Optical design and characterization of a multi-depth vision simulator

TL;DR

Katsim introduces a compact near-eye vision simulator that unifies subjective post-surgical vision simulation with objective IOL evaluation by synchronizing an amplitude-modulated SLM, RGB illumination, and a fast varifocal lens to render three depth planes within a single frame at $60$ fps, equating to an effective depth coding rate of $180$ Hz. The system decouples depth modulation from eyebox position, enabling a configurable eyebox of $1$–$5$ mm and a depth range of $0.2$ m to infinity, with a $9.15°$ field of view and fixed angular magnification. Optical design via Zemax confirms stable magnification across depths and shows an OTF above $0.5$ for spatial frequencies beyond $30$ cycles/degree. The device supports both subjective patient counseling and objective IOL characterization, including CTF/MTF and defocus curves, demonstrated with a model eye and multiple IOL types, while real-time pupil-tracking steers imagery through optically clear regions of the lens. Limitations include lack of accommodation dynamics and need for in-vivo validation; future work aims to expand FOV and plane count and to validate clinically, enabling broader adoption in preoperative planning and IOL development.

Abstract

We present a vision simulator device (Katsim), a compact near-eye optical display designed for assessing postoperative corrected vision, preoperative intraocular lens (IOL) assessment, and objective IOL characterization. The system forms a virtual image using an amplitude-modulated LCoS spatial light modulator (AM-SLM), RGB LED illumination, and a high-speed varifocal lens. In the proposed architecture, the LED illumination and varifocal lens diopter changes are triggered in synchrony with the SLM RGB subframes, rendering three depth planes perceptually simultaneously via high-frequency time-multiplexing. Operating at 60 frames per second (fps), the system achieves an effective 180 Hz depth-coded cycle, enabling sharp, multi-depth rendering within a dynamically adjustable depth range from 0.2 m to optical infinity. The system's eyebox is configurable from 1 to 5 mm, while maintaining a fixed spatial location and preserving angular magnification regardless of changes in focus or eyebox size. The designed system features a 9.15-degree field of view. An integrated infrared pupil-tracking module detects non-cataractous regions of the cataractous crystalline lens, and the projected imagery is mechanically steered through those clear zones in real time. The proposed vision simulator supports both subjective simulation of post-surgical vision for patient-specific counseling and objective optical evaluation of IOLs, including resolution and contrast fidelity (e.g., modulation transfer function, contrast transfer function, and defocus curves). By decoupling depth modulation from eyebox position and size, the system offers a modular, portable platform that supports enhanced preoperative planning, personalized IOL selection, objective IOL characterization, and use as a novel research vision tool.

Figures (8)

• Figure 1: Overview of the KATSIM depth-adjustable near-eye display system. (a) Optical schematic of the KATSIM setup, incorporating an SLM and a varifocal lens; Pol: Polarizer. (b) Illustration of multi-depth-resolved content projected onto the retina. (c) A subject undergoing a visual test with KATSIM. Insets: (i) optical image of the proposed electro-optical hardware; (ii) human–machine interface software screen for multifunctional control of KATSIM, showing the patient’s cataractous crystalline lens captured by the pupil tracker. (d) Content image captured by a camera at the eyebox plane, focused at 1 m, illustrating the corresponding retinal image. See Visualization 1 for a demonstration of the three-depth operation and the eyebox-plane camera capture.
• Figure 2: (a) Zemax optical layout of the system, showing the SLM, varifocal lens, and eyebox-projection; incorporating lenses: La = AC254-030 and Lb = AC254-050 (Thorlabs), Lc = 6-element Edmund Optics lens (part number 45760). (b) Simulated CTF of proposed system (blue) compared with diffraction-limited performance (black). The simulation was performed for a 3 mm eyebox diameter.
• Figure 3: (a) Temporal synchronization of RGB subframes with varifocal lens modulation enables full-color 3D image generation by assigning distinct depths (d1, d2, and d3) to each color channel within a single frame. (b) Conceptual illustration of the three depths corresponding to RGB subframes. (c) System magnification versus virtual image (VI) distance, showing strong agreement between experimental measurements and simulation.
• Figure 4: Camera-captured eyebox patterns for different light-source diameters (0.4–2.2 mm) and checkerboard inputs on the SLM illustrate how source size influences modulation transfer across spatial frequencies. The camera sensor (without additional imaging optics) was placed at the eyebox (exit-pupil) plane. For a 3 mm pupil (aperture), low-frequency patterns transmit efficiently, whereas high-frequency components are partially filtered because their higher-order diffracted beams lie outside the aperture, an effect that is more severe with cataract-level apertures ($\sim$1 mm).
• Figure 5: Comparison of small (400 µ m) and large (2.2 mm) illumination-source diameters on the diffuser for black-and-white content at three depths: far (4 m; panels a,d,g), intermediate (60 cm; panels b,e,h), and near (25 cm; panels c,f,i). Panels a--f use the small source; panels g--i use the large source. In all images, the camera was positioned at the eyebox (exit-pupil) plane, and the camera lens was focused sequentially at far, intermediate, and near distances. A larger source expands the eyebox and enhances perceived depth stratification, whereas a smaller source increases depth of field, resulting in sharper focus across multiple planes. See Visualization 2 for the effect of varying the illumination diameter on perceived depth stratification; see Visualization 3 for independent RGB-intensity control of each depth plane and varifocal-lens dioptric tuning enabling independent depth-plane adjustment from 25 cm to optical infinity.