VS 117
Dr. Clifton Schor
Tuesday 4-6-99
Notes by Angela

Announcements:
1. There were two handouts, #6 and #7
2. Quiz on Thursday April 15th
3. Read chapters 5 and 7 for quiz
4. There is now an appendix to the reader on the web site. It is about neurological evaluation of patients. Dr. Schor would like us to read it.

Background information leading to chapter 5 in reader:

As optometrists, we need to know about neurological disorders. We can look for neurological disorders in the brain by looking at the oculomotor system. Metabolic diseases such as hyperthyroid, hypothyroid, systemic diseases such as brain aneurysms, and neurological disorders such as multiple sclerosis can all affect the oculomotor system. Multiple sclerosis is also known as "the young person's disease." It hits in the late 20's to early 30's and affects the entire central nervous system.

There are 3 ways to categorize oculomotor disorders:

1. Congenital - This is genetically determined and not life threatening. Our main duty as optometrists is to talk to the parent and let them know their child's life will be limited in some ways and tell them how they can cope with it. An example is albinism, which tends to cause a decreased visual acuity and nystagmus. These patients have some smearing of the retinal image and receptor anomalies, which leads to a decreased resolution. Prism is used to reduce the amplitude of the nystagmus, which will also help the visual acuity.

2. Developmental - Usually secondary to some congenital problem.
a. Here, the optometrist can intervene and prevent the disorder from occurring. We look for risk factors which may lead to the disease. An example is an uncorrected refractive error, which is a risk factor for partial blindness. If left uncorrected, an anisometropic eye could develop a neurological deficit which leads to a decreased visual acuity. This is called amblyopia. No one is born with amblyopia, i.e. there are no specific genes for it.

b. There are genes for strabismus, however, which may lead to amblyopia. Optometrists look at family history, strabismus, high refractive error, and greater than 2D of anisometropia as risk factors for the occurrence of amblyopia.

c. If a patient has >2D of anisometropia, the more hyperopic eye will tend to be amblyopic because patients don't like to over accommodate in the hyperopic eye.
Over accommodation causes accommodative esotropia

d. Strabismus can cause anisometropia and anisometropia can cause strabismus. Both of these can cause amblyopia.
e. Optometrists can help by catching developmental disorders and coax along the binocular vision system to develop correctly.

3. Acquired - In these cases, optometrists are screeners, they don't treat the problem. Need to refer to a neurologist.
Examples:
a. Car accidents - precipitates damage to a muscle or nerve. The abducens and the trochlear nerves are the most likely to get damaged because they have the longest pathways. Damage to the abducens (VI) causes lateral rectus paresis. This usually causes an esotropia that is so large that the patient self refers to a neurologist. Damage to the trochlear (IV) nerve causes superior oblique paresis. Patient may see double occasionally, which is subtle and the patient may not catch it. Also, hypertropia occurs, but patients usually compensate for it without realizing it using a head tilt (see below).

b. Metabolic disorders - such as hyper- or hypothyroid. Can cause exophthalmus or enopthalmus.

c. Autoimmune disorders - such as Graves disease

d. Demyelination of cranial nerves (multiple sclerosis) - causes muscle problems

e. Aneurysm in the Circle of Willis - The Circle of Willis is a weak part of the vasculature . AN aneurysm here will press down on the brain stem and affect cranial nerve III.

There are 3 anomalies of the oculomotor system that optometrists look for: (All of which can either be congenital, developmental, or acquired.)

1. Strabismus, or eye turn - any misalignment of the eye not compensated for by vergence.
2. Nystagmus - shaky eye, jittery eye movement.
-can have a pendular pattern ( sinusoidal harmonic motion) or Jerk wave form
-can be slow or fast (called ocular flutter when fast)
3. Saccadic disorders
a. hypermetric - when overshoot target and eyes have to move back
b. hypometric - when undershoot target and eyes make staircase motion

If you have an adult with a little flutter that is barely noticeable and the patient is generally unaware of the problem, it could be indicative of a cerebellar tumor. Usually the patient has some feeling of discontent in these cases.

Oscillopsia - occurs in people with recently acquired nystagmus. Person sees the world as unstable and moving around when their eyes move. Patients tend to eventually adapt to this and the world then looks stable to them.

Strabismus (we will get more of this with Dr. Portnoy next year)
1. concomitant - angle of squint (angle of eye turn) is constant in all directions of gaze. Tend to be indicative of congenital and developmental disorders. Indicates a disorder in the central control mechanism.
2. nonconcomitant - deviation varies with the direction of gaze. Indicates that a specific muscle or muscle group is affected. Indicative of acquired disorders.

Phorias can also be concomitant or nonconcomitant.
A long term concomitant strabismus can turn into a nonconcomitant strabismus. Consider an eye with constant esoptropia , i.e. eye doesn't move at all. In this case, the medial rectus can have "secondary contracture." The muscle gets stiff and shortens due to atrophy. Due to stiffening, the angle of squint gets bigger as the patient tries to use the medial rectus. This produces a nonconcomitant eye turn.

AV patterns can result from secondary contractures involving the obliques and vertical recti:
"A" pattern = in up gaze patient is more eso, while in down gaze patient is less eso.
"V" pattern = in up gaze patient is less eso, while in down gaze patient is more eso.

What is optometrist's job?
b. To determine whether the motor problem is developmental, congenital, or acquired.
c. If it is an acquired disorder, determine whether a referral is necessary. When writing to a specialist, just describe the symptoms but don't diagnose anything. Explain the chief complaint, what tests were performed, and tell them you would like them to further evaluate the patient.

Chapter 5 of reader - Orbital Geometry

The vestibular ocular reflex is mediated by a series of canals. (Figure 1)
x there are 3 sets of canals: the anterior set, posterior set, and horizontal set
x the canals are arranged in orthogonal planes, i.e. they are perpendicular to on another
x this allows us to precisely resolve the motion of the head in any meridian
The canals have a "push-pull" organization to make the response linear:
x the posterior canal on one side of the brain is parallel to the anterior canal on the other side of the brain
x if the posterior canal on the right is stimulated, the anterior canal on the left is inhibited. The brain then takes the difference in stimulation to interpret the head motion.

(insert 1st figure from ch. 5)

Extraocular muscle (EOM) orientation (Figure 2)
x Also arranged in 3 planes which are orthogonal
1. Horizontal plane- contains lateral and medial recti
2. Obliques - lie in plane which forms a 51 angle with the midsagittal plane
3. Vertical recti - lie in plane which forms a 23 angle with medial wall of orbit

(insert 3rd and 2nd figures from ch. 5)

Eye and extraocular muscles have ball and socket arrangement (Figure 3)
Ù the eye rotates about a single point, called the center of rotation (centrode).
Ù the point of insertion of the muscles relative to the point of rotation determines the action of the muscle.

Comparison of orientations of canals and EOMs between rabbit and cat (Figure 4)
Ù Rabbits have their visual axes pointing out the side of their heads, they do not much overlap of the visual fields and don't have good binocular vision
Ù Cats have foveas and have visual axes more forward than rabbits. Visual axis points out about 29 from midsagittal plane.
Ù In both cats and rabbits:
a. obliques are parallel to the posterior canals
b. vertical recti are parallel to the anterior canals
c. medial and lateral recti are parallel to the horizontal canals
Ù This orientation shows us that the muscle arrangements stayed the same through evolution even though the visual axis migrated forward. EOMs want to be parallel to the canals, independent of where the visual axis is pointing.
Ù Tells us that the primary goal of the EOMs is to work with the vestibular system to stabilize the visual world.
Ù If a certain group of canals is activated the muscles parallel to them are also activated, this is what stabilizes the world for us.



(insert 4th figure from ch. 5)

Streptomycin - was used a long time ago to treat motion sickness. Later found out that it kills the hair cells in the vestibular system. There was a physician who took a lot of streptomycin. He found that his world was in constant opscillopsia. He had a huge lack of image stabilization. He had to prop up pillows around his head in order to read. This demonstrates that without the vestibular system our lives would be miserable, everything would appear smeared.

We must describe motion of the eyes relative to the visual axis, not relative to the head. If we looked at the motion of the head, muscles in both the rabbit and the human would respond similarly. However, we really need to describe motion of the eyes relative to the motion of the visual axis in space. For example, look at the superior oblique. It has opposite actions in humans vs. rabbits. In the rabbit, its action is elevation. In the human, its action is depression. All this depends on which way the visual axis points.

There are several ways to learn what each of the EOMs does:

1. Look at insertion of muscle relative to the center of rotation of the eye:




(Draw figure from notes)




2. Look at Pascal's benzene rings:



(Draw figure from notes)





3. Memorize table in reader (Figure 5) - for purposes of this class, the primary actions of the obliques in torsion.

(insert 7th figure from ch. 5)

4. Memorize Figure 6

(insert 6th figure from ch. 5)

5. Look at which muscle lets you look in different directions of gaze (Figure 7)

(insert 8th figure from ch. 5)

The direction the eyes are pointing determines which muscles control the movement:
Ù During adduction the obliques are the main vertical movers. If you have damage to the obliques you get a noncomitant deviation. There is a bigger deviation when the eyes are turned in.
Ù During abduction the vertical recti become the main vertical movers.

Diagnostic direction of gaze (or field of action) - the field of gaze in which a particular muscle is a pure vertical mover.
Ù diagnostic gaze for obliques is in adduction
Ù diagnostic gaze for vertical recti is in abduction

We can use distortion tests such as Maddox rod and red lens to determine which muscle is weakened or paralyzed. (See Figures 8 and 9)

Ù in this test, the image is on the fovea of the fixing eye and off the fovea of the deviating eye.
Ù the direction of the non foveal percept is opposite the direction that the deviating eye is pointing
How it works:

(draw figure from notes = figure 8)

(insert 9th figure from ch. 5)

Figure 9 shows a left superior oblique paresis. The left eye has trouble looking down and in. Put a Maddox rod in front of the right eye and measure the vertical deviation in the 9 cardinal directions of gaze. The target appears to be lower here because the left eye is actually elevated. Find where the deviation is the largest, this is a signal to which muscle is damaged.

(insert 10th figure from ch. 5)

In Figure 10, each picture represents an anomaly of the right eye. The red/black dot is non-foveal. It is seen in a direction opposite to where the eye is pointing.

(insert 11th figure from ch. 5)

Figure 11 shows a left superior oblique palsy. This is the most commonly seen nonconcomitant form of strabismus. In primary gaze the left eye is slightly elevated. When the patient tilts head to the side of the weak muscle the vertical deviation increases. If the patients tilts their head to the opposite side, there is a decrease in the vertical deviation. The head tilt used to minimize the strabismus is called ocular torticollis. These patients tilt their head when walking around. Must be distinguished from orthopedic torticollis, which is a stiff neck.