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Dancing Eyes
Tobi Owoyemi
Sara Parrot Ph.D.
Hee-Jung Park M.D.
March 1, 2013
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Hiram Powers, an American sculptor, once said “The eye is the window of the soul... The
intellect and the will are seen in the eye; the animals look for man's intentions right into his eyes.
Even a rat, when you hunt him and bring him to bay, looks you in the eye.” (Edwards 161). The
eyes are more than just the body’s method of visual perception; they reveal a person’s character
and intent. The occurrence of damage in such a vital necessity to life is what prompts the
presence of ophthalmologists. This paper will discuss a specific disorder to the eyes called
nystagmus, and observe a step to the process in treating this disorder, which is measuring the
sharpness of the eye’s vision. The paper will start off with a basic background on nystagmus as
well as its causes and standard treatments. It will then discuss why ophthalmologists believe that
it is a challenging disorder to cure, due to the fact that current treatments yield very little positive
results. Finally I will compare the standard method of visual acuity testing which is the ATS
(Amblyopia Treatment Study) with the potential method of testing visual acuity which is an ipad
app—SVAT (Simplified Visual Acuity Testing).The main purpose of this research is to
investigate whether or not visual acuity is being properly accounted for in nystagmus patients, or
whether or not the treatments simply do not work.
Nystagmus can easily be described as an involuntary rhythmic shaking or wobbling of
the eyes. The term nystagmus is derived from the Greek word, “nystagmus”, which was used to
describe the wobbly head movements of a sleepy or inebriated individual (“eye associates”).
Nystagmus can be classified by characteristics of the eye movements like whether or not the eyes
move back and forth like a pendulum or whether they move slowly in one direction and then
rapidly in another. Doctors also look at whether or not the eyes move laterally or vertically and
by how much they do so. They also take note of how fast the eyes move. There are various
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methods of classifying nystagmus. Traditionally nystagmus has been divided into two groups.
Sensory nystagmus is related to vision loss and motor nystagmus is related to the control of
muscle function. There are over 45 types of nystagmus. However, they can be broken down into
two groups: Acquired nystagmus and congenital nystagmus. Just like many diseases nystagmus
can have a number of causes known and unknown. These causes can be narrowed down based on
whether the nystagmus is congenital or acquired (“Understanding Nystagmus”).
As one could imagine, the area of the brain that controls eye movement does not
function properly in nystagmus patients. A specific type of nystagmus, acquired nystagmus
occurs only later on in life and is generally seen in adults. may be brought on by certain
medications such as Phenytoin (Dilantin) - an antiseizure medication, excessive alcohol, trauma,
or any sedating medicine that can impair the labyrinth's function (“What Causes Amblyopia”).
Any disease of the brain especially pertaining to the motor system such as multiple sclerosis or
brain tumors can cause nystagmus if the areas controlling eye movements are damaged.
Additional causes of acquired nystagmus include stroke, and thiamine or vitamin B12 deficiency.
When thinking of acquired nystagmus, one should majorly consider neurological disorders, as
well as a patient’s medicinal intake (“Nystagmus”).
Congenital nystagmus or early onset nystagmus often accompanies vision loss acquired
at birth or soon after and may be one of the first signs that a child has a loss of vision(“AAPOS
Nystagmus”). About 1 in every 1000 children has nystagmus. In 80-90% of cases, it is a side
effect of vision loss from eye diseases such as albinism, aniridia, optic nerve hypoplasia,
achromatopsia congenital cataracts, coloboma or retinopathy of prematurity (“Understanding
Nystagmus”). This type of nystagmus can be observed around two to three months of age. In
some cases of nystagmus, patients may present with mild vision loss not associated with other
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diagnosed ocular diseases. This type of nystagmus is therefore often categorized as idiopathic
where the cause is unknown.The typical nystagmus related to vision loss during childhood is a
pendular nystagmus where the eyes rotate back and forth evenly (“Stanford Research”). Patients
with early onset nystagmus do not notice the movement of their vision when their eyes shake,
they will see their world in continuous flashes at a time—this is due to the fact that their brain
completely shuts off for about a millisecond (KTEF 2011 PPT). Although nystagmus is
associated with early vision loss, it may vary from stress, emotional status and direction of view.
It is uncommon to permanently worsen over time. In fact, nystagmus often improves mildly from
childhood to adulthood. Most cases of early onset nystagmus are associated with ocular disease
many of which are inherited conditions. With a strong family history, dominant, recessive and xlinked patterns have been reported. The severity of nystagmus often varies amongst members of
an involved family.
Patients with nystagmus have many unique problems that are often evaluated by low
vision specialists or ophthalmologists skilled in treating nystagmus. Simple tests like visual
acuity can be misleading as the vision may decrease if the patient is under stress or has latent
nystagmus which causes an increase in nystagmus in both eyes when one eye is covered. The
visual acuity testing requires special steps to insure an accurate measurement. Low Vision
specialists also use special testing techniques during the refraction to measure the eyeglass
prescription and prevent inaccurate results from latent nystagmus. Reducing stress during testing
is another method used by ophthalmologists to obtain the best results possible. In addition,
patients with nystagmus frequently have other vision problems such as astigmatism that require
prescription eyeglasses(“AAPOS Nystagmus”). This is particularly true of patients with albinism
and retinopathy of prematurely. Eyeglasses, however, do not cure nystagmus. Prisms may be
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added to the eyewear to improve the patient’s cosmetic appearance by changing the null position
to a slightly more normal position. Prisms may also be used to induce more convergence,
turning in of the eyes, which may reduce nystagmus slightly (“Nystagmus Treatment”). When
bifocals are prescribed the null position is considered. Placing a small bifocal in the normal
position may not be usable in a patient who must turn his or her eyes far to the left to have the
best vision.
Contact lenses have been shown to aid some nystagmus patients. One theory is that the
tactile feedback of feeling the contact lenses on the eyes may lead to better control of the
movement and allow the patient better vision. Another benefit of contact lenses is that they
move with the eyes and thus provide better image quality. Several surgical procedures have been
developed to reduce null positions and thus improve a patient’s cosmetic appearance. Botox,
botulinum toxin, has been used to paralyze ocular muscles and thus reduce nystagmus. It has not
become a practical treatment since the effect of this drug lasts only three to four months and
requires injection into the ocular muscles under general anesthesia. Baclofen has also been used
to lessen certain forms of nystagmus (“Medical Dictionary”).
The ATS software is the standard method of measuring visual acuity in nystagmus
patients; this method along with computerized versions of the Snellen eye chart attempt to
measure visual acuity from a distance of six meters by either a single letter at a time or by a line
of different letters. As explained earlier, nystagmus patients have eyes that are constantly and
involuntarily “shaking”. For them to try to focus on a single letter at once, talk less of a row of
different letters, will certainly cause their nystagmus to worsen. If the patient’s nystagmus is
worsened at the time of testing then the doctor cannot genuinely measure the patient’s true
potential vision because of unpredictable fixation attempts of the eyes. Although nystagmus is
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already a hard disorder to treat, the ATS method of visual acuity testing brings forth very little
positive results. This very reason is what prompted the ophthalmology staff at Johns Hopkins
Hospital to ask the question “Are we accurately measuring visual acuity to find out what the
acuity would be if the eyes were still?” (KTEF 2012 PPT)
The idea of a full field test of repeating letters to measure the visual acuity of
patients with nystagmus started on a series of cards each containing a two dimensional
array of identical Snellen E’s (“Eccentric visual acuity in patients with macular disease”).
The cards would be flipped and rotated randomly allowing for foveation points in the
eye. In addition the full field cards would allow the patient to be closer to the cards since
nystagmus dampens when focusing on a near target (KTEF 2011 PPT). Subsequently,
the need for accurate fixation is reduced since the patient does not have to focus on one
letter.
My mentor, Hee-Jung Park M.D. along with some of her colleagues, including the
renowned David Guyton, M.D. developed the idea of incorporating the full field E cards
into a computerized version called SVAT (Simplified Visual Acuity Testing) which can
be used on the new ipad. This method of visual acuity testing comes with several
advantages over the ATS method of acuity testing. Not only is SVAT adaptive to patient
response, but it is also completely randomized and removes bias from doctors when it
comes to judging exact visual acuity in a patient (KTEF 2011 PPT).
Dr. Park and her colleagues conducted a research using 21 patients (42 eyes) with
congenital idiopathic nystagmus and 11 patients (22 eyes) with oculocutaneous albinism.
The mean vision improvement among these patients was 2.4 (SD ±2.3) lines when using
the Full Field E test compared to the Linear E test in congenital idiopathic nystagmus
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patients, and 0.9 line (SD ± 1.3) in the patients with oculocutaneus albinism. The
difference in vision observed between these groups of patients was statistically
significant (p=<0.001) in congenital idiopathic nystagmus and (p = 0.01) in patients with
oculocutaneous albinism. Vision measured using Full Field E test was better compared to
Single E test by average of 1 line in congenital idiopathic nystagmus patients and by 0.1
line patients with oculocutaneous albinism. The difference in vision measured between
the Single E and Full Field E is statistically significant in congenital idiopathic
nystagmus (p=< 0.001), but not in oculocutaneous albinism (p= 0.9) (“A New Way to
Measure…”).
Congenital Nystagmus has no cure; it is characterized by, involuntary, variable
and repetitive oscillations of the eyes with the patient being unable to predict where the
points of reversal will occur. Partly because of this uncertainty of fixation, nystagmus
reduces visual function. So we start at looking for reasons why there is no cure. Is it
because we are not measuring the patient’s eyes correctly for their potential visual
acuity? Or is it simply because there is no cure? The conventional visual testing using
Snellen lines underestimates the visual acuity measured in nystagmus patients.The Full
Field E test is an easy tool to use in office to test potential visual acuity in patients with
congenital nystagmus (“A New Way to Measure...”). This current research being
conducted uses the Ipad Software SVAT (simplified visual acuity testing) to test patients
using a full field viewing of around 50 letters at a time and garners results. It then
compares its results with that of the ATS (amblyopia treatment study). Ophthalmologists
want to validate whether or not Full-Field testing is able to measure the potential visual
acuity—how vision would be if eyes were still-- in patients with nystagmus. The
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advantages of a full field test such as the randomized letters and the 1 meter distance are
hoped to make a significant difference.