I’ve gone to an optometrist for the second time. The first time was in '84 when I started flying. Today I went again, since I’d like to get back in the saddle.
My prescription looks like this:
SPHERE CYLINDER AXIS
OD -0.25 -0.25 054
OS -0.25 -0.50 117
I don’t wear my (23-year-old) glasses except when I fly, and it’s been a long time since I’ve been. (9/11 made things difficult – i.e. the fleet was grounded for months – and then there were time or money issues. The only thing flying was time!) The optometrist said my vision ‘isn’t that bad’. But what does that mean? Obviously not 20/20. But 20/what? What do the numbers mean? Would i be a good candidate for LASIK? (I didn’t ask the optometrist, as I thought that would be like asking a barber if you need a haircut.)
MPSIMS: He gave me a full eye examination and pronounced my eyes healthy. Only he put some drops in that dilated my pupils. It was an interesting drive home! And he said I could use some +0.75 reading glasses for very small print, but they’re not really necessary. Yet. I get my new glasses next week.
Sphere describes the fundamental curvature of the lens in diopters; positive values describe a converging (convex) lens, used for far-sightedness while negative values describe a diverging (concave) lens for nearsightedness. Cylinder, also in diopters, specifies the cylindrical component needed to correct astigmatism and the axis states the rotation of this cylinder from the vertical in degrees. OD and OS are Oculus Dexter and Oculus Sinister, which is fancy Latin for right and left eye, respectively.
If he does not offer LASIK (and I am not sure how many optomerists (as opposed to ophthalmologists) do), he would be fine to ask, as he could not be making money off a service he does not provide.
My understanding, (subject to correction), is that presbyopia (“elder eye,” the nasty loss of clear vision that strikes two days before one’s 40th birthday), is a condition that lasts roughly 15 to 25 years during which time one’s eyes constantly change shape (messing up the natural focus of the eye). Performing LASIK to correct vision at that point is a waste of money because, regardless of the surgery to correct the lens, the shape of the whole eye continues to change, rendering any small correction to the lens transitory. For people in their 20s (before presbyopia) and people in their 60s (at the end of the presbyopia changes), LASIK is fine, but for that specific period, it s a waste of time and money.
Presbyopia is not caused by the eye changing shape. It is mostly caused by hardening of the lens, and also possibly partly by weakening of the focusing muscles. It gets more difficult to focus at near objects, and at presbyopia’s most advanced stage a person’s eyes are focused permanently at infinity. There is no surgery to correct this, so most people eventually need glasses for reading and other activities that require close focus.
Surgery to correct myopia (nearsightedness) can make it harder to cope with presbyopia, since myopia and presbyopia tend to cancel each other out (i.e. people with myopia can focus closer than normal, so they can go longer without presbyopia making their lives difficult). Astigmatism and farsightedness can also be corrected with surgery, but one would still need corrective lenses to focus on close objects. That is, for those with presbyopia surgery would sometimes make things worse and, when it didn’t, would still not eliminate the need for glasses in all situations.
The refractive error (the -0.25 part) can’t really be converted exactly to a visual acuity (the 20/whatever part) because they measure different things. There’s some correlation, but no one-to-one conversion factor. To measure your visual acuity, you need to find a Snellen chart or ask your doctor.
If all you need is a third-class medical certificate, you may not need corrective lenses for such a minor refractive error. The standard is (I think) only 20/40, the same as for driving in most states. For a second- or first-class certificate you need corrected acuity of 20/20, so you probably would need the glasses.
"Isn’t that bad’? I’d say not. The sphere goes negative from 0 for myopia, and -.25 is barely anything. From here, the sphere measures the refractive error, or “the degree to which images received by the eyes are not focused on the retina (myopia, hyperopia, or astigmatism) measured in diopters”.
My eyes are kind of bad and are -6.00 and -7.00. Mom’s are legally blind and something like -13.00 or -14.00.
You are correct - the standard for third class medical certficates is correctable to 20/40. Second and first class require correctable to 20/20. Please note that is for the US. Other countries have varying requirements.