VS117
1/27/98
Coops
Shilla Patel
The website for this class is http://schorlab.berkeley.edu
User Name : VS117
Password : Hering,1
Old midterms, finals, course reader and figures and this year's coops can
be found on this website
This weeks lecture deals with measurement of eye movement.
Refer to today’s handout
These are the clinical conditions for which you evaluate eye movements
(objective or subjective).
1) Steadiness of eye when it tries to aim (fixate).
Aim a pen light at patients eye and ask them to fixate it steadily. If
you see the eye jitter or move around, that’s abnormal. Normal fixational
eye movements are too small to see by direct observation. This observed
unsteadiness is called Nystagmus. You can enhance your view of the eye
by using a plus lens (5D) to magnify it.
2) Binocular alignment
Is there an eye turn (strabismus)? The patient attempts to use 2 eye to
fixate a single point. When there is a strabismus, one eye may be deviating
up, down, inward, or outward.
3) Do eyes move together synchronously (Hering's law)?
If there is a weakened muscle the eyes don’t move synchronously. If
the right lateral rectus is paretic, when the patient looks rightward, the
right eyes movement is restricted while the left eye is not. You get a
non conjugate or non yolk movement of the eye that results in a right esotropia
in right gaze. You measure eye movements to detect non-conjugacy and it’s
an indication of a paretic muscle, which could indicate damage to one of
the muscles or cranial nerves.
4) Phoria
Phoria is the position of rest of the eyes. When you cover one of the eyes,
the covered eye turns to some position of rest. The deviation of the covered
eye from its uncovered aligned position is called the Phoria. It’s
really an error of eye alignment when one eye is covered. THE reason this
is important is that under binocular conditions, patients have to overcome
phorias to see singly and if it’s a big phoria, they’re working
hard all the time to maintain binocular alignment and this can cause a lot
of discomfort.
5) Accommodative response of eye
Accommodation results from constriction of ciliary body and it is measure
clinically to evaluate presbyopia (aging of accommodation) and infacility-
(sluggish accommodation).
6) Pupillary Constriction
Both direct and consensual. To detect CNS disease.
A good source on the pupil is : Adler’s Physiology of the Eye.
7) Reading eye movements
Some patients can’t read; they have learning disabilities. Schor demonstrated
the Visigraph that records eye movements and plays them back to so the patient
can see their eye movements while reading. You can teach patients to read
a little more effectively.
8) Neurological Problems
Manifest themselves as saccadic disorders where eyes make too large or too
small a saccade. We also evaluate smooth following of eyes. If patients
have trouble following moving targets, they make these quick catch up saccades
(cogwheel eye movements). This can indicate a cerebellar disorder.
SUMMARY OF ROUTINE CLINICAL TESTS:
Begin your clinical exam with a confrontation test.
You sit directly in front of the patient and you aim a pen light at the
patients eyes and telling them to fixate track the pen light if it moves.
You’re looking for stability of fixation, smoothness of pursuits,
yoking movements of eye and deviations of one eye (strabismus). You do
all this at beginning of eye exam. You also look at near point of convergence
and measure interpupillary distance. The chief complaint and case history
are obtained before you begin the confrontation test. Visual acuity is
measured after that.
MEASUREMENT OF EYE POSITION AND MOVEMENT
Let’s talk about how we observe eye position and eye movements.
These are the 2 general categories for techniques.
1) Subjective methods - means you or the patient is interpreting movement
of their eye. No permanent record of this
2) Objective methods - provides some electronic representation of the eye
location , rotation and direction of gaze.
The one used the most is direct observation (subjective).
You look at the pupil margin or limbus margin and look for lateral or vertical
movements of limbal margin.
Direct Observation is good but not very sensitive. If someone has strabismus, how small a movement can be detected staring at the eye? about 2 - 4 prism diopters. This means that the eye has to move 2-4 cm before you can detect it.
Another way to do this is to shine a light at the eye and observe the location of the corneal reflex with respect to the center of the pupil.
A corneal reflection of the light source will be seen. Observe location of this reflection relative to pupil center and as eye moves around, the light reflex will move to but not as much as the pupil center. If the eye moves to the right, the corneal reflex will appear to shift slightly to the left of pupil center or its prior location. The amount of shift indicates how much the eye rotated. For corneal reflex measures, every 1mm = 10 degrees of eye rotation.
This method is less sensitive that the previous one involving the limbus movement.
Catoptric images. - (reflected image from the optical surfaces of the eye). Purkinje first observed reflections from various ocular surfaces and these are known as Purkinje images
The 1st (P1) is reflected from the anterior surface of the cornea
The 2nd (P2) is reflected from the posterior surface of the cornea
The 3rd (P3) is reflected from the anterior surface of the lens
The 4th (P4) is reflected from the posterior surface of the lens
If you held a candle in front of the eye, you would see 3 images
The 2nd Purkinje image is too dim to see and it is almost superimposed
on the 1st image
The 1st and 2nd images are erect
The 3rd is the largest and erect
The 4th is inverted and the smallest
When the eye accommodates, the front surface of the lens becomes more
curved and the 3rd Purkinje image gets reduced in size. So one way to measure
accommodation is to look at the size and intensity changes of the 3rd Purkinje
image
We quantify eye position by describing the distance of the corneal reflex
(1st Purkinje image) from center of pupil. What that describes actually
is an angle. The angle is refereed to as either kappa or lambda and it
indicates the angular separation between pupillary axis which is where you
see the center of the pupil and either the line of sight or the visual
axis which is where you see the light reflex.
The center of the pupil is called the pupillary axis and the angle between
the pupillary axis and visual axis is called kappa. The visual axis connects
nodal point of eye to fovea The pupillary axis is a ray connecting the
center of pupil that passes normal to surface of cornea.
Angle lambda is between the pupillary axis and the line of sight. The
line of sight goes from pupil center to object of regard (what your looking
at).
The optical axis is a ray that passes through nodal point that’s perpendicular
to surface of cornea. It forms an angle alpha with the visual axis and
an angle gamma with the fixation line (connects the fixation target to the
center of rotation of the eye).
Clinically we measure angle lambda, however it is referred to incorrectly
as angle kappa. To measure lambda, you observe the corneal reflex ( the
line of sight) and pupil center (pupillary axis). The separation between
the 2 is an angle lambda that is quantified as 10 degrees of eye rotation
for every mm separation of the corneal reflex and pupil center .
The figure shown above represents left eyes of an infant and adult. The
pupillary axis is pointing temporal ward so that you will see the light
along the visual axis which will be slightly nasal ward. In adult, normally
there is 1/2 mm shift of light source in nasal direction which corresponds
to 5 degrees . So normally, our papillary axis and visual axis are separated
by 5 degrees. Optics of eye and pupil aren’t exactly centered on visual
axis. In an infant, it’s twice as much. A baby will have their corneal
light reflex 1mm nasal ward from the center of the pupil.
Sign convention
Normally you see the corneal reflex 1/2 mm nasal ward from pupil center
( a positive angle). If it were temporal ward, it would be a negative angle.
This is a child with a left esotropia (nasal ward eye turn of the left
eye). The right eye’s corneal light reflex is slightly nasal from
center of pupil. In the left eye, it’s displaced temporally. Compare
the two eyes and notice the difference. How far temporally is light reflex
displaced from normal 1/2 mm nasal location? At least 2mm. This child
has (2mm x10 degrees) 20 degree eye turn inward. Detecting and quantifying
strabismus is one purpose of looking at the corneal light reflex. If the
eyes are aligned, the corneal reflexes should be symmetric. If they’re
not, it indicates that one eye is turned in or out. This test is called
the Hirschberg and it’s used frequently, especially for kids.
The smallest eye turn most people detect by direct observation, without
the corneal reflex, is around 18-20 degrees
Quantification Procedure for angle Lambda:
Hold a pen light stationary and have the patient look at pencil which you
move to change the location of the corneal reflex. In the normal example
above of a plus 0.5 angle lambda, you want to move the eye nasal ward until
you see the reflex centered at the pupil. If the patient is looking at
you with the left eye, you want to move the pencil to the right causing
the left eye to turn in and cause the corneal light reflex to shift so it
appears centered at the pupil. If you are at a viewing distance of 1/2
meters away from the patient, and you move the pencil 1cm to center the
reflex, angle lambda equals to 2 prism diopters. The amount you actually
have to rotate the eye to center the corneal reflex measures the angle lambda.
The following slide illustrates this.
Another way to do this is to put prisms in front of eye and displace corneal
reflex until it looks centered. If you have an eso ( eye is turned inward)
you use a BO prism and it will displace reflex onto center of pupil That
test is called the Krimsky. You use this on infants.
Demo - Erich Graf’s eyes were shown on the TV monitor. BO prisms were put in front of his eyes and this caused the corneal reflex to move nasal ward. Prof then demonstrated a cover test on Kyle. He alternately covered each eye to find the phoria (position of rest of the eye)
Clinically, we call angle lambda angle kappa. Know correct definition of each but clinically , even though we measure lambda, we’re going to call it kappa.
Distortion Tests.
You put a Maddox rod over one eye and shine a pen light on the other eye.
One eye sees a red streak and the other eye sees a white light. If the
red streak does not fall on the fovea of the eye, the patient will see a
separation between the light source and the red streak. You ask the patient
how separated white light is from the red streak and that tells you how
much the eye is deviated.
You can use prisms to move the red streak onto the light source. When
it’s on the fovea, the patient will see the red streak superimposed
on the white light. The amount of prism you need to do this tells you how
much the eye is turned.
A variation of the Maddox rod is called the Bagolini lens. An Italian ophthalmologist smeared glasses with a lacquer film and when you look at a light source through this lens, you see lines perpendicular to the direction of the smeared lacquer. You can use this for patients with strabismus to see if they’re fusing or not when both of they’re eyes are open (binocular state). They’ll see a vertical streak in one eye and a horizontal streak in the other and if they don’t see the 2 lines cross, they have a strabismus. The Maddox rod occludes one eye but the Bagolini lens allows both eye to see the world.
Haploscopic tests
They are basically stereoscopes
They present independent targets to the two eyes. For example, one eye sees a soldier and one eye sees a house. If there’s an eye turn, the target will not fall on the fovea so that the soldier will not appear in the house. The eye turn is measured by rotating the mirrors so the patient sees the soldier in the house. The amount you rotate the mirror equals the magnitude of the eye turn.
There is also a Brewster Lenticular Stereoscope.
It takes a +5 D lens and cuts it in half. Each eye looks through 1/2 of
the +5D lens.
you can adjust separation of the targets so they fall on the fovea’s and the separation. of the targets indicates the amount of binocular misalignment.
Filter Tests.
2 types of filters used to separate targets.
Polaroid and Red - Green (Anaglyphs)
As with the stereoscopes, you have independent targets for each eye
You have red projected targets seen by the red filtered eye and greed
projected targets seen by the green filtered eye. Common test that uses
these red green filters is the Landcaster. This is used to measure comitance,
the yoking of the eye.
Landcaster procedure: You have a patient fixate on a green target and then
take a red laser and aim the laser so it appears superimposed on the green
targets. Only red filtered eye sees the laser and only the green filtered
eye sees the green target. If they put a laser spot to the right of the
green target, when the right eye is trying to aim at the red laser, it’s
actually aiming to the right of it. That indicates divergent deviation.
They repeat this task in different directions of gaze to test for comitance
or yoking of the two eyes. If the misalignment of the eyes varies with
direction of gaze, this is refereed to as a non comitancy. It’s symptomatic
if a paresis of a muscle. It’s a noncomitant deviation. This could
be caused by an over action of the right lateral rectus or an underaction
of the left medial rectus. You could analyze which muscle was weakened
by looking at pattern of deviations in different directions of gaze. If
test is done at 1m and separation is 5cm, it would be a 5 prism diopter
deviation.
Entopic techniques
Entopic perceptions are perceptions that result from structures within
the eye. One such structure is the optic radiations (Henley's fiber layer
of the retina). The nerve fibers come from the ganglion cells and project
out to the optic nerve head.
The pattern of fiber projections from the fovea act as light polarizers. If you put a Polaroid filter in front of eye that spins, and you look into a uniform field, you’ll see a dark band spinning around that corresponds to the polarization of light. This is refereed to as Haidinger’s brush. It happens to be directly superimposed on the fovea. Have a patient look at a uniform field through a spinning Polaroid at a fixation target. They’ll see the brush off the one side if they’re not using their fovea to fixate and you can estimate the amount of fixation error by asking them to indicate how far the foveal target is from the brush. This is used a lot in amblyopia, which is a condition of reduced sight where people don’t use the fovea to fixate with.
Maxwell’s spot
Yellow macular pigment causes this entoptic percept. IT is a UV protecting
device. It blocks out short wavelengths. You combine blue and red in
a cobalt filter. when you look through the filter at a uniform field, you’ll
see a little pink spot called Maxwell’s spot. What you’re really
seeing is your yellow macular pigment which is blocking the short (blue)
wavelengths. You can ask a patient to look at a target and indicate how
far it is from the pink spot. This test is also used to detect amblyopia.
Electro Oculography (EOG)
put electrodes on face that record voltage potential eye has naturally.
The retina has a neg. potential and the cornea has a positive potential.
As eye looks left and right, electrodes sense proximity of the positive
corneal charge.
This is used a lot in infants. Used to measure OKN to find the visual acuity in a baby. This is the most used objective method.
I’m finally done with these coops!!!!!!!!!!!!!!!!!!!!!!!!!!! but one more thing. Dr. Schor wants us to read Chapter 16 in the reader by next week.