The iris itself shows a decreased number of circumferential folds and iridodonesis in cases of lens subluxation [27]. The sclera is thin.

There is little information available regarding the vitreous in Marfan syndrome. A frequent finding is liquefaction of the central and posterior vitreous. Evidently, in areas of lattice degeneration, the vitreous may be abnormally attached.

Strabismus is a frequent finding in Marfan patients, caused, among others, by abnormal connective tissue laxity due to missing fibrillin in the pulley. Consequentially, the rate of amblyopia is high (additionally increased by ametropia as well as axial changes).

Lens

The zonules and lens capsule in the healthy eye are rich in fibrillin, which is secreted by the nonpigmented epithelium of the ciliary body [28]. It stands to reason that alterations of fibrillin influence the lens development. In fact, capsular fibers and zonular fibrils are abnormal in size and structure in Marfan patients. The zonular fibers adjacent to the lens are few in number, and at times the lens capsule is almost devoid of zonules. Instead of radial bunches of fibrillin fibers, disorganized fibrillin-positive fragments are found dispersed on the anterior capsule [29]. Additionally, the fibers are weakened toward the lens capsule.

In most cases, the lens has normal size and shape, but microspherophakic lenses can be found, characterized by small size and spherical configuration with increased anteroposterior thickness [23].

Retina

The healthy retina contains fibrillin in the vessel walls only [30]. The eye in Marfan syndrome is in many ways similar to an eye with axial myopia. The peripheral retina shows myopic degenerative changes, lattice degeneration, atrophic holes, chorioretinal pigment proliferation, white without pressure, and vitreous traction syndromes. The choroid is mostly thin and the anterior retina stretched. Retinal breaks and scleral crescents can be seen. Though sharing many similar findings with myopia, in the observations of Maumenee, there was no Fuchs’ spot present

Fig. 20.1 Superotemporal subluxation of crystalline lens in a patient with Marfan syndrome. Note sparse zonular fibers

[23]. Furthermore, there was no posterior staphyloma seen in any patient. According to older publications, it seems that the macula is normally developed [31].

Lens Subluxation

Lenticular abnormalities are the most common ocular feature present in patients with Marfan syndrome; among them, ectopia lentis is the most frequent problem, with microspherophakia and lens opacities being less common.

In general, most cases of lens subluxation overall are caused by trauma. Among the heritable dislocations that are associated with skeletal dysplasias, Marfan syndrome is the most common one.

Clinical Findings

Lens subluxation occurs in about 60% of patients with Marfan syndrome [23], half of them bilateral and symmetric, presenting in early childhood (Figs. 20.1 and 20.2) [32]. Subluxation remains mostly stable since childhood; only 7.5% of all patients progress with increasing age until complete luxation.

Symptoms include decreased vision and monocular diplopia. Apart from lens dislocation, ophthalmologic examination may reveal iridodonesis and irregular astigmatism. Cross et al. found a

Fig. 20.2 Superonasal subluxation of crystalline lens in another patient with Marfan syndrome. A single inferior zonular bundle is still intact

Table 20.1 Ectopia lentis—differential diagnosis

Genetic

With systemic manifestation

Marfan syndrome Homocystinuria Weill-Marchesani syndrome Sulfite oxidase deficiency Hyperlysinemia

Isolated

Simple ectopia lentis (congenital/delayed) Ectopia lentis et pupillae

Aniridia Megalocornea

Nongenetic

Trauma

Lues

Persistent hyperplastic

superotemporal direction of dislocation in 67% of all cases; dislocations into the vitreous or anterior chamber were rare [31]. Another relative common feature is a backward dislocation of the lens, causing a gap between the pupillary border of the iris and the anterior lens surface [23].

Pathogenesis

Lens subluxation occurs due to an asymmetrical excess of laxity in zonular fibers. In the presence of dislocation, the zonules are stretched. In cases of localized stretching, the edge of the lens can be notched (pseudo lens coloboma).

The subluxation causes anterior shift of the lens/iris diaphragm and thus anterior displacement of the focal point of the eye. This leads to myopic shift, which is aggravated by thickening of the lens, bringing along an increased refractive power [33].

Differential Diagnosis

Several systemic conditions can be associated with lens subluxation (Table 20.1). The most important one to be differentiated from Marfan syndrome is surely homocystinuria. In this syndrome, affected patients present with similar marfanoid skeletal features and cardiovascular abnormalities. After the age of 5 years, myopia is rapidly developing; lens dislocation is usually downward—atypical for Marfan syndrome. Histologic examination shows deficiency of

zonular fibers adjacent to the lens and atrophy of the ciliary body [34]. This differential diagnosis should be considered in patients with negative family history. The diagnosis is made by laboratory testing.

Weill-Marchesani syndrome can come along with ectopia lentis as well. The typical presentation is with shallow anterior chamber and microspherophakia, complicated by papillary block glaucoma.

Rare conditions associated with lens subluxation are hyperlysinemia, sulfite oxidase deficiency, and isolated familial ectopia lentis.

Treatment

Mild stable subluxation may be corrected by glasses or contact lenses. But progressive dislocation, worsening cataract, or development of glaucoma might necessitate surgical intervention.

In the past, surgical removal was not an accepted method due to severe and frequent complications as postoperative retinal detachment [35]. Alternative treatment strategies as peripheral iridectomy and photocoagulation of the iris provided only slight visual improvement and did not treat lens-associated complications [36]. The introduction of modern operative technique and instruments significantly decreased the rate of retinal detachment by avoiding vitreous incarceration and removing vitreoretinal adhesions.