The eye functions as a very sophisticated camera, ensuring that the light entering the eye is properly focused, so that we can see the world around us clearly. When this mechanism does not work perfectly, the image formed is not very clear, and the disease is called refractive error.
How does the eye focus images perfectly?
To focus and see an image clearly, there are several structures which must work perfectly, and in coordination within the eye:
Cornea:The cornea is the transparent dome-shaped front part of the eye, which allows light to enter, and also focuses light rays on the retina. The retina is the light sensitive portion at the back of the eye, which enables us to see.
Lens: The natural lens of the eye is transparent and flexible, located directly behind the iris and the pupil. It also helps to focus light and images on the retina. The lens has the ability to change its curved shape, so that it helps you to focus on objects that are at different distances. With age, this ability of the lens is lost, and we need glasses for near work and reading, this is called presbyopia.
Retina: The light rays and images are focused by the cornea and lens directly onto the retina, which is light-sensitive, like the film in a camera. It transmits images via the optic nerve to the brain for interpretation.
Read Also: (What is Retina in the Eye?)
What are the common refractive errors?
When the vision is not sharp due to improper focusing of light, the doctor says you have a refractive error. This can be because the focusing power of the lens and cornea do not correspond to the length of the eyeball so that the image is not directly formed on the retina.
Myopia or Nearsightedness: In this, you can see near objects clearly, but distant objects are blurred. This is because the light rays are focused in front of the retina. This happens when the focusing power of the cornea and lens is very high, or when the eyeball is too long.
Hypermetropia, hyperopia or far sightedness: In this, distant objects can be seen more clearly than near objects. This is because light rays are brought to focus behind the retina, because either the focusing power of the cornea and lens is very low, or because the eyeball is short in length.
Astigmatism: Astigmatism is a refractive error in which the blurring of vision is because of irregular shape of cornea or lens. Normally, the surface of the cornea is rounded, but in astigmatism, it is shaped more a like an American football. This means the power needed for correction in different meridians is different.
What are the symptoms of refractive errors?
Symptoms of refractive errors include:
Blurring of vision
Tiredness and fatigue of eyes
Sore, painful eyes
Eye strain
Squinting or misalignment of eyes
Headaches
Decreased vision in one or both eyes not corrected by glasses also, called lazy eye or amblyopia
What is the treatment for refractive errors?
Refractive errors can be treated by:
Use of glasses
Use of contact lenses
Surgical treatment:
LASIK including variants like Fem to LASIK, Contoura LASIK and SMILE eye surgery
Surface ablations
Implantable Collamer Lenses
Refractive lens exchange or clear lens extraction