(10) speed, brightness and size of the ret reflex

what factors influence speed of the ret reflex

the amount of refractive error in an eye

residua ametropia once you start to correct

angle of tilt of the retinoscope beam

extent to which the lght arriving at the px eye is diverging or converging

slow dim movements can even be confused with reversal since movement direction is ambiguous 

speed of reflex

anything in the middle is moving very slow

anything at the bottom moing very fast

line curves at 1.5-: gets revrsal when the residual ametropia is 1.50, means their WD is 67cm

the reflec reverses/changes direction when RA= -1.50D

at this point no movement is seen and the reflex speed becomes infinite on the graph as brightness changes instantly 

• left side: high myopia

reflex becomes with. graph shows fast movements 

• right side: high hyperopia

reflex becomes against, showing fast movements

in the middle aound the 1.50 reflex slows down, close to neutrality so slope becomes extremely steep → infinte theoretical speed

reflex speed

(W/W+K) x angle of mirror tilt

speed factor (SF)- whats plotted on the y axis : W/ W+K

w= working distance

K= ocular refraction

eg if wd is 67cm, W= 1/0.67 = +1.50D

if K = -1.50, the SF is infinate as W+K = 0

SF is -ve (against movements) if there is more myopia than -1.50D

SF is +ve with movements if there is less yopia than -1.50D or if the eye is emmetropic or hyperopic

size of the reflex

how much the pupil is filled with the reflex

high myopia: Mr is between patient and practitioner and far from the ret 

mr is between patient and practitioner so against movements seen 

only the blue rays go into the practitoners eyes meaning will see a small pupil reflex as nt all light is passing into the eye 

moderate myopia; Mr between px and practitioner but close to the ret

as the practitioner gets closer to the far point more of the pupil s filled

low myopia: mr is just behind practitioners eye

pupil will be filled

close to the retinoscope

low myopia: far point located a larger distance behind the practitioners eye 

pupil will be smallwe 

will start to see with movements, as gone too positive 

high hyperopia

pupil will show up as smaller, further from the Mr

lower hyperopia: far point further behind patients eye

more of the pupil is filled, closer to the far point

far point at the ret mirror, naturally or using trial case lens 

will either see a full pupil, or nothing, as the ble rays dont pass through the gap in the mirror 

when light leaves px eye and brought to focus at ret mirror, then flash will be seen