The maximum negative eye power is typically around -20 diopters.
Near Normal visual impairment: 20/30-20/60. Moderate visual impairment: 20/70-20/160. Severe visual impairment: 20/200-20/400, or 11-20 degrees on the visual field. Profound visual impairment: 20/500-20/1000 visual acuity, or 6- 10 degrees on visual field.
Visual acuity less than 20/200 is considered legally blind, but to actually fit the definition, the person must not be able to attain 20/200 vision even with prescription eyewear. Many people who would be legally blind without eyewear can function well in everyday life with appropriate glasses or contact lenses.
What are the highest and lowest-strength reading glasses available? The lowest-strength reading glasses have powers of +0.25 diopters, whereas high-strength ones can go well beyond +2.50 diopters—in rare cases, all the way up to +4.00.
At values +0,25 to +3,0 diopters we speak about slight defect, values +3,25 to +6,0 diopters represent medium farsightedness, from +6,25 to +9,0 diopters we talk about high defect. Serious defect (from +9,25 up) comes with impaired vision, but not only in the near but also for further objects.
First: What does it mean to be "legally blind?" In most states, if you have distance visual acuity less than 20/200 that is not correctable with glasses/contact lenses, you are legally considered to be "severely visually handicapped" (which used to be called "legally blind").
Blindness is also defined as visual acuity of less than 3/60, or corresponding visual field loss to less than 10 degrees, in the better eye with best possible correction.
-3.00 diopters or less is mild. -3.00 to -6.00 diopters is moderate. -6.00 to -9.00 diopters is severe.
The maximum negative eye power is typically around -20 diopters. This means that if you have myopia of -20 diopters, you will need to wear glasses or contact lenses with a power of -20 in order to see clearly.
The Maximum power of eye lens of the normal relaxed eye is approximately 60 dioptres.
Mild: -0.50 to -3. Moderate: -3.25 to -5.00. High: -5.25 to -10. Extreme: greater than-10.
Mild: -0.50 to -3. Moderate: -3.25 to -5.00. High: -5.25 to -10. Extreme: greater than-10.
A person who cannot see at six metres what a normally-sighted person can see at 60 metres or has a field of vision restricted to 20 degrees diameter or less (normal field of vision is 180 degrees) or a combination of both (reduced visual acuity and field of vision) is considered legally blind.
If your number is between -0.25 and -2.00, you have mild nearsightedness. If your number is between -2.25 and -5.00, you have moderate nearsightedness. If your number is lower than -5.00, you have high nearsightedness.
A refractive error greater than -6 is when an optometrist might diagnose high myopia in a patient. Low myopia can have a refractive error as low as -0.25, while moderate myopia caps out at -5.75. If left untreated and with age, high myopia can progressively worsen to a greater degree of refractive error.
You are legally blind when your visual acuity drops below 20/200 even with best possible correction or if you have a visual field less than 20 degrees. You are not legally blind as long as you can see 20/200 with your glasses.
Thus the maximum number of power that can be corrected through Lasik surgery is -8.0. Whereas the maximum limit for plus number is +5.0. If you have more power, then correcting your cornea will result in a disturbance of vision.
From early childhood to young adults
These vision problems usually stabilize when development is complete at around age 21. It is rare for myopia or hyperopia to continue to progress past age 20.
20/30 to 20/60 vision in the better eye, even with correction glasses, is considered mild vision loss or mild low vision. 20/70 to 20/130 vision is moderate low vision. 20/200 to 20/400 is severe low vision. If you suspect that you may have vision impairment, it's always best to consult with an eye specialist.
Having a prescription of -8.50D just means you are very short-sighted and as long as you can see around 20/20 with Spectacles or contact lens, you are not legally blind. If when wearing spectacles or contact lenses and the vision in one eye is 20/200 or worse then you would be legally blind.
Visual acuity less than 20/200 is considered legally blind, but to actually fit the definition, the person must not be able to attain 20/200 vision even with prescription eyewear. Many people who would be legally blind without eyewear can function well in everyday life with appropriate glasses or contact lenses.
Is 15/15 vision better than 20/20 vision? No. 15/15 vision means normal sharpness of vision at 15 feet, just as 20/20 indicates normal sharpness of vision at 20 feet. For onsistency, doctors of optometry in the United Sates use 20 feet as the standard for measuring sharpness of vision.
A lens Rx for -14 Diopters tells us you have a very, very high degree of nearsightedness (myopia). This would be considered in the "severe" range. Of all the people who are myopic, less than 2% are worse than -10 Diopters.
While there is no guarantee that a sudden change in vision will cause blindness, ignoring sudden vision changes highly increases the likelihood that you will go blind. We cannot stress this enough: If you experience rapid changes in vision quality, see a doctor as soon as possible.
According to the WHO, legal blindness is when a person has a visual acuity of less than 20/400, or a visual field of fewer than 10 degrees, even with corrective lenses.