The human eye is a complex organ and various structure need to function perfectly in order for you to have a great vision. But things are not always perfect and certain things might not work as they should. Today we will take a closer look into the types of refractive errors, their causes, symptoms, and treatments.
But first let’s take a closer look at the components of the eye that help you have a clear vision:
- The Cornea – it has the shape of a dome and it forms the front part of the eye. It’s basically like a window and it allows the light to enter the eye. It doesn’t have any blood vessels, but it does have plenty of nerve endings. The process that helps you see things clearly starts right here in the cornea.
- The Lens – this is the next structure that helps with focusing light and images, and it is located under the iris and the pupil. It is flexible and elastic, and it is made of transparent tissue. Its flexibility allows it to change its shape depending on whether you are looking at a close object or one that is far away. This is possible thanks to the ciliary muscles that contract or release, which then leads to the changing lens’ shape.
- The Retina – this tissue covers the inside of the eye and it is sensitive to light. The cornea and the lens are focusing the images onto the retina, and the cells located here are converting it into electrical impulses. These impulses are then carried to the brain through the optic nerve. The signals are then interpreted by the brain as visual images.
In order to have a clear image, the rays of light need to come together exactly on the retina. Refractive errors occur when the lens and the cornea are forming the signal either in front of the retina or behind it. Now let’s take a closer look at the types of refractive errors. These are:
It is also known as near-sightedness and it occurs when people can see close objects clearly, but do not see distant objects very well. In this case the distance between the cornea and the retina is too long, and the light rays focus in front of the retina, instead of on it. It is usually inherited and discovered in childhood, and sometimes it becomes worse during the teenage years when the body is growing fast.
This one is known as far-sightedness and as you may already know, it is the opposite of Myopia. In this case, people see far away objects clearly, but do not see close objects too well (they appear as blurry). The distance between the cornea and the retina is too short, and light rays are focused behind the retina, instead of on it. It appears in childhood and may become better with time. Some people witness hyperopia differently, and may not see very clear regardless if the object is close or far away.
This condition happens because of the aging process of the eye. As years pass by, the lens becomes more rigid and does not change its length that easily anymore. So, in this case, it becomes harder to read at a close distance. Presbyopia can take place whether the person has the other 3 refractive errors mentioned in this article, or not. So it can be combined with any of them.
This condition happens because the cornea doesn’t have a regular shape. A healthy cornea should be curved equally in all the directions (looking like a basketball). So when the light enters it, it is focused equally in all directions. But if the cornea is asymmetric (looking more like an American football), then the vision gets affected as well. A person that has astigmatism will see the world just like you see it in a distorted mirror. This condition affects sight for both close and far away objects, and images appear blurry and stretched out.
While presbyopia usually affects middle-aged people, the other conditions can affect anyone, regardless of age and sex. If parents have a certain refractive error, this can be transmitted to their kids as well. The symptoms include:
- Having a double vision
- Seeing things in haze (blurred vision)
- Having headaches and eye strain
- Getting a sense of glare when looking at bright lights
Diagnose – In order to determine if someone has any refractive errors, that person must go through a detailed examination of the eyes. The simplest tests consist of asking the patient to read a special chart through various lenses. The test is performed by a specialist (an ophthalmologist or optometrist) by using a special device. The doctor will ask the patient to look at the images through lenses of different strengths, and he will fine tune until the person gets a clear vision. In the case of small children and people with cognitive disabilities that can’t provide any feedback, the doctor will perform the process of retinoscopy.
Treatment – The easiest and most common treatment is that of prescription glasses. The doctor will tell you exactly what kind of lenses to wear. People who do not want to wear glasses can opt for contact lenses instead. In this case, the lenses become the first surface of the eye, and they will refract or focus the rays of light in order to provide a clear vision. If they are used and maintained properly, contact lenses can offer great results without the hassle of wearing something on your face. It is important to clean them as indicated in order to avoid any infections of the eye.
There are also various types of laser surgeries (PRK, LASIK, LASEK or epi-LASIK that change the curvature of the cornea in order to correct the refractive error. Refractive surgery has both pros and cons, and it should be discussed with the surgeon first, in order to take the best decision.