CATARACTS

1.Explain the derivation of the word cataract.

Cataract comes from the Greek word cataractos, which describes rapidly running water. Rapidly running water turns white, as do mature cataracts.

2.What is the leading cause of blindness worldwide?

Believe it or not, cataracts, which are treatable, remain one of the leading causes of blindness worldwide.

3.What is a nuclear sclerotic cataract?

A nuclear sclerotic cataract describes the sclerosis or darkening that is seen in the central portion of the lens nucleus. This type of cataract is typically seen in older patients. As the equatorial epithelial cells of the lens continue to divide, they produce compaction of the more central fibers and sclerosis.

4.What produces the brown color seen in cataracts?

The brown color comes from urochrome pigment.

5.What is “second sight?” How is it associated with nuclear sclerotic cataracts?

As patients develop nuclear sclerotic cataracts, the increased density of the lens causes the patient to become increasingly nearsighted. As a result of their nearsightedness, many patients who required spectacles to help them read find that they are able to read small print up close without glasses. In the past, this phenomenon was termed “second sight.” Of interest, patients erroneously believe that their eyes are getting stronger or better, whereas the opposite is the case. Second sight indicates progression of the cataract.

6.What are the typical symptoms of nuclear sclerotic cataracts?

In general, all types of cataracts cause decreased vision. Nuclear sclerotic cataracts tend to cause problems with distance vision but preserve reading vision because of the above-mentioned nearsightedness.

7.What are posterior subcapsular cataracts?

Posterior subcapsular cataracts are granular opacities seen mainly in the central posterior cortex just under the posterior capsule. They have a hyaline type of appearance.

8.What are the symptoms of posterior subcapsular cataracts?

Unlike patients with nuclear sclerotic cataracts, patients with posterior subcapsular cataracts often have good distance vision but typically have blurred near vision. In addition, patients with posterior subcapsular cataracts often have extreme difficulty with glare so that in dim illumination they function well, whereas with bright illumination their vision decreases significantly.

9.What are the associated systemic findings in patients with cataracts?

In general, nuclear sclerotic cataracts are seen in elderly patients, although they may occur in young patients as well. In younger patients, they are often associated with high myopia.

Posterior subcapsular cataracts are common in patients with diabetes, patients who have taken steroids, and patients with a history of intraocular inflammation, such as uveitis.

10.What are the major potential causes of cataracts in infants?

Common causes of congenital cataracts include familial inheritance, intrauterine infection (e.g., rubella), metabolic diseases (e.g., galactosemia), and chromosomal abnormalities. Complete evaluation by a pediatrician is mandatory for any infant with a congenital cataract.

11.What is a morgagnian cataract?

A morgagnian cataract is a mature cataract in which the cortex liquefies and the mature central nucleus can be seen within the liquefied cortex.

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12.What is phacolytic glaucoma?

Phacolytic glaucoma may occur with morgagnian and mature cataracts. Liquefied cortex traverses the capsular membrane and enters the posterior chamber, producing an inflammatory response that clogs the trabecular meshwork and results in elevated intraocular pressure.

13.What is phacomorphic glaucoma?

As the cataract matures, the lens becomes enlarged (intumescent). As the lens enlarges, it pushes the iris root and ciliary body forward, narrowing the angle between the iris and the peripheral cornea in the region of the trabecular meshwork. If the angle becomes narrow enough, the pressure may become elevated because of angle closure. Treatment involves removal of the cataract.

14.What is pseudoexfoliation? What is its relationship to cataracts?

Pseudoexfoliation is a condition in which basement membrane material from the zonules and lens capsule is liberated onto the anterior lens capsule and anterior chamber. Patients with pseudoexfoliation have a predisposition for the development of glaucoma, presumably because of clogging of the trabecular meshwork by the exfoliated material. Patients with pseudoexfoliation often present a challenge for the cataract surgeon because their pupils tend to dilate poorly, and they often have weak or loose zonules that cause intraoperative complications with disinsertion of the zonules. Because of their propensity for developing glaucoma, patients often have postoperative pressure elevations.

15.A patient underwent successful and uncomplicated cataract surgery, and years after the surgery, the intraocular lens (IOL) completely dislocated. What associated ophthalmic condition would the patient be likely to have?

The patient would be likely to have pseudoexfoliation.

16.What is true exfoliation syndrome as opposed to pseudoexfoliation syndrome?

True exfoliation is found in glassblowers who stand in front of hot furnaces throughout the day. Large sheets of material come off the anterior lens capsule. Such cataracts are termed glassblower’s cataracts. With modern techniques of processing glass, they are no longer seen. Because the type of material produced in pseudoexfoliation seemed similar to the material produced in a glassblower’s cataract, it was termed pseudoexfoliation to distinguish it from the exfoliative material produced by heat exposure.

17.What systemic syndromes should be considered in a patient with a spontaneously dislocated natural lens?

In these patients, the zonular support system has been disrupted. Spontaneous dislocation of the lens is most common in Marfan’s syndrome and homocystinuria. Typical patients with Marfan’s syndrome are tall, thin, and lanky and exhibit arachnodactyly. The lenses in Marfan’s syndrome tend to dislocate superiorly. In homocystinuria, the lenses tend to dislocate inferiorly. Trauma also should be considered in all patients with a dislocated lens. Rarely, pseudoexfoliation can be a cause.

KEY POINTS: DISLOCATED AND SUBLUXATED LENSES

1. Patients with a natural lens that is dislocated should be evaluated for trauma.

2. Marfan syndrome most often causes lenses to dislocate superiorly. Patients need evaluation for possible cardiac and aortic abnormalities and retinal detachments.

3. Homocystinuria most often causes lenses to dislocate inferiorly. Patients have a high risk of thromboembolic events.

18.What other clinical findings are common in patients with a traumatic cataract?

Blunt trauma may produce a cataract. Patients often have associated sphincter tears and may even have iridodialysis or angle recession. If the trauma has been severe, some or all of the zonules may be broken, causing the lens to be mobile within the eye. This phenomenon is called phacodonesis. Retinal detachment and optic neuropathy also may be present and cause decreased vision.

19.What are the indications for cataract surgery?

The basic indication for cataract surgery is reduced visual function that interferes with activities of daily living. This indication obviously varies, depending on the patient’s age and degree of activity. For instance, a 40-year-old accountant with an early posterior subcapsular cataract may be much

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Interestingly, even if patient discontinues his tamsulosin for up to 4 weeks prior to cataract surgery, the pupil abnormalities persist. Surgical strategies for dealing with this situation include utilizing a highly cohesive viscoelastic agent and iris retractors.

www.ascrs.org.

25.What is the difference between an anterior chamber lens and a posterior chamber lens? What is “the capsular bag”?

A posterior chamber lens is typically utilized in routine cataract surgery. During surgery a circular opening termed a capsulorrhexis is made in the capsule that surrounds the cataractous lens. The cataract is removed and then the new lens is placed into the capsular bag, which is the membrane that is left behind once the cataract is removed. This region of the eye is termed the posterior chamber, hence the IOL that resides there is termed a posterior chamber lens.

At times it is not possible to place a posterior chamber lens because of either inherent weakness in the capsular bag or an intraoperative complication that disrupts its integrity. In these cases one of the options is to place a lens in the front (or anterior) portion of the eye, hence the term anterior

chamber lens. Anterior chamber lenses fixate in the eye by resting on the scleral spur. If not positioned correctly, these IOLs have the potential to chafe the sensitive uveal tissue in the iris and create complications.

26.What is posterior capsular opacification? What is a secondary membrane? Can a cataract grow back?

The new IOL replaces the cataractous lens by resting inside the capsular bag. Slowly, over time, residual epithelial cells in the capsular bag can grow across the posterior portion of the capsule and cause it to become hazy or cloudy. Over time, the capsule can become so cloudy it may seem as if the cataract has “come back.” The cataract can never come back, but the secondary membrane can become cloudy, causing the vision to deteriorate as if the cataract were recurring.

27.What is a YAG capsulotomy?

When the reduced vision becomes clinically significant, the patient may undergo an Nd:YAG capsulotomy. The initials are an acronym for neodymium, yttrium, aluminum, and garnet, which are the materials utilized to allow the laser to function properly and open the membrane.

28.What is the origin of the term laser?

Laser is actually an acronym for light amplification by stimulated emission of radiation.

29.What is the difference between an “intracap” and an “extracap”?

An intracap describes intracapsular cataract extraction. This is the “old” type of cataract surgery back in the days when patients had a very large incision made at the corneoscleral limbus and the entire

lens surrounded by the lens capsule was removed (usually with the aid of a freezing probe termed a cryoprobe as well as α-chymotrypsin to dissolve the zonules). In these cases no lens was replaced and the patient was left aphakic.

In an extracap or extracapsular surgery, the capsule surrounding the lens is opened and the cataractous lens removed. The capsule, however, remains in the eye to support and hold the new posterior chamber IOL.

30.What is couching?

Couching describes an ancient technique for cataract surgery in which a needle was inserted into the eye and used to push the opaque cataract back into the vitreous cavity. Although the complication rate of this was extremely high and the visual result limited, in antiquity it would allow patients with mature light perception cataracts to be able to regain a limited degree of vision.

Bibliography

Datilles M: Clinical evaluation of cataracts. In Tasman W, Jaeger E, editors: Duane’s clinical ophthalmology, vol. 1. ­Philadelphia, 1996, Lippincott-Raven, pp 1–15.

Datilles M, Kinoshita J: Pathogenesis of cataracts. In Tasman W, Jaeger E, editors: Duane’s clinical ophthalmology, vol. 1. Philadelphia, 1996, Lippincott-Raven, pp 1–9.

Datilles M, Magno B: Cataract: clinical types. In Tasman W, Jaeger E, editors: Duane’s clinical ophthalmology, vol. 1. ­Phildelphia, 1996, Lippincott-Raven, pp 1–25.

http://ophthalmologyebooks.com

1.What are the indications for cataract surgery?

In general, the decision to have cataract surgery is elective. It is based on a patient’s personal needs and the physician’s judgment as to the probability of vision improvement. For some people, even a slight loss of vision is unacceptable. Others may choose to delay surgery because their cataracts do not seriously interfere with their lives. The key question is whether the patient perceives the cataract as interfering with his or her quality of life. Of course, the physician must be aware of state visual acuity requirements for driving.

2.What are two nonsurgical methods of managing a cataract?

•Refraction: Patients with a cataract may experience a myopic (nearsighted) shift or so-called second sight. Occasionally, glasses can compensate for such shifts. However, if the shift is large and unilateral, binocular vision may be compromised by image size differences between the two eyes. This anisometropia may push patients to have surgery.

•Pupillary dilation: An expanded pupil allows light rays to enter around a central cataract (such as a posterior subcapsular cataract) rather than be blocked by light rays that attempt to pass through a hazy cataract.

3.What preoperative tests are used to gauge visual impairment?

No single test adequately describes the effect of cataracts on a patient’s visual functioning, but the most widely used tests are:

•Snellen visual acuity (i.e., 20/20).

•Potential acuity testing. This test estimates postoperative visual acuity by projecting a Snellen acuity chart through the patient’s cataract. Most often, it is used to determine whether a patient’s visual symptoms are due more to cataract or to retinal disease.

•Glare/contrast sensitivity testing. This test simulates lighting conditions outdoors and determines a patient’s vision when functioning under more normal conditions. The high-contrast situation in a Snellen test can overestimate a patient’s abilities. A patient may have 20/40 acuity in a dark room but may have 20/100 with glare testing, which could significantly impair driving.

KEY POINTS: TESTS OF VISUAL IMPAIRMENT

1.Snellen visual acuity

2.Potential acuity testing

3.Glare testing

4.Contrast sensitivity testing

4.What are the basic steps in removing a cataract?

1.The pupil is dilated with medications.

2.The eye and eyelids are disinfected with an antiseptic, usually iodine based.

3.The eye and eyelids are anesthetized, and a speculum is placed to keep the eyelids open.

4.An incision is made into the anterior chamber (AC).

5.A viscoelastic (viscous, protective gel) is injected into the AC.

6.The anterior capsule is opened with a capsulotomy or capsulorrhexis to gain access to the lens mass.

7.The nucleus is removed manually or by phacoemulsification.

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Figure 22-1.  Retrobulbar injection. If the tip of the needle strikes the floor of the orbit as it is inserted (see 1 above), it is withdrawn slightly and directed more superiorly (see 2 above). (From Jaffe NS, Jaffe MS, Jaffe GF: Cataract surgery and its complications. St. Louis, Mosby, 1990.)

8.The residual cortex is removed.

9.An intraocular lens (IOL) is inserted.

10.The wound is closed.

5.How is the eye anesthetized for surgery?

Most surgeons prefer local rather than general anesthesia for adult cataract surgery. Less commonly, facial akinesia with a short-acting agent such as lidocaine or hyaluronidase (a diffusion enhancer) may be given to prevent squeezing of the eyelids during surgery. There are three types of local anesthesia:

•Retrobulbar: Anesthetic (usually a combination of a shortand a long-acting agent with hyaluronidase) is injected inside the muscle cone to achieve akinesia and anesthesia of the globe (Fig. 22-1).

•Peribulbar: Anesthetic is injected outside the muscle cone. Although this block takes longer to take effect (12–25 minutes), there are fewer potential complications because a shorter needle is used.

•Topical: Advances in technology have allowed skilled surgeons to perform the cataract procedure in 10–15 minutes. With such short operative times, prolonged anesthesia and akinesia become less critical. Topical drops or gels of short-acting agents such as lidocaine or tetracaine may be used to anesthetize the eye sufficiently to complete the procedure. The advantage to the patient is instantaneous binocular vision postoperatively without the risk of injection-related, potentially sight-threatening complications.

•Intracameral: As an adjunct to or substitute for topical anesthetics, intraocular administration of preservative-free lidocaine with or without dilating agents is being adopted by many surgeons.

6.What are the disadvantages of topical anesthesia for cataract surgery?

•Because there is no akinesia, the eye can move during surgery.

•Patient selection is crucial. Patients need to be able to follow the commands of the surgeon.

7.What is couching?

Couching is one of the most ancient surgical procedures and it was the first known technique of cataract removal. Although, the technique was first described by the Indian physician Susruta ca. 800 BC, copper surgical instruments that could have been used for couching have been found in the tomb of the Egyptian king Khasekhemwy ca. 2700 BC11. Popular in the United States until the 1850s, couching involves piercing the eye with a needle, then dislocating the entire lens backward and downward into the posterior chamber. Although it may seem crude by modern surgical standards and prone to myriad complications, it is still performed in the Third World where advanced technology is not available.

8.What are the two most common ways to remove a cataract?

•Intracapsular surgery was the procedure of choice from its discovery by Jacques Daviel in 1752 until the early 1970s. It is accomplished with a cryoprobe, an instrument that freezes the tissue. Intracapsular surgery is rarely performed in the United States today except in cases of dislocated lenses.

•Extracapsular cataract extraction (ECCE) is the most popular technique. There are two types—manual extraction and phacoemulsification. Both methods require the use of an operating microscope that permits magnification. In extracapsular surgery the anterior capsule of the lens

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A B

C D

E F

Figure 22-2.  Extracapsular extraction. A, Multiple small cuts are made in the anterior capsule. B, A full-thickness incision is completed with scissors. C, The nucleus is removed. D, The cortex is aspirated. E, The inferior haptic is inserted through the incision and passed under the iris. F, The tip of the superior haptic is grasped with a forceps and advanced into the anterior chamber; as the superior pole is clearing the edge of the pupil, the arm is pronated to ensure that when the haptic is released, it will spring open under the iris and not out of the incision. (From Kanski JJ: Clinical ophthalmology: a systematic approach, ed 2, Boston, Butterworth-Heinemann, 1989.)

is removed, the hard nucleus is expressed, and the remaining soft cortical fragments are removed with either an automated or a manual device (Fig. 22-2). The advantage of extracapsular surgery is preservation of the posterior capsule, which permits a pocket for an intraocular lens. This method also minimizes the complications associated with vitreous loss.

9.What is phacoemulsification?

Invented by the late Dr. Charles Kellman in 1967, phacoemulsification is a sophisticated form of extracapsular surgery that permits mechanical removal of a cataract through a 3.0-mm incision

(Fig. 22-3). This reduction in incision size results in faster visual recovery and fewer complications, making phacoemulsification still one of the most significant advances in cataract surgery. Conventional extracapsular surgery requires a wound size of 150 degrees (approximately 10 mm).

10.How does the phacoemulsification machine work?

Although the machine is complex, its functions are simple: irrigation, aspiration, and ultrasonic vibration via a handpiece. The phacoemulsification handpiece consists of a hollow 1-mm titanium needle that fragments a cataract by vibrating at 40,000 times per second. The fragmented pieces are then aspirated through the tip of the needle and into a drainage bag. An irrigation solution flows from a bottle suspended above the machine and into the eye through the needle. This fluid serves to cool the needle and to maintain proper anterior chamber depth.

11.What are the advantages and disadvantages of phacoemulsification?

•Advantages are a small incision, fewer wound problems, less astigmatism, more rapid physical rehabilitation, and less risk of expulsive hemorrhage.

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Figure 22-3.  The removal of nuclear material by phacoemulsification. (From Koch PS, Davidson JA: Textbook of advanced phacoemulsification techniques. Thorofare, NJ, Slack, 1991.)

Figure 22-4.  Left, Can-opener capsulotomy. Right, Continuous-curve capsulorrhexis. (From Koch PS, Davidson JA: Textbook of advanced phacoemulsification techniques. Thorofare, NJ, Slack, 1991.)

•Disadvantages are machine dependency, a longer learning curve with complications while transitioning, and expensive equipment. Phacoemulsification is more difficult in patients with dense nuclei and/or poor pupillary dilation.

12.How is a capsulotomy performed?

There are two types of capsulotomies: a can-opener capsulotomy and a continuous-curve capsulorrhexis (CCC). The can-opener capsulotomy is a series of jagged punctures performed with a bent needle. Although it is simple to perform, it is prone to peripheral extension of its jagged edges. The CCC is made by tearing the capsule so that the edges remain sharp, well demarcated, and strong. Forces are distributed more evenly and prevent an anterior capsule extension from becoming a posterior capsular tear. This approach permits safe utilization of phaco techniques that use shearing or rotational forces. Implants are held more securely and center better (Fig. 22-4)

13.Where is the nucleus phacoemulsified in the eye?

The nucleus can be disassembled in the anterior chamber or in the capsular bag. Anterior chamber removal is less popular because of the higher risk of corneal endothelial damage. However, in cases with capsular rupture, this method of removal can prevent nuclear pieces from moving posteriorly into the vitreous.

14.Are there different ways to phacoemulsify the nucleus?

The nucleus can be disassembled as a whole (sculpting) or by first being split (nucleofractis) into pieces. Harder nuclei are more readily and safely removed with a splitting technique within the capsular bag. However, a capsulorrhexis is mandatory because the forces exerted during splitting may cause peripheral extension of a can-opener capsulotomy with possible posterior capsular rupture.

The type of capsulotomy and anticipated method of cataract extraction are closely interrelated. The planned location and technique of nucleus emulsification are affected by such variables as nucleus consistency (hard or soft lens), pupil size, zonular (lens ligament) integrity, and the presence of intraoperative complications.

15.Are lasers used to remove cataracts?

Patients love lasers, and this is a question they frequently ask. Femtosecond lasers can now assist or replace several aspects of manual cataract surgery. These include the creation of the initial incisions

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in the cornea, the creation of the capsulotomy, the reduction of preexisting astigmatism, and the initial disassembly of the lens. Phacoemulsification is still required to remove the partially disassembled, presoftened lens. The technology is purported to be safer and to deliver improved outcomes by many; however, further data will be required to prove these assertions.

16.Once a cataract is removed (aphakia), what are the options to restore vision?

•Thick aphakic glasses are rarely used today because they create visually annoying magnification (approximately 25%) and distortion.

•Contact lenses are a better alternative to visual restoration (magnify only 7%), but many elderly patients do not possess the manual dexterity necessary to handle them. Long-term extended-wear lenses can help in this regard.

•Intraocular lenses are the best and most common alternative to restoration of normal vision after cataract surgery, because they almost duplicate the aphakic eye. Magnification is minimal, and peripheral vision is normal.

17.Who invented intraocular lenses?

In 1949, Sir Harold Ridley was the first person to insert an implant into the posterior chamber. Most authorities agree that this was one of the most significant advances in cataract surgery.

18.Of what are implants made?

During World War I it was noted that British Spitfire fighter pilots who had Plexiglas (polymethylmethacrylate (PMMA)) embedded in their eyes from shattered canopies tolerated the material well. PMMA lenses became the gold standard. Advances in technology led to the creation of soft or foldable materials made from silicone and acrylic materials. These materials have come into favor mainly because they can be inserted through much smaller incisions.

19.Describe the most common design and shape of IOLs

Implants are composed of an optical portion called the “optic” and a nonoptical portion called the “haptic,” which is used for fixating the IOL.

Most optic designs are unifocal (distance only). Multifocal and accommodating designs, which reduce or eliminate the need for computer and/or reading glasses, are now available. Toric IOLs, which can correct preexisting astigmatism, are also available. Optics can be round or oval, with or without positioning holes, and range in size from 5 to 7 mm. Lens haptics can be looped or plate style (mostly seen in foldable implants) and made of the same material as their optics or a different one. Anterior chamber lenses are designed with special haptics that allow proper fixation in the delicate anterior chamber angle.

20.What are the most common positions of IOLs?

The most common positions are capsular bag, ciliary sulcus, and anterior chamber. Capsular bag fixation is preferred because it affords excellent lens stability far away from the corneal endothelium. In more complex cases with no means of capsular support, iris or scleral fixation of the IOL are reasonable options.

21.Is an implant indicated in every aphakic patient?

No. Implants are generally not used in children or in eyes with severe anterior segment disease or inflammation. However, implants to treat children who are aphakic are becoming more common.

22.How is the power of an IOL determined?

The most common method of determining IOL power (P) uses a regression formula called SRK. The formula is P = A − 2.5L − 0.9K. The components of this formula include the axial length (length of the eye) measurement (L), which is determined by A-scan ultrasonography or more accurately by partial coherence interferometry; the average corneal curvature (K), which is determined by keratometry; and an A constant (A), which is specific for each lens type. The closer the implant is to the retina, the greater the A constant. Therefore the A constant is larger for posterior chamber implants than for anterior chamber implants. Newer IOL calculation formulas have been gaining in popularity. These thirdand fourth-generation formulas, such as the SRK/T, Haigis, Olsen, and Holladay II formulas, have offered surgeons the ability to predict IOL powers with uncanny accuracy. These next-generation formulas are especially important in determining IOL power in extremely short or long eyes and in eyes that have had previous refractive surgery.

Intraoperative wavefront aberrometry with the ORA (Wavetec) and Holos (Clarity Medical Systems) devices has added yet another dimension of precision and accuracy to these power determinations.

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