Lens type Flashcards
What do plus lenses do?
- Converge lights
- Thicker in the center
- Magnify objects
- Correct hyperopia
What do Minus lenses do?
- Diverge light
- Thinner in the center
- Minify objects
- Correct myopia
What should you keep in mind when designing lenses?
The greater the difference between the patient PD and the frame PD, the more lense will need to decentered in the frame
Why should designing lenses properly be important for plus lenses?
Plus lenses could be thick and can pose a problem with the nose pad adjustments.
Why should designing lenses properly be important for the minus lenses?
Minus lenses could be thick and can pose a problem with the temporal side to look unappealing. It can also reduce peripheral vision.
What are aspheric lenses?
- They are lenses that are not spherical.
- Can include single-vision and progressive lenses
What does the minus lens prescription for aspheric lenses look like?
The surface gradually steepens toward the lens edge.
What does the plus lens prescription for aspheric lenses look like?
Have a front surface that gradually flattens towards the edge of the lens of the plus lens prescription.
What is single vision Aspherics?
Have a more complex front surface design than a spherical design that gradually changes the curve from the center to the lens edge.
What are the advantages of aspheric designs?
- Increased edge-to-edge lens clarity that results in better optics, especially in higher-power prescription
- A single base curve on a spherical lens may satisfy clear vision centrally, but the eye looks peripherally aberrations can reduce the quality of vision.
What are the benefits of aspheric lenses?
- Provides substantial benefits for both nearsighted and farsighted wearers.
- Aspheric design plus high index materials are good options for patients with a prescription over +/-2.00D
What do bifocal lenses provide?
- Two distinct powers, usually for near vision and distance
- The top portion of the lens allows wearers to see objects in the distance
- The bottom portion or segment, provides viewing at near for tasks such as reading.(14 to 16 inches)
- No intermediate range of vision for the wearer, so this lens is best suited for prescriptions with +2.00D or less of add power.
What are bifocal lenses one-piece mold type made out of?
One piece is made from one piece of glass or plastic and the lens surface is ground with two different curvatures.
What is fused lens in bifocal lenses?
Two different materials with their own index of refractions
How can you tell if the lenses are fused or a one-piece molded lens?
- A fused segment line can’t be felt when you run your finger across the lends surface.
- One piece design will have a raised surface
What is flat top bifocal?
- Half moon, straight top, D segment
- The most common are flat top 25,28, and 35
- The number represents a measurement in mm of widest portion of segment
What is round Bifocal?
- Round segment or kryptok lenses
- Limited areas of near vision
- Widest portion is usually 22 or 24 mm
- Not commonly used today
What is executive bifocal?
- Also known as ben franklin style
- Segment line goes straight across
- Widest reading area available
- Thicker and heavier with noticeable segment line
- Only one optical center for lens
- Not commonly used today
What is blended bifocal?
- The segment line is blended to hide the outline
- Blur area remains at the segment line
What is the recommended area for bifocal segment line to be at?
To be fitted to the lower lid margin
What is Trifocal lenses?
- Have three points of focus for distance, intermediate and near
- Consider for patients with over +2.00D add
How are trifocal lenses helpful for?
- Computer users
- Piano player to see music sheet
- Driving
What is the range of vision viewed through a tricocal lens?
- Near vision at 14-16 inches for activities such as reading a book
- Intermediate vision at 18 inches to arms length for activities such as seeing a computer monitor
- Distance vision to drive a car or watch TV
What kinds of style does the trifocal lenses have?
- Flat top and executive
- They are like their bifocal counterparts with an intermediate segment added directly above the reading segment
What are the most common flat top trifocal?
- Flat top 7 by 28 mm
- Flat top 8 by 35 mm
- The 28 and 35 indicate the widest portion of the segment in millimeters
- The 7 and 8 represent the depth of the intermediate segment in millimeters
What is the general trifocal power?
Generally, 50% of the added power unless it is noted differently on the prescription
What is the general segment line for trifocal?
The segment line is generally fit to the lower pupil margin in normal room illumination
What are progressive lenses?
- Also known as progressive addition lenses, PALs, or multifocal.
- Offers the prebyopic patient a naturally smooth, continuous transition through distance, intermediate, and near power
- No visible lines to hide the fact that the patient needs help with reading
Explain what the curves of the progressive lens look like?
- Curves are graduated vertically in the center, brought out to the sides of the lenses and blended.
- Although most of that blended areas is eliminated when the lenses are cut down to fit the eyeglass frame, the sides areas in the periphery that remains do not provide the best vision.
What is hard designs in progressive lenses?
Have clear peripheries in the upper distance and lower near areas concentrating the peripheral distortion to the middle periphery of the lens.
What is soft design in progressive lenses?
Tend to distribute the astigmatism from the center lens corridor into the top distance and bottom near areas allowing for a wider intermediate area.
What is the best vision when using progressive lenses?
- Turn the head
- Look directly at the objects
Is there still an issue with seeing blurs areas in the progressive lenses?
No, due to having new technologies to eliminate most concerns
Is there a way to identify the manufacturer, lens style, and add power for the progressive power?
- Yes, there are markings on the lens that will appear when using black light or instruments with appropriate lighting to magnify the markings more easily.
- The symbols can be interpreted using the progressive lens identifier supplied by OLA member labs
What are progressive centration and cut-out charts?
To verify that both the PD and the fitting height are correct after the lens has been fabricated or to confirm if the elns black is large enough be used for frame size and the amount of decentration necessary.
How do you verify the Fitting height for progressive lenses?
- Start by marking the etchings on the lens
- The markings on the lenses, center the bridge of the frame on the vertical dash line
- Place the 180 degree line on the horizontal line marked “0”
- Look directly down on the frame and note where the eyewire hits on the bottom set of numbers
- Each horizontal line represents 2mm.
- Count the lines to determine the segment height, or refer to the line markers
How do you verify the PD for progressive lenses?
- Look at the vertical lines numbered 25 to 35 mm
- Center the bridge of the frame on the vertical dashline
- Make sure you have the same number of diagonal lines on each side of the bridge
- The fitting cross of the progressive lens should correspond with the patient’s monocular PD
How do you verify the lens cutout for progressive lenses?
- Begin by marking the patient’s fitting height and distance PD on the sample lens, creating a cross
- Place the lens cross over the layout chart cross to verify that the lens will fit onto the frame
- If the eye wire of the frame falls within the large cut-out circle, the black will cut out in the lab
- If the lens does not fite, choose another, more suitable frame that will accommodate the lens.
Where should the fitting lens for progressive lens be marked?
Bisectin the pupil
What is the most common lens style?
- The double D segment where the lower segment is for near vision and the upper segment is made for near or intermediate distance
- While the middle portion maintains the distance vision
Are there progressive lenses made for computers?
- Yes, computer lenses have two power ranges allowing the wearer a wide, clear view at intermediate and near
- It’s important to remember that this lean does not provide distance vision and should not be recommended as a primary lens
- Should present all patients who spend a lot of time on the computer
If the high plus lens needs to be decentered in the frame, it will most likely result in:
More thickness nasally
If the high minus lens needs to be decentered in the frame, it will most likely result in:
More thickness temporally
What is not an advantage of aspheric lenses versus spherical lenses?
Decreased peripheral distortion
