Ophthalmic Complications of Craniosynostosis and the Impact of Endoscopic Repair

Acknowledgment

None

Funding: Children’s Hospital Ophthalmology Foundation Chair Funds

Introduction

Craniosynostosis often affects the growth and development of the orbit resulting in morphologic changes of the orbital rim, the trajectory of the orbit, and internal volumetric proportions. ^, As such, there are a many ways that vision and ocular alignment are threatened. Ophthalmic abnormalities commonly associated with craniosynostosis include ptosis, exposure keratopathy, astigmatism, amblyopia, papilledema and optic atrophy, and strabismus both from primary abnormalities of extraocular muscle anatomy and their trajectory within the orbit, and secondary changes that can occur after fronto-orbital advancement (FOA). As such, regular ophthalmic evaluation is essential to prevent vision loss from these multitude of causes, many of which are treatable. Some centers have reported that 25% to 40% of syndromic craniosynostosis patients will have a best corrected visual acuity (BCVA) of 20/40 or worse in their better eye under various protocols of surveillance. In this chapter, we review the ophthalmic complications associated with craniosynostosis, what is known about their incidence and severity, and what we have learned when craniosynostosis is treated by endoscopic strip craniectomy (ESC) and orthosis rather than by FOA.

Ophthalmic Complications of Craniosynostosis

Refractive Errors and Amblyopia

Several studies have demonstrated that astigmatism is common. Mayer and colleagues have reported that 25% of healthy children between 1 and 48 months of age have at least 1 diopter (D) of astigmatism. Dobson and colleagues reported that the incidence of astigmatism (of at least 1 D) decreases from 50% in children 4.5 to 5.5 years of age to 12% in children 7 to 9 years of age. They concluded that “against-the-rule” astigmatism disappears by school age in most children. Craniosynostosis, whether syndromic or nonsyndromic, is frequently associated with higher degrees of oblique astigmatism, anisoastigmatism (significant difference in the amount of astigmatism in one eye compared to the other), and anisometropia (difference in refractive error comparing one eye to the other) which increase the risk of amblyopia. In a retrospective study evaluating patients with different forms of craniosynostosis, Hertle and colleagues reported that astigmatism was found in all patients with Crouzon syndrome (25 patients), 13 of 15 patients with Apert syndrome, and 9 of 18 patients with other forms of craniosynostosis. They noted that refractive errors are a significant cause of vision loss in this population for several reasons. Detection and adequate treatment may be limited if photophobia from exposure keratopathy limits the ability to perform an accurate refraction, and midface retrusion combined with relative exorbitism or proptosis creates technical challenges to wearing glasses or other forms of optical correction.

Nonsyndromic Craniosynostosis

Unilateral Coronal Synostosis (UCS)

Denis and colleagues evaluated 39 patients with UCS and reported anisoastigmatism of at least 1.5 D in 9 patients with equal frequency in the ipsilateral or contralateral eye. In contrast, Levy and colleagues reported that 54% (21 out of 39) of patients had at least 1 D of astigmatism, and of these patients, 76% had 1 D or greater astigmatism in the eye contralateral to the fused coronal suture. Only 7 out of 39 patients had spherical anisometropia. Amblyopia was found in 38% (15 of 39 patients), 80% of the time in the contralateral eye. Tarczy-Hornoch and colleagues found that 56% of 25 children with UCS had amblyogenic anisometropia, 79% on the side opposite to the synostosis. A similar observation was demonstrated by Macintosh and colleagues, who evaluated 52 patients with UCS and reported that 44% (25 patients) had greater than 1 D of anisometropia. One retrospective study of patients with UCS did not note an association of amblyopia with anisometropia. Ethnic differences have been reported by Tarczy-Hornoch and colleagues, who found a statistically significant difference in the prevalence of amblyogenic anisometropia among Hispanic UCS patients (72%) compared with non-Hispanic UCS patients (14%) ( P = .02).

The higher incidence of astigmatism in the eye contralateral to the fused suture in UCS has been explained by a downward displacement of the orbital roof which may place subtle pressure on the globe, altering corneal curvature. It is well-known that vascular malformations or masses in the eyelid produce secondary astigmatism by this mechanism (pressure on the globe). ^, Using 3-dimensional (3-D) computed tomography (CT) images to study a cohort of infants with UCS, Lo and colleagues demonstrated that the two eyes have different height-to-width ratios (orbital index).

Metopic Craniosynostosis

In a retrospective series of 91 individuals who had isolated metopic craniosynostosis, 20.9% (19 patients) had astigmatism, 5.5% (5 patients) had myopia, 5.5% (5 patients) had hyperopia, and 5.5% (5 patients) had anisometropia. A total of eight patients had amblyopia. Of these patients, amblyopia was caused by a combination of refractive error and strabismus in five patients and refractive error alone in three patients. Hypotelorism and upslanting of the lateral canthus is often associated with metopic synostosis.

Syndromic Craniosynostosis

In a retrospective series of 144 patients with syndromic craniosynostosis including Apert, Crouzon, Pfeiffer, and Saethre-Chotzen syndromes, Khan and colleagues reported that 39.8% of patients had BCVA of 20/40 or worse in the better seeing eye and 64.6% of patients had BCVA of 20/40 or worse in at least one of their eyes. Forty percent of patients had 1 D or greater of astigmatism in one of their eyes. Oblique astigmatism was present in at least one eye of 64% of these patients. The prevalence of astigmatism differed from one syndrome to another, with approximately 30% in Saethre-Chotzen syndrome patients, 43% in Crouzon syndrome patients, 45% in Pfeiffer syndrome patients, and 52% in Apert syndrome patients. The astigmatism may result, in part, from the downward slant of the superior orbital rim. Anisometropia of at least 1 D was found in 18% of patients compared to 3.5% of age-matched children without craniosynostosis. A review of 71 patients with Crouzon syndrome by Gray and colleagues demonstrated that 35% had vision loss in at least one eye and 9% had bilateral visual impairment. Amblyopia was a common cause of vision loss present in 21% of patients. Seventy-seven patients had significant ametropia. Fifty-seven percent had hyperopia of at least 2 D and 20% had myopia of at least 0.5 D. Consistent findings were reported by Tay and colleagues in a retrospective series of 55 patients with syndromic craniosynostosis (Apert, Crouzon, Pfeiffer, Saethre-Chotzen) or cranio-fronto-nasal dysplasia. Of these patients, 40% had visual impairment (35.5% bilateral and 9.1% unilateral), and amblyopia (16.7%) as well as ametropia (25%) were major risk factors. Forty percent of patients with syndromic craniosynostosis had astigmatism. There was a lower prevalence of hyperopia (18%) compared to that reported by Gray and colleagues (57%). ^,

Apert syndrome is mostly caused by fibroblast growth factor receptor gene 2 (FGFR 2) point mutations, either Ser252Trp or Pro253Arg. Patients with S252W mutation are far more likely to demonstrate significant astigmatism (82%) compared to those with P253R mutation (14%) ( P = .005). BCVA less than 20/40 in at least one eye was more prevalent in the S252W mutation group (60% compared with 12.5% in P253R mutation group) ( P < .05).

Several theories have been proposed to explain the high prevalence of astigmatism in syndromic craniosynostosis including exposure keratopathy with subsequent corneal distortion, ptosis especially in Saethre-Chotzen syndrome, and orbital dysmorphology and asymmetry.

Strabismus

Strabismus is a common oculomotor disorder in craniosynostosis, whether syndromic or nonsyndromic, with reported incidence ranging from 39% to 91% compared to an incidence of 2% to 3% in children under 6 years of age without craniosynostosis. In nonsyndromic single suture synostosis, it is most often found in patients with UCS. Several genetic mutations have been associated with craniosynostosis syndromes ^, and some of these mutations appear to increase the risk of strabismus in these sub-popuations. Strabismus is more common in Apert syndrome patients with S252W mutation (91%) compared with those with the P253R mutation (85%) and have a higher risk of superior rectus (SR) underaction ( P = .024) and are more frequently treated with strabismus surgery (64% compared with 14% in P253R mutation group) ( P = .039). The strabismus can be horizontal, vertical, or both, but the most common pattern is V-pattern strabismus characterized by horizontal, vertical, and torsional misalignment ( Fig. 7.1 ). A similar study reported that strabismus was more common in the S252W mutation group (47% compared with 39% in P253R mutation group); however, the difference was not statistically significant ( P = .546).

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