The Nystagmus of Achromatopsia

 

"When I open the blinds, a diffuse foggy light bounces in through the glass and brightens the room. Katy squints and cries....  I look into her face and notice that her pupils' wandering is more pronounced."

                                   Ellen Tomaszewski, My Blindy Girl

Nystagmus may be one of first signs, which alerts parents that their infant may have a vision problem. Nystagmus is an involuntary rhythmic shaking or wobbling of the eyes. The term nystagmus is derived from the Greek word, “nmstagmos”, which was used to describe the wobbly head movements of a sleepy or inebriated individual. Nystagmus has also been described as “dancing eyes” or “jerking eyes”.

Nystagmus often accompanies vision loss acquired at birth or soon after. In achromatopsia, it may be 3 to 6 months before the nystagmus is observed by parents. In infants with rod monochromatism, the nystagmus is usually rapid frequency and of low amplitude (fast moving, but only a small angle). It often decreases over the first 10 years of life which may improve visual acuity. In blue cone monochromatism there may be less nystagmus and it may improve significantly with age.

 

Knut Nordby, researcher and achromat, reported that his parents saw no nystagmus or light aversion until age seven months. Then things changed.

"My eyes had started to quiver from side to side (i.e. horizontal, pendular nystagmus) and my eye-movements were irregular. I had begun to blink continuously and partially close my eyes, or squint (looking through the narrow slits between the eyelids), in bright light, and I habitually avoided bright light, something I had not done before."

            - Knut Nordby, Researcher and Achromat

The  nystagmus in achromatopsia is typically a pendular nystagmus. The eyes rotate back and forth evenly, much like a pendulum. Patients with the onset of nystagmus from childhood do not notice the movement of their vision when their eyes shake.  Other forms of nystagmus may intermittently occur in achromatopsia including both horizontal and vertical jerk nystagmus. 

 

 Nystagmus is usually a sign of decreased vision in a small child. It is not unique to achromatopsia. Any sign of nystagmus in a young child requires immediate medical intervention. Onset of nystagmus in a child requires an immediate comprehensive examination. This is usually performed by a pediatric ophthalmologist. After an initial diagnosis of achromatopsia, the child should be referred to a doctor specializing in low vision rehabilitation to help the parents learn how to organize their child's world, deal with eyewear and filters. The low vision specialist may make recommendation for other services such as a visual impairment teacher and/or occupational therapy. See the Children's section on this website developed by Dr. Laura Windsor.

 

Fluctuations in Vision

Nystagmus patients often experience fluctuations in their vision.  An increase in speed and or change in direction of the nystagmus may be influenced by stress, the patient’s emotional state, fatigue, direction of view, covering one eye and in achromatopsia when battling glare and light. Understanding these issues allows the parents and teachers to create a better environment. 

 

The Null Position:  Unusual Head and Eye Positions

Some patients with nystagmus find a unique position of their head and eyes that slows the nystagmus allowing them to have better vision. This is called the null position and varies with each person. Teachers, friends and family must understand and support the patient’s unusual head or eye position. A well meaning family member telling the child to not tilt  their head may do harm. The child should be encouraged to adjust their head or eyes to where they see the best. We must also distinguish between a null position from nystagmus and a headtilt downward to avoid bright light in many achromats.

 

Surgical Options for Nystagmus

 

Currently, there are two main surgical procedures for nystagmus. The first surgical procedure is used to change the null position to avoid unusual head tilts. If a child must tilt his or her head in an extreme manor to reach the null position, where the nystagmus slows, eye muscle surgery can shift the position of the eye and eliminate much of the head tilt.

The second surgical procedure, a rectus four muscle tenotomy, has potential to improve visual acuity, by slowing the nystagmus. The rapid movement of nystagmus allows only brief fleeting periods, when the image is stable on the retina. If we can slow the movement of the eye, by reducing the nystagmus we can increase the time the image is stable on the retina, and thus, improve the quality of the vision.

This procedure was conceived by Louis Frank Dell Osso, Ph.D., an electrical engineer and one of the world’s top authorities on nystagmus. He heads the Daroff-Dell’Osso Ocular Motility Laboratory, Louis Stokes Cleveland Department of Veterans Affairs Medical Center. He is also an individual with nystagmus.

Dell’Osso theorized that cutting the tendon attachments of the eye muscle to the globe of the eyes and immediately reattaching them in the same position would also cut feedback nerves that tend to increase the speed of the nystagmus. In 1998, his theory was proven correct in an experimental surgery on a dog.

Dell'Osso worked then with Richard Hertle MD, pediatric ophthalmologist then at the University of Pittsburgh. in the development of this procedure. Dr. Burnstine soon joined their research efforts. In 1999, Dr. Burnstine, pediatric ophthalmologist, at the Akron Children's Hospital performed the first horizontal tenotomy procedure on a human. Since then Dr. Burnstine has performed hundreds of these procedures.

Dr. Burnstine reports on average about a 20% improvement in vision straight ahead and a 50% improvement in peripheral vision. This procedure has been now been successful in children and adults. Dr. Burnstine is one of a small but growing group of pediatric ophthalmologist performing this procedure. It is an outpatient procedure that takes less than an hour. Patients may be back to work or school in one to three days.
 

Dr. Burnstine may be reached at Akron Children’s Hospital, Akron, Ohio.

 

Contact Lenses and Nystagmus

Contact lens have long been prescribed in an attempt to provide feedback of the eye movement and thus slow nystagmus and thus improve vision. In some patients, we see significant benefits of the contact.  In a recent study of infantile nystagmus using new waveform analysis and the eXpanded Nystagmus Acuity Function (NAFX), the authors found that contact do provide a feedback to slow the nystagmus and reported:

 

"Contact lenses allowed the subject to see “more” (he had a wider range of high-foveation-quality gaze angles) and “better” (he had improved foveation at each gaze angle)."

Infantile nystagmus syndrome: Broadening the high-foveation-quality field with contact lenses. Giovanni Taibbi, Zhong I Wang, Louis F Dell’Osso Clinical Ophthalmology October 2008 Volume 2008:2(3) Pages 585 - 589 Giovanni Taibbi, Zhong I Wang, Louis F Dell’Osso

We routinely fit patients with achromatopsia with filtered contact lenses. The magnitude of benefit from the filter for achromats is far more important than the feedback of the contact lenses. Hopefully patients experience both benefits.