Prisms
The parts of a prism include its...
Apex and base
The weight in grams of one cubic centimeter of any given material is called?
Specific Gravity
Refractive power of the cornea...
43 diopter
The index of refraction is calculated by?
Calculated by dividing the speed of light in air by the speed of light in that material
Segment height
Plus or minus 1.0mm
What is a Prism diopter?
A prism of 1.0 0D produces the appearance of a 1cm shift in position of an object being viewed at a distance of 1m
Crown glass most frequently uses...
Material and glasses called for,relatively strong,cleans easily and resists corrosion, can be rendered impact resistant through heat or chemical methods
What is the Optic Chiasm?
Point at which optic nerve fibers cross in the brain
Define refraction...
The bending of waves as it passes at an angle from one medium to another
Base curve
Plus or minus 0.75 D
What is a Formula prism diopter?
D=1/f
When D is diopter and f is the focal length of a lens in meters
So if I know the lens has a focal length of 0.50m my lens diopter power is 2.00
The most popular lens material used today for a variety of single vision and Multifocal lens, inherently impact resistant, fragmentation is called...
CR39
What is Myopia?
Near sightedness, difficulty seeing distant objects when light rays are focused on a point in front of the retina
A theory made by famous Isaac Newton staying that light is made up of a stream of particles...
Corpuscular Theory
Multifocal add(power in distance)
___ to 8.00 above ___
0.00 to 8.00 above 8.00
The Minus lens as prism is present everywhere except...
Apex to Apex
Prism is present everywhere in a lens except for the point at which the spices meet
Polycarbonate is a...
High index of refraction combined with a low specific gravity make lenses made of this material especially thin and light
The relay station in the central nervous system for transmission of visual impulses from optic tract to optic radiation of the brain is called the...
Geniculate body
The denser the material...
The more the latest slowed down,the more it is deviated from its original course
Fill in the blank:Prismatic imbalance (mounted pair)
Vertical 0.333 or _______________
MRPs within 2.5mm or _____________
MRPs within 1mm
Horizontal 0.667
Plus lens as prisms are present everywhere except...
Base to base
Prism is present everywhere except at the optical center which is the point faces come together
An ideal candidate for these lenses in the early presbyopia since lower add powers result in wider intermediate and near zones and less peripheral distortion
Progressive Bifocals
Types of Tunics...
Fibrous tunic,vascular tunic,neutral tunic
Where is light bent?
Towards the base of the prism
Fill in the blank:
Sphere power in diopters
0.00 to ___ above ___Tolerance
Plus or minus 0.__D
Plus or minus __%
0.00 to 6.50
Above 6.50
Plus or minus 0.13D
Plus or minus 2.0%
The Prentice rule States what?
States that the power of the prism is equal to the power of the lens in diopters times the amount of the centration in millimeters divided by 10
Prism diopters = (F x dec in mm)/10
How do you minimize distortions from aphakic spectacle lenses?
This is one in which the shape is not spherical, but rather...
Through the use of aspheric front surfaces
Emulates the shape of the human cornea which is steeper in the center and gradually gets flatter as it radiates toward the periphery
Index of refraction for the cornea,crystalline lens,aqueous humor,vitreous humor...
Cornea - 1.37
Crystalline lens - 1.42
Aqueous humor - 1.33
Vitreous humor - 1.33
What rule states that the power of prism is equal to the power of the lens in diopter times the amount of the centration in millimeters divided by 10?
Prism diopter = (f x dec in mm)/10
Prentice rule
Fill in the blank:
Cylinder power in diopters
0.00 to ___
2.12 to ___ above ___
0.00 to 2.00
2.12 to 4.50 above 4.50
What method is used when a lens is viewed from the front with the base direction to the right becomes 0.Likewise,prism with the best direction to the left (bass out for the right eye and base in for the left) becomes 180°?
The 360° method with prism
What is often used in high prescriptions for the purpose of minimizing lens thickness, consists of a carrier lens and a bowl?
Lenticular design
When do the eyes converge?
The ice covering when viewing an object that in your distance as when reading,the pupillary distance for near vision is narrower than that for distance reading
The base curve theory is...
What do you always w at the front base curve to be?
The curve from which all other curves are measured
As close to +6.00 as possible
Fill in the blank:
Cylinder power (Tolerance)
Plus or minus 0.__D
Plus or minus 0.15D
Plus or minus __%
Plus or minus 0.13D
Plus or minus 0.15D
Plus or minus 4.0%
Slab off (or bicentric grinding) induces prism in what direction?
Slab off induces base prism. It can be used,for example, on the least positive (most negative) lens to reduce vertical imbalance when patient looks down to read
Vascular tunic AKA Uveal tract is composed mainly of...
It contains these 3 parts...
Blood vessels and supplies outer retinal layers
Iris,ciliary body,and choroid
What happens when the ciliary body contracts?
The zonules relax allowing the lens to thicken, adding power, allowing the eyes to focus up close
Plus Rx:
Base curve = spherical equivalent +6.00
Minus Rx:
Base curve = 1/2 the spherical equivalent +6.00D
Spherical equivalent:add exactly 1/2 the cylinder power to the sphere power
These are all part of what rule?
Vogel’s rule
Fill in the blank: Cylinder axis
0.125 to ____
____ to 0.750
0.875 ___ to 1.500 above ____
0.125 to 0.375
0.500 to 0.750
0.875 to 1.500 above 1.500