Aphakia, the absence of the crystalline lens, may occur as a result of trauma, lens subluxation or dislocation, or surgical management of a visually significant cataract. Pupillary block is a complication of cataract surgery with or without lens implantation. Pupillary block in aphakia was a significant complication following round-pupil cataract extraction (without sector iridectomy). This is also possible if an iridectomy was performed but was small and placed in the extreme periphery.
Pupillary block is the most common mechanism of angle closure after cataract extraction. This mechanism can be divided into 2 types, namely, anterior pupillary block and posterior pupillary block. A firm apposition between the pupillary margin and other surfaces anterior or posterior to the iris may lead to a pupillary block. The pupillary aperture may be obstructed by the anterior hyaloid surface, the intraocular lens, or the posterior capsule. A postoperative inflammation following an intracapsular cataract extraction may cause complete posterior synechiae between the iris and the intact anterior hyaloid membrane. A shallow anterior chamber favors formation of these adhesions. Adhesions may occur just between the pupillary margin and the anterior hyaloid surface. Such an occlusion is characterized as anterior pupillary block. The aqueous accumulates between the vitreous and the iris causing the peripheral iris to balloon forward.
A distinct mechanism is seen following extracapsular cataract extraction. A greater amount of postoperative inflammation, due to sensitivity to lenticular cortical material, leads to iridocapsular adhesions. This is seen more frequently after congenital cataract surgery. The aqueous humor accumulates between the iris-capsule diaphragm and the anterior hyaloid face, an area known as the canal of Petit. The pressure from the aqueous trapped in the posterior chamber displaces the iris forward. This is posterior pupillary block. The block impedes the forward movement of the aqueous to the anterior chamber leading to iris bombé, obstruction of the angle, and possible formation of peripheral anterior synechiae.
The absence of an iridectomy facilitates the development of pupillary block. Occasionally, this may also occur in eyes with a visible iridectomy if the iridectomy becomes occluded by iridocapsular adhesions.
A similar mechanism of pupillary block is seen with phacomorphic glaucoma and is referred to as anterior aqueous misdirection perilenticular. The aqueous humor accumulates around and behind the crystalline lens leading to lens-iris contact and the obstruction of anterior aqueous movement.
While no data exist, pupillary block was common during the era of intracapsular cataract extraction. Many cases are asymptomatic and are only recognized during routine examination. The time of presentation is variable. Pupillary block may present in the immediate postoperative period but has been described from weeks to even years after surgery.
Congenital cataracts should be removed early in order to achieve the best possible visual outcome. Pupillary block with secondary angle-closure glaucoma within a few months following surgery has been linked to the cataract extraction. It seems that there is a need to reevaluate the appropriate time for cataract surgery in infants.
According to one study, 11% cases of silicone oil injection in aphakic patients resulted in angle closure and high intraocular pressure (IOP) due to obstruction and tamponade of the trabecular meshwork.
In aphakia, pupillary block impedes the forward movement of the aqueous through the pupillary aperture. With continuous production of aqueous the peripheral iris bows forward (iris bombé). This condition then leads to obstruction of the iridocorneal angle; formation of peripheral anterior synechiae (PAS), further aggravating the passage of aqueous toward the angle; rise in the IOP; and glaucomatous disc damage and associated visual field defects.
In this era of intraocular lenses, pupillary block is seen not only in older individuals who are rendered aphakic but also in infants who undergo surgery for congenital cataracts.
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