The American Board of Opticianry and National Contact Lens Examiners (ABO-NCLE)

fibrous tunic

consists of the sclera and the cornea

vascular tunic

consists of the iris, choroid, ciliary body, responsible for nourishment

nervous tunic

the inner layer of photoreceptors and neurons which consists of the retina

rods and cones

nervous tunic or neural layer contains the special photo (light) receptors known as

macula

approximately 120 million rods spread towards the outside of the retina and about 6 million cones concentrated near the center. where light will focus in a healthy eye

fovea

e highest concentration of cones is found at, center of the macula

anterior chamber

between the cornea and the iris

posterior chamber

between the iris and the lens

vitreous chamber

found between the retina and the lens and is filled with a thicker gel-like substance called vitreous humor which maintains the shape of the eye

cornea

Light enters the eye through the transparent, dome

epithelium

The cornea consists of five distinct layers: 1. The outer most layer, rests on Bowman's membrane

Bowman's Membrane

2. The next layer, which acts as a protective barrier

stroma

3. between the two membranes makes up 90% of the thickness of the cornea

Descemet's Membrane

4. separates the stroma and the endothelium

endothelium

5. The inner most layer, removes water from cornea, helping to keep the cornea clear.

iris

amount of light allowed through the pupil is controlled by, colored part of the eye

The iris has two muscles: 1. The dilator muscle

opens the iris allowing more light in

2. The sphincter muscle

closes the iris

crystalline lens

Just behind the pupil, purpose of the lens is to focus light on the retina

accommodation

The process of focusing on objects based on their distance

ciliary body

lens achieves accommodation with the help of the

zonules

The ciliary body is attached to lens via fibrous strands called

Palpebrae

Another term for the eyelid

Medial Canthus

This is the point where the upper and lower eyelids meet near the nose. In layman terms, "the corner of your eye."

Lateral Canthus

This is the point where the upper and lower eyelids meet towards your ear.

Eyelashes

Strong hairs that run along the upper and lower palpebral margins. They are there to filter debris from entering the eye.

Meibomian Glands

Located along the inner margin of the eyelids the glands secrete a liquid that keeps the eyelids from sticking together. These secretions make up part of the tear film.

Fornix

Actual location is behind the eyelid or palpebra and along the sclera. It is where the two layers of the conjunctiva meet and join.

Lacrimal Gland

: INSIDE THE ORBIT OF THE EYE The gland that produces the bulk of the tears. It is located above the lateral canthus in a depression in the bone that surrounds the eye

Lacrimal Puncta

Small openings (pores) located at the medial canthus that allow the accumulated tears to drain off the eye. The tears drain through the nasal cavity which is why when you cry your nose runs!

Lacrimal Canals

The path the tears take from the eye to the lacrimal sac and then to the nasal passage.

Lacrimal Caruncle

Located at the medial canthus the lacrimal caruncle also produces a liquid that soothes and lubricates the eye. These secretions combine with those from the Meibomian glands to make up the eyes tear film.

Cornea

The clear lens or structure that covers the iris or the colored part of the eye. The cornea is the first major structure that refracts light as it enters the eye. It has no blood supply and gets all of its oxygen directly from the air.

Pupil

The opening created by the iris changing size

Sclera

"the whites of your eyes." The sclera is a thick, tough and fibrous layer that provides the structure of the entire eyeball.

Limbus

Where the cornea blends into the sclera

Iris

The colored area under the cornea that opens and closes to regulate light entering the eye.

Palpebral Conjunctiva

The layer that covers the eyelids.

Ocular or Bulbar Conjunctiva

The layer that covers the exposed portions of the eye.

Lateral Rectus

Rotates eye laterally or out towards the ear. Attaches directly to the side of the eye and runs straight back.

Superior Rectus

Eye looks up. Attaches directly to the top of the eye and runs straight back.

Medial Rectus

Rotates eye medially or in towards the nose. Attaches directly to the side of the eye and runs straight back.

Inferior Rectus

Eye looks down. Attaches directly to bottom of the eye and runs straight back.

Inferior Oblique

Eye rolls, looks up and to the side. Attaches along the lateral side of the eye and runs under the eye passing over the inferior rectus and attaches medially.

Superior Oblique

Eye rolls, looks down and to the side. Attaches under the superior rectus, passes through a bony spur known as the Trochlea, and then follow the path of the superior rectus. The raised attachment point provides the muscle the ability to give the eye rotation.

Emmetropic Eye

Notice that in the emmetropic eye all the rays of light entering the eye all focus on the retina right where they need to be to provide crisp sight without the need of corrective lenses.

Presbyopia

Presbyopia makes us unable to read fine print, thread a needle, or do fine work without the aid of magnification. Presbyopia is when the crystalline lens can no longer change shape and provide accommodation. It remains in the flatter less plus shape shown in blue. Prescriptions for presbyopia will show corrections for distance, if required, and the additional notation of an add power as in one of these examples: Add +2.50 Add +1.25

Simple Myopia

Simple because all the rays of light entering the eye focus at the same spot, it is the wrong spot, but they all meet at the same place. The retina is further back from the cornea than in an emmetropic eye, so the rays fail to reach the back of the eye and the retina. Persons with myopia are nearsighted; they are capable of seeing things at "near" distances, or up very close to their eyes. They can read fine print, thread a needle, and work with tiny objects. They cannot see a street sign down the road or a bird high in a tree, without correction. Myopia is corrected with minus lenses. It is easy to remember: Just think my-opia and mi-nus lenses. A prescription for a person with simple myopia would be written like one of these examples: -1.00 Sphere -2.50 Sphere

Simple Hyperopia

In simple hyperopia all the rays of light entering the eye focus at the same spot, it is the wrong spot, but they all meet at the same place. The retina is further forward toward than the cornea in an emmetropic eye, so the rays are trying to focus on an imaginary point beyond the back of the eye. Persons with simple hyperopia are farsighted; they are capable of seeing things in the distance or far off. They can easily see a street sign half a mile down the road and a bird high up in a tree. They cannot see fine print, thread a needle, or do detail work without correction. Hyperopia is corrected using plus lenses. A prescription for a person with simple hyperopia would be written like one of these examples: +1.00 Sphere +2.50 Sphere

Simple Myopic Astigmatism

In simple myopic astigmatism some of the rays of light entering the eye fall short of their intended spot on the retina, but some fall directly on the fovea, where they need to be. Simple myopic astigmatism is corrected using toric lenses. One focus point of the eyeglass lens will provide no correction, or have 0.00 power, for those rays that are falling where they are needed. Another focus point of the lens will have power for the rays that need to be redirected to the correct place on the retina. A prescription for a person with simple myopic astigmatism would look like one of these examples: 0.00 -0.50 X 45 -0.50 + 0.50 X 135 0.00 -2.00 X 130 -2.00 +2.00 X 40

Simple Hyperopic Astigmatism

In simple hyperopic astigmatism some of the rays of light entering the eye focus on a spot beyond the retina, but some fall directly on the fovea where they need to be. Simple hyperopic astigmatism is corrected using toric or sphero-cylinder lenses. One focus point of the lens will provide no correction, or have 0.00 power, for those rays which fall where they should. Another focus point of the lens will have power for the rays that need to be redirected to the correct place on the retina. A prescription for a person with a simple hyperopic astigmatism would look like one of these examples: +1.50 -1.50 X 45 0.00 +1.50 X135 +2.50 -2.50 X 130 0.00 +2.50 X 40

Compound Myopic Astigmatism

This condition is no longer simple, because the rays of light entering the eye do not all meet at the same place. They all fall short of their intended spot on the retina, but some fall closer than others. Depending on the degree of astigmatism (the degree to which the cornea is misshapen) the individual may see objects as bent or distorted in shape as well as blurred. A prescription for a person with a compound myopic astigmatism would look like one of these examples: -1.00 -0.50 X 45 -1.50 +0.50 X 135 -2.50 -2.00 X 130 -4.50 + 2.00 X 45

Compound Hyperopic Astigmatism

This condition is no longer simple, because not all the rays of light entering the eye meet at the same place. They all focus on a spot beyond the retina, but some come closer to the fovea than others. Depending on the degree of astigmatism (the degree to which the cornea is misshapen) the individual may see objects as bent or distorted in shape as well as blurred. A prescription for a person with a compound hyperopic astigmatism would look like one of these examples: +1.00 -0.50 X 45 +0.50 +0.50 X 135 +2.50 -2.00 X 130 +0.50 +2.00 X 40

Mixed Astigmatism

In the eye with mixed astigmatism some rays fall ahead of the retina while others try to focus on a spot beyond the retina. People with mixed astigmatism are neither nearsighted nor farsighted, but instead will have poor vision in all areas. A prescription for a person with a mixed astigmatism would look like one of these examples: +1.00 -2.00 X 45 -1.00 +2.00 X 135 +2.00 -2.25 X 67 -0.25 + 2.25 X 157

186,000 miles per second

Light is a form of radiant energy. It acts as both a particle and a wave. It travels at the fastest known speed in our universe which is

the visible spectrum lie between 400nm and 700nm.

Red light is at the longer end of the spectrum and violet light at the shorter end. A common acronym used to remember the order of colors in the visible spectrum is ROY G BIV (red, orange, yellow, green, blue, indigo, and violet).

ultraviolet (UV)

Just below 400nm

infrared (IR)

just above 750nm

refraction

As light moves from one transparent medium to another, at any angle other than perpendicular to the material surface, the change in speed will also result in a change in direction. This change is direction is called

index of refraction

"n" is the notation, n tells us how much a given material will slow down and change the direction of a ray of light passing through it. The higher the index or "n" the thinner a lens can be and produce the same power. Common index numbers include, 1.498, 1.523, 1.586, 1.60, 1.67, and 1.74. It is a scientific absolute that the higher the index of refraction, the thinner a lens can be and still produce the same diopter value. • A lens with an index of refraction of 1.74 and a power of - 6.00 will be thinner than a lens with an index of refraction of 1.53 with the same power of - 6.00.

D = 1/f

The formula for a diopter is this: When D is diopter, and f is the focal length of a lens in meters. So if I know that a lens has a focal length of 0.50 meters 1/0.50 = 2 My lens diopter power is 2.00

F = 1/D

The formula can also work the other way so that f is equal to 1/D, So if I know that a lens is 2.00 diopters 1/2.00 = 0.50 My lens focal length will be 0.50 or half a meter.

It's Jeopardy Time! 186,000 Miles per second

the speed of light

1.74

an example of an index of refraction

D = 1/f

the formula for diopter

400-700 nm

range of visible light in nanometers

apex to apex or base to base

all ophthalmic lenses are two prisms, stacked either

meniscus lens

term used for modern optical lenses, because its shape is like the shape of a meniscus moon

converges

Light passing through a plus lens

diverges

Light passing through a minus lens

Rays of light entering a prism always

bend around the base of the prism

The image or object being viewed through a prism always

shifts towards the apex

Nominal Lens Formula

"DL = D 1 + D 2" is a short cut to lens powers, when DL is the total power of the lens, D1 is the front surface power, and D2 is the back surface power. Example for spherical lens: D1= + 8.00 D2= -10.00 +8.00 + -10.00 = -2.00 So DL = -2.00 Example for sphero-cylinder lens: Prescription required: -1.00 -0.50 X 45 Front Base Curve = +2.00 Back curves to be ground -3.00 / -3.50

D1= + 6.00 D2= -12.00 +6.00 (+) - 12.00 = So DL =

-6.00 Sphere

Prescription required: -1.50 -1.00 X 45 Front Base Curve = +3.00 Back curves to be ground /

-4.50 / -5.50

base curve

"The curve from which all other curves are measured."