Hi there fine Meowers,
In this post Jake requests us to help Endmyopia with a nice and compact glossary of terms, designed to give newbies a compact reference to the terms that we utilize. Please add to and edit the following definitions if you feel like helping ol’ uncle Jakey out a little here.
We use two categories, general eyesight terminology and Endmyopian specific:
Endmyopia specific (thanks @mag):
Active focus - The process of looking at an object or text that is slightly beyond your eyes’ (together with any corrective lenses) maximum focus distance (i.e. slightly blurry) and in a relaxing way, waiting for your eye to clear up the blur. Note: you may have to train your eyes to be able to do this first.
Ciliary spasm - A contraction of the ciliary [see: ciliary muscle] in which a thickened state of the lens lingers following a period of close-up vision. Absent ciliary relaxation, the lens is unable to refocus on objects situated at a greater focal distance, thereby producing a state of myopia.
Ciliary muscle - A smooth fibrous muscle internal to the eye which surrounds the flexible lens. Through both contraction and relaxation, the ciliary function changes the shape of the lens, thereby changing the distance upon which the eye can properly focus.
Differentials - As “normalised” but lenses reduced further in refractive power such that you can only see as far as your most common screen distance leaving a small amount of blur.
Distance to blur - The distance you can see JUST before objects/text start to become blurry.
Focal point/Focal plane - The distance at which an object (or, in the case of focal plane, a flat surface perpendicular to the line of sight) appears to be in proper focus to the viewer. This distance is a function of the particular shape of the lens within the eye at the moment of viewing and will also be affected by the shape and strength of any corrective lenses placed between the eye and the object (or surface) being viewed.
Full prescription - The lenses prescription that allows you to see to “infinity”/the horizon without any blur. Using this prescription things you see should not become blurry at any distance, only smaller. With these, your viewing distance is limited only by subject size/eye resolution, not by blur.
Normalised - Lenses (glasses or contacts) that have a refractive power lower than your full prescription but high enough to provide distance vision with only a small amount of blur (enough to practice active focus). “Small amount” is subjective and is different for each person.
Eyesight in general (thanks @HectorVazquezPeralta) :
Accommodation - the ability of the eye to flex the lens in the eye and change focal distance.
Circle of least confusion - The geometric area of light focus inside the eye that is the best compromise for astigmatism correction. This is approximately located at the point light focus of your “spherical equivalent” (sphere + cylinder/2) would be, but is a circle instead of a point.
Myopia - (more commonly known as shortsightedness) is, as contrary as what we have been taught, a refractive state in which a person who suffers from it isn’t able to see things clearly at the distance.
Myopic /hyperopic defocus - Myopic defocus is when images are blurry because you’re nearsighted. Hyperopic defocus is when images are blurry because you’re farsighted. Defocus can be accentuated or canceled with lenses. A person with good vision wearing plus lenses would introduce myopic defocus.
Pseudo myopia - or NITM (Near Induced Transent Myopia) is the previous stage for lens induced myopia. The pseudo myopia is just a symptom caused by the strain generated from an excessive amount of work seeing something up close, generally Computers or Smartphone screens.
Spherical equivalent - Sphere power + 1/2 of cylinder power. This approximates the same total lens strength without astigmatism correction.
Presbyopia - The inability to change your natural lens focus due to normal age related lens stiffening.
Hyperopia - Farsighted
Please feel free to make these better, comments below for discussion purposes. I would like to get some input on the question of whether we need to add eyesight problems to the general list, thinks like cataract, glaucoma, retinal detachment come to mind, vote on it in this poll please:
- Add eye health related terms to the glossary
- Don’t add them, it’ll make for too long of a list
- Add them, but under it’s own header
- I’m impartial
@Laurens: I’d like to start by adding the following terms (and cross references):
-optician - a technician that fits and dispenses glasses and contacts, in many locations this is a licensed profession.
-Anisometropia (diopter ratio)
-Astigmatism/cylinder correction - a plus spherical lens focuses light on a point, a cylinder lens focuses light in a line. If you see directional smear blur, you will probably be prescribed a cylinder in your glasses.
-prism - a lens that changes the angle of all light passing through it, meaning that looking straight ahead you’ll see an image off to the side.
Often used to treat lazy eye/amblyopia.
-axis - the angle of the cylinder correction
-accommodative amplitude (I never spell that word right)
-ciliary spasm/accommodative spasm
-overcorrection (has two meanings)
-accommodative lag and lead
-index of refraction
I’ll think of more, too.
Thanks @Dlskidmore for your great additions to these terms!