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Technical Report: A New Method for Determining Image Distance for Stand Magnifiers.

David Lewerenz¹, Kara Hanson¹, Gregory Hopkins

¹Department of Ophthalmology, School of Medicine, University of Colorado, Anschutz Medical Campus, Aurora, Colorado.

Optometry and Vision Science : Official Publication of the American Academy of Optometry

|December 1, 2020

Summary

Clinicians can now accurately measure stand magnifier optical properties using a novel method. This technique efficiently determines image distance and divergence, crucial for low vision rehabilitation.

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Area of Science:

Optometry
Low Vision Rehabilitation
Optical Metrology

Background:

Stand magnifiers are essential tools in low vision rehabilitation.
Accurate optical properties, such as image distance, are critical for effective magnifier selection.
Existing methods for measuring these properties may have limitations.

Purpose of the Study:

To introduce and validate a novel, clinically practical method for measuring the image distance of stand magnifiers.
To offer an alternative with potential advantages over previously described measurement techniques.

Main Methods:

A novel technique using convex lenses to focus emerging light from the stand magnifier onto a surface.
Calculation of the emerging light's divergence and subsequent image distance based on lens power and measured distances.
Validation through inter-clinician consistency checks and comparison with manufacturer-published data.

Main Results:

The novel method demonstrated high consistency among three clinicians, with minimal variation in divergence (≤0.37 D) and image distance (0.6–3.1 cm).
Measurements correlated well with manufacturer specifications, showing a maximum deviation of 3.7 cm (mean 1.3 cm).
Dioptric divergence measurements also showed favorable agreement with manufacturer data (max 0.48 D, mean 0.17 D).

Conclusions:

The described method offers an expedient and clinically accurate approach for evaluating stand magnifier divergence and image distance.
Accurate image distance and divergence measurements are vital for determining a magnifier's enlargement ratio.
This method supports clinicians in selecting appropriate optical aids for individuals with low vision.