Medical glossary

Sleep

Circadian rhythm

The body's internal 24-hour clock that signals when to be awake and when to sleep. It is influenced by light and your usual routine.

Sleep hygiene

A set of habits that help you sleep better: a regular bedtime, a calm evening, a dark and quiet bedroom.

Falling asleep

The transition from being awake to sleep. If it regularly takes a long time, that's a reason to look at your evening habits and, if needed, talk to a doctor.

Daytime sleepiness

The urge to fall asleep during the day in ordinary situations. If it gets in the way of work or study, it's worth discussing with a specialist.

Insomnia

Persistent difficulty sleeping that affects how you feel during the day. It is assessed and treated by a doctor, not by a reference guide.

Autoplay

A feature that starts the next episode automatically. Turning it off is a simple way to take back the decision about when to stop.

Vision

Accommodation

The eye's ability to shift focus from distant objects to near ones. When you look at a screen for a long time, this system works for long stretches without rest.

Eye strain

A feeling of heaviness, dryness or stinging in the eyes after long screen use. It usually goes away after rest; if it doesn't, you need an eye examination.

Blinking

A reflex that keeps the surface of the eye moist. When people concentrate on a screen, they blink less often.

Dry eye

A gritty or stinging feeling when the surface of the eye isn't moist enough. The cause and ways to help are determined by an eye doctor.

20-20-20 rule

Advice from ophthalmology associations: every 20 minutes, look for 20 seconds at something about 6 metres, or 20 feet, away.

Ophthalmologist

A doctor who specialises in eye health: tests vision, prescribes glasses and finds the causes of eye complaints.

Movement

Sedentary behaviour

Time spent sitting or lying down without moving, other than sleep. WHO advises limiting it and breaking it up with any activity.

Physical inactivity

A lack of movement in everyday life. Long evenings at the screen without breaks are one of its common causes.

Moderate physical activity

Movement that makes you breathe faster but still lets you talk, such as brisk walking. WHO recommends that adults get 150–300 minutes of it a week.

Posture

The way you habitually hold your body when sitting and standing. What matters is not a perfect pose but being able to change it regularly.

Sitting break

Any moment when you get up and move: walk around, stretch, fetch some water. Even short breaks count.

Research

Guideline

A conclusion by an expert organisation based on many studies. More reliable than a single study or a news article.

Screen time

Time spent in front of any screen. WHO guidelines for young children refer specifically to sedentary screen time.

Correlation

A link in which two things change together. It does not prove that one causes the other.

Sample

The group of people a study was carried out on. Its size and make-up determine who the findings apply to.

Systematic review

A study that gathers and compares the results of many studies on one question. Guidelines are often based on such reviews.

Where these words appear in the reference

• Methods

  Breaks and movement, lighting and screen distance, headphone volume: simple approaches with no miracle products.

• Prevention

  How to reset your screen habits in a week: a viewing plan, lighting, breaks, movement and a set bedtime.

• Research

  Where screen-time advice comes from and how to read news about studies without panicking.

• Series and sleep (in Russian)

  A note at the series' archived address: how to watch series in the evening and still get enough sleep.

• Screens and eyes (in Russian)

  A note at the series' archived address: why screens tire your eyes and how breaks help.

• Sitting long (in Russian)

  A note at the series' archived address: how to set up your viewing spot and get up between episodes.

Read next

• Methods

  Breaks and movement, lighting and screen distance, headphone volume: simple approaches with no miracle products.

• Research

  Where screen-time advice comes from and how to read news about studies without panicking.

• Sources

  Which guidelines this reference is based on, why it contains few figures and where its limits lie.