Non-orthogonal lenses, in which the principal meridians of the cylinder surfaces are not perpendicular to each other, can be used to improve vision in the condition of irregular astigmatism. A procedure is developed that allows raytracing and image-quality analysis with such lenses. A non-orthogonal surface was developed as a user-defined surface in the programme Ansys Zemax OpticStudio using a bi-cubic meridional mapping function. The function consists of two third-order polynomial sub-functions, each for mapping the actual ‘on surface’ meridian to an effective meridian that determines the meridional curvature for the two sectors of meridians bounded by the principal meridians. Equations were derived for partial derivatives across the surface, as Zemax requires these for raytracing through a user-defined surface. Examples are shown of tangential and pupil power maps for a thin orthogonal (conventional) +5.00 DS/+2.00 DC × 180 lens and for a non-orthogonal +5.00 DS/+2.00 DC (60) × 180 lens. The orthogonal lens has principal meridians 180° and 90° while the non-orthogonal lens has principal meridians 180° and 60°. For the orthogonal lens, both maps show regular changes in power with meridional angle, and the sagittal power map is rotated by 90° relative to the tangential power map. For the non-orthogonal lens, the sagittal power pattern shows sharp changes in power. The non-orthogonal surfaces were replicated using the ‘grid sag’ surface of Zemax, and the user-defined surface was verified. Surface fitting using Zernike polynomials returned only a reasonable approximation to a non-orthogonal surface. A type of non-orthogonal optical surface based on two third-order polynomials is presented. Aspects of its geometrical optics properties were investigated, including confirming the non-orthogonality of its axes. This type of surface may have utility in the correction of irregular astigmatism, such as occurs in keratoconus.

We present a technique for wide-field OCT imaging of the cornea using self-referenced interference of the anterior corneal surface with the underlying corneal structure. The method employs a custom objective lens that ensures that the probing beam remains nearly perpendicular to the anterior corneal surface, effectively utilizing it as a reference to generate interference. This approach allows for high-resolution, three-dimensional imaging of corneal layers over a 9mm optical zone. Tests on human subjects show the ability of the system to quantify the anterior corneal layer thickness.

To provide a more sophisticated explanation of the optics involved when retinal ‘shadows’ are seen in scanning laser ophthalmoscopic images during the wear of multisegment and diffusion optic spectacle lenses. Images were recorded with a system that uses a scanning broad line fundus imaging principle in participants with undilated pupils wearing a multisegment spectacle lens. The live infra-red preview display of the system was also acquired during image recording. Ray-tracing and image simulations were performed, assuming a Maxwellian illumination system in which a source was refracted first through a lens and then through a model of a multisegment spectacle lens focused onto the pupil of an eye model and hence to the retina. A detector surface was positioned slightly in front of the retina to record the irradiation distribution. The light source was varied from 0.1 μm to 1.8 mm in diameter to investigate the effect of light source size on retinal irradiation distribution. The retinal shadow pattern was visible on the live infra-red preview display, as reported previously. However, the recorded images of the retina do not exhibit the same shadow pattern. The simulations predict that the circular shadows corresponding to lenslet positions become progressively less discernible with increasing light source size. An explanation is provided for the shadows on retinal images due to multisegment lenses, which may be observable under certain illumination conditions.

SIGNIFICANCE:This study describes a new technique that integrates an electrically tunable lens with a dynamic infrared photorefractor for real-time manipulation of blur feedback for human ocular accommodation. This technique is straightforward to implement, and it also overcomes the limitations of present paradigms used for opening the blur-feedback loop (e.g., pinholes and low spatial frequency difference of Gaussian targets). PURPOSE:To describe and validate a technique for real-time manipulation of blur feedback for ocular accommodation by integrating an electrically tunable lens with a dynamic eccentric infrared photorefractor. METHODS:The EL-16-40-TC-VIS electrically tunable lens (Optotune, Dietikon, Switzerland AG) and the PowerRef 3 eccentric infrared photorefractor (PlusOptix, Nuremberg, Germany) were independently calibrated and integrated via a Secure Shell network protocol. The electrically tunable lens was positioned before the right eye, which accommodated multiple times to 2D step changes in optical vergence. The photorefractor captured consensual accommodative changes through the infrared filter occluded left eye at 50 fps. Blur feedback to the right eye was canceled by feeding in the sign-reversed refraction data into the electrically tunable lens in real-time at 25 fps. The feasibility of this setup to minimize robust blur-driven accommodative step responses was tested on five pre-presbyopic adults. RESULTS:All subjects showed robust monocular, blur-driven accommodative responses at baseline, with a median response magnitude of 1.54 D (1.47 D to 1.54 D). The responses were reduced to only baseline fluctuations following blur-feedback manipulation. The median response magnitude following blur-feedback manipulation (-0.34 D [-0.35 D to 0.09 D]) was significantly different from baseline values (Wilcoxon Sign rank test; p=0.043). CONCLUSIONS:The integration of an electrically tunable lens with the photorefractor provides a real-time method for manipulating blur feedback during ocular accommodation. This technique may be a promising tool for investigating sensorimotor properties of accommodation and refractive error development. Alternate schematics for manipulating the blur feedback, expanded operating range of the electrically tunable lens, and reduced signal transmission delays may be considered in the future to enhance the efficacy of this technique.

Accommodation is the process by which the eye changes focus. These changes are the result of changes to the shape of the crystalline lens. Few prior studies have quantified the relation between lens shape and ocular accommodation, primarily at discrete static accommodation states. We present an instrument that enables measurements of the relation between changes in lens shape and changes in optical power continuously during accommodation. The system combines an autorefractor to measure ocular power, a visual fixation target to stimulate accommodation, and an optical coherence tomography (OCT) system to image the anterior segment and measure ocular distances. Measurements of ocular dimensions and refraction acquired dynamically on three human subjects are presented. The individual accommodative responses are analyzed to correlate the ocular power changes with changes in ocular dimensions.

Purpose: To quantify the angular-dependence of monofocal intraocular lens (IOL) power. Setting: Ophthalmic Biophysics Laboratory, Kallam Anji Reddy campus, L V Prasad Eye Institute, Hyderabad, India. Design: Laboratory study. Methods: Experiments were performed on IOLs from two different manufacturers (APPALENS 207, Appasamy Associates and SN60WF, Alcon Laboratories). IOL powers ranged from 17 to 25 D. The IOLs were mounted in a fluid-filled chamber and the on-axis and off-axis powers were measured using a laser ray tracing system over the central 3 mm zone with delivery angles ranging from -30° to +30° in 5° increments. The position of the best focus was calculated for each IOL at each angle. The angular dependence of IOL power was compared with theoretical predictions. Results: Peripheral defocus increased significantly with increasing incidence angle and power. The peripheral defocus at ±30° increased from 5.8 D to 8.5 D when the power increased from 17.5 D to 24.5 D for APPALENS 207 and from 4.9 D to 7.4 D when the power increased from 17 D to 25 D for SN60WF. The mean difference between the measured and theoretical tangential power at ±30° was 0.50 ± 0.16 D for the APPALENS 207 and -0.40 ± 0.10 D for the SN60WF, independent of IOL power. Conclusions: IOLs introduce a significant amount of peripheral defocus which varies significantly with IOL power and design. Given that peripheral defocus is related to lens power, replacement of the natural lens (approximately 24 D) with an IOL will produce a significant difference in peripheral defocus profile after surgery.

We measured the average group refractive index (RI) of 120 isolated lenses from 120 human donors (age: 0.03 to 61 years). The average group RI was calculated from a measurement of the optical thickness of the lens using optical coherence tomography and the apparent window shift of the test chamber caused by the lens. The estimated measurement uncertainty was ±0.004. The group RI at 880 nm was converted to phase RI at 589 nm using the dispersion equation of water and protein. From 2 to 61 years, the mean value of the RI was 1.415 ± 0.002 (group index at 880 nm) and 1.406 ± 0.002 (phase index at 589 nm) independent of age (p = 0.774). Two lenses from donors of age 0.33 and 3 months had significantly lower RI (group index: 1.405 and 1.403; phase index: 1.396 and 1.394). From age 2 to 61, the average lens RI is constant with age within the measurement uncertainty (±0.004).

Purpose: The assessment of myopigenic environmental risk factors such as near-work relies on subjective data. Although diaries and questionnaires on near-work show correlation to some degree, it remains unknown how they may correspond to ground truth. This is an important consideration because valid estimates of near-work have great utility for understanding the mechanisms by which dioptric demand drives excessive eye-growth, which is not yet entirely understood. To this end, we assessed a novel eye-tracking system to quantify near-work. Method: We compared subjective entries from diaries to objective data on accommodative demand acquired with a three-dimensional eye-tracker in 20 participants. Each test involved approximately one-hour exposure to ecological near-work environments. Furthermore, topographical dioptric demand maps were computed in retinal coordinates. Results: Our study suggests a frequent mismatch between objectively and subjectively labeled data of near-work tasks (concordance 74.6%). Objective and subjective estimates of dioptric demand showed a moderate correlation and were not significantly different (R2 = 0.59, P = .35). Instead, accommodative demand with an agreement between objective and subjective near-work labels showed a high correlation and were significantly different (R2 = 0.79, P = .016). The accumulated topographical dioptric demand of ecological near-work environments did not present myopigenic defocus stimuli to the retina periphery. Thus extreme close-up near-work presented peripheral defocus stimuli that have been proposed to curb excessive eye growth. Conclusions: The proposed objective measurement method may provide improvements over subjective methods for estimating near-work parameters. Translational Relevance: The topographic dioptric demand maps highlight a possible conflict of causal mechanisms of the two myopia models: “excessive near-work” and “peripheral optical defocus.”

Purpose: To determine whether lens mechanical dynamics change with age and with accommodative demands. Methods: Lens thickness microfluctuations were measured using a high-speed custom-built spectral domain optical coherence tomography system in five young adults (20 to 25 years old) at 0 diopters (D), 2 D, 4 D, and maximum accommodative demand and in five prepresbyopes (38 to 45 years old) under relaxed and maximal accommodation. For each state, the measurements were repeated four times during the same session. Images of the central 2-mm zone of the lens comprising 170 A-lines/frame were acquired for 10 seconds, and axial lens thickness change was measured. Lens thickness microfluctuations (µm²/Hz) were assessed by integrating the power spectrum of lens thickness microfluctuations between 0 and 4 Hz. Results: The amplitude of lens microfluctuations was higher in the accommodated states than in the relaxed state in both age groups. Lens microfluctuations were higher in young adult participants than in prepresbyopes, with a significant difference in relaxed and maximally accommodated states (P = 0.04 and P = 0.04). In the young participants, the amplitude of microfluctuations reached a plateau at maximum accommodation. Conclusions: Lens mechanical dynamics are both age and accommodation dependent. The decrease in lens thickness microfluctuations with age is consistent with an age-related increase in lens stiffness or decrease of the ciliary muscle displacement. The lens does not contribute to the high-frequency component of ocular dioptric microfluctuations.