streak RET

Question 1

what happens in mixed astigmatism eye with streak RET ?

Answer 1

• take an eye with RX +1.00/-2.50 x 110
• +1.00 x 110 ( with movement )
• -1.50 x 20 ( against movement )
• ( horizontal meridian ) reflex is twisted with respect to streak that is the first clue that we got astigmatic eye - equivalent of eccentric move in spot ret
• ( vertical meridian ) twisted streak , thus indicating astigmatic eye

Question 2

how does the twist in the streak comes about ?

Answer 2

• take two principal meridians at oblique axis
• we sweep down along 90 meridian
• we get an slow against response along 30
• 120 meridian we get fast against
• this eye has slow compound myopic astigmatism
• streak moves much quicker in one meridian that what it does in another meridian
• the twist of streak is caused by the difference in speed of the two meridians - provided you are not sweeping along one of those principal meridians

Question 3

how must you rotate streak with respect to twist ?

RX +1.00/-2.50 x 110

Answer 3

. rotate streak away from twist
. sweep along meridian perpendicular to streak always
. we get with movement from streak reflex we see within the pupil
. when we sweep in opposite direction reflex fills pupil much more than in hypermetropic meridian ?

Question 4

which meridian do you correct first in RX +1.00/-2.50 x 110 ?

Answer 4

. correct the most positive / least negative meridian first ( 110 )
. as you correct a hypermetropic meridian add + 0.75 the streak reduces in width

Question 5

what happens to streak with when correcting hypermetropia ?

Answer 5

. streak width reduces

Question 6

what does the streak reflex relative to pupil depend on ?

Answer 6

. W= working distance ( -1.50 )
. X= the immediate source location
. K=subject ametropia

Question 7

explain width of the streak reflex when correcting hypermetropia ?
x = -1D
W = - 1.50 D

Answer 7

. when correcting high levels of hypermetropia the relative width of streak reflex is close to + 1D completely fills pupil , as we reduce to + 2D the width of streak relative to pupil starts to drop very rapidly , till it fills the pupil with relative width of -1 or higher and that is filling it in opposite direction
. so what you will see is width streak narrow then expand again to fill pupil

Question 8

explain width of the streak reflex when correcting myopia ?
x = -1D
W = - 1.50 D

Answer 8

. if we correct myopic meridian the curve looks different

. the values are always closer than +1 , reflex will always fill pupil no matter what the ametropia is