Research Advances on a Novel Compact Double-Pass Intraocular Scatter Measurement System

Academic Background

According to the World Health Organization (WHO), cataracts are the leading cause of blindness globally, accounting for approximately 50% of all blindness cases. More than 20 million people worldwide suffer from vision loss or severe impairment due to cataracts. Current treatments primarily depend on surgical procedures, wherein the cloudy lens is removed and replaced with an artificial intraocular lens to restore vision. However, ongoing research into cataract pathology has fueled greater hope for drug-based prevention and treatment. The realization of this hope largely depends on precise monitoring of early cataract symptoms.

In the early stages of cataracts, symptoms are often subtle or difficult to detect. As the disease progresses, the refractive medium in the eye becomes increasingly cloudy, leading to elevated intraocular scatter—a key pathological change associated with cataract development. Monitoring variations in intraocular scatter is, therefore, considered critical for the early diagnosis of cataracts.

Among traditional methods for measuring intraocular scatter, the Double-Pass (DP) technique has been widely adopted in clinical practice. By analyzing the degree of blur in the retinal Point Spread Function (PSF), this method evaluates intraocular scatter using the Objective Scatter Index (OSI). However, since the PSF contains information about both scatter and aberrations, the presence of higher-order aberrations can significantly affect measurement accuracy—especially under larger pupil diameters. Current approaches to correcting the impact of aberrations on PSF often rely on complex and expensive Adaptive Optics (AO) systems, limiting their application in standard clinical settings. Thus, there is considerable value in developing a low-cost, high-accuracy system capable of effectively mitigating aberrations for intraocular scatter measurement.

Research Background

The study, titled “Compact and Aberration Effects-Shielded Objective Intraocular Scatter Measurement System,” was authored by Junlei Zhao, Zitao Zhang, Yanrong Yang, and others from prominent research institutions such as Chengdu University of Traditional Chinese Medicine and the Chinese Academy of Sciences. The study was published in the February 1, 2025 issue of Biomedical Optics Express.

Research Workflow and Key Features

a) Research Workflow

The study introduces a novel compact double-pass intraocular scatter measurement system that eliminates the influence of aberrations to achieve precise evaluations of intraocular scatter.

1. System Design and Composition

The proposed system integrates three optical paths: the illumination path, far-field path, and wavefront sensing path. Specific components include:

• Illumination Path: Utilizes an 840 nm super-luminescent diode (SLD) as the light source, guiding light through multiple lenses and beam splitters into the eye.
• Far-Field Path: Captures the Double-Pass Point Spread Function (DP PSF) images. To correct astigmatism induced by beam splitters, rotating cylindrical lenses are incorporated, with the final PSF image recorded by a CCD camera.
• Wavefront Sensing Path: Uses a Shack-Hartmann wavefront sensor to detect wavefront aberrations, retrieving seven orders of Zernike aberration coefficients for PSF reconstruction.

2. Aberration Correction and OSI Calculation

Initial OSI values (OSI0) are derived from DP PSF images, while wavefront data is used to compute the influence coefficient of aberrations (△OSI). The accurate Objective Scatter Index (OSI1) is then calculated by subtracting △OSI from OSI0.

3. Experimental Validation

The study tested artificial model eyes paired with optical filters and real human eye data from three volunteers, evaluating performance under pupil diameters of 4 mm and 6 mm. Experimental goals included verifying measurement accuracy after aberration correction, as well as assessing stability and consistency of results.

b) Novel Techniques and Algorithm Implementation

The proposed system incorporates the following innovative features: 1. Shack-Hartmann Sensor as an AO Alternative: Replacing traditional adaptive optics systems with a Shack-Hartmann sensor significantly reduces equipment costs and complexity by eliminating aberrations in a post-processing step. 2. Aberration Reconstruction with Zernike Polynomials: Zernike polynomials are employed to reconstruct wavefront aberrations’ effects on the PSF, followed by Fourier transforms for PSF computation. 3. Customized Optical Components and Simulation Models: To validate system accuracy and repeatability, the team designed an artificial model eye combined with optical filters to simulate various scatter conditions.

c) Core Experimental Results

Key findings include: 1. The maximum deviation when measuring OSI0 for a static artificial eye compared to the Optical Quality Analysis System (OQAS) was 0.016, while for human eyes, it was 0.019—demonstrating high consistency between the two systems. 2. Measurement deviations in seven orders of Zernike coefficients, compared to a standard interferometer, were within 0.04 µm—sufficient for △OSI computations. 3. When correcting aberrations under a 6 mm pupil diameter, measurement accuracy improved by 28.9% compared to a 4 mm pupil diameter, with significant benefits under high-aberration conditions.

d) Study Conclusions

The proposed system offers a low-cost, accurate, and compact platform for measuring intraocular scatter, significantly improving measurement precision while maintaining a small device footprint. This system remains precise even under large pupil diameters or high-aberration conditions, making it highly adaptable for clinical applications.

Additionally, the system supports accurate detection of higher-order aberrations, expanding its utility for multifaceted diagnostic needs in ophthalmology.

e) Research Highlights

1. Introduced the use of Shack-Hartmann sensors to replace AO systems, reducing complexity and cost.
2. Successfully devised a reliable measurement approach suitable for larger pupil diameters and high-aberration scenarios.
3. Achieved superior accuracy compared to existing platforms (e.g., OQAS) while maintaining compactness and affordability.

Research Significance and Future Outlook

This novel system presents remarkable potential for clinical applications, particularly in early cataract screening, where cost-effective, high-accuracy detection is essential. The technological breakthroughs highlighted in this study may help democratize access to ophthalmic diagnostic tools and offer data support for future drug development efforts.

Future research could focus on further enhancing the system’s performance and ease of operation, broadening its clinical applicability to diverse scenarios, such as precise diagnosis of complex ocular conditions. The research team may also need to address limitations in aberration detection for severe cataract patients to expand the system’s usability.