Zernike polynomials are often used as an expansion of corneal height data and for analysis optical wavefronts. Accurate modeling surfaces with involves selecting the order polynomial based on measured data. We have compared efficacy various classical model selection techniques that can be utilized this purpose, propose approach bootstrap. First, it is shown in simulations bootstrap method outperforms techniques. Then, proved technique most appropriate context fitting to elevation data,...

To compare the repeatability within anterior corneal topography measurements and agreement between with Pentacam HR rotating Scheimpflug camera a previously validated Placido disk-based videokeratoscope (Medmont E300).Contact Lens Visual Optics Laboratory, School of Optometry, Queensland University Technology, Brisbane, Queensland, Australia.Normal eyes in 101 young adult subjects had measured using (6 repeated measurements) (4 measurements). The best-fitting axial power spherocylinder was...

Purpose. To investigate static upper eyelid pressure and contact with the ocular surface in a group of young adult subjects. Methods. Static was measured for 11 subjects using piezoresistive sensor attached to rigid lens. Measures were derived from an active cell (1.14-mm square) beneath central margin. region between surface, authors used pressure-sensitive paper lissamine-green staining Marx's line. These measures, combined readings, derive estimates pressure. Results. The mean width...

Purpose To investigate the changes occurring in axial length, choroidal thickness, and anterior biometrics of eye during a 10-minute near task performed downward gaze. Methods Twenty young adult subjects (10 emmetropes 10 myopes) participated this study. measure ocular gaze, an optical biometer was inclined on custom-built height- tilt-adjustable table. Baseline measures were collected after each subject distance primary gaze control for minutes to provide washout period previous visual...

In this study we evaluated the accuracy and precision of three placido-disk videokeratoscopes (the Keratron, Medmont TMS) one videokeratoscope that uses raster-stereogrammetry technique (PAR-CTS) in elevation topography with six test surfaces. The surfaces were a sphere, an asphere, multicurve, bicurve Each instrument performed well on certain surfaces, but none instruments excelled all results showed high Keratron measuring multicurve not high. TMS PAR-CTS poorer than for surface better...

Purpose. Videokeratoscopes provide a wealth of information about the topography ocular surface. Although there have been numerous studies accuracy and precision videokeratoscopes with inanimate test objects, little exists on their (repeatability) for real eyes. Methods. To investigate stability surface in inter-blink period, 10 patients were recruited videokeratoscopy. Tear break-up time was measured videokeratographs acquired immediately post-blink again at 4, 8, 12 seconds post-blink....

Abstract With the increased popularity of wavefront sensor devices there has been significant interest in relating subjectively measured sphero‐cylindrical refractive error to objectively aberrations. We investigate applicability four different measures for objective refraction assessment that are derived from a set estimated Zernike coefficients. Two based on second‐ and higher‐order polynomials while other two dioptric power representations. For latter, closed‐form expressions powers focal...

We consider analytical modeling of the anterior corneal surface with a set orthogonal basis functions that are product radial polynomials and angular functions. Several candidate were chosen from repertoire in unit circle invariant form respect to rotation about origin. In particular, it is shown referred herein as Bhatia-Wolf polynomials, represents better more robust alternative for elevation data than traditionally used Zernike polynomials. Examples given normal corneas abnormal...

It is known that eyelid pressure can influence the corneal surface. However, distribution of and contact area biomechanics changes are unknown. Although these factors difficult to directly measure, analysis eyelid-induced topographic morphometry enables some inferences be drawn.Eighteen subjects, aged between 19 29 years, with normal ocular health were recruited. Corneal measured after 4 conditions consisting 2 downward gaze angles (20 40 degrees) types visual tasks (reading steady...

High-speed videokeratoscopy (HSV) is an emerging technology that has the potential to acquire information on dynamics of corneal topography and tear-film behavior. We show surface regularity asymmetry indices, which are traditionally used for characterizing stability precorneal tear film, have limitations in context HSV because they highly sensitive natural ocular microfluctuations. To overcome this problem, we propose a new microfluctuation-independent indicator. It based root-mean-square...

To investigate the influence of soft contact lenses on regional variations in corneal thickness and shape while taking account natural diurnal these parameters.Twelve young, healthy subjects wore four different types days. The were two materials (silicone hydrogel or hydrogel), designs (spherical toric), powers (3.00 -7.00 diopter). Corneal topography measurements taken before after 8 h lens wear 2 days without wear, using Pentacam HR system. RESULTS.: toric caused greatest level thickening...

The purpose of the study was to investigate changes in axial length occurring with shifts gaze direction.Axial measurements were obtained from left eye 30 young adults (10 emmetropes, 10 low myopes, and moderate myopes) through a rotating prism 15° deviation, along foveal axis, using noncontact optical biometer each nine different cardinal directions over 5 minutes. subject's fellow fixated on an external distance (6 m) target control accommodation, also deviation. Axial performed 25°...

To assess corneal refractive changes after 15-minute visual tasks and their association with eyelid morphology.Contact Lens Visual Optics Laboratory, School of Optometry, Queensland University Technology, Brisbane, Queensland, Australia.Eighteen young subjects normal ocular health were recruited. Corneal topography was measured a videokeratoscope before 4 conditions consisting 2 downward gaze angles (20 degrees 40 degrees) types (reading steady fixation). Anterior eye photography in used to...

In this paper, novel procedures were developed using a thin (0.17 mm) tactile piezoresistive pressure sensor mounted on rigid contact lens to measure upper eyelid pressure. A hydrostatic calibration system was constructed, and the influence of conditioning (prestressing), drift (continued increasing response with static load), temperature variations examined. To optimally position sensor-contact combination under margin, an <i xmlns:mml="http://www.w3.org/1998/Math/MathML"...

To investigate analytically whether higher-order wavefront errors comprising combinations of trefoil along 30 degrees (trefoil30), vertical coma, and spherical aberration could provide cues to sphero-cylindrical refractive error development.A total 25 test wavefronts, subdivided into five different types levels root mean square (HO-RMS), were created for the study. One type contained only, producing HO-RMS between 0.1 0.5 microm. Four trefoil, various sign also From power maps 2025 added...

Summary Working life expectancy is the future time that a person expected to spend in employment. The paper concerned with its estimation jointly times spent related states of ‘on disability pension’ and ‘other alive’. method, which novel this field, first estimates year- age-dependent probabilities being interest by large sample multivariate logistic regression. Estimates probabilities, subsequently expectancies, are given for case Finnish women men aged 16–64 years selected period...

Purpose. To extend the area of standard corneal topography maps, one central map is combined with six peripheral maps after correlating them in a custom written computer program. Methods. The point corresponding to vertex normal found each maps. Data from can then be added on edges create that extends limbus horizontally and vertically. Results. average size 15 subjects was 11.3 ± 0.3 mm 10.3 vertically, compared 9.2 0.4 7.5 0.7 vertically for single These values represent an increase...

Abstract A life history can be regarded as a random process that evolves with age through various states of health before terminating absorption into the state death. Health expectancies are occupation times non‐absorbing and their estimation is interest. continuing major problem has been lack satisfactory longitudinal data on which to base estimates result standard inferential techniques may not relevant. Supposing only cross‐sectional available, we propose method generally applicable first...

Skew ray ambiguity is present in most videokeratoscopic measurements when azimuthal components of the corneal curvature are not taken into account. There have been some reported studies based on theoretical predictions and measured test surfaces suggesting that skew significant for highly deformed corneas or decentered measurements. However, effect tracing through data has studied depth.We evaluated significance its analyzed optics. This achieved by devising a procedure which we compared...

The intrinsically photosensitive retinal ganglion cells (ipRGCs) signal environmental light, with axons projected to the midbrain that control pupil size and circadian rhythms. Post-illumination response (PIPR), a sustained constriction after short-wavelength light stimulation, is an indirect measure of ipRGC activity. Here, we measured PIPR in young adults various refractive errors using custom-made optical system.PIPR was on myopic (-3.50 ± 1.82 D, n = 20) non-myopic (+0.28 0.23 19)...

Changes in corneal optics have been measured after downward gaze. However, ocular aberrations during gaze not previously measured. A commercial Shack-Hartmann aberrometer (COAS-HD) was modified by adding a relay lens system and rotatable beam splitter to allow on-axis aberration measurements primary with binocular fixation. Measurements the (COAS-HD system) were validated against conventional aberrometer. In human eyes, there significant changes (p<0.05) defocus C(2,0), astigmatism C(2,2)...

Background. Myopia prevalence varies across the country among schoolchildren in China. Recently, environmental factors have been shown to be important myopia development and progression. Given China’s geographical diversity with variable factors, we investigated whether could explain regional variations mainland Methods. We searched PubMed, Web of Science, Chinese Science Periodical Databases for studies reports China from years 1979 2019. Data on (annual sunshine hours, temperature,...