Cataract surgery is the most commonly performed surgical procedure worldwide. The generally preferred method in adults and older children preserves the posterior portion of the lens capsule and thus is known as extracapsular cataract extraction. An incision is made at the limbus or in the peripheral cornea, either superiorly or temporally. An opening is created in the anterior capsule (anterior capsulorhexis), and the nucleus and cortex of the lens are removed. (The femtosecond laser can be used for the initial incision, capsulorhexis, and other parts of the procedure, but its value for routine use is uncertain.) An intraocular lens is placed in the empty “capsular bag,” thus supported by the intact posterior capsule.
The technique of phacoemulsification is now the most common form of extracapsular cataract extraction in developed countries. It uses a handheld ultrasonic vibrator to disintegrate the hard nucleus such that the nuclear material and cortex can be aspirated through a small incision of approximately 2.5 to 3 mm. This same incision size is then adequate for insertion of foldable intraocular lenses. If a rigid intraocular lens is used, the wound needs to be extended to approximately 5 mm. In developing countries, particularly rural areas, the instruments for phacoemulsification are often not available. Manual sutureless small incision cataract surgery (MSICS) is based on the traditional nuclear expression form of extracapsular cataract extraction, in which the nucleus is removed intact, but using a small incision. The cortex is removed by manual aspiration. MSICS may be indicated for dense cataracts unsuitable for phacoemulsification.
The main intraoperative complication of extracapsular surgery is posterior capsular tear, for which the main predisposing factors include previous trauma, dense cataract, unstable lens, and small pupil, possibly leading to displacement of nuclear material into the vitreous (“dropped nucleus”) that generally necessitates complex vitreoretinal surgery. Postoperatively, there may be secondary opacification of the posterior capsule that requires discission using the neodymium:YAG laser (see Posterior Capsule Opacification later in the chapter).
There are many styles of intraocular lenses, but most designs consist of a central optic and two legs (or haptics) to maintain the optic in position. The optimal intraocular lens position is within the capsular bag following an extracapsular procedure. This is associated with the lowest incidence of postoperative complications, such as pseudophakic bullous keratopathy, glaucoma, iris damage, hyphema, and lens decentration. The newest posterior chamber lenses are made of flexible materials such as silicone and acrylic polymers, allowing the lens implant to be folded and thus decreasing the required incision size. Lenses with multifocal optics can provide good vision for both near and distance without glasses. If there is inadvertent damage to the posterior capsule during extracapsular surgery, an intraocular lens can be placed in the anterior chamber or sutured to lie in the ciliary sulcus. Methods of calculating the correct dioptric power of an intraocular lens are discussed in Chapter 21. If an intraocular lens cannot be safely placed or is contraindicated, postoperative refractive correction generally requires a contact lens or aphakic spectacles.
The patient is usually ambulatory on the day of surgery but is advised to move cautiously and avoid straining or heavy lifting for about a month. The eye may be patched on the day of surgery. Protection at night by a metal shield is often suggested for several days after surgery. Topical postoperative antibiotics and anti-inflammatory drops are used for 4–6 weeks after surgery.
Complications of Adult Cataract Surgery
Cataract surgery in adults has a very low rate (2–5%) of complications that result in permanent impairment of vision. The most serious but rare complications are perioperative intraocular hemorrhage (< 0.5%) and postoperative intraocular infection (endophthalmitis, 0.1%), either of which can result in severe visual loss or removal of the eye. Suspicion of endophthalmitis requires vitreous tap for microscopy and culture and intravitreal injection of antibiotics (see Table 22–1). Vitrectomy is sometimes indicated (see Chapter 9). Other complications include retinal detachment, cystoid macular edema, glaucoma, corneal edema, and ptosis.
Posterior Capsule Opacification
About 10% of eyes require treatment for posterior capsule opacification following uncomplicated phacoemulsification surgery (Figure 8–9).
Posterior capsule opacification (“after-cataract”).
Persistent lens epithelium on the capsule favors regeneration of lens fibers, giving the posterior capsule a “fish egg” appearance (Elschnig’s pearls). The proliferating epithelium may produce multiple layers, leading to opacification. These cells may also undergo myofibroblastic differentiation. Their contraction produces numerous tiny wrinkles in the posterior capsule, resulting in visual distortion.
The neodymium:YAG laser provides a noninvasive method of creating an optical window in the posterior capsule (see Chapter 23). Complications include a transient rise in intraocular pressure, damage to the intraocular lens, and rupture of the anterior hyaloid face with forward displacement of vitreous into the anterior chamber, potentially leading to rhegmatogenous retinal detachment or cystoid macular edema. The rise in intraocular pressure is usually detectable within 3 hours after treatment and resolves within a few days with treatment. Small pits or cracks may occur on the intraocular lens but usually have no effect on visual acuity.
Childhood Cataract Surgery
Cataract surgery in young children is often hindered by more difficult anterior capsulorhexis, as well as the frequent need to make an opening in the posterior capsule (posterior capsulorhexis) and to remove part of the vitreous (anterior vitrectomy) to reduce the incidence of posterior capsule opacification, which is much higher than after adult cataract surgery. The cataracts are less dense than in adults and can usually be removed by an irrigation–aspiration technique, without the need for phacoemulsification.
Optical correction can consist of spectacles in older bilaterally aphakic children, but most childhood cataract operations are followed by contact lens correction, with adjustment of power as the refractive status of the eye changes with growth. Intraocular lenses are also used in some cases. They avoid the difficulties associated with contact lens wear, but there are difficulties calculating the appropriate power.
The visual prognosis for childhood cataract patients requiring surgery is not as good as that for patients with age-related cataract. The associated amblyopia and occasional anomalies of the optic nerve or retina limit the degree of useful vision that can be achieved in this group of patients. The prognosis for improvement of visual acuity is worst following surgery for unilateral congenital cataracts and best for incomplete bilateral congenital cataracts that are slowly progressive. Glaucoma is a common long-term complication.