Myopia, commonly known as nearsightedness, is a widespread refractive error where distant objects appear blurry because the eye focuses light incorrectly. For most people, this condition is corrected simply with glasses or contact lenses. However, a specific classification known as high myopia carries distinct structural risks that can threaten long-term vision health. Understanding the difference is important because high myopia involves physical changes to the eye that increase the likelihood of serious complications, moving the concern far beyond a simple need for stronger lenses.
Defining High Myopia
High myopia is clinically defined by a refractive error of -6.00 diopters or worse, meaning an individual requires a strong corrective lens to achieve clear distance vision. This severity level represents a fundamental change in the eye’s anatomy. The underlying cause is the excessive elongation of the eyeball from front to back, a measurement known as the axial length. When the eye grows too long, typically exceeding 26 millimeters, the internal layers are stretched over a greater surface area. This stretching causes the thin, light-sensitive retina and its underlying supportive structures to become thinner and more fragile. This physical strain is the root cause of the heightened risk for vision-threatening conditions later in life.
Retinal Detachment and Tears
One of the most immediate and serious risks associated with high myopia is the potential for a retinal tear or a full retinal detachment. The mechanical stretching of the peripheral retina makes this tissue abnormally thin and vulnerable, often resulting in areas of weakness like lattice degeneration. As the clear, gel-like substance inside the eye, the vitreous, naturally liquefies and shrinks with age, it can tug on the fragile, attached retina.
This traction can create a small tear or hole in the peripheral retina, which then allows fluid from the eye’s center to seep underneath the tissue. When this happens, the retina separates from the blood vessels that provide its oxygen and nourishment, leading to a retinal detachment. This event is a medical emergency because the detached tissue quickly loses function, potentially leading to irreversible vision loss if not surgically reattached within a short time.
Individuals with high myopia must be vigilant for acute warning signs. These symptoms include a sudden shower of new floaters (dark specks or cobweb-like shapes drifting across the vision), flashes of light (photopsia), or the appearance of a shadow or curtain moving across the field of vision. Immediate evaluation by an eye care specialist is necessary, as early laser treatment can often seal a tear before it progresses to a full detachment.
Progressive Myopic Maculopathy
In addition to the acute risk of detachment, high myopia presents a progressive threat to the macula, the central area of the retina responsible for detailed vision. The stretching caused by axial elongation stresses the macula, leading to a degenerative condition known as myopic maculopathy. This condition is a leading cause of visual impairment in people with high myopia.
The continuous stress leads to the progressive atrophy, or thinning and breakdown, of the macula’s supportive layers, including the retinal pigment epithelium and the underlying choroid. This atrophy results in a gradual, irreversible loss of central vision needed for tasks like reading and recognizing faces. Clinical signs of this damage include lacquer cracks (breaks in the deeper layers) and posterior staphyloma (an outpouching of the back of the eye).
A complication that can rapidly accelerate vision loss is myopic choroidal neovascularization (CNV), where abnormal, fragile blood vessels grow under the macula. These vessels leak fluid or blood, causing sudden distortion and blurring of central vision. While treatments like anti-VEGF injections can manage myopic CNV, the underlying structural damage remains, making careful, long-term monitoring essential.
Monitoring and Managing High Myopia
Managing high myopia involves consistent monitoring to detect complications when interventions are most effective. Individuals typically require a comprehensive dilated eye examination annually, allowing the specialist to thoroughly inspect the entire retina, especially the vulnerable periphery and the macula.
Specific diagnostic technologies track the eye’s structural health. Optical Coherence Tomography (OCT) provides high-resolution cross-sectional images of the macula and retina, detecting subtle thinning, fluid accumulation, or early signs of maculopathy. Measuring the axial length tracks the physical progression of eye elongation, which helps assess overall risk.
Patients should wear protective eyewear during sports to avoid blunt trauma that could trigger a retinal tear. Anyone with high myopia must be educated on the symptoms of retinal detachment and maculopathy, understanding that any sudden change in vision, flashes, or new floaters necessitates an immediate, emergency eye examination.