General EYE ADVICE

Relationship Between Near Work, Myopia and Astigmatism

In addition to choosing the appropriate (if any) myopic correction for near work, the eyecare professional should also ensure that he/she prescribes for any amount of astigmatism that the eyes may have when they are focused at near. As this amount can be different from the amount of astigmatism that the eyes have when focused at distant objects, the practitioner should ideally perform a separate test for the astigmatism while the patient focuses at a near object.

The main reason for the change in astigmatism at near is related to the presence of a separately innervated focusing mechanism for the optical defect of astigmatism. This mechanism is often referred to as meridional or astigmatic accommodation. Although the presence of this separate control for astigmatism has been disputed in the past, I have presented the necessary evidence at an international optometic conference in 1997 in support of the presence of meridional accommodation. A good understanding of the mechanism will enable the eye care practitioner to prescribe proactively. That is, he/she can then more confidently predict the way that the visual system reacts to any visual correction, thus enabling the practitioner to chose a prescription that will help the patient have better eyesight in the long term. You may wish to refer any health professional who is interested in reading this scientific paper to the "Eyecare Professionals" division of this website or directly link to Meridional (Astigmatic) Accommodation.

Wearing the appropriate amount of astigmatic correction is important for several reasons. If the prescription for astigmatism is not optimal, this can lead to fatigue or eye ache, especially when there is concurrent long-sightedness of the eyes as well. Also, the vision at near can become blurred due to fatigue of the neuro-muscular system that is involved in controlling the eye's astigmatism (i.e. Meridional Accommodation system). To overcome this slightly blurred vision, one often leans forwards to see small print better from a closer distance. This may happen without the individual being conscious of it, and is associated with some adverse effects. Firstly the individual has to focus harder because of the closer distances involved, leading to more rapid fatigue and/or the development of myopia (short-sightedness). Another adverse effect of leaning closer towards small print on a VDU etc., is increased neck tension, which in the long term may cause more permanent neck problems and headaches.

An ideal yet simple way of keeping a good distance from books or other printed material is to use a reading stand. This has several benefits. Firstly it will help to prevent eye fatigue and myopia. A reading stand enables printed material to be presented at right angles to the line of sight and also enables a greater reading distance. This helps to prevent excessive focusing of the eyes and allows the reader to more easily refocus onto a distant object as he/she is already facing almost straight ahead. (See Appendix I below for benefits of regularly refocusing into the distance.)

Another benefit of a reading stand is that it will allow the reader to rest his/her back on the chair's back support and have the head comfortably supported in a fairly erect posture. This will minimise the strain on the spine and its muscles, and help to prevent neck pain and related headaches. In cases where the paper is glossy, a reading stand can also help to minimise glare caused by overhead lights.

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