Cataracts

Introduction

A cataract is a clouding of the natural lens in the eye. It is not a “growth” or a tumor. Rather, it represents a degradation of the clarity of one of the most important optical structures in the eye. The word “cataract” originally meant “waterfall.” The term became associated with the eye disease because a patient’s view of the world through a cataract was thought to be similar to looking through a waterfall, with distortion of the ability to see through the falling water.

Figure 1 shows the basic anatomy of the eye. The two most important optical elements in the eye are the cornea and the lens. These two structures bend light rays to focus on the retina, which is at the back of the eye. In a parallel to the camera, the cornea and lens function as the lens system of a camera, whereas the retina functions as the film, or, with digital cameras, electronic screen. The nerve impulses created by the light on the retina then pass back along the optic nerve through the brain, ultimately ending up at the image processing portions of the brain known as the occipital lobes.

The lens is suspended by thousands of tiny fibers known as zonules in the space directly behind the pupil. The pupil is the opening in the center of the iris. The iris is the colored portion of the eye that is able to expand or contract depending upon light exposure. The iris functions in a fashion similar to the aperture of the light control system in a camera.

Cataracts are the number one cause of vision loss in the world. This fact is startling to people who live in developed countries, where access to medical care is excellent compared to underdeveloped countries. In many regions of the world, the supply of cataract surgeons cannot keep up with the volume of patients losing functional vision due to cloudiness of the lens in their eye. Systems have evolved to deliver basic cataract surgery as efficiently and economically as possible in the developing world, but the loss of vision due to cataract formation in these areas continues to increase.

Causes of Cataracts 

The lens becomes a cloudy cataract when the proteins in the lens “denature”, or become disorganized. An every day example of denaturation of protein occurs when an egg is fried. The clear albumin denatures and becomes white upon contact with heat. A slowly progressive version of denaturation leads to the cloudiness in the lens that we call cataract.

Aging is the most common cause of cataracts. Several environmental factors have been proven to increase the rate of aging of the natural lens. The best documented of these is smoking cigarettes. It is generally believed that exposure to environmental ultraviolet light also contributes to the denaturation of the lens proteins. Fundamentally, the denaturation process is due to oxidation.

Endocrine disorders frequently trigger accelerated denaturation of the lens. The most common of these disorders is diabetes mellitus. Numerous medications have been associated with cataract formation. Trauma, either a blunt blow to the eye or a penetrating injury, frequently will trigger cataract formation, as will intraocular surgery. The lens is a relatively fragile structure from a metabolic standpoint, and any stress on the lens physiology leads to loss of clarity.

Finally, some cataracts have a genetic component. Early formation of cataracts, in the absence of other identifiable causes, may have a familial predisposition.

Table 1 lists many of the causes of cataract formation.

A special category of cataract is congenital and infantile cataract. In these cases, the lens system does not develop properly during the embryologic stage of growth, resulting in a cloudy lens. Depending upon its severity, this may require urgent cataract surgery in an infant, or there may be sufficient clarity so that surgery can be deferred until the child is older and the eye better developed.

Prevention

The most effective prevention of cataract formation consists of avoiding most of the risks outlined above. In the absence of stresses to the lens system, either traumatic or endocrine, a healthy diet and lifestyle are generally believed to markedly reduce the risk of cataract formation or its rate of progression once cloudiness of the lens occurs. The most beneficial anti-cataract substances are antioxidant chemicals, either as dietary supplements or naturally occurring in foods.

Treatment

Indications

            The most common reason to treat a cataract is the presence of a functional impairment that is consistent with the loss of vision attributable to the cataract. The simple presence of an opacity of the lens, in the absence of functional impairment, does not, in and of itself, necessitate surgery except in special circumstances. Occasionally an ophthalmologist may request cataract surgery in order to monitor disease within the eye, where the presence of a cloudy lens impairs the ability to diagnose or treat other diseases that may be resulting in permanent damage to the eye. This occurs occasionally in diseases such as glaucoma, diabetes affecting the retina, or age-related macular degeneration.

The primary treatment of cataracts is surgery. However, early in the formation of a cataract, the dominant visual problem may be a shift in the focus of the lens, where a change in glasses may be adequate. Typically this shift is in the direction of causing artificial nearsightedness (myopia). A simple change in the glasses prescription can delay the need for surgery. In special circumstances, a patient may be able to “see around” a local opacity in the lens if the pupil size is altered with the use of dilating drops. This is unusual, however.

 

Surgery

            There are many variations on cataract surgery. This chapter will discuss only the most common scenarios. Cataract surgery is typically performed as an outpatient, either in a Hospital Outpatient Department of surgery (HOPD) or in an Ambulatory Surgery Center (ASC). This means that the total time in the surgical center is less than would be the case for an overnight hospitalization. Occasionally the medical status of the patient or the overall functional level of the patient, including being one-eyed, may lead the surgeon to recommend a one night stay in the hospital.

Being comfortable during the surgery is the role of anesthesia. Some surgical techniques allow the patient to be reasonably comfortable during the surgery with the use of numbing solutions in and around the eye. This is known as topical anesthesia. An alternative is to numb the eye with an injection of anesthetic around the eye, termed retrobulbar or  peribulbar anesthesia. This type of injected anesthetic is similar to how a dentist makes an area of the mouth numb for dental procedures.  A patient commonly is given sedation intravenously during the anesthetic injection so that there is little reaction to the medication. The ocular muscles are not coordinated in the hours immediately after such an injection. Therefore the eye is typically patched for at least several hours, and, in some cases, overnight.

The key steps of typical cataract surgery performed using the “small incision” technique are as follows:

The eye is initially “prepped and draped.” This consists of applying an antiseptic solution to the skin and the surface of the eye, and then a sterile type of plastic or cloth sheet to isolate the eye to reduce the chance of germs getting into the surgical incision.

(Video clip illustrating following points should be inserted here) In the first step of the procedure, the surgeon typically creates two incisions. A small incision is placed to the side. This gives the surgeon the ability to inject various fluids and also creates a port for the introduction of manipulating instruments. This incision is typically known as the side port or paracentesis. If the cataract surgery is being performed with topical anesthesia, it is at this stage that the surgeon typically places an anesthetic solution inside the eye. Previously the surgeon or the assistants have placed numbing solutions on the outside of the eye, so that these steps are painless to the patient.

At this point in the procedure, the main incision is created. It is through this incision that the cataract will be removed and the replacement lens inserted. The most common type of cataract surgery performed in developed countries is known as phacoemulsification. This technique uses ultrasound to break up the hard central part of the cataract in order to remove the lens through a small incision. This technique was invented by Dr. Charles Kelman in 1967. Multiple improvements in this technique as well as the ability to insert the replacement lens through a small incision ultimately led to its current position as the most common technique for performing cataract surgery. The principal advantage is the small incision, which allows more rapid recovery of a stable level of vision without shifts in the shape of the eye that cause astigmatism. Properly performed, phacoemulsification is generally less traumatic to the eye because of the microsurgical maneuvers that minimize the amount of tissue manipulation and therefore reduces the healing time.

            In some cases, however, the circumstances may make another procedure more appropriate. For example, a very large and dense cataract may lead a surgeon to choose the alternate approach known as extracapsular cataract extraction (ECCE). In this approach, the entire hard core of the cataract, known as the nucleus, is removed intact through a larger incision that is approximately 10mm in width. These incisions are typically sutured. In underdeveloped countries, where phacoemulsification may represent unacceptable cost due to the equipment and supplies, ECCE can be the standard procedure for most patients.

In the phacoemulsification procedure, after the main incision and side port incisions have been made, the anterior chamber is stabilized with the injection of a thick substance known as an OVD (ophthalmic viscoelastic device) The front surface of the lens is then opened. This opening is made in a circular fashion called capsulorrhexis. It is through the capsulorrhexis that the surgeon removes the protein of the lens and then inserts the replacement plastic lens. The natural lens has a delicate surrounding membrane, similar to plastic food wrap, which is known as the capsule. The goal of the cataract surgery is to remove all of the protein while leaving the capsule intact other than the front opening.

            The next step in the procedure is to loosen the contents of the protein material inside the capsular bag by using the waves of injection of a salt-like fluid. This step is known as hydrodissection. Typically the surgeon will inject the salt solution in several directions and then rotate the lens material in the capsular bag in order to fully loosen the lens to facilitate the next steps in the surgery.

            Ultrasound is then used to remove the hard nucleus in the center of the cataract. This is done with the use of the phacoemulsification probe. This is a hollow needle that vibrates at approximately 40,000 times per second due to ultrasound crystal that is located in the hand piece held by the surgeon. The vibration of the tip breaks up the hard nucleus in a manner similar to a microscopic jackhammer. In addition, effects known as cavitation created by the ultrasound also help break up the hard nucleus. There are many surgical variations to this portion of the case. Once the hard central nucleus is removed, the semisoft next layer, referred to epinucleus, is then removed, typically through a combination of aspiration and “flipping” of the nuclear shell, as shown in the video clip.

            In both the ultrasonic removal of the nucleus and the aspiration of the epinucleus, in addition to the action of the vibrating ultrasonic tip, the other key technology is the aspiration of the material through the hollow tip of the surgical needle, replacing the aspirated material with the inflow of salt solution. All three of these functions (ultrasound, aspiration, and irrigation) are controlled by the surgeon utilizing a foot pedal. This foot pedal sends the surgeon’s commands to a sophisticated computer-controlled device that modulates all of the surgical parameters in order to allow the safe and effective removal of the lens material.

            After the removal of the nucleus and epinucleus, the soft outer layer of the cataract, known as cortex, is then removed with a different style of irrigation and aspiration tip. The cortex material is typically “stripped” as it is peeled away from the capsule. At the end of this portion of the procedure, the surgeon has left the capsular bag intact with a central opening in the front and all of the lens protein material removed.

 

Intraocular Lens

            Having removed the natural lens, the surgeon next places an artificial lens known as the intraocular lens (IOL). The development of the intraocular lens revolutionized rehabilitation after cataract surgery. Prior to the IOL, patients who had cataract surgery were faced with using either extremely thick glasses or a thick contact lens in order to refocus the light on the retina. The thick glasses are both unsightly and heavy, but also have considerable optical distortion. Contact lenses functioned better from an optical standpoint, but because many cataract patients are elderly, learning how to use a contact lens, with insertion and removal on a daily basis, was a major challenge at best. Many patients could not successfully learn to use contact lenses. For a brief period, extended wear soft contact lenses were employed as an alternative, with the ability, in principle, to leave these lenses in place for several weeks at a time. However, an unacceptable number of patients developed severe eye infections from these extended wear lenses. When the intraocular lens became available, therefore, it represented an enormous breakthrough in restoring normal vision with a normal lifestyle to the cataract patient.

            The initial invention of the IOL is credited to Mr. Harold Ridley, a London ophthalmologist. He was inspired to develop an acceptable plastic lens by his observation of eye injuries suffered by Royal Air Force fighter pilots injured during World War II. Pieces of the Plexiglas airplane canopies that were exploded by bullets and became shrapnel sometimes entered the eye. Mr. Ridley noticed that the Plexiglas (chemically known as polymethylmethacralate) was well tolerated inside the eye without any evidence of immunologic reaction to the material by the eye. Ridley realized that the Plexiglas might make an acceptable material for an artificial lens.

            Through the 1950s and 1960s, many surgeons struggled with developing methods of placement and stable fixation of the IOL. Progress during this period was slow as different lens models were developed and implanted on a limited basis. In addition, manufacturers needed to develop highly refined techniques so that these tiny devices did not have problems such as sharp edges that would cause inflammation or chemical contamination introduced during the sterilization process. In the 1970s the improving results prompted a more widespread interest in IOL implantation, and by the 1980s placement of an IOL had become a standard part of cataract surgery. The final critical step in making IOL implantation nearly universal was the development of the method of IOL implantation that allowed the IOL to be placed within the capsular bag, so that the IOL was in exactly the same position as the natural lens, combined with the development of compressible materials that allowed the IOL to be introduced through the small incision made possible by phacoemulsification. The marriage of the two technological advances of phacoemulsification and what are technically known as foldable posterior chamber intraocular lenses has led to a dramatic improvement in the successful rehabilitation of patients undergoing cataract surgery. In the developed countries using phacoemulsification for removal of the cataract, the intraocular lens materials widely used are solid silicon or a semi-soft acrylic plastic. In both of these cases, the optical portion of the IOL, which is the largest portion of the lens, can be compressed in a rolled manner so that it can be inserted through the small incision, but with the memory of the material causing it to return to its original shape once it is unfolded inside the eye. Figure 2 shows a typical IOL. Note that the optical portion is approximately 6mm in diameter, as that is large enough for the size of most human eyes. For both size and weight considerations, a larger optic is not used. Instead, peripheral spring-like struts, known as haptics, extend from the optic portion out to the peripheral part of the capsular bag, establishing  stable centration and fixation of the IOL inside the capsular bag. These haptics can be made of the same material as the optic, or can be made of a flexible alternate material, such as polymethylmethacralate or polyimide.

            In some cases, the anatomy of the eye or difficulties encountered during surgery do not allow for the IOL to be placed in the capsular bag. In that case, the surgeon sometimes will place a posterior chamber IOL in front of the capsular bag, supported by the front part of the capsule and/or non-dissolving sutures. Alternatively, there are several styles of anterior chamber IOLs that are placed in front of the iris, when there is inadequate support from zonules and capsule posteriorly.

            Not all patients require the same power IOL, just as people require different strength glasses to see well. Even in the same patient, it is common for the two eyes to have slightly different power requirements. The two factors that are the strongest determinants of the correct IOL power are the optical power of the cornea at the front of the eye and the overall length of the eye, which is the distance from the cornea and the IOL to the retina where the light should be focused. Precise determination of these parameters has been the subject of intense development in the decades since IOL implantation became common. The corneal power is typically determined by a device that measures the curvature of the cornea and mathematically derives the optical power from that. The length of the eye is determined by either ultrasound (technically known as A-scan biometry) or by a newer technique known as partial coherence interferometry. Once the corneal power and the length of the eye are known, the surgeon will then utilize one or more formulas to calculate the power of the lens desired for an individual patient. This power depends not only on all the measurements made, but the optical characteristics of the specific IOL that will be used.

            At this point in the preoperative planning, several decisions need to be made. The first is whether the goal of the implanted IOL is to give the patient good distance vision, reading vision, or something in between. In cases of a cataract in only one eye, where there is a large optical correction in the fellow eye that does not require cataract surgery, the better choice sometimes is to pick an IOL power that keeps the two eyes matched. The decision about the target power for the IOL is based on a discussion by the surgeon and/or the surgical staff with the patient about lifestyle and function.

Premium IOLs

Aspheric optics

            The surgeon also has several choices regarding IOL optical design. A recent improvement in the optical design of IOLs has been an appreciation of the impact of matching the overall optical contour of the IOL to the optical characteristics of the cornea. The peripheral corneal optics have a distortion technically known as positive spherical aberration. The young natural lens has negative spherical aberration that almost perfectly neutralizes the corneal spherical aberration. This natural compensation mechanism diminishes with age as the natural lens grows in size, even before it becomes a cloudy cataract. The shape of the IOLs that were implanted until recently did not take into account the issue of spherical aberration. The surgeon now has several choices of IOLs that have been designed to either partially or completely mimic the contour of the young natural lens, with either neutral or negative spherical aberration, and clinical studies have shown that use of these lenses can improve overall optical performance measured in ways beyond the simple 20/20 chart. In addition, matching the IOL to the cornea has significance in patients who have had prior refractive surgery. The surgeon needs to know prior to cataract surgery whether a patient has had a refractive procedure such as LASIK.

 

Presbyopia correction

            Another option in IOL optics relates to the correction of presbyopia. Presbyopia is the technical term that refers to the loss of ability to shift the focus from distance to up close. The natural lens in a young eye is able to change its optical power through the action of a muscle in the eye known as the ciliary muscle. When a young person wants to see an object up close, the brain sends nerve impulses to the ciliary muscle. The ciliary muscle contracts, changing the tension on the zonules that support the lens, and the flexible young lens is able to change shape in a manner that adds enough optical power to bring things into focus that are close to the eye. As we age, the natural lens stiffens, and the ability to see up close correspondingly diminishes. For most people, somewhere in the 45 year old time frame is when you begin to notice that you can’t focus up close as well, and start to have to hold objects further away in order to see them. Eventually your arms are not long enough and the print is not big enough, and you start using reading glasses or bifocals.

            Although there is no current method for restoring natural accommodation to the aging lens, nor is there a way of perfectly simulating the natural accommodation system, several alternatives have arisen to partially restore the ability to see at distance and near, both without glasses. One of these is known as an accommodating IOL. In this lens design, the goal is to make the optic of the IOL have flexibility in its attachment, so that the optic can shift position slightly when the ciliary muscle receives the nerve impulse to attempt to see up close. The optic of the IOL, in principle, is able to then move forward enough to give added optical power.

            The alternative design is known as a multifocal IOL. In a multifocal IOL, some of the light energy is in focus for the distance, and other light is in focus for near objects. This occurs simultaneously. The image processing system of the brain sorts out the images for each distance.  The multifocal IOL has no requirement for movement of the optic.

 

Astigmatism Management

            As mentioned briefly above, astigmatism refers to the optical distortion that occurs when the optics of the eye, usually due to the curvature of the cornea, result in an focusing contour that has a shape similar to the side of a football, instead of the side of a round ball. As a result, in astigmatism, the light rays are not focused to a single point, but rather smeared out.

            Astigmatism is measured in the cornea in several ways. A keratometer measures the curvature of the maximum and minimum curvature portions of the cornea, which are 90 degrees apart in a normal cornea. A more sophisticated analysis is performed with computerized corneal topography. These devices analyze hundreds of points on the curvature of the cornea and then create a “map” of the corneal powers, similar to the contour maps of the hills and valleys of the earth. In the case of corneal topography, the hills are areas of high refractive power, and the valleys are areas of low refractive power.

            The incisions in cataract surgery can, in and of themselves, affect the curvature of the cornea. The small “side-port” incisions usually have minimal impact on astigmatism. A larger incision can create shifts in astigmatism. This is most common in the case of extra capsular cataract extraction (ECCE) where the incision is 10mm wide or more. In these large incisions, tight suturing can create increased corneal curvature and higher corneal power. Loose suturing or slippage of the sutures as the patient heals can create a flat zone. A flat zone has reduced corneal optical power.

            In the case of typical phacoemulsification, the incision has a small impact on astigmatism, generally between 0.25D and 0.5D of flattening in the meridian where the incision is located.

            If a patient has a minimal amount of astigmatism that should be corrected, then orientation of the principal incision on the appropriate meridian of the astigmatism can result in some improvement. In most cases, however, standard phacoemulsification incision is too small to have a significant impact. Therefore, the surgeon must employ one of two methods to treat patients who have large amounts of astigmatism. The first method is known as astigmatic keratotomy. In astigmatic keratotomy, the surgeon places one or two incisions into the peripheral cornea in the meridian that has the largest amount of power (known as the steep meridian). In the most commonly employed form of astigmatic keratotomy, these incisions are placed at the far periphery of the cornea, and are referred to as limbal relaxing incisions. The incisions are deep into the cornea but do not fully penetrate the cornea. The length of the incision and the distance from the center of the cornea are the primary factors that the surgeon varies to determine the amount of effect. In addition, the older the patient, the larger the effect of an otherwise identical incision.

            An alternative approach to correcting large amounts of astigmatism is the selection of an IOL that has astigmatism correction in the IOL power, similar to the astigmatism correction that a pair of glasses might have. These IOLs are called toric IOLs. At the time of surgery, the surgeon orients the rotation direction of the IOL to match the astigmatism and neutralize it. The surgeon typically chooses the power of the astigmatism correction based on a measurement of the astigmatism in the cornea preoperatively. This information is entered into a computer program that calculates the correct power of the lens inside the eye to best neutralize the curvature of the cornea and result in the minimal amount of residual astigmatism that can be obtained. In most cases these IOLs are stable, but there is a small chance that the IOL will rotate in the capsular bag and need to be repositioned in the early postoperative period in a second procedure.

 

Patient shared billing

            Both the astigmatism correcting (toric) IOLs and the presbyopia correcting IOLs (accommodating IOLs and multifocal IOLs) have considerably higher manufacturing costs and higher surgeon effort, both preoperatively in the planning phase and intraoperatively. Medicare and other third party carriers have declined to pay this extra cost, but, in order to avoid blocking patient access to these desired features, allow the surgeon and the surgical facility to charge the patient directly for the balance. This is technically known as patient shared billing. Patient shared billing is in use in other areas of medicine as well, where the third party carriers provide basic coverage but allow the patient to purchase “upgrade” products or services.

 

Postoperative Recovery

            In an uncomplicated cataract extraction and IOL implantation surgery, most patients will see reasonably well on the first postoperative day and be largely recovered within one to two weeks. This rapid recovery is due to the small incision in phacoemulsification and the reduced amount of secondary inflammation and tissue response attributable to the delicacy of the microsurgery approach of current phacoemulsification and foldable IOL cataract surgery. Depending upon the type of anesthesia employed and the surgeon’s preference, some patients are instructed to begin postoperative medications on the day of surgery, while others begin the day after. Most patients will use two or three medicated drops postoperatively. Some patients will require more depending upon their eye condition. At a minimum, medicated eye drops are used for minimizing inflammation and to reduce the potential for infection. The surgeon will give specific instructions to the patient about the desired regimen, as well as other aspects of eye care, such as when to wear eye protection, cleaning of the eyelids, and managing situations such as exercise and showering and hair washing. Typically a patient will be seen and examined by the surgeon within one to two days after surgery and then one or two times further during the postoperative period, depending upon the type of surgery and the postoperative course as well as the surgeon’s preference.

Complications

Intra-operative Complications

            The most common problem that occurs during cataract surgery is the development of a defect in the capsule. This defect can be an opening in the edge of the anterior circular capsulorrhexis, a defect in the posterior side of the capsule, or both. This complication occurs at a low rate. Both surgical techniques and the instrumentation have improved considerably to minimize this risk, but this problem will sporadically occur under the best of circumstances.

            The importance of the capsule is related both to the type of IOL that can be implanted and to possible secondary problems that can arise when the capsule is open. The surgeon has options with regard to the IOL style and location of placement, and typically has a backup plan for every patient with regard to the IOL implantation should the capsule develop a defect.

            When the capsule is not intact, the secondary problems that can occur relate to the creation of communication between the front part of the eye (the anterior chamber) and the back portion of the eye where the vitreous jelly (technically, the vitreous humour) occupies the space behind the lens up to the retina. If vitreous comes through a defect in the capsule, the surgeon must clean this up in a surgical maneuver known as a vitrectomy. Even with a thorough vitrectomy, other retina-related risks are increased, particularly inflammatory swelling of the part of the retina involved in detailed vision (known as cystoid macular edema, or CME) and retinal detachment. CME and retinal detachment also occur sporadically in uncomplicated cases as well, but the incidence is higher when there has been prolapse of the vitreous through a defect in the capsule.

            A related problem is weakness in the zonules, the tiny fibers that support the capsule and attach it to the wall of the eye. Some patients have weakened zonules. This can be due to previous trauma, a condition known as pseudoexfoliation, or simply be spontaneous. In cases of partial loss of zonular integrity, the surgeon can use additional stabilizing implant devices to give mechanical support to the remaining zonules. However, if the zonular weakness is severe, the entire capsular bag complex can destabilize, resulting in vitreous loss and subsequent related complications.

            When the capsule develops a defect early in the case or the zonular weakness is severe, it is possible for the lens material to fall backward into the vitreous jelly. In some cases this will require the surgeon to leave the lens material temporarily, and arrange for a second surgery, often by a consultant in vitreo-retinal surgery, who will use specialized techniques to remove the lens material from the back portion of the eye.

            Another operative challenge occurs when the pupil does not respond well to dilating drops. This occurs in many situations, including patients who have had prior inflammation inside the eye, use some glaucoma medications, have the previously mentioned condition known as pseudoexfoliation, or sometimes just have unusual  anatomy. A particular challenge is presented by some of the medications used for blockage of urinary flow due to an enlarged prostate gland in men. The best documented issue occurs with tamsulosin (Flomax), a selective alpha-1A adrenergic blocker. In these patients, the iris typically dilates poorly and also exhibits loss of tone, so that it becomes structurally unstable and has a predilection for prolapsing through the incision or being engaged by the cataract surgery instruments inadvertently. The condition has acquired the descriptive term of IFIS, which stands for intra-operative floppy iris syndrome. Patients taking any of the systemic medications used to relieve prostate urinary flow problems should alert the surgeon to this preoperatively. There are established and effective extra surgical steps that can be taken to minimize the problem with IFIS, but these need to be planned in advance, and for that reason it is critical that the surgeon be informed of the use of this medication, either currently or in any time in the past.

            The rarest, but one of the most dreaded complications during cataract surgery, is major bleeding inside the eye. In the worst of circumstances, this occurs in a mechanism similar to a burst aneurysm in other parts of the body. This condition can result in what is known as suprachoroidal hemorrhage with damage to the retina, and in the worst of circumstances, the forceful extrusion of the ocular contents, including the retina, out of the incision. Fortunately this condition, which usually cannot be anticipated, is extremely rare. With the small incision used in phacoemulsification and foldable IOL implantation, the risk of this complication, and particularly the risk that it will develop loss of ocular tissue, has been greatly reduced.

 

Post-operative Complications

            Unexpected amounts of postoperative inflammation can occur either due to infection or from non-infectious sterile causes. All patients have some degree of sterile inflammation after cataract surgery, but this is usually well controlled with the topical eye drop medications that are customarily prescribed. Patients with diabetes mellitus and patients with preexisting inflammatory diseases of the eye (uveitis) are more prone to inflammation. Prolonged and complicated surgery also predispose to postoperative inflammation. In some cases, however, the cause of the inflammation can be difficult to determine.

            Occasionally the IOL may move out of position. There are a variety of reasons for unstable fixation. If the IOL moves to an extent that the optical performance of the IOL is impaired, then surgical re-intervention may be required. In some cases the existing IOL can be repositioned and stabilized. In other cases, a different type of lens may need to be placed, in a procedure known as an IOL exchange.

            Other portions of the eye occasionally have problems after cataract surgery. The retina may develop inflammation (particularly CME, discussed above) or retinal detachment that requires surgical repair. The incidence of retinal detachment in uncomplicated surgery is higher than the incidence in patients who have not had any cataract surgery. It is generally believed that the rate of spontaneous retinal detachment after cataract surgery is less with modern phacoemulsification and IOL implantation, compared to older styles of surgery, but spontaneous detachments still occur. Sometimes detachments occur years after the cataract surgery. Patients who are nearsighted are more prone to spontaneous retinal detachment before and after cataract surgery compared to the general population. This is due to the fact that a nearsighted has a longer eye and the retina is typically thinner as well as the vitreous jelly more likely to be disturbed.

            Another sporadic problem is either the onset of new glaucoma or worsening or preexisting glaucoma. Glaucoma is a disease due pressure in the eye that slowly damages the optic nerve that carries vision signals from the eye back to the brain. If the pressure elevation is severe, a patient may have eye pain. If the pressure elevation is more moderate, or develops slowly, then the patient usually does not have any symptoms, and may lose peripheral vision to a severe extent without any awareness. The doctor checks the pressure in the eye on a routine basis in order to detect glaucoma. In patients with preexisting glaucoma that is not well controlled, the surgeon may recommend combining the cataract surgery with a glaucoma procedure to relieve the pressure in the eye. Most commonly, this involves one of several types of procedures to create pathways for the fluid to escape the eye at lower pressure than the natural outflow channels for the intraocular fluid.

            The clear front window of the eye, the cornea, not infrequently will have some swelling and wrinkling immediately after cataract surgery. This is because the inner layer of the cornea, the endothelial cells, are responsible for pumping water out of the cornea in order to keep it clear. Because the endothelial cells are fragile and are located on the inner layer of the cornea, the unavoidable disturbance of the cataract surgery may trigger a temporary disruption of the pumping. In most cases this will clear over time, sometimes rapidly and sometimes more slowly. In a few cases, however, the endothelial pumping function may not recover. In that case, a corneal transplant may be required to bring in a new supply of living endothelial cells from a donor. In Fuch’s corneal dystrophy, there is an accelerated loss of the endothelial cells with age compared to the normal slow loss that occurs normally. In many, but not all cases, the doctor can detect the presence of Fuch’s dystrophy before surgery, and alert the patient that there is a higher risk of corneal swelling with cataract surgery that may require a subsequent corneal transplant. In some cases, it is apparent that the cornea is already swelling, and the surgeon may recommend proceeding with a combination of cataract surgery and corneal transplantation in one procedure.

            Refractive and optical problems after cataract surgery also occur. A refractive complication would mean that the achieved outcome of the desired focus of the IOL is not achieved. For example, a patient might desire excellent distance vision, but end up either nearsighted or farsighted, or with some astigmatism, all of which would take away from the quality of the distance vision without glasses. This can be corrected with glasses or contact lenses, however. Alternatively, a more permanent solution could be considered, either an exchange of the IOL, a secondary IOL that is placed on top of the original (termed a piggyback IOL), or corneal refractive surgery, such as LASIK. The other form of optical complication that occurs sporadically is disappointment with the performance of a premium IOL, such as a presbyopia correcting IOL. In some cases, the desired distance and near vision is not achieved. The surgeon may be able to re-intervene and improve this situation either through medical or surgical treatment. Some patients, however, have ongoing optical issues that cannot be resolved. In that case, the patient will have to decide whether to accept the current status of the vision or whether to consider an exchange of the IOL for another type.

Posterior Capsule Opacification

            In most cases of cataract surgery the backside of the capsule, known as the posterior capsule, is clear at the end of the surgery. In some cases the cataract has caused a clouding of the posterior capsule that cannot be removed at surgery. In patients where the capsule is initially clear, in the months to years after the cataract surgery the posterior capsule may become cloudy. Considerable effort has been expended to design IOLs that reduce the rate of posterior capsule opacification (PCO). Nevertheless, PCO remains a fairly common event after cataract surgery. PCO is not considered a complication, because it is a natural healing event that occurs in a substantial number of patients. Because it is a common event, a specific laser was invented that allows the surgeon to make an opening in the posterior capsule that lines up with the pupil. The remainder of the posterior capsule supports the IOL. The only opening that is necessary is a relatively small percentage of the capsule that is aligned with the pupil. The specific laser employed is the Nd-YAG laser, and the procedure is known as posterior capsulotomy. (Insert figures). The laser does not dissolve or vaporize the capsule. Rather, each laser pulse creates a small amount of localized pressure. The very fragile capsule will develop an opening with each of these pulses, and multiple pulses are then interconnected to create the clear opening for the restoration of vision. The laser procedure is done in the office, most commonly, or in an ambulatory surgery center. The laser pulses are not felt by the patient, and the procedure is painless.

Conclusion

            Clouding of the natural lens with impairment of important daily functions is commonplace in our aging societies. Over 2 million cataract surgeries are performed each year in the United States. As the population ages, and expectations for retention of a high level of physical and mental activity grow due to the improved health in the later years of life, the demand for cataract surgery will continue to grow. The advances in cataract surgery with microsurgical technology have progressively lowered the complication rate and increased the speed of full recovery. With the advent of more sophisticated customized IOL technology, patients have recently experienced a further expansion of the opportunities for rehabilitation, with a return of both distance and reading vision, not experienced since youth, or the elimination of astigmatism that may have been present since childhood.

            Cataract surgery has, therefore, steadily become both a procedure to eliminate a disease (the clouding of the lens) and also the opportunity for functional rehabilitation (refractive surgery).