Maddox rod & wing Flashcards
what does the maddox rod test
the size of the heterophoria
which patients can you not use maddox rod to measure
hetertropia
what type of phoria does the maddox rod allow to see than can’t be seen with cover test
cyclophorias
what does the maddox rod not show about a phoria
does not allow the assessment of the degree or control/compensation of a heterophoria
what causes the eye to take up the heterophoric position with the maddox rod
because the retinal image in one eye is distorted into a streak of light which cannot be fused with the spot of light seen by the other eye
which distance is maddox rod usually used to assess
far distance (but can be used for intermediate and near distance)
what is used to cause a spot of light to turn into a streak with the maddox rod
a series of highly powered cylinders
the first focal line is formed so close to the eye that the patient will not attempt to accommodate to see it
where is the second focal point of the eye that is fully corrected, where the patient perceives the spot as a red streak
on the retina
what does the red colour of the rod help with
helps the patient differentiate between the streak and spot light
which orientation is the maddox rod placed in order to measure horizontal phorias
placed horizontally before the eye, which causes the streak to be oriented vertically
what does the relationship between the streak of light seen and the spot of light indicate
the type of heterophoria
what does it mean when the streak and spot both coincide with one another
the image must be falling on the fovea of each eye i.e. there is no deviation
if the maddox rod is placed before the right eye, and the spot is seen on the right side of the spot, what phoria does this indicate
exophoria
the streak has crossed over to the left hand side of the spot
if the maddox rod is placed before the right eye, and the spot is seen on the left side of the spot, what phoria does this indicate
esophoria
the streak has not crossed over the spot
where is the spot in relation to the streak with a right hyperphoria, if the maddox rod is placed in front of the right eye
spot seen above the streak
where is the spot in relation to the streak with a left hyperphoria, if the maddox rod is placed in front of the right eye
spot seen below the streak
infront of which eye should the maddox rod be placed in front of and why
infront of the eye with the better visual acuity as the poorer eye may suppress the streak image
in which eye and at which direction should the prism be facing when measuring the amount of deviation in maddox rod
prism placed in front of the eye with the maddox rod and base in the direction of the deviation of the red line/streak (opposite to the spot)
what is the amount of prism required to align the spot and the streak known as
the dissociated heterophoria
how will the streak appear in the maddox rod test in the presence of a cyclophoria
the streak will tilt away from the horizontal or vertical
which type of phoria is it not possible to measure the size of the deviation
cyclophoria
what can be done to avoid the problem where the streak appears to wander in the maddox rod test
an occluder should be used to cover the eye seeing the streak and a measurement taken just as the cover is removed
list the steps of how you would use the maddox rod test on the test chart 2000
- it is not possible to produce a bright enough spot light on the computer screen, therefore a red bar is used instead
- full distance correction in place and PD’s set to distance
- direct px to view the vertical red bar
- the maddox rod is placed before the right eye and is oriented so it is 90 degrees to the orientation of the bar on the screen e.g. a vertical bar on screen needs a MR with the lines horizontal in order to measure a horizontal phoria
- the px sees a thin vertical red line with the MR in the right eye and a vertical red bar in the left eye
- the orientation of the bar is switched by pressing any of the cursor keys on the keyboard
- the patient is asked if the thin red line seen by the eye with the MR, passes through the red bar seen by the other eye or is it to the right or left or even at an oblique angle
- if the thing red line with the MR is on the left of the red bar = exphoria
- if the thin red line with the MR is on the right of the red bar = esophoria
- prisms are used to align the two streaks: prism is placed over the eye with the MR, and the base is in the direction of the deviation of the thin red line
- gradually increasing power of prisms in 0.50^ steps, align the thin red line with the centre of the red bar
- to measure vertical phorias, rotate the MR so that the axis is vertical
- using the arrows on the remote control, change to a horizontal bar on the screen
- px will see a horixontal thin red line in the right eye and a horizontal red bar on the left eye
- ask the px whether the thin red line is above or below or straight through the red bar
- with the MR before the right eye: the thin red line above the red bar = left hyperphoria
- with the MR before the right eye: the thin red line below the red bar = right hyperphoria
how do the eyes take up their heterophoric position i.e. achieve dissociation in the maddox wing test
dissociation is achieved by a septum, which forces the two eyes to view separate objects, fusion of differing images is impossible
what is the fixed working distance of the maddox wing
33cm
what correction is required to be used during the maddox wing test
near correction where necessary
what does one of the eyes view in the maddox wing
the horizontal and vertical scales marked with the numbers and type of deviation
one side of the scale consists of odd numbers and the other of even numbers
which phoria does the odd numbers on a maddox wing correspond to
esophoria
which phoria does the even numbers on a maddox wing correspond to
exophoria
what does the second eye view in the maddox wing
the two arrows, one pointing to each of the scaled
what indicates the size of the heterophoria with maddox wing
the position of the arrow in relation to the scale
how is it possible to measure a cyclophoria with the maddox wing
by using a scale on the side of the instrument
what position is it important to hold the maddox wing in and why
important to hold the instrument down slightly to stimulate the position of the eyes when reading, otherwise the results may be inaccurate
why is complete dissociation not seen with the maddox wing (causing a disadvantage)
the black background it seen by both eyes
list the 2 disadvantages to the maddox wing which lead to inaccuracies
- complete dissociation is not achieved: as black background is seen by both eyes
- number on the scales are large: which provides poor stimulus to accommodation
what are the drop cells in the maddox wing usually used for
spheres, to assess the link between accommodation and convergence (AC/A ratio)
list the full method of how to carry out a maddox wing test
- reduce the PD of the trial frame to the patient’s near PD
- ask the patient to hold the maddox wing up to their eyes so they can see through the apertures
- direct the patient to the horizontal scale and ask them which number the white arrow point to (even numbers = exophoria, odd numbers = esophoria)
- record the size an direction of the horizontal phoria at 33cm
- direct the patient to the vertical scale and ask them which number the red arrow points to
- record the size and direction of any vertical phoria at 33cm
