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Reading with Low Vision

Several weeks ago, a reader wrote requesting information on reading and near vision. This month’s column is for her.

Many factors influence reading and near vision, from measuring visual acuity, magnification, and environmental modifications. Some of this was covered two months ago in my writings on Presbyopia, but the rest I address here.

Visual acuity for reading is measured much like distance vision, with a fraction. Most practitioners use ‘M’ notation, but if you look at the fraction, the ratios translate well with distance vision (20/40, etc.). The top number reveals the distance tested, typically 40 cm or 0.4 meters (M). The bottom number indicates the size of the line read. Therefore 0.4/0.4M is equivalent to 20/20 visual acuity, and 0.4/4.0M is equivalent to 20/200 visual acuity.

For those with vision impairments, magnification may be utilized to enlarge print to a comfortable reading level.

There are two kinds of magnification. The first is called relative size magnification, which means that the apparent size of the object is increased. Hand held magnifiers and closed caption televisions (CCTV’s) work on this principal.

The second is called relative distance magnification. If you hold a penny at arms’ length, it is impossible to read the date, but pulling it closer to your eye will make the date appear bigger. This is how relative size magnification works. By putting lenses in glasses which allow the person to focus at a very close distance to the eye, the size appears larger due to the proximity. These lenses also provide some degree of relative size magnification.

Once the apparent size of the print is increased so that it may be comfortably read, three more modifications enrich the reading experience and improve comfort. These seem like simple ideas, when you read them, but they are the most overlooked aspects of low vision rehabilitation that I encounter in private practice.

The first overlooked aid is a simple piece of black cardboard or paper. This underlines the text being read, allowing the eyes to more easily follow the line and decreasing the number of time the person loses their place. Black paper underlining text provides a major benefit in those with eye movement disorders, such as Nystagmus, and macular disease like Stargardt’s disease or age related macular degeneration.

The second facet of reading often underaddressed is posture. Utilizing a reading stand or clipboard to hold text at a comfortable height and distance improves posture. This decreases neck and back pain while reading, making the process more enjoyable.

Finally, and this is the most important tool for fluent reading, is lighting. A good light positioned properly increases contrast, reduces glare, and increases the amount of light entering the eye. All too often, those with low vision succeed with optical aids in-office, but discover that in their home environment they do not perform as well. It is not the device that has changed, only the lighting. Although an inexpensive solution, it is a key one.

Lighting will be covered in more detail next month, with tips on positioning lights, types of bulbs to purchase, and how to enhance contrast.

J. Hensil