Esotropia is a type of strabismus or eye misalignment in which the eyes are “crossed,” that is, while one eye looks straight ahead, the other eye is turned in toward the nose.
Congenital (Infantile) Esotropia-If Uncorrected into Adulthood
Congenital (infantile) esotropia is a type of strabismus which appears within the first six months of life. Within the first four months of life, eye alignment may be unstable. If misalignment of the eyes persists thereafter, a consultation with a pediatric ophthalmologist is warranted. Generally, the amount of crossing, or angle of deviation, for patients with infantile esotropia is large, measuring 15 degrees or more. The amount of farsightedness or hyperopia in these children, however, is usually insignificant.
One to two percent of children have infantile esotropia. The child may cross fixate, that is, view objects on the right side with the left eye and vice versa. Children with infantile esotropia often alternate their vision between the two eyes by crossing one eye or the other. Other children constantly cross the same eye, which may indicate that amblyopia, or decreased vision (despite refractive correction), is developing in one eye.
Since the amount of farsightedness in children with infantile esotropia is typically small, the magnitude of crossing is large and prevents development of stereoacuity, and the chance of outgrowing the condition is slim, surgical treatment is recommended. Surgery is optimally performed between the ages of 6-9 months, but before age 2 for the most benefit to the development of depth perception.
Adults with uncorrected infantile esotropia can sometimes see 20/20 with each eye separately (with or without glasses) but do not have any appreciable stereoacuity. If the adult is also amblyopic (has reduced best corrected vision of one eye), the amblyopia will not be correctable (although the patient may need a better pair of glasses), but the patient’s eye misalignment can still be addressed. Unlike an infant with infantile esotropia who undergoes successful eye alignment surgery before the age of two, the adult patient would not have the potential to develop fine three-dimensional vision with the same surgery.
Adults with a history of infantile esotropia, corrected or not, may have also developed vertical misalignment of an eye, especially when looking to the side (see photo below). Approximately 75% of children with infantile esotropia develop inferior oblique overaction, which is best recognized when the patient looks up and in. The eye looking toward the nose elevates higher than the opposite eye. When both inferior oblique muscles overact (or sometimes if inferior oblique overaction of one eye is marked), then the eyes usually cross more in downgaze than in upgaze (in a V pattern). In addition to oblique muscle dysfunction, there is a tendency for one eye to drift upward and sometimes outward, a condition known as dissociated vertical deviation (DVD). This condition occurs in up to two thirds of patients with congenital esotropia. In addition, it is usually bilateral and asymmetrical.
Accommodative esotropia is a form of strabismus that most commonly begins between 2 and 4 years of age but may show onset between 4 months to 6 years of age in farsighted children who reflexively cross their eyes when they focus or accommodate. During accommodation, a small muscle inside the eye contracts and causes the natural lens to change its shape and focus images properly on the retina at the back of the eye.
Signs of Accommodative Esotropia
Noticeable crossing of the eyes is usually the primary sign. This crossing may only be evident when the child intently views a near object or when the child is tired or not feeling well. Some children complain of double vision, squint, or rub one of their eyes, most often the misaligned eye.
Diagnosis and Treatment
Full-time use of appropriate farsighted glasses often controls the esotropia. With glasses, the child will not need to accommodate, and hence the associated eye-crossing reflex will disappear. However, after removing the glasses, the crossing will reappear, perhaps even more than before the child began wearing glasses. If glasses with farsighted correction control the crossing, eye muscle surgery is not recommended.
Esotropia Controlled at Distance with Single-Vision Glasses Yet Still Significant at Near
If glasses control the crossing when the child looks in the distance, but not adequately when the child focuses at near (greater than 5 degrees more crossing), bifocals are usually prescribed to enable the child to have straight eyes at distance and near.
Partially-Accommodative or Decompensated Esotropia
In certain individuals, eyeglasses control a portion of the eye crossing, but enough turning still remains to interfere with or prevent optimal formation of stereoacuity. This is referred to as partially-accommodative esotropia. In these cases, surgery is should be performed to correct the eye crossing not controlled by wearing glasses. Alternatively, for some children, esotropia which used to be controlled with glasses may “deteriorate” and significant crossing may develop even while the children wear glasses. If significant esotropia is evident despite proper glasses, eye muscle surgery is required to attain good ocular alignment.
If an adult patient had accommodative esotropia controlled with single vision glasses, accommodative esotropia with greater crossing of his/her eye at near controlled with bifocals, or partially-accommodative esotropia which was controlled with glasses and surgery at a young age and his/her amblyopia, if present, was treated with patching and or atropine drops in addition to glasses on a timely basis, the adult could have good eye alignment and vision.
Amblyopia (Lazy Eye) Associated with Accommodative Esotropia
It is not uncommon for children with a history of accommodative esotropia to have amblyopia or decreased vision in one eye (usually the eye that does most or all of the crossing and often the eye with the larger refractive error). Likewise, adults with a history of accommodative esotropia and untreated or inadequately treated amblyopia as a child (before approximately age nine) will be amblyopic.
Do Children Outgrow This Problem?
Children more often outgrow accommodative esotropia than not. The majority of children are born hyperopic and become less so (emmetropize) over time, especially those with lesser degrees of hyperopia. Alternatively, hyperopic children can, of course, become worse. Some children manage to maintain straight eyes without glasses prior to or within their early teen years, while others need proper farsighted glasses or contact lenses to control the esotropia. In general, the need for hyperopic glasses or contact lenses to control eye crossing decreases with age and is therefore much less prevalent in adulthood than during childhood.
Acquired Non-Accommodative Esotropia
Esotropia can occur after infancy and be insignificantly responsive to farsighted glasses, thereby falling outside the categories of congenital (infantile) or accommodative esotropia. Acquired esotropia can arise in children who have been farsighted for a while and have not had glasses or in children who were initially responsive to glasses but later develop eye crossing even while wearing spectacles or contact lenses of the proper power. Eye muscle surgery can correct such deviations and usually restore binocular vision if the patient had it.
Esotropia Secondary to or Associated with Other Conditions
Duane syndrome represents a constellation of eye findings present at birth that results from an absent 6th cranial nerve nucleus and an aberrant branch of the 3rd cranial nerve that innervates the lateral rectus muscle.
Duane syndrome most commonly affects the left eye of otherwise healthy females. Duane syndrome includes several variants of eye movement abnormalities. In the most common variant, Type I, the eye is unable to turn outward to varying degrees from the normal straight ahead position. In addition, when the patient tries to look straight ahead, the eyes may cross. This may lead a person with Duane syndrome to turn his/her head toward one side while viewing objects in front of him/her in order to better align the eyes. When the involved eye moves toward the nose, the eye retracts slightly back into the eye socket causing a narrowing of the opening between the eyelids. In Type II, the affected eye possesses limited ability to turn inward and is generally outwardly turning. In Type III, the eye has limited inward and outward movement. All three types are characterized by anomalous co-contraction of the medial and lateral rectus muscles, so when the involved eye moves towards the nose, the globe pulls back into the orbit and the vertical space between the eyelids narrows. The eye may also drift up (upshoot) or down (downshoot) as it moves toward the nose.
Although restoration of full eye movements in patients with Duane syndrome may not be possible, eye muscle surgery can effectively correct eye misalignment in primary (straight ahead) gaze, eliminate an abnormal head position, and expand one’s field of single-binocular vision, especially if performed early in the patient’s life. If the abnormal up and down movements of the eye or the narrowness of the eyelid opening significantly affects eye appearance, surgery may also be of benefit.
Sixth Nerve Palsy
Sixth nerve palsy refers to a weakness of the nerve that supplies impulses to the lateral rectus muscle, the eye muscle that mainly moves the eye outward. This is usually an acquired condition which presents with gradual or sudden onset of eye crossing, double vision, and inability of the eye to move outward. An abnormal face turn to the side of the paretic sixth nerve may occur in order to relieve the double vision. Causes of sixth nerve palsies can be secondary to viral illnesses, head trauma, brain tumors, and other causes of increased intracranial pressure . Small blood vessel disease associated with diabetes or high blood pressure is a common cause of sixth nerve palsies in adults.
Sixth nerve palsies generally improve over the course of several (sometimes up to six) months. After a period of observation, if recovery is incomplete and residual eye crossing remains, eye muscle surgery can eliminate the eye crossing in straight ahead gaze and relieve symptoms of double vision. Restoring single vision in right and left gaze in addition to primary gaze depends on the severity of the sixth nerve palsy and the surgical procedure performed.
Thyroid-Related Eye Disease
Although adults with thyroid-related eye disease most often present with vertical eye deviation, esotropia is frequently associated with this condition. Extraocular muscles enlarge with fluid and lymphocytic infiltration, become inflamed, and then fibrotic. The extraocular muscles are affected in the following order: Inferior, medial, superior, and lastly, the lateral rectus muscles. These changes cause the affected muscles to become asymmetrically or unequally tight, which leads to restricted eye movements, lid retraction, and prominent-appearing eyes. Sometimes patients benefit from orbital, eye muscle, and lid surgery, in that order. These changes can occur even with normal thyroid bloodwork.