Optics Lecture 1 Introduction to Lenses and Refractive Error

Electromagnetic Spectrum

All of the frequencies or wavelengths of electromagnetic radiation

Visible light

400-700 nm

We treat light as a

wave

Wavefront

a series of concentric circles (waves) that travel away from the source that created it

Traveling energy!

Rays are ____ to wavefronts

perpendicular

Vergence

indicates how curved the wavefront is

Steeper vergence

more curved/ smaller circle

closer to the source

Flatter vergence

less curved/larger circle

travels away from the source

divergence

light recalling away from a source

wavefronts get larger and flatter

Convergence

light rays headed toward a focal point

wavefront get smaller and steeper

Wavefronts travel ----- the source of origination

away from

The closer to the source the ----- the curve, the ----- the wavefront, the ----- the wavefront

steeper

smaller

stronger

The farther from the source the ----- the curve, the ----- the wavefront, the ----- the wavefront

flatter

bigger

weaker

Rays indicate the ----- the wavefront is traveling and are ------ to the wavefront

direction

perpendicular

Wavefronts moving away from the source are -----

diverging

Wavefronts moving towards a focal point are ----

converging

Refraction

The bending of a wave as it passes at an angle from one medium to another

how and why do lenses refract light?

When light goes from air into a different substance of higher refractive index it

slows down and changes direct

The extent to which it changes direction depends on

the angle the light ray makes with the surface of the substance (angle of incidence) as well as the curvature of that surface

radius of curvature determines the

dioptric power

dioptric power determines

where the light will focus (focal point)

Convex lens

converges the light

feels thicker in the middle than at the edges

Concave

diverges the light

fells thinner in the middle than at the edges

refractive error

There is an error causing the light to not hit the retina = the image is not clear

lenses have the power to change the ----- of light.

vergence

For an image to look clear, the focal pint must be on

the retina

The power of the eye comes from

the cornea and the natural lens

the cornea and the natural lens are both

convex and converge any light that enters the eye

If the power of the eye is appropriate given the length of the eye

the light focuses on the retina and the patient sees clearly

This is called

Emmetropic!

Myopic Eye

light tays focus in front of the retina

(nearsighted)

Why may someone be myopic

the eye is too powerful

the eye is too long

punctum remotum (far point)

farthest point an object can be held and still be clear

Far point gets ---- to the eye as myopia increases

closer

Hyperopic

light rays focus behind the retina

why is someone a hyperope (farsighted)

the eye is too weak

the eye is too short

punctum proximum (near point)

nearest point an object can be heard and be seen clearly

near point gets _____ from the eye as Hyperion increases

further

Unit of measurement for the power of the lens

Diopters

Plus lenses are

convex

Convex plus lines make the light more

convergent

pulls the focal point forward

Minus lenses are

concave

concave minus lenses make the light more

divergent

pushes the focal point back

Minus lense properties

concave

thick edge and thin centers

Minus lens: the stronger the power of the lense the ---- the radius of curvature

the thicker the edges, the ---- the center

steeper

thinner

Properties of plus lenses

convex

thin edge

thick center

magnify object

Refractive error

an error in the way the light refracts or is displaced as it enters the eye

pure myopia and hyperopic are ---- refractive errors

spherical

Spherical Refractive error corrected with

spherical lenses

Astigmatism occurs when

the eye is not spherical in shape but oval

astigmatism refractive error is corrected with

cylindrical lenses

Spherical eyes

cornea/natural lenses are spherical

- symmetric

- same curvature in all meridians

- same power in all meridians

- light entering the eye focuses at a point either in from of or behind the retina

Spherical Refractive Errors

all parts of the image appear equally blurred

Astigmatic Cornea

cornea is strength alone an axis 0-180 degrees

one meridian has the flattest curvature

90 degrees away is the steepest curvature

Light entering an astigmatic eye forms

2 lines images either in front of, behind, or straddling the retina

Astigmatic refractive errors

images are not equally blurred

correcting lenses will NOT have equal power in all meridian's

OD

oculus dextrus

right eye

always top line

OS

oculus sinister

left eye

OU

Oculus uterque

both eyes

Spectacle Rx: Sphere

myopic or hyperopic component

Spectacle Rx: Cylinder

astigmatic component

Spectacle Rx: Axis

orientation of astigmatic component

Axis of the correcting cylinder is described by its -----meridian

flat

Cylindrical component of spectacle Rx ------- line images

superimposes/collapses

Spherical component of spectacle Rx puts collapsed line images ------ after they have been collapsed

onto the retina

see examples in lecture