Although the exact etiology of euryblepharon is largely unknown and no specific genes or loci have been observed,¹,⁴ several pathogenetic mechanisms may help explain the clinical manifestations of this condition. A short anterior lamella, partial or complete developmental hypoplasia of the palpebral portion of the orbicularis oculi causing undue tension on the skin, or an abnormally elongated lateral canthal tendon are among the more plausible theories. Other less conceivable etiopathogenetic mechanisms include indirect pull of the platysma on the eyelid, defective fetal separation of the lids, and localized congenital displacement of the lateral canthi.⁴,⁵,⁶,⁷,⁸,⁹

The most obvious clinical manifestation of euryblepharon is increased length and width of the palpebral aperture. A typical clinical sign is that the lower lid and less commonly the upper lid appears to “hang away” from the globe laterally,⁶ as if the eyelid is “too big” for the globe (Figure 33.1). This may be an inaccurate description because euryblepharon is typically associated with a vertical lower eyelid shortening rather than lengthening. Whether this vertical shortening is also associated with horizontal shortening⁸ or paradoxical horizontal lengthening of the lower eyelid⁷ is contentious in the literature. Typically, euryblepharon symmetrically involves both lower eyelids but asymmetric cases have been described.⁵ Euryblepharon may occur in isolation without any ocular or systemic associations, or may be associated with several different local or systemic anomalies.

Locally, it may occasionally be observed concurrently with ptosis, distichiasis, telecanthus, strabismus, or abortive cryptophthalmos.¹,⁵,¹⁰ Systemically, euryblepharon is the quintessential defining feature of blepharocheilodontic (BCD) syndrome (Figure 33.2) and Kabuki-makeup syndrome.⁵,⁶ It has rarely been described with Noonan¹¹ and Barber-Say syndromes¹² and multiple endocrine neoplasia syndrome type 2B (MEN 2B).¹³ BCD syndrome is a rare disorder characterized by lower eyelid euryblepharon, upper eyelid megaloblepharon, distichiasis, bilateral cleft lip and palate, hypodontia, conical teeth, and imperforate anus. The syndrome is inherited in an autosomal dominant fashion with incomplete penetrance, but de novo mutations have also been described. Two genetic loci have been identified so far for the disease (16q²² and 11q12).¹⁴,¹⁵,¹⁶ Kabuki syndrome (also known as Kabuki-makeup syndrome or Niikawa-Kuroki syndrome) derives its name from the peculiar characteristic dysmorphic facial features that are highly reminiscent of the makeup pattern of Kabuki artists, the ancient theatrical form of Japanese opera. Hallmarks of this genetic disease include euryblepharon, high arched eyebrows, depressed nasal tip, and prominent ears. Systemic features include skeletal anomalies (brachydactyly, spinal anomalies, and a short fifth finger), cleft lip and palate, mental retardation, postnatal growth retardation (short stature), and dermatologic anomalies (persistent fetal pads on the fingertips). The syndrome
more commonly occurs in children of Japanese ancestry in a sporadic fashion, but other ethnicities have been described. The full phenotype appears to evolve, compounding the early diagnosis of the disease.¹⁷,¹⁸,¹⁹