Prescribing for Reading
Magnifying print to make it easier to read for individuals with central vision loss from macular degeneration and other visual disorders can be accomplished with optics using strong reading glasses, magnifiers. Unfortunately both of these techniques require the user to hold the material very close which makes it uncomfortable and fatiguing. Reading at a normal working distance is perhaps one of the most requested activities by the visually impaired. The only optical option available to provide magnification at more normal working distances are telescopes focused for near. Seeing the print requires higher magnification, while being able to track across the line requires a wide field of view. Telescopes can either be focusable or fixed focus for the desired working distance. Of course, the stronger the magnification of the telescope the narrower its field of view will be. Fortunately the field of view of telescopes is like a cone—the further away you are from the material the more you can see at once. Galilean telescope can provide an ample field of view up to approximately 2x power, while Keplerian telescopes provide wider fields of view when powers above 3x are required.
We suggest these steps to determine whether a telescope will be helpful to your patient for reading
- Position a Keplerian telescope in front of their preferred seeing eye with their distance correction in place (if any) with a power that provides ample magnification to achieve 20/40 (6/12) at distance.
- Determine the furthest distance that the individual can be from the reading material. Often, it’s convenient to place the material on a reading stand to position it upright—it can be further than arm’s reach as they can lean in to turn the page when necessary. Make certain it’s well illuminated.
- Focus the telescope for the working distance determined in step #2.
- Determine whether the telescope provides enough magnification for the user to read the text.
- If they can read it well, try a lower power device to gain a wider field of view.
- If they cannot read it well, try a higher power device to provide higher magnification.
- Determine if the field of view is wide enough for the user to read fluently.
- If they cannot track fluently, try to increase the working distance (and refocus the telescope).
Some other hints
- A binocular device may be able to provide a wider field of view, however you need to determine the most promising working distance first so that the binocular telescopes can be aligned and converged for that distance.
- Determine whether the reading material will be at eye-level or lower down. This will help determine the proper position and angle of the telescope in the carrier lens and frame.
- No matter how wide the field of view can be achieved, it still will cover only a few inches of print. Users will need to learn to move their head and eyes together to track along the page.