There are times when we are so absorbed in a good book that we do not notice that the light has faded. Or we read books while travelling in a dimly lit bus or train. With the availability of tablets and e-readers, many people now have the habit of reading at bedtime with the lights off. When we were kids, most of us have sneaked a torch inside the bed covers to read an interesting book. We have been told by our parents that reading in dim light will affect our vision and make us get spectacles.
Is good lighting while reading very crucial? Can reading in insufficient light cause any long-term adverse impact on our vision? Read on to know the answer.
Dark Adaptation: Compensatory mechanism of the eye in the dark
Our eyes have two types of photoreceptors (light sensors) in the retina, called as cones and rods. Cones are responsible for vision in higher levels of light (photopic vision) and colour vision. Rods are responsible for vision in low light levels (scotopic vision).
When we move from a well-lit area to a dark area, or when the light around us reduces suddenly, certain changes occur in our eyes that help us adjust to this new light setting:
- The sensors in the retina both the rods and cones start producing more light-sensitive chemicals. The cones make this sensitivity adjustment over a short period, while rods increase their sensitivity over an extended time range.
- The iris muscle relaxes to make the central opening (pupil) larger to allow more light to enter the eye.
Reading in dim light can cause eye strain
When you read, the eye has to focus an image of the words onto the retina. When you are looking at a nearby object, the muscles that control the shape of the lens (known as ciliary muscle) contracts and makes the lens bulge and become rounder (increasing the focusing power).
When the light is low, focusing becomes a difficult task as the contrast between the printed words and the paper is not that great, and this decreases the eye’s ability to distinguish visual detail. The eyes have to work harder to distinguish the words from the page, which can strain the eye muscles.
When there is eye strain for a prolonged duration, the eye muscles become tired. This strain can cause some symptoms like pain in the eyes, headache, back pain, neck pain and blurring of vision. You can also experience dryness of eyes as you tend to blink less often when you focus intently on an object. These symptoms of strain last for a short duration and eventually go away.
Dim-light damaging vision is not proven
There are no research studies that have studied the long-term effects of reading in dim light. However, the consensus of a majority of ophthalmology specialists is that reading in dim light does not damage the eyes. It causes discomfort which is completely harmless and goes away with rest. If the symptoms persist once you stop straining your eyes, then consult an eye doctor. You may have an underlying refractive error, which might be the cause of the persistent symptoms.
Follow these simple tips while reading in dim light to reduce the strain on the eyes:
- Adjust the available light such that it falls directly on the book or e-reader screen without causing a glare.
- Blink often while reading.
- Focus on something at a distance or across the room every 15- 20 minutes.
- Take brief breaks every hour or so when reading for a long duration.
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- Vreeman RC, Carroll AE. Medical myths. BMJ. 2007 Dec 22;335(7633):1288-9.
- Perception Lecture Notes: Light/Dark Adaptation. Department of Psychology, New York University. http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/light-adapt/light-adapt.html. Accessed Sep 2. 2016