Patient Education - Eye Diseases and Conditions

A word about resources: We hope the information presented below is helpful in providing a starting point for understanding strabismus and amblyopia

For further information, try the web site of the American Association for Pediatric Ophthalmology and Strabismus, AAPOS.org. For those with medical backgrounds or insatiable curiosity, you may want to read the appropriate articles in eMedicine. Alternatively, reviewing a textbook at a medical library, such as the books published by Drs. Spiegel and Wright, may be informative. Of course, you may end up with more questions than when you started. A quality ophthalmologist may be your best resource. Good Luck!!

 

 

Strabismus is the general term referring to any abnormal misalignment of the eyes. There are many varieties of strabismus, briefly covered below.

 

Strabismus in childhood is a fairly common problem. Most instances are isolated, meaning that there is no dangerous neurologic or systemic medical condition causing the problem or associated with the problem. (Your Ophthalmologist must figure out whether a given instance is benign or worrisome; this is one instance where experience counts!). Following is a brief discussion of the main types of childhood strabismus. Remember this is only a limited introduction, as the field of strabismus is very large and there are many complexities and subtleties that we will not try to cover here. Also, make sure to read about amblyopia, a condition that often goes along with strabismus.

 

Esotropia means the eyes cross inward. The most common variety is called accommodative esotropia or refractive esotropia. The typical scenario is that a child with previously straight eyes begins crossing at age 2 to 5 years, with greater crossing looking at near objects than distant ones. The right or the left eye may cross, or the child may alternate eyes, meaning that child switches using the right and left eyes from moment to moment. It just depends on whether the child has a dominant eye. Usually, but not always, a moderate to large degree of farsightedness is found, and glasses are prescribed. If the eyes respond optimally and the eyes remain straight with the glasses on, this is deemed a good response and the glasses are worn as the main treatment. Sometimes bifocal glasses are used in this condition. If the eyes cross despite the proper glasses being worn properly, then eye muscle surgery is usually indicated. 

 

Another common variety of esotropia (though less common than refractive esotropia) is called infantile or congenital esotropia. This is a large angle crossing that present at birth or before six months of age, and neurologically isolated. This condition is not related to farsightedness and most require eye muscle surgery. The optimum age for surgery in this condition is from 5 months to one year.

 

Exotropia means the eyes deviate outward. The most common variety is referred to as intermittent exotropia. This condition comes on at any age, and consists of occasional outward drifting of either eye. Typically, the drifting occurs when the individual is looking in the distance in contrast to near, or when fatigued, ill, or under the influence of medication or alcohol. Either eye may deviate depending on whether one eye is dominant. Double vision may occur when the eyes are misaligned. In cases in which the deviation is under poor control (frequent drifting, eye strain, loss of depth perception, etc.), then surgery is indicated.

 

Hypertropia is a vertical misalignment of the eyes. It may occur in isolation but more often accompanies another type of strabismus.

 

The causes of the strabismus types mentioned above are poorly understood. Strabismus tends to run in families, but no specific gene is known to account for the condition. It is not yet possible to predict if a child will develop strabismus based upon family history. Generally speaking, one can say that there is a faulty relationship between the brain’s signal to the eye muscles and the muscles’ response. Other types of strabismus are caused by a mechanical restriction of the muscle, a weakness a nerve to the muscle, or problems with the connective tissue in the eye socket. Strabismus of all types is more common in children with developmental problems such as prematurity, cerebral palsy, Down’s syndrome and other genetic conditions, and as a consequence of vision loss of any cause. Common causes of strabismus in adults include stroke, Graves’ disease, nerve weakness, trauma, vision loss, and recurrent or residual childhood strabismus.

 

Duane’s syndrome when certain nerves to the extraocular muscles become misdirected during in utero development. The result is that the eyes may be straight, esotropic, or exotropic. There is limitation of eye movement, and often one can observe the affected eye retracting into the eye socket with attempted movement. Ninety percent of cases are bilateral and severe cases require surgery.

                       

Brown’s syndrome is caused by an impairment of the trochlear tendon’s ability to pass through the trochlea. The result is that the affected eye cannot be fully elevated when the eye is looking toward the nose. Brown’s syndrome may be congenital or acquired, unilateral or bilateral. Severe cases require surgery.

 

Amblyopia is a type of decreased vision caused by impaired visual development. Development of normal vision requires proper visual experience from infancy to childhood. If that does not occur, then the vision will lag. There are three types of amblyopia, named for their causes. In strabismic amblyopia, a child with strabismus, one eye is habitually deviating, leading to suppression, and causing amblyopia. In anisometropic amblyopia, a blurred image on the retina prevents normal visual experience and leads to amblyopia. In occlusion amblyopia, conditions such as cataract and ptosis prevent light rays from properly reaching the retina, causing amblyopia. Amblyopia usually affects one eye, but may be bilateral in instances such as bilateral cataracts. Treatment of amblyopia is individualized, and may involve glasses, patching the dominant eye and eye drops.

 

The fact that human eyes are positioned a few inches apart permits each one view a slightly different image. Even though the images are not identical, they are close enough that the brain fuses the two images to create one combined image in the mind. In the normal situation, this creates the perception of objects that are solid and contain depth, and are a certain distance away. This process is called stereoscopic vision. It is a type of depth perception that relies on two, well-aligned eyes, each with good acuity. This quality is in effect most at near distances, at 10 feet or closer. High grade stereoscopic vision is needed for optimal hand-eye coordination, and near activities.  Other types of depth perception only need one eye to operate. For instance, we know that if an airplane flying overhead appears small, it must be quite far away. Only one eye is needed to make this judgment.

            Double vision, or diplopia, means that two images are perceived instead of one. The most common type seen in our office results from the eyes being misaligned. If the diplopia resolves when one eye is closed, then the patient has binocular diplopia. If the eyes are misaligned horizontally, then two images will appear side by side. Vertical misalignment of images results in vertical double vision. Combined misalignment causes oblique diplopia. On the other hand, if the diplopia persists when one eye is closed, the patient has monocular diplopia. The common causes are corneal scars, uncorrected astigmatism, cataracts and retinal conditions. Your ophthalmologist should be able to determine the type of diplopia readily in the office.

 

Children frequently have the automatic ability to suppress the visual information from a deviating eye. This may be considered a fortunate adaptation because it prevents double vision. However, a chronically suppressed eye may develop amblyopia, as described above. Adults who had childhood strabismus with suppression may retain this characteristic for life, resulting in strabismus without diplopia.

 

We all (those of us with 2 healthy eyes) have a type of diplopia called physiologic diplopia. To demonstrate this phenomenon, hold a pencil vertically about 6 inches from your face and look directly at it. Then, hold your thumb out directly behind it at arm’s length. As you maintain focus on the pencil, you will see two thumbs. This is normal and our brain naturally suppresses any confusion this type of double vision may create. However occasionally a child will discover this phenomenon, causing worry to the family until it can be explained.

 

Ophthalmic prisms are use in assessment of ocular misalignment as well as treatment of certain varieties of strabismus. Diagnostic prisms are used to measure the angle of deviation of the eyes, which in turn is needed to classify the type of strabismus and determine its severity, and also to plan surgery. In patients with small angles of misalignment, prisms may be used therapeutically, being incorporated into glasses. Fresnel press-on prisms are clear, pliable plastic films which are affixed to glasses. They are useful in treating strabismus and aiding in the prediction of how a patient will respond to surgery.

 

Botox (botulinum toxin) is a long-acting neuromuscular poison. Although it has become most well known for its use in reducing wrinkles, its original use and research was in patients with strabismus, in which the liquid toxin is injected into the extraocular muscles. In strabismus treatment, Botox is most often used in conjunction with conventional surgery. Most strabismus surgeons consider conventional techniques to be more predictable and long lasting.

 

At Focus On You, we continually strive to make our services and expertise available to you and your family. That means we have ongoing discussions with insurance companies, HMOs, and Primary Care Providers aimed at improving access of patients to our services. If you or you child has a condition that requires our attention, please ask your PCP to request a referral, or call our office and we will try to assist you in any way we can!