Overview of refractive errors

Eye Anatomy

The human eye works much like a digital camera: – Light is focused by the cornea — the clear front surface of the eye acting like a camera lens. – The iris of the eye functions like the diaphragm of a camera, controlling the amount of light reaching the back of the eye. – The eye’s crystalline lens is located directly behind the pupil and further focuses light. This lens helps the eye automatically focus on near and approaching objects. – Light focused by the cornea and crystalline lens (and limited by the iris and pupil) then reaches the retina which acts like an electronic image sensor of a digital camera, converting optical images into electronic signals. The optic nerve then transmits these signals to the visual cortex.

What are refractive errors?

Refractive errors occur when the shape of the eye prevents light from focusing directly on the retina. The length of the eyeball (longer or shorter), changes in the shape of the cornea, or aging of the lens can cause refractive errors.

Refraction is the bending of light as it passes through one object to another. Vision occurs when light rays are bent (refracted) as they pass through the cornea and the lens. The light is then focused on the retina. The retina converts the light rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images we see.

The most common types of refractive errors are myopia, hyperopia, presbyopia, and astigmatism. Refractive errors have become a huge issue for the health quality of people in general and especially in children.

– The rate of children in Vietnam with refractive errors hasincreased at an alarming rate. It is estimated that around 15% of children attending school in Vietnam (around 4 million) have to live with refractive errors and are in need of treatment.

– In Hanoi, a throughout survey in 2008 showed that 83,13% of the children with refractive errors are using eyeglasses for vision correction, and only 67,5% of them have correct eyeglass prescription.