Myopia, commonly known as nearsightedness, is a widespread vision condition where distant objects appear blurry. This occurs because the eye focuses light in front of the retina, rather than directly on it. It is a refractive error, meaning the eye does not bend light correctly to achieve clear vision.
Understanding Myopia’s Measurement
The severity of myopia is quantified using diopters (D), a unit indicating the optical power of a corrective lens. A negative sign precedes the diopter value, signifying a diverging lens is needed to shift the focal point back onto the retina. Myopia is categorized into distinct levels based on these measurements.
Mild myopia encompasses refractive errors up to -3.00 D, indicating a relatively low degree of nearsightedness where distant objects are only slightly blurred. Moderate myopia ranges from -3.00 D to -6.00 D, representing a more pronounced level of vision impairment requiring stronger corrective lenses. High myopia is defined as a refractive error greater than -6.00 D, signifying substantial nearsightedness that often carries increased ocular health considerations.
What Causes Myopia and How It Progresses
Myopia primarily develops when the eyeball lengthens excessively from front to back, or when the cornea, the clear front surface of the eye, becomes too steeply curved. Both of these structural alterations cause incoming light rays to converge and focus in front of the retina.
Genetic predisposition plays a significant role, with children of myopic parents having a higher likelihood of developing the condition. Environmental factors also contribute to its onset and progression, particularly extended periods spent on close-up activities such as reading, studying, or using electronic devices. Conversely, spending more time outdoors, especially during childhood, has been observed to help slow the progression of myopia. Myopia often begins in childhood, typically between ages 6 and 14, and can worsen throughout adolescence due to rapid eye growth. It generally stabilizes in the late teens or early twenties once eye growth ceases.
Recognizing Myopia’s Symptoms
Individuals with myopia experience several noticeable symptoms. The most direct sign is blurred vision when viewing distant objects, while near vision remains clear. Other common indicators include excessive blinking and frequent headaches from eye strain.
Children with myopia might also constantly rub their eyes or squint to bring distant objects into sharper focus. Early detection of these symptoms is important, especially in school-aged children, as uncorrected myopia can lead to significant eyestrain and headaches. This can negatively impact a child’s academic performance and overall quality of life.
Types of Myopia and Their Health Implications
Myopia is not a single, uniform condition; it presents in various forms, each with distinct characteristics and potential health implications. Simple myopia is the most common type, where the eye is otherwise healthy, and vision correction with eyeglasses or contact lenses restores clear sight. This form usually stabilizes in adulthood without progressing to more severe complications.
High myopia is often considered an eye disease due to the increased risk of associated ocular complications. The greater elongation of the eyeball in high myopia stretches and thins the retina and other internal eye structures. This stretching can predispose individuals to serious eye conditions, including retinal detachment, where the light-sensitive tissue at the back of the eye pulls away from its supporting layers.
Individuals with high myopia also face an elevated risk of developing early cataracts, which are clouding of the eye’s natural lens, and glaucoma, eye conditions that damage the optic nerve. A more severe form, known as pathological or degenerative myopia, is characterized by extreme and progressive elongation of the eyeball. This leads to profound degenerative changes within the retina and other internal eye structures, causing vision impairment that often cannot be fully corrected with standard eyeglasses or contact lenses. Pathological myopia can result in significant and permanent vision loss due to progressive damage to the macula and other retinal areas.
How Myopia is Managed
Managing myopia involves various strategies aimed at correcting blurry vision and, in some cases, slowing its progression. Non-surgical methods are common options for vision correction. Eyeglasses and contact lenses work by adjusting how light enters the eye, ensuring it focuses directly on the retina for clear distant vision.
Orthokeratology (Ortho-k) involves wearing specially designed rigid contact lenses overnight. These lenses gently reshape the cornea while sleeping, providing clear vision during the day without the need for glasses or contact lenses. This method can also help slow the progression of myopia in children. Surgical interventions are typically reserved for adults whose refractive error has stabilized, usually after age 18 or 20.
Laser eye surgeries like LASIK (Laser-Assisted In Situ Keratomileusis) and PRK (Photorefractive Keratectomy) reshape the cornea using a laser to permanently alter its curvature. For individuals with very high levels of nearsightedness or those unsuitable for laser surgery due to thin corneas, lens implants, such as implantable collamer lenses (ICLs), can be surgically placed inside the eye. While myopia cannot be cured, these diverse treatments effectively manage symptoms and, for some, mitigate further progression of the condition.