Severe nearsightedness, also called high myopia, is defined as a prescription of more than -6.00 diopters. At this level, distant objects are extremely blurry without correction, and the eye itself has physically changed shape in ways that carry long-term health risks. The American Academy of Ophthalmology classifies myopia into three tiers: mild (less than -3.00 diopters), moderate (-3.00 to -6.00), and severe (beyond -6.00).
What the Numbers on Your Prescription Mean
Diopters measure how strongly a lens needs to bend light to bring your vision into focus. A prescription of -1.00 means you struggle to see distant road signs clearly. At -6.00, you can’t recognize faces across a room. Someone with -10.00 or -15.00 may only see clearly a few inches from their face without glasses or contacts.
Eye care professionals also measure axial length, which is the distance from the front to the back of the eyeball. A typical eye is roughly 24 millimeters long. In high myopia, the eye has grown longer, sometimes exceeding 26 millimeters or more. There’s no single axial length cutoff that perfectly maps to -6.00 diopters, since other factors like the curvature of the cornea also affect your prescription. But axial length matters because a longer eyeball means the retina is stretched thinner, and that stretching is where the serious complications come from.
Why Severe Myopia Is More Than Blurry Vision
High myopia isn’t just an inconvenience that glasses or contacts fix. The elongated shape of the eye creates structural vulnerabilities that persist even after vision correction. The retina, the light-sensitive tissue lining the back of the eye, becomes thinner and more fragile as the eye stretches. This puts people with severe nearsightedness at meaningfully higher risk for several sight-threatening conditions.
Retinal Detachment
The stretched retina in a highly myopic eye is more prone to tears and detachment, where the retina peels away from its supporting tissue. The lifetime risk of retinal detachment in high myopia is roughly 20 times higher than in someone with normal vision. Even moderate myopia (beyond -3.00) carries about a 10-fold increased risk. Retinal detachment is a medical emergency that requires surgery to prevent permanent vision loss, and the risk goes up further after cataract surgery, with one study finding a 7-fold increase in highly myopic eyes compared to non-myopic eyes after the procedure.
Myopic Macular Degeneration
This is a condition distinct from the age-related macular degeneration you may have heard of. In myopic macular degeneration, the stretching of the eye damages the macula, the central part of the retina responsible for sharp, detailed vision. It’s remarkably common in people with high myopia. A systematic review in the British Journal of Ophthalmology found that roughly 47% of people with high myopia show signs of myopic macular degeneration, with individual studies reporting rates anywhere from 25% to 71%. This is the leading cause of irreversible vision loss in people with severe nearsightedness.
Glaucoma
People with high myopia are also significantly more likely to develop glaucoma, a condition where pressure damages the optic nerve. A large study published in Ophthalmology found that people with high myopia were about 3 times more likely to need glaucoma surgery than those with normal vision. For the most serious type of glaucoma surgery, that risk jumped to 4 times higher. Glaucoma is particularly tricky to catch in myopic eyes because the optic nerve already looks unusual due to the eye’s elongated shape, which can mask early damage.
How Severe Myopia Is Corrected
Glasses and contact lenses work well at any prescription level, though very high prescriptions mean thicker lenses and, for glasses, noticeable distortion at the edges. High-index lens materials help reduce thickness, but people with prescriptions beyond -10.00 or -12.00 often prefer contacts for optical quality and comfort.
LASIK is an option for many people with myopia, but it works by reshaping the cornea, and there’s a limit to how much tissue can be safely removed. For people with severe myopia, that limit is often exceeded. Implantable collamer lenses (ICL) fill this gap. ICL surgery involves placing a thin lens inside the eye, in front of the natural lens, and it can correct prescriptions up to -20.00 diopters. It’s often the preferred surgical option for people whose myopia is too high for LASIK.
Regardless of which correction method you use, it’s important to understand that correcting the blur doesn’t eliminate the structural risks. A -9.00 eye that’s been corrected to 20/20 with LASIK still has a stretched retina. Regular dilated eye exams remain essential for catching complications early.
Slowing Progression in Children
Myopia typically starts in childhood and worsens through the teenage years as the eye continues to grow. The earlier it starts and the faster it progresses, the more likely it is to reach the severe range. This has made myopia control in children a major focus of eye care.
Low-concentration atropine eye drops are one of the most studied interventions. A network meta-analysis comparing eight different concentrations found that a 0.05% concentration reduced the risk of myopia progression by about 61% compared to no treatment. Higher concentrations (0.5% and 1%) were slightly more effective at slowing the change in prescription but came with more side effects like light sensitivity and difficulty focusing up close. The 0.05% dose offered a strong balance of effectiveness with fewer downsides, performing nearly as well as the higher doses for slowing the physical elongation of the eye.
Specialty contact lenses, including multifocal designs and orthokeratology lenses worn overnight, also slow progression. Increased outdoor time during childhood, at least 80 to 120 minutes per day, is consistently linked to lower rates of myopia development, though the mechanism isn’t fully understood. None of these approaches stop myopia entirely, but keeping a child’s prescription from crossing into the severe range can substantially reduce their lifetime risk of complications.
What Regular Monitoring Looks Like
If your prescription is -6.00 or higher, annual dilated eye exams are the minimum. During these exams, your eye doctor checks the retina for thinning, tears, or early signs of macular changes. They may also use imaging technology to create detailed maps of your retinal layers, which makes it possible to spot subtle changes from year to year.
Between appointments, knowing the warning signs of retinal problems matters. A sudden increase in floaters (those drifting spots or strings in your vision), flashes of light in your peripheral vision, or a shadow creeping across part of your visual field all warrant an urgent visit. These can signal a retinal tear or detachment, and early treatment dramatically improves outcomes.