Ophthalmic Optics and Dispensing (20%) Flashcards
What is a Diopter?
Unit of measure for lens
* 1 diopter focuses light at 1 meter
* 2 diopter focuses light at 1/2 meter
* 3 diopter focuses light at 1/3 meter
What is a Plus Lens used for?
Corrects hyperopia & presbyopia
Do Plus Lenses Magnify or Minimise Objects
Magnify Objects
Do Plus Lenses Converge or Diverge Light?
Light is converged
Are Minus Lenses Convex or Concave?
- They are Concave lenses
- Thin in center and thicker on the edge
Spherical Lenses
- Same power in all meridians
Rays of light deviate in same direction
Cylindrical Lenses
Rays of light deviate in more than 1 direction
Do Minus Lenses Magnify or Minimise Objects
Minimise Objects
Do Minus Lenses Converge or Diverge Light?
Light is diverged
What is the Axis on a Rx?
- Where the cylinder is positioned
- From 1 to 180 degrees
What is the Add Power on Rx?
- Additional Plus power needed to view things at near & arm’s length
- (Done by using multi-focals)
What is a Prism used for?
To correct patient’s eyes not aligned correctly
What shape is a Prism?
A transparent wedge shape (similar to pyramid)
Does a prism displace or focus light?
Displaces rather than focuses light.
Is light bent towards the base or the apex of a Prism?
Base
How much does 1 Prism Diopter deviate light?
1 cm for every 1 meter of distance
What is a Plano-Cylinder (Pl-Cylinder) Lens?
No power in 1 meridian & power in other meridian 90 degrees away
Sphero-Cylindrical Lens (Sph/Cylindrical)
A lens used to treat myopia/hyperopia and astigmatism.
Single-vision
Used to correct a single vision problem such as nearsightedness, farsightedness, astigmatism. (Ex: Distance only, Reading only)
Aspherical Lenses
- Has wider field of view
- Thinner lens profile
- Works well for spherical lenses
Multi-focal Lenses
- Lens designed with multiple powers to be used at different distances.
- Corrects presbyopia
Bifocal Lenses
- Has power for viewing at 2 distances distinguished with a line
- Commonly prescribed to people with presbyopia who also require a correction for myopia, hyperopia, and/or astigmatism
Trifocal Lenses
- Has power for viewing at 3 distances (Distance,intermediate & Near)
- Visible lines in between regions.
- Mostly used by people with advanced presbyopia who have been prescribed 2 diopters or more of reading addition.
Progressive Lenses
- Has gradual change in power. (No visible line between regions)
- Distance at the top & near at the bottom
- Three optical zones - correct for distance, intermediate and near vision
- Allows wearer to more seamlessly transition to each optical zone.
Pupillary Distance (PD)/ Interpupillary Distance
- Distance in mm between the centers of the pupil of each eye.
- The P.D. can be obtained using a millimeter ruler or a pupilometer.
- Reason for taking the patient’s P.D. is because the center of the lens sits directly in front of the center of the patient’s eyes.
Steps to Measure PD
1.) Focus on area being measured which is the distance between the centers of the pupil of each eye.
2.) Face the patient about 40 cm distance between examiner and the patient.
3.) Place a millimeter rule resting on the patient’s nose.
4.) Have patient look at your open left eye, while closing your right eye
5.) Line up zero point of rule with temporal edge of patients right pupil
6.) Ask patient to look at your open right eye (while you close your left eye).
7.) Reading is taken from the rule, where it aligns with the nasal edge of the patient’s left pupil. Record that number.
*If it is hard to see the edge of the patient’s pupil, because of a dark iris, use the temporal edge of the limbus of the right eye and the nasal limbus of the left eye.
Pupilometer/ Pupillometer
Hand held instrument that measures pupillary distance (PD)
Seg Height Measurement - Bifocal
Measurement from bottom most edge of lens to lower eyelid.
Seg Height Measurement - Trifocal
Lowest point of lens to bottom of pupil
Seg Height Measurement - Progressive
Measurement from bottom most edge of lens to center of patient pupil.
Lens Material - Glass
- Hardest surface
- Most scratch resistant
- Best optics
Cons
* Heavy
* Easy to break or shatter
Refractive Index: 1.5
Lens Material - Plastic (CR-39)
- Less likely to break or shatter
- Lightweight
- Easily tinted
- great optics
Con
* Not impact resistant
* Less scratch resistant (can be treated to be more scratch resistant)
* Thicker than glass
Refractive Index: 1.5
Lens Material - Polycarbonate
- Harder to break or shatter
- Safety lens for children, athletes & monocular patients
- Less scratch resistant (always treated for scratch-resistance)
- Thinner than glass or CR-39 lenses
- Lightweight
Cons
* Doesn’t tint
* Has distortions and aberrations in lens.
Refractive Index: 1.6
Lens Material - Trivex Material
- Mid-Index lens
- Safety lens for children, athletes & monocular patients
- Less scratch resistant (always treated for scratch-resistance)
- Free from distortions & aberrations
- Thinner than glass or CR-39, but slightly thicker than polycarbonate
- Impact resistant
- Lightweight
- Great optics
- Tints easily
Refractive Index: 1.5
Lens Material - Hi-Index
- Thinnest lens materials and thus provide a better cosmetic appearance for eyeglasses in higher prescriptions.
- Less scatch resistant
Con:
* Optical quality reduced
* Not impact resistant
Refractive Index: 1.6-1.7
5 Lens Coatings
- Scratch-Resistance
- Anti-reflective
- Ultraviolet
- Mirror
- Sports
*Also: Blue light protection
Scratch Resistance Coating
Made from resin that protects the lens from many surface scratches
Anti-reflective coating
- Eliminates internal lens reflections = Increase visual acuity
- Reduces glare at night
- Good for playing sports, and using a computer.
- More visibility of wearer’s eyes to observers
- It allows all the light to pass through the lens so the light doesn’t get trapped on the lens which causes the glare spots.
Ultraviolet coating
Filters out UV light and protects the eye from potentially damaging UV light both indoors and outdoors.
Mirror coating
- Reflects some of the light striking lens
- Increases density of lens
Sports coating
- Improves contrast sensitivity
- Reduces glare
Blue light protection
- Block or filter blue light given off digital screens
- Glare protection
- Reduce damage to retina
Frame Materials
- Plastic
- Metal
- Titanium
Frame Materials - Plastic
- Made of rugged polymers
- Need heat to make material more pliable & able to bend
Frame Materials - Titanium-based alloy
- Example: Flexon
- Lightweight, hypoallergenic, corrosion resistant
- Memory metal, so bendable & will return to original shape
- Difficult to adjust
Optics
The scientific study of sight and the behavior of light
What Are The Two Lens Types?
-Plus/ Convex
-Minus/Concave Lense
Components of Lens Prescription
1.) Sphere- first number listed indicates how much myopia or hyperopia the patient has.
2.) The cylinder- second number listed indicates the amount of astigmatism the patient has.
3.)The axis- last/third number preceded by “X”. It is the position of astigmatism anywhere from 1 to 180 degrees.
Last component is add power if progressive Rx.
What is lowest sphere power?
0.25 diopters (+ or -)
What is lowest Add Power?
+ 0.25 diopters
What measurements does a Lensometer measure?
-Measures the sphere power
-cylinder power
-the cylinder axis of the lens
-the amount of prism in the lens,
-the base direction of the prism
-the powers of the multi-focal lenses
Zyl/ Acetate Frames
Plastic frame.
-Made of rugged polymers that are most common frame material.
-Lightweight
-easily adjustable
-comes in many colors.
Metal Frames
-Front and temples comprised of metal.
-Adjusting frames usually requires special pliers and other tools.
-Lenses usually held in place by an eyewire that is tightened with a screw to hold it in place.
Pro: Very adjustable
Flexon Frames
Titanium based alloy. Referred to as memory metal because of ability to come back into shape even after being twisted, bent or crushed.
-lightweight
-hypoallergenic
-corrosion resistant.
Con: Expensive
What is the first and most important step of frame selection?
Patient’s Prescription
Rules for proper fit
1.) Width of frame- approximately equal to the width of the patient’s face.
2.) Bridge of frame- Should rest flat on the sides of the nose.
3.)Temple length- Should be long enough to extend over the patient’s ear and far enough beyond to balance the weight of the front of the frame.
Frame Fit for Longer Face
Greater the vertical depth of the frame should be.
Frame Fit for Shorter Face
Smaller the vertical depth of the frame should be.
What is the Cosmetic Criteria for Frame Fit?
Upper eyewire of the frame should contour the shape of the patient’s eyebrow.
Goal is to balance the features of the face.
To minimize the features of a round or square face shape, fit a frame that has the opposite features
Required Elements To Order Eyeglasses
1.) Frame color
2.) Eyesize
3.) Bridge size
4.) Temple length.
5.) Specify the prescription for the lenses in each eye
6.) P.D. at far and near (when applicable)
7. Lens design (single-vision, bifocal style, etc.)
8.) Lens material
9.) seg height (if not single- vision),
10.)Any tints or coatings that should be used.
Four Types of Eyeglass Lenses
- Single-vision
- Bifocal
- Trifocal
- Progressives
Categories of Eyeglass Frames
- Full Frame
- Semi-rimless
- Rimless
What is a prism Lens?
Lens that displaces light rather than focuses light
What is best Indicator of Well Fitting Frame?
A well centered eye.
If too big will cause the eyes to be positioned to near the bridge of the frame.
If too small will cause the eyes to be positioned to near the outer portion of the frame.
Frame Bridge Types
1.) Saddle- Most common. For best fit it should be like a saddle on a horse no gaps.
2.) Keyhole- Great for smaller noses. The smaller space between the lenses are the best point of contact.
3.) Low Bridge- Best plastic option for very small and flat bridges.
Photochromic Lens
- Transitions
-Lens darkens when exposed to UV light
-In absence of activating light the lenses return to their clear state.
-may be made of polycarbonate, or another plastic
Polarized Lenses
Minimize glare in bright, sunny, outdoor settings.
Blocks light on a horizontal plane like a window blind.
Principles of Frame Selection
1.) Style
2.) Shape
3.) Type of Eyeglass Prescription
Refractive Index
How much light slows down as it passes through the lens.
Beryllium Frame
Type of metal frame.
-lightweight
-durable
-flexible
-extremely corrosion resistant.
Cons: Expensive
Titanium Frame
Metal frame.
-Lightweight
-durable
-hypoallergenic.
Con: Expensive
Stainless Steel Frame
Metal frame.
-Light to Medium Weight
-durable
-less expensive than titanium -hypoallergenic
Monel Frame
Metal frame. Inexpensive
Con: Can cause allergic reaction.
Aluminum Frame
Metal frame.
-Lightweight
-durable
-corrosion resistant
-slightly flexible.
Cons: Expensive
Nylon Frames
Plastic frame.
-Lightweight
-durable
-good for sport and sunglasses.
Optyl Frames
Plastic/ Epoxy resin frame.
-Very bendable
-comes in translucent and opaque colors.
-Important to let air dry after heating.
Neutralizing lenses
Using lenses that are equal in magnitude but opposite in direction to neutralise the spectacles, so there is no overall effect.
(Ex: +2.50 sphere in a spectacle lens is neutralised with a -2.50 spherical trial frame lens.)
Generally start with right lens first, unless there is a notable difference in the powers of the left and right lenses (look at the thickness of the lenses) then choose the lens that is more powerful to neutralize first.
