The fusion of the eyelids is an integral part of the embryologic development of the human eyelid. This remarkable process, which starts in the 8th week of gestational life, involves only the peridermal and epidermal layers, whereas the mesenchyme remains intact and unfused. The eyelids remain fused until the 18th-20th week of fetal life when they start to separate. This is a slow, painstaking process that continues until the 24th week of fetal life. When the eyelids are still fused at birth, ankyloblepharon occurs.¹² Eyelid fusion at birth has also been reported in the context of significant prematurity as a normal physiologic phenomenon.²

Ankyloblepharon can be congenital or acquired. There are two distinct types of congenital ankyloblepharon. When there is a full-thickness fusion of the eyelids, the condition is termed congenital or classic ankyloblepharon (Figure 25.1).⁶,⁷ However, when both eyelids are only partially fused by fine bands or skin tags, the condition is termed ankyloblepharon filiforme adnatum (AFA), a term that was coined by von Hasner in 1881 to set this condition apart from classic ankyloblepharon (Figure 25.2).⁶,⁷,⁸ AFA can be isolated or syndromic. In its syndromic form, AFA is mostly associated with ectodermal dysplasias, which are a group of about 180 conditions characterized by abnormal development of ectodermal tissue including the skin, teeth, nails, hair, and sweat glands.¹³,¹⁴ AFA is classified according to its systemic associations into six subtypes that are summarized in Table 25.1.

Acquired causes of ankyloblepharon include chemical trauma, burns, or physical injuries, cicatrizing diseases of the conjunctiva like Stevens-Johnson syndrome or ocular cicatricial pemphigoid, and inflammatory diseases such as herpes simplex blepharoconjunctivitis, particularly when it occurs in immunocompromised patients, and may rarely occur following lacrimal or eyelid surgery. Other rare causes include ulcerative blepharitis, diphtheritic conjunctivitis, trachomatous conjunctivitis, or systemic 5-fluorouracil treatment (Figure 25.3).¹⁷,¹⁸,¹⁹,²⁰,²¹,²²,²³ Ankyloblepharon can also occur temporarily from cyanoacrylate glue.²⁴,²⁵ In a sense, a permanent tarsorrhaphy is an acquired surgically induced ankyloblepharon.

Congenital ankyloblepharon is characterized by full-thickness inner canthal or outer canthal fusion of both upper and lower eyelids (Figure 25.1).⁷ When it occurs laterally, pseudoexotropia is observed. When it occurs medially, fusion usually occurs to the lacrimal puncta. The plica semilunaris and caruncle may be absent, the lacrimal passages are rudimentary, and there is an apparent esotropia. The eye is usually normal, but the condition may be associated with microphthalmia or anophthalmos.⁷

AFA may occur sporadically or be transmitted in an autosomal dominant fashion.⁴ It classically manifests as unilateral or bilateral elastic or distensible strands or bands of tissue that partially fuse the upper and lower eyelids.¹³ These bands typically originate from the gray line between the cilia anteriorly and the orifices of the meibomian glands posteriorly.³,⁶,⁷ They vary from 0.5 to 5 mm in width and may range from 1 to 10 mm in length (Figure 25.2). In contrast to the classic congenital ankyloblepharon, the adhesions in AFA are usually observed in the central two-thirds of both eyelids and are not encountered near the medial or lateral canthi.⁶,⁸