Blurry vision when tired: eye strain, dry eyes and when to check

Reading, working at a screen or driving all demand sustained focusing. The muscles inside the eye that adjust the lens, and the muscles that keep both eyes pointing at the same near object, work harder at close range. After hours of this, or after a poor night of sleep, the eyes feel tired and the print may seem to swim, double slightly or go soft.

Because this blur usually clears after a rest or a night’s sleep, it is generally a sign of fatigue or dryness rather than damage. It is still useful information, since some people with uncorrected long-sightedness, astigmatism or the early need for reading glasses first notice it only when tired.

The College of Optometrists defines computer vision syndrome, also known as digital eye strain, as the combination of eye and vision problems associated with the use of computers, tablets, smartphones and electronic reading devices. It says many people spend 10 or more hours per day viewing these displays, frequently without adequate breaks.

It notes that small portable screens may mean reduced font sizes and closer viewing distances, which increase the demands on focusing and eye alignment, and that blink patterns differ between printed and electronic displays. It reports around 40% of adults and up to 80% of teenagers may have significant visual symptoms, principally eye strain, tired and dry eyes.

The same source says that eye care practitioners should modify the standard eye examination to meet today’s visual demands, which is a reason to tell your optometrist how many hours you spend on screens.

The NHS lists itchy, sore, gritty, red, blurry, light-sensitive or more watery than normal eyes as signs of dry eyes. It says you may be more likely to get them if you are over 50, wear contact lenses, look at computer screens for a long time without a break, spend time in air-conditioned or heated rooms, smoke, drink alcohol, take certain medicines such as some antidepressants or blood pressure medicines, or have a condition such as blepharitis, Sjögren’s syndrome or lupus.

Blur from dry eyes often fluctuates and may clear briefly after blinking. The NHS suggests cleaning your eyelids every day, resting your eyes, positioning your screen just below eye level and using a humidifier if the air is dry, and says a pharmacist may be able to suggest eye drops, gels or ointments.

These are general measures drawn from the NHS dry eyes advice and the points above, and none replaces an eye examination.

• Take regular breaks from screens and look at something in the distance.

• Position the screen slightly below eye level and at a comfortable distance.

• Use good lighting and avoid reading in dim conditions.

• Clean your eyelids daily if they feel gritty or crusty.

• Remove contact lenses and wear glasses to rest your eyes, as the NHS suggests.

• Do not stop prescribed medicines without medical advice, even if you think they cause dry eyes.

If blur happens often, lasts beyond a rest, or you are straining to read, an optician appointment is sensible. The NHS says to see an optician or GP if dry eyes persist after trying home treatments for a few weeks.

Some patterns should not be put down to tiredness. The NHS says to call 999 or go to A&E for changes to sight such as wavy lines, flashing or loss of vision, if it hurts to look at light, or if you have a red eye with severe headache and nausea. It advises an urgent GP appointment or NHS 111 if the eye is painful and red, or if you wear contact lenses and have a red eye, which could be infection.

Cataracts, which the NHS says usually develop slowly, can also cause blurred vision, glare and difficulty reading, so persistent blur in someone older deserves a proper review.