Hospital for Sick Children's, The: Atlas of Pediatric Ophthalmology & Strabismus, 1st Edition

7

Lens

Alex V. Levin

Thomas W. Wilson

David Rootman

The lens of the eye is derived from surface ectoderm, which invaginates into the optic vesicle during embryogenesis. This newly formed lens vesicle contains an outer capsule and is lined with primary lens epithelium. The posterior fibers elongate anteriorly to fill the vesicle. Secondary lens fibers emanate from the equatorial lens and migrate anteriorly and posteriorly to form the Y sutures. The primary lens fibers that are encircled by these secondary fibers are compacted to form the embryonic nucleus. The secondary fibers interior to the Y sutures make up the fetal nucleus. Additional fibers are laid down exterior to the Y sutures, forming the cortex. This complicated process is regulated by a variety of genes with differential expression in terms of location and time of development. The morphology of pediatric cataracts often reflects these stages of differentiation. Significant amblyopia and subsequent vision loss can occur from these opacities. Early surgery with optical correction is crucial for visual development.

Cataracts can be isolated genetic or nongenetic conditions or the result of systemic disease and systemic medications, in particular steroids. Cataracts may also be part of congenital syndromes. Heritable cataracts may be unilateral or bilateral. Attention must be paid to cataract morphology as this will provide information on cause, heritability, and management strategies. Some small cataracts may be managed medically, whereas more significant visual axis obstruction will require surgery.

The lens is suspended on the anterior vitreous face behind the pupil by the zonules (suspensory ligaments). A wide variety of systemic disorders, covered elsewhere in this atlas, may be associated with zonular weakness or dehiscence resulting in ectopia lentis. This chapter will focus on the causes of isolated ectopia lentis due to ocular malformation. Buphthalmos (Chapter 10: Glaucoma, Fig. 10.1) can also cause ectopia lentis. Isolated autosomal dominant and autosomal recessive forms may also be observed.

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Figure 7.1 Mittendorf Dot

Mittendorf dot is a small, gray or white opacity on the posterior capsule of the lens. It is the area where the hyaloid artery system attaches to the lens during ocular development. The opacity is not vision threatening and typically does not progress. A hyaloid remnant is seen here with some radiating persistent fetal circulation on the posterior surface of the lens.

 

Figure 7.2 Tunica Vasculosa Lentis

Tunica vasculosa lentis is the primitive vasculature that envelops the developing lens of the fetus as the forward extension of the hyaloid system. This fine network of vessels regresses starting at 28 to 30 weeks of gestation, but regression may be delayed by systemic illness. It clears centrally first and can be an accurate marker of gestational age. It is not visually significant. The left image is taken in a premature baby that is younger than the child on the right.

 

Figure 7.3 Anterior Subcapsular Cataract

Anterior subcapsular cataract is an opacity that lies on the posterior surface of the anterior lens capsule. It is often traumatic in cause but may be an isolated heritable opacity or associated with Alport syndrome (often in the anterior lenticonus, not shown here) or atopic dermatitis. There may be a central focal white opacification of the anterior capsule, shown here, with the gray base of posterior subcapsular opacity. The latter may enlarge and become visually significant. However, if the opacity remains small (<3 mm), medical management with pharmacologic dilation of the pupil and patching of the other eye may result in good vision outcomes.

 

Figure 7.4 Anterior Dot Polar Cataract

Anterior dot polar cataracts are small white opacities located centrally on the anterior lens capsule. Two thirds are unilateral. Although usually visually insignificant, other ocular findings may include amblyopia, anisometropia, persistent pupillary membrane, and strabismus. Progression is uncommon but patients should be examined at regular intervals, especially in the first year of life. Autosomal inheritance may be observed.

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Figure 7.5 Anterior “Tractional” Cataract

This lens opacity is always associated with a persistent pupillary membrane strand to which it is attached. This is a remnant of the neural crest–derived iris stroma network that covers the pupil during ocular development. The opacity in the lens capsule, with or without an underlying anterior subcapsular opacity, is usually eccentric to the visual axis and therefore visually insignificant. Enlargement of the subcapsular component is rare but follow-up is recommended, especially in the first year of life. The pupillary membrane strand often lyses spontaneously over time. This is a nongenetic unilateral lens opacity.

 

Figure 7.6 Cerulean Cataract

Cerulean cataract, also known as “blue dot” cataract, may be an isolated heritable cataract or associated with systemic disorders such as Down syndrome. The multiple opacities appear as small, bluish-white amorphous dots located in the cortical material of the lens. More coalescence of the opacity may be seen in the nucleus, at the sutures, or in the posterior cortex. Crystallin gene mutations (CRYBB2, CRYGD) have been associated with autosomal dominant forms of cerulean cataract.

 

Figure 7.7 Lamellar Cataract

Lamellar cataracts are opacities outside the lens nucleus and are contained within the cortex. The central lens is often clear. The cortical fibers are laid down in concentric layers. At the point where the cataractogenic event occurs, one layer becomes opacified. As seen here, arclike opacities, which appear to be perpendicular to the lamellar opacity (arrow), arc around the lamella. These are called cortical riders. Lamellar cataracts are often progressive and many will require surgical removal, although the opacity may seem more severe than the visual acuity.

 

Figure 7.8 Embryonal Nuclear Cataract

Embryonal cataracts involve the most central portion of the lens nucleus. They are typically not progressive but can be visually significant. The embryonic nucleus is formed within the first 2 months of gestation as primary lens fibers extend forward from the back of the lens vesicle and are then compressed into a central core by surrounding secondary lens fibers. These cataracts are often genetic and bilateral. If they disrupt the central 3 mm of the retinoscopy reflex, then surgery is usually indicated.

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Figure 7.9 Fetal Nuclear Cataract

A fetal nuclear cataract is a lens opacity involving the fetal nucleus, which is the portion of the lens delimited anteriorly and posteriorly by the Y sutures. It contains a central core, the embryonal nucleus, which is also often opacified as well. Although the fetal cataract is typically nonprogressive, it can cause visual loss and require surgery. Nuclear cataract, especially when associated with microphthalmia, significantly increases the risk of aphakic glaucoma following cataract surgery.

 

Figure 7.10 Pulverulent Cataract

Cataract centralis pulverulenta consists of a small central grayish globular opacity containing small white granules. There is also often a multitude of tiny dustlike opacities throughout the cortex as well as the nucleus. The opacities may be confined to one or more lamellae and may be of different sizes in different parts of the lens. It is located within the fetal nucleus and has an autosomal dominant inheritance. Many genes have been associated with both autosomal recessive and autosomal dominant pulverulent cataracts.

 

Figure 7.11 Sutural Cataract

Sutural cataracts occur at the Y sutures, which are formed from developing secondary lens fibers as they surround the embryonal nucleus. These lens opacities may progress but are not usually visually significant. They are usually isolated ocular abnormalities and may be inherited as an autosomal dominant condition due to mutations in the crystalline genes CRYBB2 or CRYBA1.

 

Figure 7.12 Posterior Subcapsular Cataract (PSC)

The posterior subcapsular cataract is an opacity on the anterior surface of the posterior capsule. This type of cataract is associated with chronic steroid use, radiation exposure, inflammation, and trauma. PSC can also be an isolated heritable ocular abnormality, usually autosomal dominant. It is often visually significant, requiring surgical correction. However, in childhood the vision is often surprisingly better than one might expect from the examiner's view of the opacity.

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Figure 7.13 Posterior Lenticonus

Posterior lenticonus is lens opacity secondary to absence or thinning of the posterior lens capsule with progressive overlying cortical opacification. As shown here, there is a characteristic posterior bowing of the lens capsule. Speckled white opacities on the posterior capsule surrounding the defective area may be seen. Because of its location, posterior lenticonus is commonly visually significant, requiring either refractive correction or surgical removal, even if there is no opacity within the bowed portion of the posterior capsule.

 

Figure 7.14 Persistent Fetal Circulation (PFC)

Formerly known as persistent hyperplastic primary vitreous (PHPV), PFC is due to a persistence of the primitive hyaloid vasculature of the developing eye. The fibrovascular stalk extends from the posterior lens posterior to the optic nerve. This patient demonstrates the characteristic vascularized posterior capsular plaque associated with pulled-in ciliary processes. Poor pupillary dilation and microphthalmia with a shallow anterior chamber are also frequent. If unilateral, this is a nongenetic disorder. In less than 10% of cases, bilateral PFC may be seen. These children have a higher incidence of developmental delay and other systemic malformations.

 

Figure 7.15 Persistent Fetal Circulation

The remnant of the fetal hyaloid vasculature is seen extending from the posterior lens capsule (left image) to the optic nerve (right image). The stalk may or may not have patent vasculature. During surgical removal, this blood vessel will often bleed, requiring electrocautery. The posterior stalk can be associated with distortion and detachment of the macula. Retinal distortion is seen in the right image. This may preclude visual rehabilitation after cataract surgery.

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Figure 7.16 Persistent Fetal Circulation

Persistent fetal circulation is a persistence of the anterior hyaloid system. The hyaloid system normally flares out over the anterior vitreous face on its way to envelop the lens. When normal regression does not occur, a fibrovascular opacification occurs and appears on ultrasound biomicroscopy as a double linear echo (arrows). This membrane may insert at the ora and result in retinal traction, if not dialysis, during surgery. Involvement of a vitreoretinal surgeon may be appropriate for cataract surgery.

 

Figure 7.17 Total Cataract

The entire lens is opacified in this photograph. Surgical removal should be performed as soon as possible in an attempt to restore the vision. View of the posterior pole is not possible and therefore B-scan ultrasound is advised. Many of the cataracts pictured in this chapter can progress to a total white cataract. Therefore, the surgeon must be prepared to encounter such problems as posterior lenticonus or other types of primary cataract opacities.

 

Figure 7.18 Ectopia Lentis et Pupillae

Ectopia lentis et pupillae is a developmental abnormality where the lens is dislocated in one direction and the pupil is displaced in the opposite direction. The pupil tends to be oval and dilates poorly. There may be zonular deficiency in the quadrant toward which the pupil is displaced, thus resulting in the lens moving in the opposite direction. An autosomal recessive inheritance pattern has been reported. An adequate visual axis may be obtained in some cases with pharmacologic dilation of the pupil, but surgery would be required if the lens is displaced significantly.

 

Figure 7.19 Ectopia Lentis in Persistent Fetal Circulation

This slide demonstrates an ectopic lens secondary to persistent fetal circulation (formerly known as persistent hyperplastic primary vitreous [Fig. 7.14]). Note the opacity on the posterior pole of the lens. Presumably due to the contraction of the fibrovascular membrane, the lens has shifted laterally and slightly superiorly. The ciliary body can be seen nasally. Surgery would be needed to clear the visual axis.

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Figure 7.20 Microspherophakia

In microspherophakia, the lenses are small and round. This may be a primary disorder of lens size or a secondary finding due to weak zonules. The entire lens is visible through the dilated pupil. Dislocation of the lens into the anterior chamber and pupillary block glaucoma can occur. Associated systemic conditions include Weil Marchesani syndrome, in which patients will demonstrate skeletal abnormalities including short stature with a large thorax, short spadelike hands, brachycephaly, and a depressed nasal bridge. This syndrome may be inherited as an autosomal dominant (mutations in the fibrilin-1 gene, FBN1, at 15q21.1, which also is responsible for Marfan syndrome [Chapter 28: Skeletal, Fig. 28.8]) or autosomal recessive (mutations in the ADAMTS10 gene at 19p13.3-13.2) disease.

 

Figure 7.21 Dislocated Lens in Anterior Chamber

In this photograph, the lens is dislocated into the anterior chamber causing papillary block glaucoma. This may result in iritis, corneal edema, and pupillary block. The latter is due to the strong attachments between the pediatric anterior vitreous face and the back of the lens. As a result, when the lens comes forward, vitreous is dragged through the pupil. If the pupil constricts around the vitreous, block occurs and intraocular pressure can be dramatically high. Although the lens may float back behind the pupil with pharmacologic dilation in the supine position followed by pharmacologic miosis, surgery is usually recommended to prevent recurrences. Complete forward dislocation is more common in disorders where zonules break (e.g., homocystinuria, Chapter 20: Metabolic, Fig. 20.3) or in microspherophakia (Fig. 7.20), as opposed to disorders where the zonules stretch, as in Marfan syndrome (Chapter 28: Skeletal, Fig. 28.8).