Clinical Aspects

Even though anterior polar cataracts and posterior subcapsular cataract involve the same mechanism of visual disturbance and both occur in the visual axis, patients experience more severe visual symptoms with posterior subcapsular opacities. Patients may have relatively little visual impairment with anterior polar cataracts, but may

Figure 1 Anterior polar cataract. Courtesy of Choun-Ki Joo MD PhD.


Be severely impaired by PSCs. During cataract surgery, the anterior polar-type cataract may be removed easily after continuous curvilinear capsulorhexis, followed by phacoemulsification.

Anterior polar cataracts may present as a congenital (autosomal dominant inherited) or acquired opacities, secondary to uveitis or trauma. In the slit-lamp examination, anterior polar cataract usually has a star shape. It can lie flat on the lens surface or protrude forward from the lens as a small pyramid. However, the cause of most anterior polar cataracts is unknown in the Korean medical literature (Figure 1).

Anterior polar cataracts are divided into two groups. Opacities associated with the lens capsule and cataracts also involve the anterior lens fiber cells. Several theories may explain the mechanism of congenital anterior polar cataract. One suggests that the opacity may develop from an intrauterine infection, causing the transformation of epithelial cells. According to another theory, normal nutrition of the lens may be adversely influenced by a persistent vascular tunica that can lead to lens opacity.

Generally, anterior polar cataracts do not affect visual acuity as severely as those at the posterior pole. Traditionally, it has been thought that anterior polar cataracts <2 mm in size are unlikely to interfere with vision sufficiently to induce amblyopia. However, Jaafar and Robb noted a surprisingly high incidence of visual morbidity in 63 patients with anterior polar cataracts. More than one-third of patients were found to have strabismus, anisometropia, or amblyopia. They found that amblyopia did not result from enlargement of anterior polar opacities but occurred secondary to strabismus, anisometropia, and the presence of asymmetrically shaped opacities. Wheeler and colleagues also reported a high incidence of amblyopia. Amblyopia was related to three probable causative factors: (1) size of the opacity, (2) asymmetry of the opacity, and (3) superimposition of cortical changes.

Posterior subcapsular cataracts (Figure 2) occur at the posterior pole of the lens and are most often related with

Figure 2 Posterior subcapsular cataract. Courtesy of Choun-Ki Joo MD PhD.

The aging process. They are mainly due to posterior migration of lens epithelial cells from the equator. These epithelial cells cluster, form balloon cells, and interdigitate with adjacent lens fibers and the deeper cortical fibers, breaking them down. The result is the lacy, granular, iridescent appearance of PSCs.

Patients with PSCs tend to have relatively good distance-acuity in low-light conditions, but markedly reduced near vision with glare in bright light or with night driving. The reason for this is that the reduced aperture in brighter light prevents the entrance of the more peripheral light rays, resulting in more light passing through the opacity. In PSCs, the opacity is also closer to the nodal point ofthe eye. It has been suggested that this is the reason that the PSC decreases visual acuity more significantly than does anterior polar cataract, although this remains a controversial explanation.

Posterior subcapsular cataract is the typical cataract type seen with different intraocular diseases (high myopia, retinitis pigmentosa, diabetes mellitus, uveitis, etc.), trauma, or drugs (corticosteroids, antimalarial agents, etc.). However, the cause of the cataract cannot be established from only the ocular appearances. PSCs may develop as isolated entities or may be associated with other types of lens opacities. Often, some granules and vacuoles are found in front of the posterior opacity.

The PSC is one of the most difficult challenges for the cataract surgeon because of the increased tendency for rupture of the posterior capsule during cataract removal. Osher and colleagues reported a 26% incidence of capsule rupture in a series of 31 cases, and Vasavada and Singh reported a 36% incidence in a series of 22 cases. Das and colleagues reported that posterior capsule rupture occurred in 25 (31%) eyes, and was more common in young patients (<40 years). These authors reported that posterior capsule rupture was more common in extracapsular cataract extraction with phacoemulsification. Many

Table 1 Comparison of the main features of anterior polar and posterior subcapsular cataracts

Cataract type

Anterior polar cataract

Posterior subcapsular cataract

Location

Anterior visual axis

Posterior visual axis

Causes

Congenital, uveitis, trauma

Aging, intraocular disease, drugs (steroids), ionizing radiation

Effect on visual acuity

In congenital cases, little effect or increased risk of amblyopia. In acquired cases, effect mostly in early stages

Impairment, even in early stages; glare and decreased visual acuity, especially in bright sunlight or when driving at night; vision better in dim illumination

Surgical outcome

Easily removed after continuous curvilinear capsulorhexis and standard cataract surgery

High incidence of posterior capsular rupture


Techniques have been introduced to protect the posterior capsule during cataract surgery. Howard Fine and colleagues placed emphasis on avoiding pressure on the posterior capsule and stated that careful viscodissection of lens material will help the surgeon successfully meet this challenge. A comparison of anterior polar cataract and PSC is presented in Table 1.

See also: Cortical Cataract; The Epidemiology of Cataract; Genetics of Age-Related Cataract; Genetics of Congenital Cataract; Lens Structure; Normal Age-Related Changes: Crystallin Modifications, Lens Hardening; Nuclear Cataract; Posterior Capsule Opacification.

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