the optics of your retinoscope

Question 1

what are the principles of retinoscopy ?

Answer 1

. illuminate fundus
. image formed at subject’s far point
. reflex formed- bright glow seen in pupil
. mirror rotation
. observations - direction/speed/brightness
. neutralisation of refractive error
. reversal obtained - far point of eye with working lens in place at the retinoscope
. correction determined - minus working distance lens

Question 2

what is in self-luminous retinoscope ?

Answer 2

. brow rest
. beamsplitter/mirror
. aperture selector - the smaller the aperture the more sensitive measure of reversal
. vergence slide - moves up and down - this controls the vergence of the beam that leaves the retinoscope - we want this beam to be diverging near reversal - keep vergence slide down
. on/off switch/rheostat
. bulb + batteries in handle

Question 3

what are the two types of retinoscope ?

Answer 3

. streak or spot retinoscope
. the difference between the two is the bulb you put into them
. can change bulb to convert between the two

Question 4

when is it particularly good to use streak retinoscope ?

Answer 4

. advantages in astigmatism

. this is because the streak retinoscope allows some indication of the meridians at an early stage

Question 5

what does spherical ametropia mean ?

Answer 5

spherical ametropia means the refractive error is the same in all meridians

Question 6

describe the major optical elements of the retinoscope ?

Answer 6

. light source - small bright bulb in streak ret - produces uniform source of light - to give a uniform reflex

. condensing lens - to collect light that would otherwise be sent outside and hit the walls of the retinoscope

. makes rays less diverging to focus more of the light on to the mirror at the top of the retinoscope

. mirror - angled at 45 deg - directs the light from the handle of the retinoscope towards the eye you are looking at
- mirror can have a sight hole or be semi-silvered ( most common )

.aperture - allows you to switch between to size aperture
small aperture = greater sensitivity during reversal = also reduce light so will be difficult to use

Question 7

what happens when you take light source and condensing lens ?

Answer 7

. condensing lens forms a virtual image of real light source
. the real light source - its virtual image is what we call effective source , its the effective position of source , if we take out the condensing lens
. we can place it with effective source with light diverging from it
. we do this because it’s hard when we have to turn the light through a right angle

Question 8

where is the image of effective source located ?

Answer 8

. there is an image of the effective source in the 45deg mirror at a position called the immediate source
. this means that it’s perfectly okay optically to consider the illumination from the retinoscope as just coming straight from that immediate source and diverging from that point

Question 9

what is the immediate source position controlled by ?

Answer 9

. vergence slide

Question 10

what is the sweeping of ret called ?

Answer 10

• this is called mirror rotation - this is when you sweep the beam along a vertical or horizontal meridian

Question 11

what happens when we sweep ret vertically along 90 deg meridian ?

Answer 11

. mirror rotates up as you tilt ret

. we divert the light upwards direction going into eye

. immediate source moves down

. blur patch on fundus which forms the reflex moves up

. BLUR PATCH ON BACK FUNDUS MOVES IN THE SAME DIRECTION AS MIRROR ROTATION

. if you sweep to right = blur patch moves to right
. if you sweep to left = blur patch moves to left

Question 12

what is the summary for optics of ret ?

Answer 12

. the optics of ret allows a variable vergence beam of light to enter the eye and illuminate the fundus

. control vergence with vergence slide

. they also allow a reflex to be observed through aperture and mirror

. the reflex is the same as red eye seen in flash photographs