Developmental anomalies of the lids

Chapter 18 Developmental anomalies of the lids




Major developmental anomalies create significant medical problems.1 They often require specific surgical or medical management. Minor anomalies are features that vary from those commonly seen in the normal population; they do not cause increased morbidity. Major anomalies are not a variation of the normal spectrum. Developmental anomalies of the eyelids can belong to both categories. They can be isolated or observed in a syndromic context.


Single developmental anomalies are divided into four categories:2



When several developmental anomalies are present, three situations are defined:




Normal development and anatomy of the eyelids



Embryology of the eyelids


Development of the eyelids is characterized by three main stages:







Morphology and anatomy of the eyelids


The eyelids have several characteristic horizontal and vertical folds.


The most conspicuous is a well-demarcated horizontal skin crease 3–4 mm above the upper lid margin, which flattens out on depression and becomes deeply recessed when the upper lid is elevated. It divides each lid into an orbital and tarsal portion. The orbital portion lies between the margin of the orbit and the crease; the tarsal portion lies in direct relationship to the globe. A tarsal plate composed of dense connective tissue is found in both the upper and lower eyelids. The upper lid tarsal plate has a marginal length of 29 mm and is 10–12 mm wide. The lower lid tarsal plate is 4 mm wide.


The palpebral fissure is the entrance into the conjunctival sac bounded by the margins of the eyelids; it forms an asymmetrical ellipse that undergoes complex changes during infancy.4 After birth, the upper lid has its lowest position with the lower eyelid margin close to the pupil center. Between ages 3 and 6 months, the position of the upper lid reaches its maximum. The distance between the pupil center and the lower eyelid margin increases linearly until age 18 months.4 By adulthood, the upper eyelid covers the upper 1–2 mm of the cornea, the lower lid lies slightly below its inferior margin.5 Palpebral fissures have a slight outer-upward inclination as the outer canthus is positioned 1 or 2 mm higher than the inner canthus. The normal orientation of the eyelids varies depending on ethnic origin. Palpebral fissure length increases during normal development.6


The principal muscle involved in opening the upper lid and in maintaining normal lid position is the levator palpebrae superioris. Müller’s muscle and the frontalis muscle play accessory roles.


The levator palpebrae superioris arises as a short tendon blended with the origin of the superior rectus from the undersurface of the lesser wing of the sphenoid bone. The levator palpebrae superioris is innervated by branches from the superior division of the oculomotor nerve.


Müller’s muscle is a thin band of smooth muscle fibers 10 mm in width that arise on the inferior surface of the levator palpebrae superioris. It courses anteriorly, between the levator aponeurosis and the conjunctiva of the upper eyelid to insert into the superior margin of the tarsus. Branches of the sympathetic nerve innervate Müller’s muscle. The eyelid is indirectly elevated by attachment of the frontalis muscle into the superior orbital portions of the orbicularis oculi muscle. The frontalis muscle is innervated by the temporal branch of the facial nerve.



Clinical evaluation of the eyelids


Dysmorphology is the study of abnormal development. Guidelines were proposed by an international group for most dysmorphologic terms.710


The clinical assessment of craniofacial features, including eyelid malformations, is based on the overall subjective qualitative clinical evaluation and on objective quantitative measurements. Qualitative anomalies are easy to define as present or absent. The frequency of a feature in the general population defined as a “variant” (present in more than 1% of people) must be distinguished from an “anomaly.” A number of anomalies useful in dysmorphology are quantitative. An objective definition of an abnormal phenotype requires knowledge of the normal variation of the trait (usually defined as ±2 SD (standard deviation) for any measurement) in a population. Some anomalies are subjective (e.g. “a coarse face”).


Morphologic measurements can be easily performed with a transparent ruler. The measurements are compared to a normal database.5



Clinical landmarks


Many lid anomalies are correlated with an abnormal orbital structure. Hypertelorism and hypotelorism, for instance, influence the appearance of the eyelids. The normal distance between the orbits varies during embryogenesis and after birth in accordance with craniofacial development.


The embryonic separation of the globes (the angle between the optic nerves at the chiasm of the fetus) progresses from a 180° angle between the ocular axes in the first weeks of development to 70° at birth, 68° in adulthood 11,12 (Fig. 18.2A). The interorbital distance (the shortest distance between the inner walls of the orbits) increases with age13 (Fig. 18.2B). The most accurate interorbital measurements are obtained from X-rays (Waters half-axial projection, or posteroanterior cephalograms) or computed tomograms.14



Clinical evaluation of the interocular distances is based on the measurement of the following lid-based landmarks:1519



An approximate “rule of thumb” is that the inner intercanthal distance should be equivalent to the palpebral length (Fig. 18.3).



There are tables presenting the change in interocular distances according to age. The clinical method for assessing interocular distance is based on a biometric study that includes measurements of the inner intercanthal distance, the outer intercanthal distance, and the interpupillary distance in Caucasians from birth to 14 years. The normal intercanthal distance is 20 ± 2 mm (1 SD) at birth, increasing to 26 ± 1.5 mm by 2 years of age. The normal interpupillary distance is 39 ± 3 mm at birth, increasing to 48 ± 2 mm by 2 years of age.4


Ethnic variations of orbital features are important; comparison of newborns from England and Africa showed that the Caucasian and the African newborns had the same inner canthal distance, whereas the outer canthal distance and palpebral fissure length were significantly smaller in Caucasian newborns than in African newborns.20


Normal growth curves for many physical parameters have been compiled by Hall et al.21




Developmental anomalies of the periorbital region



Abnormal distances between the eyelids and orbits


Conditions with abnormal distances between the eyelid landmarks are defined in Table 18.1 and schematically presented in Fig. 18.4.


Table 18.1 Conditions with abnormal spacing of the orbits and eyelids































Condition Definition Comments
Hypertelorism Increased distance of the inner and outer intercanthal distances
Hypotelorism Reduced distance between the medial walls of the orbits with reduced inner and outer intercanthal distances
Telecanthus Increased distance between the inner canthi Often mistaken as hypertelorism
  Primary telecanthus: increased distance between the inner canthi (normally spaced outer canthi and normal interpupillary measurement)  
  Secondary telecanthus: increased inner canthi distance (associated with ocular hypertelorism)  
Dystopia canthorum Similar to secondary telecanthus (telecanthus) together with lateral displacement of the lacrimal puncta Clinical tip: an imaginary vertical line passing through the lacrimal punctum cuts the cornea


Appreciation of the interocular distance is biased by the shape of the nasal bridge between the glabella and the inferior boundary of the nasal bone on a vertical axis, and between the inner canthi on a horizontal axis. Excessive interocular distance can be falsely suggested by a flat nasal bridge; prominent nasal bridges can give a false appearance of hypotelorism.



Hypertelorism


Hypertelorism corresponds to an interpupillary distance of more than 2 SD above the mean. It results from excessive distance between the medial wall or bony orbits. Hypertelorism occurs in more than 550 disorders (Figs 18.5 and 18.6) and is often subjectively appreciated and confused with telecanthus. Three pathogenic mechanisms have been suggested:13





The widow’s peak (frontal hairline with bilateral arcs to a low point in the midline of the forehead) is a consequence of ocular hypertelorism: the two fields of hair suppression are further apart than usual with the fields failing to overlap sufficiently high on the forehead. Widow’s peak is common in disorders with major hypertelorism, such as Opitz G/BBG syndrome (OMIM#145410).






Major malformations of the eyelids




Cryptophthalmos (see Chapter 17)


Cryptophthalmos is rare: there is failure of development of the eyelid folds with continuity of the skin from the forehead to the cheek.36,37 In complete cryptophthalmos, the epithelium that is normally differentiated into cornea and conjunctiva becomes part of the skin that passes continuously from the forehead to the cheek. The eyebrow is usually absent and the globes are microphthalmic. In the incomplete form, a rudimentary lid and conjunctival sac is present. Abortive cryptophthalmos presents with a normal lower lid and an absent or abnormal upper lid, the forehead skin passing directly to and fusing with the superior cornea (Fig. 18.11).



Cryptophthalmos may be an isolated finding or present as part of Fraser’s syndrome.36 Fraser’s syndrome is a rare autosomal recessive syndrome with cryptophthalmos, hypoplasia of the genitalia, laryngeal stenosis, and renal hypoplasia or agenesis.



Ankyloblepharon


Ankyloblepharon is partial or complete adhesion of the ciliary margins of the superior and inferior eyelids. Ankyloblepharon filiforme ad natum is usually a sporadic isolated malformation in which the upper and lower lids are joined by tags (easily cured by a simple surgical procedure)38 (Fig. 18.12). Ankyloblepharon may be inherited as an autosomal dominant trait. It may occur in association with ectodermal defects and cleft lip and/or palate in Hay-Wells syndrome,39 an allelic variant of the ectodactyly– ectodermal dysplasia–cleft lip palate (EEC) syndrome (see Chapter 28). Ankyloblepharon may occur in trisomy 18.40




Clefting or notching of the eyelids (“coloboma”)


Notches or clefts of the eyelid have been described as eyelid colobomas, but there is no embryologic relation with defects due to malclosure of the embryologic fissure. They are usually triangular with the base at the lid margin. The size varies from a discrete notch to a major defect with exposure keratopathy requiring surgery.41


Eyelid colobomas may occur in all areas of the eyelids but are most common in the nasal half of the upper lid. More than one lid may be involved; there may be multiple colobomas in the same lid. The eye may be normal or have abnormalities such as corneal opacities, and iris and retinal colobomas extending to microphthalmos and anophthalmos. There may be associated bands limiting ocular motility; strabismus is common.42 The cause of eyelid colobomas remains uncertain. They may be equivalent to facial clefts, but intrauterine factors may play a major role.43 Amniotic bands may cause mechanical disruptive clefting of the eyelids in the amniotic deformity, adhesions, mutilations (ADAM) syndrome.44


Coloboma of the upper lid can occur in the oculo-auriculo-vertebral dysplasia syndrome (Goldenhar’s syndrome), which has no clear genetic basis (Fig. 18.13

Jun 4, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on Developmental anomalies of the lids
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