Topic 4 to 6 Flashcards by Eliana Faye Alos

is the bending of light as it passes obliquely from one optical medium to another of different refractive index. Its definition will give rise to the factors that must be present in order for refraction to take place.

REFRACTION

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There must be light.

The light must strike the surface obliquely.

There must be at least 2 optical media.

The optical media must have different refractive indices.

PREREQUISITES FOR REFRACTION

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the boundary between two optical media.

Interface

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the light ray that is directed towards the surface

Incident Ray

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the point where the incident ray hits the interface.

Point of Incidence

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an imaginary line that passes thru the point of incidence and perpendicular to the interface.

Normal to the Surface

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the angle formed by the incident ray with the normal to the surface.

Angle of Incidence

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the light ray that leaves the surface, can be bent either towards or away from the surface.

Refracted Ray

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the angle formed by the incident ray with the normal to the surface.

Angle of Refraction

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The basic features of refraction are

easily derived from Snell’s law

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The amount of bending of a light ray as it crosses a boundary between two media is dictated by the

difference in the two indices of refraction

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When light passes into a denser medium, the ray is

bent toward the normal

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light emerging obliquely from a denser medium is

bent away from the normal

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In the special case where the incident beam is perpendicular to the boundary

there is no change in the direction of the light as it enters the second medium.

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The incident ray and the refracted ray lie in one plane at the point of incidence but on the opposite sides of the normal to the surface.

LAW #1

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The SNELL’S LAW A constant ratio exists between the sines of the angles of incidence and refraction.

LAW #2

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A ray of light passing obliquely from a rarer medium to a denser medium is bent TOWARDS the normal to the surface.

LAW #3

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A ray of light passing obliquely from a denser medium to a rarer medium is bent AWAY from the normal to the surface.

LAW #4

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A ray of light striking the surface perpendicularly is UNDEVIATED

LAW #5

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these are optical media with two plane and well-polished surfaces which are inclined towards each other.

PRISMS

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Refracting Surface

planes ABEC and plane ABFD

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These are the plane, smooth and well-polished surfaces of a prism which are inclined towards each other.

Refracting Surface

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the surface where incident rays first hit the prism (facing the object)

1st Refracting Surface

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the surface where light rays emerge or leave the prism.

2nd Refracting Surface

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Apex / Edge / Refracting Edge

line AB

The line of intersection of the 2 refracting surfaces of a prism. It is considered as the thinnest part of a prism.

Apex / Edge / Refracting Edge

Apical Angle or Refracting Angle

angle AFE or angle DBC

It is the angle formed by the 2 refracting surfaces of a prism

Apical Angle or Refracting Angle

Base

plane FDEC

It is located opposite the apex. It is considered as the thickest part of a prism.

Base

Principal Section

plane AFE or plane BDC

It is the triangular portion of the prism that is perpendicular to the base.

Principal Section

is an optical medium with two plane surfaces that are inclined towards each other

Prism

True or False Prisms are made from transparent materials such as glass, plastic and fluorite used to redirect light at a designated angle

True

True or False Prisms doesn't have the capacity to reverse the direction of light by internal reflection.

False

True or False Prisms cannot be used to reflect light, or to split light into its component colors.

False

True or False Aside from incorporating prisms in telescopes, periscopes and microscopes, prisms are used to study the reaction of the human eye to light

True

True or False Prisms are used by doctors to measure eye deviation or to exercise weak extra-ocular muscles

True

True or False Prisms are not incorporated in eyeglasses to prevent diplopia or straighten deviated eye.

False

True or False Light coming from air and incident on the first refracting surface of a prism is bent towards the base following the 3rd law of refraction (rarer to denser).

True

True or False Inside the prism, light will not continue travelling until it reaches the 2nd refracting surface.

False

T&F Here, light will travel from denser medium prism to rarer medium air.

True

T&F Therefore, following the 4th law of refraction (denser to rarer), light will be bent away from the normal to the surface or towards the base.

True

OPTICAL PROPERTIES OF A PRISM

1. A ray of light passing through a prism is bent towards the base. 2. The image of an object seen thru a prism is displaced towards the direction of the apex.

CHARACTERISTICS OF IMAGE IN THE PRISM

* Virtual * Erect or Upright * Displaced towards the apex of the prism

is a transparent piece of glass or plastic with at least one curved surface.

lens

Lens came from the latin word

lentil

a type of seed used in cooking

This lens looked very much alike with lentil

convex lens

The most common kind of lens

convex lens

T&F Ophthalmic lenses are used in the field of Optometry in so many ways - to determine the error of refraction and as correction to relieved symptoms especially blurring of vision.

True

Year? Historically, most corrective lenses have been either round or oval

since about 1800

Ophthalmic lenses may be single vision, double-vision or progressive. Thanks largely to the pioneering work of _________, the BOA Museum has possibly the most comprehensive collection of ophthalmic lenses in the world.

Mr Arthur Bennett

darken in sunlight so that you don't need to swap your prescription spectacles for a pair of sunglasses.

Photochromic lenses

two main types of lenses

convex (or converging) and concave (or diverging)

also known as positive lens or converging lens

Convex lens

the glass (or plastic) surfaces bulge outwards in the center giving the classic lentil-like shape

Convex lens

It is thicker at the center and thin at their upper and lower edges.

Convex lens

also called a converging lens because it converges rays of light that are traveling parallel to its principal axis. It is composed of infinite number of prisms positioned base-to-base.

Convex lens

also known as negative or diverging lens

Concave lens

is exactly the opposite with the outer surfaces curving inward, so it makes parallel light rays curve outward or diverge

Concave lens

It diverges rays of light that are traveling parallel to its principal axis.

Concave lens

are sometimes called diverging lenses

Concave lens

It is thinner at the center and thick at their upper and lower edges. It is composed of infinite number of prisms positioned apex-to-apex.

Concave lens

The image formed is always virtual and diminished.

Concave lens

It is a diverging lens that spreads out the light.

Concave lens

Farther and smaller than the actual entity.

Concave lens

Used to correct Myopia or Nearsightedness. Used to correct Hyperopia or Farsightedness.

Concave lens

After refraction, light rays move away from one another.

Concave lens

It is a converging lens that which converges the refracted rays.

Convex lens

The image formed can be real, virtual, enlarged or diminished based upon the position of object.

Convex lens

Nearer and larger than the actual entity.

Convex lens

Used to correct Hyperopia or Farsightedness.

Convex lens

After refraction, light rays meet at one point or appear to meet.

Convex lens

are suitable for patients with complex refractive errors including high sphere, cylinder power, special parameters, extreme powers and extreme prisms.

Specialty Lenses

They also help address vision challenges for people with medical issues such as lazy eye, cataracts, and other rare eye conditions.

Specialty Lenses

Have a single power or one range of vision, in other words they are not bifocals or progressive lenses

SINGLE VISION LENSES

It used for everyday activities, like driving reading and using computer screens

SINGLE VISION LENSES

And are also used for reading glasses to correct presbyopia (farsightedness caused by loss of elasticity of the lens of the eye).

SINGLE VISION LENSES

It comes in a wide variety of materials and coating options, including standard plastic, polycarbonate and high-index.

SINGLE VISION LENSES

What? T&F Bifocal lens is created with two different areas of vision correction. The top portion of the lens is used for distance, while the bottom portion of the lens is used for closer vision.

DOUBLE VISION LENSES True

It is the most common type of prescription lens, where one prescription power is throughout the entire lens.

DOUBLE VISION LENSES

No line bifocals is like regular bifocals progressives provide range of vision from distant to near, all without a line across the lens.

PROGRESSIVE LENSES

lenses have multiple visions distances, including intermediate, which is perfect for computer usage.

PROGRESSIVE LENSES

It is a line free multifocal lenses that gives you clear comfortable vision at all distances.

PROGRESSIVE LENSES

These are lenses which are designed to be suited in certain hobbies or jobs.

SPECIALTY LENSES

Glasses that have these lenses are also known as special-purpose glasses or eyewear and they are not made for everyday wear.

SPECIALTY LENSES

also known as A R Lens.

ANTI-REFLECTION LENSES

The modern lens material can produce a stronger prescription with a thinner and lighter lens. However, they are more prone to reflection and glare.

ANTI-REFLECTION LENSES

T&F A R will reduce the glare (night time driving). Premium A R will also strengthen and harden the lens material to prevent damage (computer users).

True

let in more light, this feature allows better vision with higher contrast and clarity especially in dim settings.

ANTI-REFLECTION LENSES

In ____, photochromic lenses were developed by _____ at the _____

1960s Roger Araujo Corning Glass Works

Photo means

light

Chromic means

color

Also known as Day and Light lenses and Transition. Normal lens to grey lens

PHOTOCHROMIC LENSES

It primarily reacts to UV lightu. When the lenses are exposed to light, the _______ molecules lenses begin to change the structure absorbing more light ad eventually darkening lenses.

"PHOTOCHROMIC" LENSES

Can be used indoor and outdoor

PHOTOCHROMIC LENSES

irritating reflection from surfaces are part of our everyday lives, they can even be dangerously limit your vision, with a ______ you can eliminate this glare.

Polarized Lens

To achieve this, size polarized lenses consist of various special layers, when reflected , the waves of sunlight change their orientation. This orientation in one main direction is called

Polarization

also known as high energy visible (HEV) light, is a type of light with short wavelengths emitting a higher energy.

Blue light

Blue light penetrates deep into the eye, so exposure may result in:

* Damage of the retina exposing the eye to hidden spikes intensity. * Long-term vision problems such as age-related macular degeneration (AMD) and cataracts. * Suppressing the natural release of melatonin and disrupting sleep.

T&F More than 80% of Americans report using DIGITAL DEVICES in the hour before going to sleep, which has been shown to disrupt sleeping patterns by increasing alertness to the brain.

True

T&F Aside from sunlight, digital screens –like those of TVs, computers/laptop, smart phones and tablet- are the most common source of individuals’ BLUE LIGHT exposure.

True

T&F The vision council recommends individuals and their child(ren) to visit a local eye care provider to discuss their digital habits and what eyewear solutions are available to relieve the symptoms of digital eye strain and reduce exposure to blue light.

True