CATARACT SURGERY

Shady Awwad, MD

HISTORY OF CATARACT SURGERY

There are allusions in the literature that cataract surgery used to be performed as early as 300 BC with no description of methods and techniques. Physicians at that time thought of cataract as a coagulation of the eye humors (“suffusion”) behind the iris, due to the white pupillary reflex produced by mature cataract (Celsus, AD 30). Constantinus Africanus (AD 1018), a monk and an Arabic oculist introduced the term "cataract" by translating the Arabic equivalent of  “suffusion” into Latin “cataracta,” which meant “something poured underneath something,” or the “waterfall.”

COUCHING

Couching is the first documented cataract surgery. Early descriptions in history came from India in 600 BC. Physicians used to insert a sharp instrument (a needle or lancet) around 4 mm posterior to the limbus or into clear cornea, pointing towards the whitish opacity. Then, in a downward movement, the lens was dislodged away from the pupil. Manipulation would stop when the patient start seeing shapes. Obviously, the patient would be left aphakic and would need to be corrected by a positive lens (e.g + 11D) which was not available early in history. Physicians at that time didn't know that the white reflex was actually the human lens nor did they know that by couching, they had established the modern concept of pars plana vitrectomy. Some variations of the couching technique included inserting a hollow needle and "aspirating" the cataract (described by Iraqi and Syrian oculists around 1000 AD. But this method shortly fell out of favor. Couching operation remained popular up through the 19th century and even up to our days in some parts of Africa and the world.

INTRA CAPSULAR CATARACT EXTRACTION

Consists of removing the lens with the capsule intact. This requires the breakage of the zonules.  Different methods to break the zonules were described, but only  the cryoprobe survived. The cryoprobe is a probe which is frozen onto the surface of the crystalline lens. With gentle teasing, the lens could be delivered without any pushing on the eye.

EXTRACAPSULAR EXTRACTION

In 1753, a French oculist by the name of Daviel (1696–1762) described a new method of cataract surgery which essentially was the first report of a planned extracapsular extraction. Oculists however continued to couch and the extracapsular technique never gained merit until later on in the 19th century. Recognizing that Daviel's method could produce vitreous loss, modern surgeon opted to Sharp's technique, which described the removal of the lens in toto (Intracapsular extraction).
     In the early 1970s, and with the introduction of the intra-ocular lenses (IOLs) and the published results on the complications of absent capsules, surgeons reverted to ECCE. Clearly an intact capsular bag with its zonules was needed to hold the IOL (as a scaffold). An intact posterior capsule was invaluable in decreasing the risk of retinal detachment and cystoid macular edema (CME),  two of the most dreadful complications in cataract surgery, especially ICCE.

PHACOEMULSIFICATION

ECCE, while offering the remarkable advantage of a preserved capsule, had still many drawback: a big incision entailed lots of sutures, which produced astigmatism postop. Optimal visual recovery could only take place after the sutures were removed, i.e. 6-8 weeks postop. Smaller incision would require fragmentation of the crystalline lens and removal of the fragments through a small wound. A new technique evolved hence in the early 1970s. It emerged with the development of a new hydrodynamic system which produced high frequency mechanical waves out of an electric current, while incorporating irrigation and aspiration all in one setting.

SURGICAL TECHNIQUE

Extracapsular Cataract Extraction

An 11 mm partial thickness incision is made along the limbus superiorly, in peripheral clear cornea (Fig. 1-A). The anterior chamber (AC) is penetrated at around 12 o'clock, and a bent needle (cystotome) is inserted into the AC and made to produce multiple radial nicks in the anterior capsule in a circular fashion keeping with a diameter of around 6-7 mm (Capsulotomy), (Fig. 1-B,C). An alternative method mainly used in phacoemulsification, Capsulorhexis, involves making a controlled circular tear, (Fig. 2-A,B). The nucleus is rocked up and down, right and left , to free the it from the surrounding capsule. The sclero-limbal incision is then completed full-thickness with scissors. The nucleus is then expressed out of the capsule by alternating pressure applied superiorly and inferiorly using special  instruments (Fig.1-D). An infusion-aspiration cannula is then introduced, passed underneath the iris and below the level of  the anterior capsule, and used to engage remaining cortical strands through suction effect (Fig. 1-E). Caution should be made not to engage the posterior capsule. Visco-elastic material (Healon®, a hyauronic based material to keep the anterior chamber well formed and preventing it from collapse) is then injected into the capsular bag to increase its volume, and hence, facilitate the insertion of the intra-ocular lens (IOL). The latter is grasped by the optic, and inserted into the bag with the inferior haptic inserterd underneath the anterior capsule. The IOL is then grabbed by the superior haptic, which is inserted in a circular motion (as if dialing using an old-style phone) and made to rest beneath the anterior capsule. The  superior haptics springs out upon release due to its flexibility and rests in the fornix formed by the anterior and posterior capsule (Fig.1-F). The visco-elastic is aspirated from the anterior chamber. The pupil is constricted using Miochol (acetylcholine) into the anterior chamber and the incision is closed using interrupted 10-0 Nylon sutures.

Phacoemulsification

A partial-thickness stab incision measuring 3 mm is made 2mm away from the limbus at 12 o'clock. The same incision can be made in clear cornea. A tunnel is fashioned in the sclera up to clear cornea. The AC is penetrated while pointing the blade towards the lens. This would create a tri-planar incision which ideally can self-seal. A Capsulorrhexis is performed using the cystotome (Fig. 2-A, B). The nucleus is loosened from its cortical and capsular attachments by introducing a cannula mounted syringe underneath the anterior capsule, but above the level of the nucleus, and injecting fluids (Balanced Salt Solution, BSS). This Step is called  Hydrodissection. Emulsification of the nucleus follows. Many techniques with different variants of the same technique have been developed. The classical technique involves carving a cross in the nucleus, then dividing into four pieces (like a pie). The pieces become then freely movable and they are then aspirated away from the capsule and emulsified (Fig. 2-C, D). This Technique is known as Divide and Conquer technique. When the nucleus is very soft, dividing it might turn out to be difficult. Carving a bowl then aspirating the thin remaining crust and emulsifying it away from the posterior capsule is an option (Bowl Carving technique)Other techniques such as Chopping and Flipping have been developed later on. The scleral or corneal incision is slightly enlarged and a foldable IOL is inserted. A figure of 8 suture is electively put over the incision.
     The only justification of a planned whole lens expression (ECCE) is a very hard lens. A hard lens like the mature cataract and catracta rubra would require longer time of emulsification, which can predispose to corneal edema.

COMPLICATIONS OF CATARACT SURGERY

INTRA-OPERATIVE

Posterior Capsular Rupture

This can often occur during phacoemulsification or during the irrigation aspiration process. If no vitreous leaks and the tear is small, a PC-IOL is inserted. If the tear is big enough to jeopardize the stability of the IOL in the posterior chamber, the iris is constricted using Miochol® and an AC-IOL is inserted in the anterior chamber. If the tear leaks vitreous, then an anterior vitrectomy is performed following which a decision is to be made whether to put an AC-IOL or delay the IOL implantation. Anterior vitrectomy can be automated (using a probe called ocutome) or mechanical, which entails applying sponges on the wound then pulling them out and cutting any sticking vitreous strands.

Expulsive hemorrhage

This is a dreadful complication that mainly happens following acute drop in intra-ocular pressure. The patient is usually hypertensive, diabetic, myopic, or having glaucoma. The short and long posterior ciliary arteries would suddenly bleed and the blood would accumulate in the supra-choroidal space. The intra-ocular pressure would then rises significantly and push the ocular content out of the eye. The surgeon should rapidly close the wound and give intra-venous osmotic agents to lower the intra-ocular pressure. Steroids should be given post-op to decrease the inflammation. Drainage of the blood should take place after two weeks when clots start liquefying. The visual prognosis is usually dismal.

EARLY POST-OPERATIVE

Acute Bacterial Endophthalmitis

It is an intra-ocular bacterial  infection which occurs in 1/1000 cases, with crippling visual complications in more than 50% of the cases, depending on the etiologic organism. The patients own bacterial flora are usually the culprits. These include Staph. epidermidis, Staph. aureus, Pseudomonas, and Proteus. Treatment include topical, intra-vitreal, peri-ocular, and systemic antibiotics together with steroid therapy when indicated.

Iris prolapse

Iris tissue may prolapse through the surgical wound. This is usually due to poor surgical closure. If not corrected, this can sometimes lead to endophthalmitis, astigmatism.

Wound leak

This is a relatively rare complication due to poor wound construction as well as poor surgical technique in closure (loose sutures.) Low IOP and shallow anterior chamber are noted. Wound leak is usually diagnosed by Seidel Test, which shows clearing of the fuorescein over the involved area due to the leak of fluid.

High intra-ocular pressure

This complication usually occur when the visco-elastic is left in the eye, or is not adequately aspirated prior to  wound closure. The visco-elastic particles would block the trabecular meshwork and raise the IOP.

Corneal edema (Striate Keratopathy)

Endothelial loss and ischemia due to manipulation during surgery as well due to ultrasonic shockwaves during phacemulsification lead to corneal decompensation and corneal edema. Endothelial folds (striae) and increased thickness of the cornea with cloudiness follow.

LATE POST-OPERATIVE

Posterior Capsule Opacification (PCO)

A frequent late complication of cataract surgery. It extremely common in children. PCO comprises any or a combination of the following:
Elshnig's perls occurs by proliferation of the anterior lens epithelium over the posterior capsule. Primary Opacification occurs following opacification of already existent posterior capsular plaques.

Retinal Detachment

Occurs mainly in eyes with posterior capsular rupture, vitreous loss, and eyes with peripheral retinal degenerations like lattice degeneration.

Cystoid Macular Edema (CME)

Also known as the Irvine-Guass syndrome. Fluids accumulate in the macula in a petaloid fashion, dropping the visual acuity. It is thought to occur due to the release of prostaglandins from the iris and the ocular structures during and after surgery. Vascular dilatation and permeability follow, resulting in CME. It is also though that vitrous traction, especially after vitreous leak can predispose to CME as well. ACIOL are also associated with a higher risk of CME.

Suture-related problems

      Astigmatism:

                Tight sutures can lead to steepening of the cornea along  the same axis. This can lead to astigmatism along the same axis (i.e. a tight suture at 12 o'clock would produce for example the following refractive error: 0+2x90).

     Reaction to the sutures

          This can include immunological (superior limbic conjunctivitis) and  mechanical reaction (giant papillary conjunctivitis).

Malposition of the IOL

A tilted IOL can produce astigmatism, monocular diplopia, optical aberrations such as halos and glare. Miotics sometimes relieve these symptoms. In severe cases, replacement of the IOL might be necessary.

Corneal Decompensation

Usually occurs when an AC-IOL is implanted. It is very rare to occur after PC-IOL insertion.