Myopia is an eye disorder when the eye is in the state of relaxation, parallel light focuses in front of, instead of on, the retina. This causes distant objects to be blurry because they cannot form a clear image on the retina. Myopia can be diagnosed during a refraction. The degree of myopia is described in terms of the power of correction. For example, if you are -0.50, you have ½ diopters of nearsightedness. When the eye is in the state of relaxation, if parallel light enters the eye and focuses right on the retina, a clear image can be formed, which is called a normal eyesight. If a distant point cannot focus properly on the retina, a refractive error is present, which is called ametropia.
Myopia can be classified into many different groups based on degrees, refractive components, and pathologic progression.
Low myopia——usually describes myopia of less than -3.00 diopters.
Moderate myopic——usually describes myopia between -3.00 diopters and -6.00 diopters.
High myopia——usually describes myopic larger than -6.00 diopters.
Axial myopia——is the most common type of myopia, which is attributed to an increase in the eye’s axial length, while the refractive performance of other refractive components such as cornea and lens is normal.
Refractive myopia——is usually caused by large curvature of cornea or lens. It is also attributed to the change in the structure or location of refractive components. The refractive performance is abnormal while the axial length is in the normal range.
Non-pathologic myopia——is usually less than 6.00 diopters, and most of the patients experience no pathological changes in the fundus. Myopic progression is usually slow. The vision can be corrected to normal with proper prescription lenses.
Pathologic myopia——is classified as a high myopic refractive error accompanied by various complications. In addition to poor vision, patients with pathologic myopia often have poor night vision, floaters, flash sensation, etc. Other risks associated with pathologic myopia include retinal detachment and damage, macular hemorrhage, and glaucoma.
What are the causes of myopia?
The underlying cause of myopia is not clear. Most scientists believe that myopia is related to a variety of factors, including genetic factors, environmental factors, bad eye habits and so on.
A large number of studies have indicated that contribution of genetic factors accounts for a certain percentage of nearsightedness. A risk for myopia may be inherited from both or one of the parents. It is clear that the occurrence of high degree of myopia is passed on through recessive genes.
Near work is one of the most common environmental factors of myopia. Other factors include poor lighting, small and obscure handwriting, long continuous reading time, and lack of outdoor activities.
Some studies have suggested that the deficiency of trace elements, dystrophic components, and air pollution are all the causes of myopia. With the popularity of electronic products in recent years, long time near work on the electronic devices has become one of the most common factors of myopia.
What are signs and symptoms of myopia?
A myopic individual can see clearly out to a certain distance, but objects placed beyond this distance appear blurry. A myopic person needs to squint or partially close the eyes when looking at distant objects. If you are nearsighted, you may also notice frequent eyestrain, eye fatigue when trying to see objects more than a few feet away, and headaches caused by eyestrain. Myopia may contribute to the development of exotropia. Myopic eyes are usually associated with weak eye muscle, and the imbalance in eye muscles can lead to exotropia. Myopia may also change the appearance of the eye. With pathologic myopia, the axial of the eye prolongs, so myopic eyes are longer and have steeper corneas than normal eyes. Myopic eyes have a deeper anterior chamber, which causes the eyes to bulge forward. Moreover, changes of fundus are commonly seen in myopic patients. When the degree of myopia is high with fundus damage, the following complications may appear.
- Retinal detachment: A myopic patient usually has thinner retina, which puts the eye at greater risk of retinal tear and detachment. Retinal detachment can cause blurred vision and even permanent loss of vision
- Macular degeneration: Increased axial elongation in pathological myopia may cause macular degeneration with macular hole and hemorrhage, leading to visual distortion.
- Double vision: High myopia may cause double vision and limit eye movements. Extreme exotropia is another symptom of pathological myopia.
- Color anomaly: Pathological myopia may lead to color anomaly, in which a person has full trichromatic color vision but does not make the same color match as the majority people do. Blue-yellow color anomaly is most common. When macula lutea is damaged, red color anomaly may also occur.
- Photophobia & night blindness: Patients with pathological myopia may be less light-sensitive. You may find bright light uncomfortable or you find it difficult to adapt to changes in lighting. When you switch to a dark environment from a bright environment, you need a long time to adjust to the darkness in order to detect objects. Different degrees of night blindness may even occur.
- Floaters: Floaters are spots in vision that look like black or gray pinpoints or strings that float in the eyes. Floaters are a natural part of eye’s aging process, and they are very common in people who have severe myopia.
Although there isn’t a specific cure for myopia, it is absolutely controllable and correctable, which generally does not affect everyday life and work. Wearing eyeglasses will aggravate myopia is a common misunderstanding. Eyeglasses and contact lenses are proven to be the best treatment options while nearsightedness is still changing.
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