Myopia

Myopia is a common eye condition often called near-sightedness or short-sightedness. It is classified as a refractive error, which means the eye does not bend light correctly to create a clear image. In a person with myopia, light from distant objects focuses in front of the retina rather than directly on it. This causes distant objects to appear blurry while close objects remain clear. Because it affects vision so significantly, it is one of the most common eye disorders globally.

The physical cause of myopia depends on how the eye is shaped or how it bends light. One major type is axial myopia, which occurs when the eyeball grows too long from front to back. Another type is refractive myopia, where the parts of the eye that bend light are too strong. This can happen through curvature myopia, where the cornea has excessive curvature. It can also occur as index myopia, caused by variations in how light moves through the ocular media. In some rare cases, the lens may shift forward due to swelling, also causing a change in focus.

Clinical classifications help doctors describe the specific nature of the condition. Simple myopia is the most common form and occurs in otherwise normal eyes. In contrast, degenerative myopia, also called pathological myopia, involves significant changes to the fundus. This type is more severe and can lead to progressive vision loss over time. There are also temporary forms, such as pseudomyopia, which is caused by a spasm in the eye's focusing system. Other specialized types include instrument myopia from using microscopes or form deprivation myopia caused by limited light exposure.

Researchers believe myopia results from a complex interaction between genetics and the environment. Genetic studies have identified 18 different loci, or locations, on 15 different chromosomes associated with the condition. These genetic factors may account for 60% to 90% of the variance in how light is refracted. However, the rapid increase in myopia rates since the 1950s suggests that environmental factors play a huge role. Factors such as urbanization, increased years of education, and spending more time indoors are linked to higher risks. Interestingly, children who spend more time outdoors may have a lower risk, possibly due to sunlight helping the eyes release retinal dopamine.

Myopia is a massive global health issue, affecting an estimated 1.5 billion people. This represents approximately 22% of the entire world population. Rates vary greatly by location and age. For example, the rate among adults ranges from 15% to 49%. Among children, the rates show even more variety: 1% in rural Nepal, 4% in South Africa, and 12% in the United States. In some large Chinese cities, the rate reaches as high as 37%.

Diagnosing myopia typically requires a visit to an optometrist or an ophthalmologist. During an exam, professionals use cycloplegics, such as atropine, to relax the eye's accommodation. This allows the doctor to get an accurate measurement of the refractive error. It is important to monitor progressive myopia with regular exams to track changes. If left uncorrected, myopia is a major cause of vision impairment alongside conditions like cataracts and glaucoma. Severe cases also carry an increased risk of retinal detachment and macular degeneration.

Fortunately, several methods exist to correct vision for those with myopia. Eyeglasses are considered the simplest and safest method of correction.

Contact lenses are another option that can provide a wider field of vision, though they carry a higher risk of infection. For permanent changes, refractive surgeries like LASIK or PRK can reshape the cornea. Another advanced procedure is the placement of an implantable collamer lens (ICL). This lens is placed inside the anterior chamber in front of the natural lens without affecting the cornea.