SVEN

Question 1

COMBINATION FRAMES

Answer 1

front made of both plastic + metal

side materials are irrelevant

Question 2

CONCOMITTANT VS INCOMITTANT

Answer 2

concomitant - same in all directions of gaze

incomittant - varies with direction of gaze

Question 3

ASTHENOPIA

Answer 3

eye-strain

Question 4

LENTICULAR LENS

Answer 4

collection of magnifying lenses

used for very high powers

Question 5

PRESBYOPIA

Answer 5

as we age, the lens continues to grow until it becomes stiff and close to the ciliary muscle

this means we can’t change focus enough to see at all distances

> 45

Question 6

3 TYPES OF FOCIMETERS

Answer 6

• conventional (in labs)
• projection
• automated

Question 7

HOW MANY FOCAL LINES DO SPHERO-CYLS HAVE?

Answer 7

two line foci (as there are two power meridians)

Question 8

FRONT-TORIC LENSES

Answer 8

front of lens contains base curve/ cross curve

back of lens has sphere curve

convex front surface

base curve/ cross curve
————————————
sphere curve

Question 9

BACK-TORIC LENSES

Answer 9

front surface contains sphere curve

back surface contains base curve/ cross curve

this form has a concave back surface

sphere curve
———————
base curve/ cross curve

Question 10

MEAN SPHERICAL EQUIVALENT

Answer 10

sphere + half of cylinder

Question 11

LENS MEASURE

Answer 11

used to measure dioptric power of a lens surface directly

measures curvature of surface

assumes lens has a particular RI

finds surface sag between 2 points

(also called lens gauge/ clock)

Question 12

ACCOMMODATION

Answer 12

ability of eye to alter the crystalline lens shape to change its focal power

Question 13

WHEN WERE VARIFOCALS FIRST CREATED?

Answer 13

been around since 1920s

first successful varifocal came into UK market in 1970 - varilux 2

Question 14

MINUS LENSES GET WHAT PRISM?

Answer 14

base in prism

Question 15

PLUS LENSES GET WHAT PRISM?

Answer 15

base out prism

need to converge more

Question 16

WHAT IS THE USUAL PANTOSCOPIC TILT IN VARIS?

Answer 16

about 10 degrees

Question 17

WHAT ARE ISO-MEAN POWER LINE DIAGRAMS IN CONTEXT OF VARIS?

Answer 17

imaginary lines on lens surface, taking form of a contour plot, showing where specified steps in equivalent sphere of local lens power are

Question 18

PANTOSCOPIC TILT

Answer 18

angle that the spectacle front/ lens makes with the vertical when being worn

can only be measured when frame is on px

Question 19

ASPHERICAL SURFACES

Answer 19

historically meant not spherical i.e. all varis were aspherical

now for ophthalmic lenses - rotationally symmetrical

Question 20

DIFFERENCE BETWEEN DEGRESSIVE (OCCUPATIONAL) + CONVENTIONAL VARIFOCALS?

Answer 20

conventional have large distance + smaller near area - aberrations concentrated in upper half

occupational have large near + smaller distance area - aberrations concentrated in upper half of lens

Question 21

INWARD ANGLE DROP

Answer 21

should be parallel to head (angle of end of side towards head)

~5-10 degrees

Question 22

HOW TO CHECK FOR A 4-POINT TOUCH?

Answer 22

place frame top down on flat surface

ear points (i.e. close to where the drop of the side starts) + top of front above each lens should all sit on the flat surface at same time

Question 23

NEURAL DENSITY TINT

Answer 23

one that transmits all visible wavelengths equally

Question 24

WHAT IS LUMINOUS TRANSMISSION IN BOTH UV + INFRA RED?

Answer 24

zero

Question 25

SOLID TINT

Answer 25

tint all the way through the lens

Question 26

DIPPED TINT

Answer 26

dye soaks into lens (plastic only)

concentration decreases with distance into lens

Question 27

WHY ARE SOLID TINTS VERY SELDOM USED FOR RX SUNGLASSES?

Answer 27

tint darkness varies with lens thickness

lens darkness varies where lens is thicker i.e. in plus lenses it’ll be in the middle of lens

large range of tints then have to be in stock to to compensate for both power + uncut size (centre thickness)

different material has to be stocked for every tint type

Question 28

EQUITINT

Answer 28

trade name (of zeiss) for a lens made up of a plano powered solid tinted layer (often photochromic) + a powered untinted layer

made up of two lenses bonded together to give lens with an even tint over whole area

now means any tint that is even over lens area I.e. independent of lens power so includes both vacuum + dipped tints

Question 29

HOW THICK IS ANTI-REFLECTION COATING?

Answer 29

1/4 wavelength thick - single layer

allows destructive interference to occur in reflected light

Question 30

MIRROR COATS

Answer 30

1/2 wavelength thick

allows constructive interference to occur in reflected light

Question 31

PLASTIC ANTI-REFLECTIVE COATING CANNOT BE APPLIED WITHOUT WHAT?

Answer 31

a hard coat

Question 32

UV ABSORBING LENSES

Answer 32

mid + high index plastics absorb almost all UV

not available for glass

Question 33

WHAT CAN AN INCREASE IN UV EXPOSURE CAUSE?

Answer 33

increase in cataract or AMD

Question 34

POLARISING LENSES

Answer 34

reduces reflections

max transmittance is 50% even with AR coating

good for fishing, skiing, driving

Question 35

HOW TO POLARISING LENSES CUT DOWN REFLECTIONS?

Answer 35

light waves oscillate in all directions but after reflection, only waves oscillating parallel to surface are left

polarising lenses act to eliminate this acting like a vertically oriented “wire grid”

Question 36

WHICH RANGE OF WAVELENGTHS ARE PLASTIC PHOTOCHROMIC LENSES BETTER AT PROTECTING THE EYE FROM THAN GLASS ONES?

Answer 36

UVA

i.e. longer wavelength UV 315-400nm

Question 37

PATIENTS SHOULD BE WARNED OF WHAT PROBLEM ASSOCIATED WITH PLASTIC PHOTOCHROMIC LENSES?

Answer 37

they remain tinted when they are older, potentially causing serious problems under low-light level conditions

Question 38

PULFRICH EFFECT

Answer 38

delayed image processing from one eye

e.g. pupil size differences