ABO Part 2: Basic Optical Principles

OD

oculus dexter, right eye

OS

oculus sinister, left eye

OU

oculus uterque, both eyes

lens

combination of front & back curves
F1+F2= total power

cornea

vison begins when light enters eye through cornea

20/40 vision

when a person can see an object at 20ft that a normally sighted person can see at 40ft

emmetropia

light comes to focus precisely on retina, no corrective lenses needed.

myopia

also known as nearsightedness. near objects are clear, light rays are focused in front of the retina

hyperopia

also known as farsightedness. far objects are near, light rays are focused behind the retina

concave lens

refocus light on retina for a myopic eye

convex

focus light rays on retina for a hyperopic eye

astigmatism

light rays don’t come into a single focus, focus on more than one spot

simple myopic astigmatism

one point comes to focus on the retina and one point comes to focus in front of the retina

simple hyperopic astigmatism

one point comes to focus on the retina and one point comes to focus behind the retina

compound myopic astigmatism

both points of light come to focus in front of the retina

compound hyperopic astigmatism

both points of light come to focus behind the retina

mixed astigmatism

one point comes to focus in front of the retina, while the other comes to focus behind the retina.

wavelength

measured in nanometers. seen by human eye between 380nm-750nm

UVA

315nm-380nm, ages skin

UVB

290nm-315nm, source of sunburns

UVC

200nm-290nm, absorbed by atmosphere

snow

reflects 80% of light

water

reflects 25% of light

sand

reflects 15% of light g

grass and soil

reflect 10% of light

index of refraction

index of refraction= speed of light in air/speed of light in medium

speed of light in air

186,000

surfacing lab standard

1.53 index of refraction

blue wavelength

shorter high energy wavelength, contributes to blurry vision

angle of reflection

angle which ray leaves reflecting surface

angle of incidence

always equals angle of reflection

Snell’s Law

formula used to calculate angle of refraction