Single Vision
What do we call a lens that has one uniform optical power across the entire surface?
Single vision lens
Convex on both sides; converging lens
What is a bioconvex lens?
A lens with distance power in main lens and a D-shaped near segment at bottom
What is a Flat Top (D-segment) bifocal?
this lens material is extremely impact resistant and commonly used for safety eyewear?
Polycarbonate (or Trivex) — impact resistant
when an image moves in the opposite direction of your hand movement when testing with a lens
what is Against motion?
three common uses for single vision lenses (list any two
Distance only; near only; computer/intermediate only
How does a plano-convex lens differ from a bioconvex lens
Plano-convex has one flat side and one convex side; bioconvex has both sides convex
this bifocal style provides the largest near viewing area and is split across the entire lens width
what is Franklin (Executive) bifocal?
What does a higher refractive index do to lens thickness?
Higher refractive index → lens can be made thinner for the same power
What does scissor motion indicate when testing a lens
What is astigmatism?
Why is accurate pupillary distance (PD) important for single vision lenses?
Ensures optical centers align with pupils so patient has clear, comfortable vision and avoids induced prism
One side convex and one concave; reduces aberrations and provides good optical quality for eyeglasses.
What is a meniscus lens
What is an Ultex lens and one reason it’s rarely used today
Large round segment placed on back surface, very heavy/thick; rare today for weight and cosmetics
Name two reasons an optician might recommend Trivex over polycarbonate
Trivex is very lightweight and has higher ABBE (better clarity) than polycarbonate; also good for drill mount
Explain how aspheric lens design changes the lens surface and name two benefits for patients with high prescriptions
Aspheric lenses flatten toward edges; benefits: thinner, lighter; reduces distortion and magnification/minification
Explain why base curve and centration matter when fitting single vision lenses.
Base curve affects optical performance and comfort; centration ensures optical center aligns with the visual axis to prevent distortion and prism
Describe the optical effect (converging or diverging) of a bioconcave lens and a common visual condition it corrects.
Bioconcave is diverging; used for myopia (nearsightedness).
Explain the main advantage and main drawback of ribbon seg
Ribbon segs give distance above and below narrow near segment — great for specific occupations but require precise height and are small
What is the ABBE number and why does it matter for patient comfort or optical quality
ABBE number measures chromatic dispersion/clarity; higher ABBE reduces color fringing and improves peripheral clarity
Describe how photochromic lenses behave inside a car
Photochromics do not darken fully inside cars because windshields block UV needed to activate the dye.
A patient needs glasses only for computer work at intermediate distance. Which single-vision prescription type would you recommend and why?
intermediate/computer single vision — set for the computer working distance so the patient has clear intermediate vision without compromising distance or near.
Compare a plano-concave lens and a plano-convex lens in terms of shape and typical use
Plano-concave has one flat one concave (diverging); plano-convex has one flat one convex (converging); used for mild divergence/convergence needs
A patient needs stable near vision and you must measure the segment height precisely. Which bifocal type from the list is most important for this measurement and why?
Flat Top (FT) — segment height critical to position near power where patient will look for close work.
List three lens treatments or coatings and give one practical benefit of each
Scratch resistant coating (protects from scratches); AR coating (reduces glare); UV treatment (blocks ultraviolet light).
A patient reports “bug-eye” appearance with conventional lenses in a high plus prescription. Which lens design could reduce this effect and why
spheric or high-index aspheric lenses can reduce magnified “bug-eye” effect by allowing a flatter, thinner profile and better controlled magnification.