Myopia has been linked not so much to screens as to the habit of reading in semi-darkness

The rise in myopia in recent years has often been attributed to the "harm of screens". But researchers from SUNY College of Optometry (New York) believe the cause may be broader: it's not the smartphone or tablet itself that plays an important role, but the way we use our vision indoors - especially when looking at close distances in low light for long periods of time.

The work, published in Cell Reports, offers a unifying hypothesis that explains why factors ranging from reading and working "up close" to bright outdoor light and even certain treatments influence the development and progression of myopia.

What's the idea

When a person focuses on a close object (book, phone, laptop), the eye "adjusts the sharpness": the lens changes (accommodation) and the pupil may constrict to make the picture clearer. Outdoors, the pupil also shrinks - but there's plenty of light, and the retina still gets enough illumination.

The problem, according to the authors, occurs indoors in dim light. In such a situation, an "unfortunate combination" is formed:

• the person is looking close for a long time,

• the pupil narrows because of focusing,

• there's not a lot of light around,
  and as a result, not enough light can reach the retina. The authors suggest that long periods of such "low retinal illumination" changes the way the visual system works - and this may be one of the mechanisms involved in the development/enhancement of myopia.

Why this may conflate different observations

The researchers note: different ways of controlling myopia (e.g. multifocal lenses, atropine drops, recommendations to be outdoors more often) may work because they reduce over-accommodation and/or help provide more "correct" retinal illumination.

In doing so, the hypothesis draws a practical cautionary conclusion: any control methods may work worse if a person regularly spends long periods of near and semi-darkness.

The authors emphasise that this is not a definitive answer, but a testable physiological hypothesis that links habits, lighting and gaze focus in new ways. Further research should confirm the extent to which this mechanism explains the increase in myopia in humans.