optics 2

Question 1

what is the wAVELEGNTH OF VISIBLE LIGHT

Answer 1

400 NM - 700 NM

Question 2

laser stands for

Answer 2

light amplification by stimularted emission of radiation

Question 3

what is snells law

Answer 3

sin(angle1) / sin (angle2) = n1/n2

Question 4

Formula for focal length?

Answer 4

f = 1/F
focal legnth = 1 / lens power

f inmeters and F in dioptres

Question 5

Power in convex and concave lens?

Answer 5

Concave lens has negative power (diverges light)

Convex lens converges light and has positive power

Question 6

Lens power in thin lenses?

Answer 6

F = (n-1) x (1/R1) - (1/R2)

R1 and R2 and radius of curvature of front of lens and back of lens respectively

Question 7

Lens power in thick lenses?

Answer 7

F = (n-1) x (1/R1) - (1/R2) + (n-1)(d) / n(r1)(r2)

d= thickness of lens

Question 8

Dioptre = 1/metre
DS = ?
DC?

Answer 8

spherical dioptres

DC = Cylindrical dioptres

Question 9

refractive error caused by?

Answer 9

corneal curve (steeper = more myopia)
Axial legnth (longer = myopic)
Refractve index of the lens

Question 10

Far point = point of clear focius in myopia. What is the formula?

Answer 10

1/ spherical dioptres = Far point ( in meters)

Question 11

at birth what is mean refractive error

Answer 11

-2 to +6 = normal refractive error

70% have astigmatism at birth

Question 12

What are the types of regular astigmatism

Answer 12

Regular- 90 degrees apart

with the rule : steepest part is vertical ( -ve cyl axis 180)

against the rule : steepest part is horizontal 9 -ve cyl axis 90)

Question 13

What are the types of regular astigmatism

Answer 13

Regular- 90 degrees apart

with the rule : steepest part is vertical ( -ve cyl axis 180)

against the rule : steepest part is horizontal 9 (-ve cyl axis 90)

Question 14

Magnitude of astigmatis is the difference between meridia

Answer 14

compund myopia/hyper etc

Question 15

correction astigmatism is

Answer 15

toric lens

steepest/stongest part of eye needs flattest/weakest part of lens when refracting

Question 16

circle of least confusion

Answer 16

where best vision is achieved with only a spherical lens

used to work out spherical equivalant power

Question 17

Best spehere = circle of least confusion = best vision

Answer 17

best sphere = sphere power + (cylinder power /2)

Question 18

Formula for transposition of lens?

Answer 18

Prescription is: A/ +B x C

Formula: (A+B) / -(B) x C+/- 180

Question 19

regarding prisms

where is the image
where is light deviated

Answer 19

imageis towards apex of prism

light deviates towards the base

Question 20

To correct strabismus with prisms, how do you point the prims

Answer 20

BASE IN for divergent squint

BASE OUT for convergent squint

Question 21

how to test vision in babies

Answer 21

20 dioptre base out in front of one eye- check both eyes and movement should be seen

Question 22

lenses and prisms

Answer 22

+ve lens (same as base up prism)

-ve lens (same as base down prism

Question 23

Prentice’s rule = prismatic power through decentred lens

formula?

Answer 23

P = cF

c = decentration (in cm) 
F =  lens power (in dioptres)

Question 24

What prism difference will start to cause proiblems?

Answer 24

more than 1.5 prism dioptres

causes double vision

Question 25

6/6 how many MAR?

Answer 25

1

Question 26

6/6 how much in logMAR?

6/60?

Answer 26

6/6 logMar 0

6/60 logMAR 1

Question 27

Blindness defintion in UK

Answer 27

<3/60 or less than 10 angles visual field

Question 28

magnification formula?

working distance of lens

Answer 28

F/4

1/F