Binocular Vision Lecture 5 - Strabismus Correction

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Questions and Answers

What happens to retinal images in the case of a tropia?

The image in one eye falls on the fovea while the other falls elsewhere. (correct)

There is no double vision experienced.

Both images fall outside of central vision.

Both images fall on the fovea.

When prescribing a prism for strabismus correction, how is the direction of the prism described?

By the apex of the prism.

By the direction of the base of the prism. (correct)

By the distance from the apex to the object.

By the angle of deviation of the light.

What is the primary function of a prism in binocular vision?

To magnify objects for clearer vision.

To enhance depth perception.

To redirect light so that retinal images align. (correct)

To increase the visual acuity of both eyes.

In the context of phoria, what does introducing a prism achieve?

It ensures associated and dissociated positions are equal. Signup and view all the answers

In a Maddox rod test, what is primarily being assessed?

The presence and magnitude of strabismus. Signup and view all the answers

What characterizes the dissociated position in phoria?

Eyes are positionally disconnected and relaxed. Signup and view all the answers

What would happen if a prism is placed in the wrong direction for strabismus correction?

It will cause further misalignment of images. Signup and view all the answers

In which situation would you typically use a Maddox Wing test?

To assess the alignment of the eyes at distance. Signup and view all the answers

What mechanism allows patients with a tropia to see a single image under certain conditions?

Neural adaptation occurs. Signup and view all the answers

What is the purpose of measuring the size of a phoria with prisms?

To quantify the deviation in eye position during dissociation. Signup and view all the answers

What is the purpose of using a Maddox rod during vision assessment?

To measure the distance between associated and dissociated positions Signup and view all the answers

If a patient sees the red line to the right of the spot during a Maddox rod test, what condition is present?

Esophoria Signup and view all the answers

When using a prism to correct an esophoria, where should the apex of the prism point?

Outwards Signup and view all the answers

What is the primary function of the Maddox wing?

To provide a single view to each eye for phoria measurement Signup and view all the answers

If the red line is seen below the spot during a test, what type of phoria is present?

Vertical phoria Signup and view all the answers

In a Maddox rod test, what condition is suggested if the patient only sees the spotlight and not the red line?

Suppression Signup and view all the answers

What results from using a base-out prism during vision assessment?

Brings the lines into alignment for esophoria Signup and view all the answers

Which of the following describes the Maddox rod's method of assessing phorias?

It distorts images beyond recognition to prevent fusion Signup and view all the answers

What type of prism is needed when the right eye shows exophoria during an assessment?

Base IN prism Signup and view all the answers

Which statement about the limitations of the Maddox rod is true?

It underestimates the magnitude of exophoria. Signup and view all the answers

In vertical phoria testing using the Maddox rod, what is indicated if the red line points to an even number?

Left hyperphoria Signup and view all the answers

How is cyclophoria assessed using the Maddox rod?

By observing the tilt of the red bar Signup and view all the answers

What is one of the primary clinical uses for the Maddox Wing?

To quantify near phorias Signup and view all the answers

What measurement does the Maddox rod provide specifically for assessing phorias?

The distance of deviation in terms of diopters Signup and view all the answers

Study Notes

Binocular Vision - Lecture 5 - Subjective Assessment of Vision

The lecture covered subjective assessment of vision, specifically using prisms for strabismus correction.
Students will be able to understand how prisms work in strabismus correction, perform a Maddox rod test, and perform a Maddox wing test by the end of the session.
Strabismus occurs when eyes are not aligned, causing the retinal image to fall on different points of the two retinas.
This leads to a condition called tropia, where the patient sees double.
Prisms refract light, deviating the image toward the apex (top point) of the prism.
The base of the prism is the bottom side of the triangular prism.
The prism is positioned to redirect falling light so that the image correctly falls on the corresponding points in both retinas.
The apex of the prism is positioned in the direction of the eye.
Optometry uses the position of the prism's base to specify direction.

Strabismus Correction using Prisms

Prisms are used to correct strabismus (squint).
Exo is Base In, and Eso is Base Out.
Phoria can be measured by determining the difference between eye positions when associating (active) or dissociating (passive).

Maddox Rod and Maddox Wing Tests

Maddox rod and Maddox wing tests are used to quantify heterophorias (small deviations) in binocular vision (not strabismus).
These tests are used to identify small vertical deviations that could be missed in a cover test.
In these tests no fusion is allowed, thus the eyes move to a dissociated position.
Maddox rod testing: Patient wears a red rod in front of one eye, causing any deviation to be visible.
Maddox wing testing: Patient wears a prism or wing-shaped lens, creating a displaced image which is used to measure the disparity between the images of each eye.

Maddox Rod

The Maddox rod uses a lens to distort the image beyond recognition, which prevents fusion.
The rod's cylindrical shape causes light distortion into a line at right angles to the groove axis.
It helps measure distance phorias.

Procedure for Maddox Rod Test

Perform it after refraction and before near work addition
Turn off the room lights and turn on the spotlight on the chart
Check for horizontal phorias: Use a Maddox Rod. Ask the patient if the red line is positioned to the left or right of the spot of light.
Check for vertical phorias: use vertical Maddox Rod. Ask patient if the red is above or below the spot of light.

Maddox Wing Procedure

Explain to the patient
Patient wears an appropriate correction
If pre-presbyopic, use distance Rx and distance PD. If presbyopic, use near Rx and centration distance.
Get the patient to hold the wing in front of their eyes
Use the test chart (with numbers) to measure horizontal and vertical phorias. Ask the patient which number the white arrow points to and which number does the red arrow point to.
Use the scale to measure cyclophorias: Ask the patient if the red bar is straight.

Horizontal and Vertical Phorias

Ortho (straight/normal vision) is when the arrows/lines are straight or at zero on the scale.
Esophoria (inward deviation) is when the arrow points at an odd number on the scale
Exophoria (outward deviation) is when the arrow points at even number on the scale.

Cyclophoria

Ortho: Red bar is horizontal
Incyclo: red bar is tilted and turned until it becomes horizontal.
Excyclo: red bar is tilted and turned until it becomes horizontal.

Other Information

Clinical notes mention limitations of the tests due to poor accommodation stimuli, leading to overestimation of XOP and underestimation of SOP.
Tests are designed for standard PD and not if PD is not standardised.
Results are recorded.
Orthophoria is recorded as a crosshair.
If there is a phoria present the prismatic power and type of phoria needs to be recorded
Maddox rod and tangent scale: Test charts with numbers and arrows enable phoria measurement.

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Description

This lecture focuses on the subjective assessment of vision, particularly the use of prisms for correcting strabismus. Students will learn how prisms function, perform the Maddox rod, and wing tests, as well as understand the implications of misaligned eyes leading to tropia.