Ординатура / Офтальмология / Английские материалы / Handbook of Pediatric Strabismus and Amblyopia_Wright, Spiegel, Thompson_2006

reference for the deviated eye. As the pseudo-fovea is the center of reference, the afterimage marked on the true fovea is perceived as coming from the peripheral visual field. With esotropia, the fovea is temporal to the pseudo-fovea and temporal retina projects to the opposite hemifield, so the right afterimage is seen on the left (Fig. 6-25C). Exotropia is just the opposite, with the fovea nasal to the pseudo-fovea and nasal retina projecting to the ipsilateral hemifield, so the right afterimage is seen on the right (Fig. 6-25D).

Other Tests for Suppression and Fusion

VECTOGRAPHIC TEST

The vectographic test is an excellent test for suppression. The test consists of two superimposed polarized slides of letters that are projected onto an aluminized screen which reflects the images while preserving polarization. The patient is asked to read the letters on the screen while wearing polarized glasses. The polarization of the glasses and the projected slides are oriented so some of the letters are only seen by the right eye, some are only seen by the left eye, and some are seen by both eyes (Fig. 6-26). Patients with normal bifoveal fusion will see all the letters. If suppression is present, the letters projected only to the suppressed eye will not be seen (Fig. 6-27). Some patients with suppression will alternate fixation and will see all the letters, although viewing them separately.

FOUR BASE-OUT TEST

This test is performed by first placing a 4 PD base-out prism over one eye. In normal subjects, the 4 base-out test induces fusional convergence. Remember, there are two movements to prism convergence: first, a version movement of both eyes in the direction of the apex of the prism, and second, a fusional vergence movement of the eye without the prism in toward the nose. With the 4 base-out test, the examiner must look carefully for the second convergence movement, as it is the sign of fusion. Patients without motor fusion and large regional suppression show no movement of either eye when the prism is placed over the nondominant eye (Fig. 6-28A) and a version (not vergence) movement of both eyes in the direction of the apex of the prism when the prism is placed over the fixing eye (Fig. 6-28B).

FIGURE 6-27. Diagram of vectograph examination of a patient with a suppression scotoma, left eye. In this case, the patient only sees images from the right eye and reports seeing an AB.

Patients with the monofixation syndrome and a small central scotoma usually show no movement when the 4 PD prism is placed over the nondominant eye. Because these patients have peripheral fusion, monofixators occasionally show a normal fusional convergence movement. A prism over the fixing eye always results in a version movement in monofixa-

tors, and some will show fusional convergence movement as well. Normal patients with bifoveal fusion often show atypical responses to the 4 base-out test.5 Some normals fail to fuse the 4 PD base-out prism, showing an initial version movement but no secondary fusional convergence movement. These patients often alternate fixation and report alternating diplopia. Other normals seem to ignore the induced phoria and show no move-

A

B

FIGURE 6-28A,B. (A) Esotropia, left eye fixing, right eye deviated with large suppression scotoma. Placing the 4 base-out prism in front of the deviated right eye produces no movement of either eye, because the image falls within the suppression scotoma. (B) Placing the 4 base-out prism in front of the fixing eye results in a version movement, with both eyes moving in the direction of the apex of the prism, because there is no suppression scotoma and the movement of the image is perceived.

ment when the 4 base-out prism is placed over one eye. Thus, a secondary fusional convergence movement on 4 base-out prism testing indicates fusion (central fusion or even peripheral fusion), but because of frequent atypical responses in normals, absence of a convergence movement does not necessarily mean an absence of fusion.

References

1.Ellis FD, Schlaegel TF. Unexpected visual recovery: organic amblyopia? Am Orthopt J 1991;31:7.

2.Kushner BJ. Abnormal sensory findings secondary to monocular cataracts in children and strabismic adults. Am J Ophthalmol 1986; 102(3):349–352.

3.Parks MM. The monofixation syndrome. Trans Am Ophthalmol Soc 1969;1242–1246.

4.Pratt-Johnson JA, Tillson G. Intractable diplopia after vision restoration in unilateral cataract. Am J Ophthalmol 1989;107:23.

5.Romano PE, von Noorden GK. Atypical responses to the four-diopter prism test. Am J Ophthalmol 1969;67:935.

6.Sharkey JA, Sellar PW. Horror fusionis: a report of five patients. J Am Optom Assoc 1999;667(12):733–739.

7.Vereecken EP, Brabant P. Prognosis for vision in amblyopia after the loss of the good eye. Arch Ophthalmol 1984;102:220.

8.Wong AMF, Lueder GT, Burkhalter A, Tychsen L. Anomalous retinal correspondence: neuroanatomic mechanism in strabismic monkeys and clinical findings in strabismic children. JAAPOS 2000:168–174.

9.Wright KW, Fox BES, Erikson KJ. P-VEP evidence of true suppression in adult onset strabismus. J Pediatr Ophthalmol Strabismus 1990;27: 196–201.

10.Wright KW, Hwang JM. Diplopia and strabismus after retinal and glaucoma surgery. Am Orthopt J 1994;44:26–30.

important study indicates that esotropia infrequently occurs at birth, whereas exodeviations are common.

Etiology

Esotropia occurring in infancy can be caused by a variety of disorders including congenital fibrosis of the extraocular muscles, Duane’s syndrome, and infantile myasthenia gravis (Table 7-2). In most of the ophthalmology literature, these rare secondary causes of esotropia are not included under the category of infantile esotropia. The etiology of primary infantile esotropia is a source of controversy and remains unknown. Costenbader suggested that hypermetropia with overconvergence plays an important role.19 Historically, there have been two basic theories for the cause of congenital esotropia and the poor binocular sensory outcomes after treatment: the Worth theory and Chavasse theory.

The Worth theory states that the esotropia is caused by a congenital absence of cortical fusion potential. This theory places the blame on a primary cortical fusion deficit present at birth and states there is no hope for obtaining good binocular function.

The Chavasse theory contends that congenital esotropia represents a primary motor misalignment, and the poor binocular sensory status so often seen in these patients is secondary to a disruption of binocular visual development caused by the infantile strabismus. Chavasse supporters speculate that patients with congenital esotropia have binocular cortical potential for high-grade stereopsis and fusion but that the presence of an esotropia during the early period of binocular visual development permanently damages binocular function.

TABLE 7-2. Differential Diagnosis of Infantile Esotropia.

Pseudo-esotropia

Congenital esotropia

Infantile accommodative esotropia

Duane’s syndrome

Sensory esotropia

Congenital sixth nerve palsy, usually transient

Möbius syndrome

Congenital fibrosis syndrome

Infantile myasthenia gravis

Neurological disease

It is likely that infantile esotropia represents a heterogeneous syndrome composed of a variety of different sensory and motor abnormalities. Factors such as early weakness of the lateral rectus muscle, hypermetropia causing accommodative convergence, abnormalities of muscle anatomy, and lack or immaturity of cortical fusion may independently or collectively predispose to the development of esotropia.

One possible cause for esotropia may relate to immaturity of sixth nerve function. The sixth and fourth cranial nerves are the longest nerves that innervate the extraocular muscles and are the last to fully myelinate. Perhaps there is a relative delay in sixth nerve maturation compared to the third nerve, which myelinates first. A relative sixth nerve palsy occurring at birth or in the neonatal period might cause the medial rectus muscle to be unopposed, resulting in infantile esotropia. It is interesting to note that inferior oblique overaction frequently occurs in patients with infantile esotropia. Inferior oblique overaction may represent an early superior oblique paresis resulting from the long fourth nerve and delay in functional maturation.

Whatever the cause or causes of infantile esotropia, there are compelling basic science and clinical studies indicating that esotropia occurring during the developmental period can permanently damage binocular vision. In addition, many infants with esotropia have the cortical potential for binocular fusion.7,21,33,37,71 These two important principles provide the basis for our treatment strategy.

Differential Diagnosis of Infantile Esotropia

The differential diagnosis of infantile esotropia includes Duane’s syndrome, congenital fibrosis syndrome, congenital sixth nerve palsy (Möbius syndrome associated with sixth nerve paresis), and infantile myasthenia gravis. These disorders all have limited abduction and, therefore, can be differentiated from infantile esotropia where the ductions should be full. This differentiation may be difficult in patients with large-angle infantile esotropia and tight medial rectus muscles. Even in these patients, however, vestibular stimulation by doll’s head maneuver reveals full ductions and good abduction saccades.

Other diagnoses include pseudo-esotropia secondary to large epicanthal folds and infantile accommodative esotropia. Infantile accommodative esotropia may be difficult to distinguish from infantile esotropia. The key to the diagnosis of infantile

accommodative esotropia is the presence of straight eyes for several months, followed by a variable small-angle esodeviation associated with hypermetropia of 3.00 or more. (See Infantile Accommodative Esotropia later in this chapter.)

Clinical Features

Infantile esotropia is characterized by a large-angle esotropia presenting from birth to 6 months of age (see Fig. 7-1). There may be a history of the angle of deviation increasing during the first few months of life.37 There is often some limitation of abduction to voluntary version testing; however, doll’s head maneuver and abduction saccades reveal normal lateral rectus function. The majority of children will be in good health otherwise, but there are some systemic associations that are well known.

Onset

The age of onset of infantile esotropia and whether it is truly congenital or acquired has been controversial. Nixon et al. reported no cases of constant esotropia among 1219 newborns, indirectly suggesting that onset in many cases is postnatal.49 In contrast, the Congenital Esotropia Observational Study (CEOS) multicenter study sponsored by the NIH (this author was study chairman) found that 43% of large-angle infantile esotropia cases were reported by the parent or guardian to have occurred at birth, whereas 23% were first noted after the first month of life.51 In a study of 3324 newborns, Archer et al.2 found three cases documented to have straight eyes at birth, later acquiring esotropia at 2 to 4 months of age. In summary, it seems that the onset of the esotropia is variable, with some cases being truly congenital while others are acquired, even several months after birth.

Character of the Esotropia

Infantile esotropia has been classically described as a large-angle constant esotropia. For the most part, this has been based on retrospective case series of patients who had undergone strabismus surgery.28,31,48 The CEOS51 also showed that esotropia occurring in the first few months of life is often small to moderate in size and is frequently variable or intermittent. In this