconus and typically-sighted individuals. Study 3 quantified the limits of agreement and intra-visit repeatability of the CamBlobs2 contrast sensitivity test and compared the results to the near Pelli-Robson contrast sensitivity test in individuals with keratoconus and typically-sighted individuals. Results: Study 1 demonstrated that decentering the wavefront-guided correction from the subject-specific location was predicted to lead to an appreciable increase in residual aberration and reduction in visual image quality. Study 2 demonstrated that there was a trend toward elevated threshold word acuity, when compared to visual acuity (which was more pronounced with near low contrast words). Study 3 demonstrated that in typically-sighted individuals, repeatability of both tests was within ± 0.20 logCS and the limit of agreement between near Pelli-Robson and CamBlobs2 scores was -0.08 ± 0.08 for right eyes and -0.05 ± 0.10 logCS for left eyes. The repeatability worsened to ± 0.30 logCS and the limit of agreement between near Pelli-Robson and CamBlobs2 scores was -0.05 ± 0.14 for the keratoconus group. Conclusions: The wavefront-guided correction must be placed at an eye-specific location to avoid reduction in optical and visual performance predicted to be noticeable to an individual. Larger font sizes are required for word recognition (especially low contrast words) than would be expected from common measurement of high contrast distance visual acuity. Both contrast sensitivity tests were repeatable and with a 0.05 correction, the CamBlobs2 scores showed an excellent agreement with those of the near Pelli-Robson contrast sensitivity test.Item Optical Profiles, Visual Performance, and Modelling Optical Changes with Multifocal Contact Lenses(2023-08) Nti, Augustine Nyarko; Berntsen, David A.; Marsack, Jason D.; Porter, Jason; De Gracia, PabloPurpose: Multifocal contact lenses are increasingly being prescribed for myopia control, and new lens designs are being developed and studied. This series of studies sought to understand the optical profiles of current multifocal contact lenses used for myopia control and how they affect visual performance, and to determine if optical modelling can be used to predict the effect of multifocal lenses on central and peripheral refraction. Methods: Four experiments were conducted. (1) The optical profiles of multifocal contact lenses were measured using a lens profiler. (2) Contrast sensitivity with a single vision and two multifocal contact lenses were measured and compared under photopic and mesopic conditions. (3) Wide-field optical eye models were generated using both measured and published biometry to determine how well these optical models can replicate measured central and peripheral ocular aberrations of individual eyes. (4) The optical eye models were used to predict central and peripheral refraction with a single vision and multifocal contact lens. Results: (1) The NaturalVue Multifocal has an increase in plus power closer to center and incorporates a higher maximum add compared to the Biofinity and Proclear Multifocal “D” lenses. Within each lens design, distance lens power affected add distribution. (2) The NaturalVue and Biofinity “D” contact lenses reduce distance contrast sensitivity under both photopic and mesopic conditions, but do not affect near contrast sensitivity. (3) The optical models developed were able to replicate aberrations of individual eyes, but the models generated by optimizing measured biometry data were more accurate than if optimizing using only published biometry data. (4) Optical eye models were generally able to predict central and peripheral refraction with a single vision and the Biofinity “D” multifocal contact lens to within ±0.25D of refractions measured with an aberrometer, but accuracy was reduced at an eccentricity of 20° on the nasal retina. Conclusion: Multifocal contact lenses differ in the amount and distribution of plus power based on lens design and labelled distance lens power, and these lenses cause reductions in contrast sensitivity. Optical modelling can be used to replicate aberrations of individual eyes and predict changes in peripheral refraction when a multifocal contact lens is worn.Item Optimizing wavefront-guided corrections for highly aberrated eyes in the presence of registration uncertainty(Journal of Vision, 2013-06) Shi, Yue; Queener, Hope M.; Marsack, Jason D.; Ravikumar, Ayeswarya; Bedell, Harold E.; Applegate, Raymond A.Dynamic registration uncertainty of a wavefront-guided correction with respect to underlying wavefront error (WFE) inevitably decreases retinal image quality. A partial correction may improve average retinal image quality and visual acuity in the presence of registration uncertainties. The purpose of this paper is to (a) develop an algorithm to optimize wavefront-guided correction that improves visual acuity given registration uncertainty and (b) test the hypothesis that these corrections provide improved visual performance in the presence of these uncertainties as compared to a full-magnitude correction or a correction by Guirao, Cox, and Williams (2002). A stochastic parallel gradient descent (SPGD) algorithm was used to optimize the partial-magnitude correction for three keratoconic eyes based on measured scleral contact lens movement. Given its high correlation with logMAR acuity, the retinal image quality metric log visual Strehl was used as a predictor of visual acuity. Predicted values of visual acuity with the optimized corrections were validated by regressing measured acuity loss against predicted loss. Measured loss was obtained from normal subjects viewing acuity charts that were degraded by the residual aberrations generated by the movement of the full-magnitude correction, the correction by Guirao, and optimized SPGD correction. Partial-magnitude corrections optimized with an SPGD algorithm provide at least one line improvement of average visual acuity over the full magnitude and the correction by Guirao given the registration uncertainty. This study demonstrates that it is possible to improve the average visual acuity by optimizing wavefront-guided correction in the presence of registration uncertainty.Item Peripheral Autorefraction Repeatability and Peripheral Defocus of Myopic Eyes with Spherical Soft Contact Lenses(2016-05) Moore, Kelly E.; Berntsen, David A.; Manny, Ruth E.; Marsack, Jason D.Purpose: Peripheral retinal defocus has been implicated in the progression of myopia. The purpose of this thesis was to assess the repeatability of peripheral autorefraction, and to determine the effect of commercially-available soft contact lenses on peripheral defocus of myopic eyes. Methods: Twenty-five young adults with spherical equivalent refractions between –0.50 D and –6.00 D were enrolled. Cycloplegic autorefraction of the right eye was measured centrally and ±20°, ±30°, and ±40° from the line of sight along the nasal and temporal retina using a modified Grand Seiko WAM-5500 autorefractor. Experiment 1) The between-visit repeatability of peripheral autorefraction measurements using the Grand Seiko was determined in normal eyes. Measurements were made at two visits separated by 1 to 15 days. Five autorefraction measurements at each location were converted to vector space and averaged. Between-visit repeatability was evaluated by plotting the difference versus the mean of the measurements at the two visits (bias) and by calculating the 95% limits of agreement (LoA). Experiment 2) Four commercially-available spherical soft contact lenses (Biofinity, Acuvue2, PureVision2, and Air Optix Night & Day Aqua) were used to correct each subject. Five measurements per location were converted to power vectors and averaged. Spherical equivalent defocus (M) was used to calculate relative peripheral defocus (RPD) while wearing each contact lens and relative peripheral refraction (RPR) with no lens on the eye by taking the difference between each peripheral measurement and the central measurement. Analyses were conducted using repeated-measures analyses of variance (RM-ANOVA) and Benjamini-Hochberg adjusted post-hoc t-tests, when indicated. Results: The mean age (±SD) and central spherical equivalent refractive error were 24.0 ± 1.3 years and -3.45 ± 1.42 D, respectively. Experiment 1) There was no significant between-visit bias for any refractive component evaluated (M, J0, J45, and RPR) at any location measured (all p > 0.05). The 95% LoA (repeatability) for defocus (M) was ±0.21 D centrally. RPR repeatability decreased with increasing eccentricity to ±0.67 and ±0.82 D at 40 degrees nasally and temporally on the retina, respectively. Experiment 2) PureVision2 did not change relative peripheral defocus (p=0.33). Acuvue2, Biofinity, and Air Optix Night & Day Aqua caused a significant myopic shift on the temporal retina (all p<0.02). Conclusion: With knowledge of the repeatability of on- and off-axis cycloplegic autorefraction with the Grand Seiko, changes in peripheral measurements can be properly interpreted in longitudinal studies. Overall, these results show that the design of spherical soft contact lenses can influence the peripheral defocus profile experienced by a myopic eye. Though spectacles have been reported to increase peripheral hyperopia, several contact lenses tested reduced peripheral hyperopia. Longitudinal studies are required to more fully understand the impact of peripheral defocus on myopia progression and eye shape.Item Quantifying the Optical, Physical, and Predicted Visual Consequences of Daily Cleaning on Conventional and Wavefront-Guided Scleral Lenses(2021-05) Wilting, Sarah; Marsack, Jason D.; Applegate, Raymond A.; Berntsen, David A.Purpose: To test whether an equivalent of 12 months of manual cleaning alters optical aberrations, base curve or predicted visual performance of conventional and wavefront-guided scleral contact lenses. Methods: Twelve scleral lenses (4 repeats of 3 designs, A-C) were manufactured in Boston XO material. Design A: –5.00 D defocus; Design B: –5.00 D defocus with –0.153 µm vertical coma; Design C: –5.00 D defocus with a full custom wavefront-guided (WFG) correction (2nd - 5th Zernike radial orders) of an eye with severe keratoconus. One lens of each design group served as a control and was not cleaned. To simulate a year of cleaning, 7 individuals cleaned 9 lenses (3 from each group) twice a day for 27 days using the palm technique and commercially available cleaners, resulting in 378 cleanings of each lens. Lens aberrations were optically profiled and base curve radii were measured at baseline and after every 42nd cleaning. Differences in higher order root mean square (HORMS) wavefront error (WFE) and base curve radii associated with cleaning were compared to clinical benchmarks using sign tests. Given that aberrations interact with one another, the change over time in the visual Strehl ratio was used to estimate the predicted change in visual acuity associated with manual cleaning. Results: For the experimental lenses, median change in Seidel spherical dioptric power was +0.01D (range: +0.001D to +0.023D). Median change in HORMS WFE was 0.013 µm (range:0.008 to 0.019 µm). Median percent change in HORMS in the three wavefront-guided lenses was 0.96% (max = 1.25%). Median change in base curve radii was 0.00 mm, with all lenses exhibiting changes (P = .002), less than the ANSI tolerance of 0.05 mm. The predicted change in visual acuity derived from the visual Strehl ratio for all coma and wavefront-guided lenses was less than 2.5 letters. Conclusion: Cleaning scleral contact lenses in a manner consistent with the method and number of cleanings that would occur over a 12-month period did not induce clinically significant changes in the optical properties, base curve radii of curvature or predicted changes in visual acuity of conventional or wavefront-guided scleral lenses.Item Repeatability and Validity of the Discovery System(2018-05) Nguyen, Mylan Thi; Berntsen, David A.; Anderson, Heather A.; Marsack, Jason D.Purpose: Evaluating an instrument’s repeatability and agreement are critical when utilizing it in research. The purpose of this thesis was to determine between-visit repeatability of the Discovery System aberrometer and the agreement between measurements made on two different Discovery Systems, a Grand Seiko WAM-5500 autorefractor, and the Complete Ophthalmic Analysis System (COAS-HD) aberrometer. Methods: Twenty-five healthy, young adults participated in two study visits separated by no more than 14 days. At each visit, cycloplegic measurements were made on the right eye. Experiment 1) Five measurements were made using the same Discovery System at two visits. At Visit 2, ten measurements were also made using the Grand Seiko WAM-5500. Discovery System refractive error values were calculated for a 3-mm and 6-mm pupil diameter. Between-visit repeatability and between-instrument agreement were evaluated using difference versus mean plots and calculating the 95% limits of agreement (LoA). Experiment 2) At Visit 2, five measurements were also made on a second Discovery System and the COAS-HD. Instrument order was randomized at each visit. Zernike coefficients were calculated over a 6-mm pupil through the sixth radial order. Between-instrument agreement was assessed using difference versus mean plots and the 95% LoA. Results: The mean age (±SD) and spherical equivalent refractive error were 23.4 ± 1.7 years and -2.91 ± 1.85 D, respectively. Experiment 1) There were no between-visit differences for M, J0, J45, higher-order root mean square (RMS), third-, fourth-, fifth-, and sixth-order RMS (all p > 0.25). Repeatability for defocus and higher-order RMS were ±0.31 D and ±0.095 microns, respectively. For a 3-mm pupil, the Discovery System measured more positive values than the Grand Seiko for M, J0, and J45 (p < 0.005). For a 6-mm pupil, there was no difference between instruments for M (p = 0.45). Experiment 2) There were no differences between the two Discovery Systems for fourth- and fifth-order RMS (all p > 0.39). There was a difference in third-order RMS (p < 0.005, 0.055 microns) and sixth-order RMS (p < 0.05, -0.005 microns) with horizontal coma (C 3, 1) accounting for the majority of the difference (p < 0.001, 0.010 microns). Between the Discovery System and COAS-HD, no differences were found for fifth- and sixth-order RMS, and spherical aberration (all p > 0.10). Differences were found for third-order RMS (p < 0.001, 0.154 microns) and fourth-order RMS (p < 0.05, -0.029 microns). Horizontal coma (C 3, 1) accounted for the majority of the third-order RMS difference between the two instruments (p < 0.001, 0.230 microns). Conclusion: The Discovery System is repeatable and would be an appropriate instrument to measure cycloplegic refractive error and higher-order aberration changes. Although repeatable, this thesis found that Discovery System measurements are not interchangeable with those made on the Grand Seiko or COAS-HD. The designer of the Discovery System is in the process of completing an update to address the between Discovery System differences.Item Tear Exchange and Midday Fogging(2017-05) Skidmore, Kelsea V.; Bergmanson, Jan P.; Miller, William L.; Marsack, Jason D.Purpose: Approximately 30% of scleral gas-permeable lens (SGP) wearing patients are affected by midday fogging (MDF). The purpose of this study was to determine the influence of post-lens tear exchange and other fitting characteristics on the presence or absence of MDF.Methods: 33 subjects were recruited for this study. 23 subjects were habitual SGP wearers (11 MDF, 12 non-MDF subjects), and 10 were non-SGP wearing normal controls. At the study visit, dry eye symptoms were quantified (TERTC DryEye Questionnaire), and lens-fitting characteristics were evaluated using ocular coherence tomography and biomicroscopy. Tear exchange rates were measured using the Fluorotron fluorophotometer. The procedure was to instill high molecular weight fluorescein(FITC) Dextran into the tear film reservoir beneath the SGP, and measure the tear fluid fluorescein concentration every 5-30 minutes over a period of 4 hours. The tear reservoir fluorescein concentrations were plotted to measure the fluorescein decay from within the tear fluid, which was used to calculate the tear exchange rate. Statistical analysis was done using student t-test and ANOVA.Results: In this study, there was less tear exchange in the MDF group (mean: 0.111%) when compared to the nonMDF group (mean: 0.417%), although statistical significance was not reached due to the high variability of the exchange rates (p = 0.26). There was no significant difference between the tear film reservoir thickness in the MDF (283um) and nonMDF (326um)groups (p = 0.53), or with dry eye scores (mean of 29.5 in MDF, 30.4 in nonMDF) (p = 0.91).Conclusions: In this study, there is no clear relationship between the amount of tear exchange during SGP wear and the incidence of MDF. Tear exchange may indeed be a factor, although additional studies are needed to clarify its role, and to further explore other contributing factors that may be involved in modulating the occurrence of MDF.Item The Role of Corneal Astigmatism When Fitting Orthokeratology Contact Lenses(2019-08) Tomiyama, Erin S.; Richdale, Kathryn L.; Marsack, Jason D.; Berntsen, David A.Purpose: About one-third of children aged 5-17 years old have astigmatism. Children with increasing astigmatism can also have an accompanying increase in myopia via axial elongation. All of the randomized clinical trials to date have excluded patients with more than 1.50 D of astigmatism and there are limited data on the success of orthokeratology in patients with moderate to high astigmatism. The purpose of this thesis was to assess the fit of sphere and toric lenses and quantify the amount of corneal astigmatism corrected, and to determine the effect of peripheral elevation and central corneal astigmatism on toric orthokeratology fitting. Methods: Two different studies were performed. The first was a retrospective analysis on 32 eyes of 16 subjects, half fitted with sphere and half with toric orthokeratology lenses. The post-treatment data after 1-3 months of successful nightly wear were compared to pre-treatment data to analyze the change in corneal astigmatism. The second study was a prospective analysis of the Pentacam tomography of 25 moderate refractive myopic astigmats (1.25 to 3.50 DC), ages 19 to 38 years. A subset of 20 subjects were fitted with Paragon Dual Axis Corneal Refractive Therapy (CRT) lenses that were worn for 10 2 days. Results: Three methods of analysis showed that the decrease in corneal astigmatism for the spherical lens group was 0.10 - 0.22 D, which was approximately 22 - 31% correction, and the toric group was 0.29 - 0.57 D, which was 20 - 36% correction (all p < 0.006). There was a strong correlation between central corneal astigmatism and corneal elevation at the 4, 6, and 8 mm chords (r = 0.979, r = 0.961, r = 0.927, respectively; all p < 0.001). After Dual Axis lens wear, the average decentration of the treatment zone from the pupil center was 0.29 ± 0.23 mm temporal and 0.13 ± 0.26 mm inferior. Conclusion: Toric orthokeratology lenses correct slightly more corneal astigmatism than spherical lenses. Central corneal astigmatism was highly correlated to peripheral elevation and may be a more expedient measure for clinical use when fitting toric orthokeratology lenses. The amount of treatment zone decentration with toric lenses was minimal which may lead to better visual performance.Item Visual Interaction of Zernike Aberration Terms from 2nd to 5th Radial Orders with Vertical Coma(2020-08) Hu, Chuan; Marsack, Jason D.; Richdale, Kathryn L.; Berntsen, David A.Purpose: Eyes with keratoconus suffer from an increased level of higher-order aberrations and decreased visual performance, even when corrected by conventional rigid contact lenses. This study aimed to characterize the visual interactions between the dominant residual aberration seen in this population (positive vertical coma: C7) and 2nd to 5th radial order Zernike aberration terms. Methods: The experiment proceeded in two parts. In part 1, individual Zernike aberration terms from the 2nd to 5th radial orders were combined in 0.05 μm steps from -2.00 to +2.00 μm with +1.00 μm of C7. The resulting combinations were used to calculate the visual Strehl ratio (VSX), which was used as a surrogate for the relative beneficial/deleterious impact of the combined condition, compared to C7 alone. For conditions where an interaction was predicted to provide the largest improvement (C6 and C17), high-contrast logMAR acuity charts were constructed to simulate the manner in which the combined condition defines the retinal image of the blurred chart. These charts were then read by three well-corrected, typically-sighted individuals through a 3.0-mm artificial pupil. In part 2, the interactions that were predicted to have a deleterious (rather than beneficial) visual interaction with C7 were characterized in greater detail. Results: In part 1, all aberration-containing conditions led to a reduction in visual image quality compared to the aberration-free condition. Levels of C6, C10, C15, C16, and C17 were identified that resulted in higher visual image quality than was observed with +1.00 μm of C7 alone. The acuities of subjects reading convolved charts had a strong correlation with the predicted performance from simulation (C6: r2 = 0.80, and C17: r2 = 0.76). In part 2, all combinations with C4, C5, C11, C12, C13, C18, and C19 were predicted to have worse logVSX than C7 alone. Conclusion: While most interactions reduced visual image quality, limited combinations provided a clinically relevant beneficial effect in the presence of C7. Future work will examine whether these effects persist as the aberration structure of the eye is made increasingly complex, up to the point it mimics an individual with keratoconus.