Video 6: Normal accommodation
- Light rays from objects successively cross four transparent zones of the eye:
- The cornea,
- The aqueous humour,
- The lens,
- The vitreous body
before arriving at the retina, the sense organ of vision.
- Whenever a light ray crosses one of these zones, it undergoes a deviation: refraction.
- The totality of such refractions result in convergence of light rays on the retina (1).
- Deformity of the lens makes it possible to “focus” and to ensure clear vision of the object, an object that is near, as well as one that is far away:
- Distant vision: the lens is very elongated and little convergent. (The eye is at rest.)
- Near vision: the lens is protruding and convergent at a maximum.
- This change in shape is called accommodation.
- Whenever light rays converge in front of or behind the retina and no longer on the retina, perception of the image is blurred.
We then refer to errors of refraction or ametropia.
- Among these errors of refraction, include the following:
- Primary symptoms:
- Distant vision is blurred.
- Symptoms that can be concomitant:
- eye dryness, caused by excessive fixation of objects, leading to eye irritation, itching, visual fatigue, sensation of a foreign or eye redness
- in children, excessive blinking or rubbing of the eyes (2).
- The world-wide incidence is difficult to estimate (ranges between 800 million and 2.3 billion (3)). According to WHO, 153 million persons live with a visual disorder related to an uncorrected error of refraction and 35 million persons suffer from decreased vision which would require management (4).