Cataracts - 12/10/2008

Cataract is a vision-impairing disease characterized by gradual, progressive thickening of the lens. It is one of the leading causes of blindness in the world today. This is unfortunate, considering that the visual morbidity brought about by age-related cataract is reversible. As such, early detection, close monitoring, and timely surgical intervention must be observed in the management of cataracts. The succeeding section is a general overview of cataract and its management.

Pathophysiology
The pathophysiology behind cataracts is complex and yet to be fully understood. In all probability, its pathogenesis is multifactorial involving complex interactions between various physiologic processes. As the lens ages, its weight and thickness increases while its accommodative power decreases. As the new cortical layers are added in a concentric pattern, the central nucleus is compressed and hardened in a process called nuclear sclerosis. Progressive oxidative damage to the lens with aging takes place, leading to cataract development. Various studies showing an increase in products of oxidation (e.g.: oxidized glutathione) and a decrease in antioxidant vitamins and the enzyme superoxide dismutase underscore the important role of oxidative processes in cataractogenesis.

Cataract can be classified into 3 main types: nuclear cataract, cortical cataract, and posterior subcapsular cataract. Nuclear cataracts result from excessive nuclear sclerosis and yellowing, with consequent formation of a central lenticular opacity. In some instances, the nucleus can become very opaque and brown, termed a brunescent nuclear cataract. Changes in the ionic composition of the lens cortex and the eventual change in hydration of the lens fibers produce a cortical cataract. Formation of granular and plaquelike opacities in the posterior subcapsular cortex often heralds the formation of posterior subcapsular cataracts.

Frequency
At least 300,000-400,000 new visually disabling cataracts occur annually in the US, with complications of modern surgical techniques resulting in at least 7000 irreversibly blind eyes. In the Framingham Eye Study from 1973-1975, cataract was seen in 15.5% of the 2477 patients examined. The overall rates of cataract in general and of its 3 main types - nuclear, cortical, and posterior subcapsular - rapidly increased with age, so that for the oldest age group, 75 years and older, nuclear, cortical, and posterior subcapsular cataracts were highest.

Mortality/Morbidity
Most morbidity associated with senile cataracts occurs postoperatively and is discussed in further detail later. Failure to treat a developing cataract surgically may lead to devastating consequences such as lens swelling and intumescence, secondary glaucoma, and, eventually, blindness.
Age is an important risk factor for cataract. As a person ages, the chance of developing a senile cataract increases. In the Framingham Eye Study from 1973-1975, the number of total and new cases of senile cataract rose dramatically from 23.0 cases per 100,000 and 3.5 cases per 100,000, respectively, in persons aged 45-64 years to 492.2 cases per 100,000 and 40.8 cases per 100,000 in persons aged 85 years and older.

History
Careful history taking is essential in determining the progression and functional impairment in vision resulting from the cataract and in identifying other possible causes for the lens opacity. A patient with cataract often presents with a history of gradual progressive deterioration and disturbance in vision. Such visual aberrations are varied depending on the type of cataract present in the patient.

Decreased visual acuity is the most common complaint of patients with cataract. The cataract is considered clinically relevant if visual acuity is affected significantly. Furthermore, different types of cataracts produce different effects on visual acuity. For example, a mild degree of posterior subcapsular cataract can produce a severe reduction in visual acuity with near acuity affected more than distance vision, presumably as a result of accommodative miosis. However, nuclear sclerotic cataracts often are associated with decreased distance acuity and good near vision. A cortical cataract generally is not clinically relevant until late in its progression when cortical spokes compromise the visual axis. However, instances exist when a solitary cortical spoke occasionally results in significant involvement of the visual axis.

Increased glare is another common complaint of patients with senile cataracts. This complaint may include an entire spectrum from a decrease in contrast sensitivity in brightly lit environments or disabling glare during the day to glare with oncoming headlights at night. Such visual disturbances are prominent particularly with posterior subcapsular cataracts and, to a lesser degree, with cortical cataracts. It is associated less frequently with nuclear sclerosis. Many patients may tolerate moderate levels of glare without much difficulty, and, as such, glare by itself does not require surgical management.

The progression of cataracts may frequently increase the diopteric power of the lens resulting in a mild-to- moderate degree of myopia or myopic shift. Consequently, presbyopic patients report an increase in their near vision and less need for reading glasses as they experience the so-called second sight. However, such occurrence is temporary, and, as the optical quality of the lens deteriorates, the second sight is eventually lost. Typically, myopic shift and second sight are not seen in cortical and posterior subcapsular cataracts. Furthermore, asymmetric development of the lens- induced myopia may result in significant symptomatic anisometropia that may require surgical management.

Cataract

Physical
After a thorough history is taken, careful physical examination must be performed. The entire body habitus is checked for abnormalities that may point out systemic illnesses that affect the eye and cataract development.
A complete ocular examination must be performed beginning with visual acuity for both near and far distances. When the patient complains of glare, visual acuity should be tested in a brightly lit room. Contrast sensitivity also must be checked, especially if the history points to a possible problem. Examination of the ocular adnexa and intraocular structures may provide clues to the patient's disease and eventual visual prognosis. A very important test is the swinging flashlight test which detects for a Marcus Gunn pupil or a relative afferent pupillary defect (RAPD) indicative of optic nerve lesions or diffuse macular involvement. A patient with RAPD and a cataract is expected to have a very guarded visual prognosis after cataract extraction.

Causes
Numerous studies have been conducted to identify risk factors for development of cataracts. Various culprits have been implicated including environmental conditions, systemic diseases, diet, and age. West and Valmadrid stated that age-related cataract is a multifactorial disease with different risk factors associated to the different cataract types. In addition, they stated that cortical and posterior subcapsular cataracts were related closely to environmental stresses, such as ultraviolet (UV) exposure, diabetes, and drug ingestion including steroids. However, nuclear cataracts seem to have a correlation with smoking. Alcohol has been associated with all cataract types.

Senile cataracts have been associated with a lot of systemic illnesses, to include the following: cholelithiasis, allergy, pneumonia, coronary disease and heart insufficiency, hypotension, hypertension, mental retardation, and diabetes.
 
Lab Studies
Diagnosis of senile cataract is made basically after a thorough history and physical examination are performed. Laboratory tests are requested as part of the preoperative screening process to detect coexisting diseases (e.g.: diabetes mellitus, hypertension, cardiac anomalies). Recent studies have shown that thrombocytopenia may lead to increased perioperative bleeding and, as such, should be properly detected and managed before surgery.

Imaging Studies
Ocular imaging studies (e.g.: ultrasound, CT scan, MRI) are performed when a posterior pole pathology is suspected and an adequate view of the back of the eye is obscured by the dense cataract. This is helpful in planning out the surgical management and providing a more guarded postoperative prognosis for the visual recovery of the patient. Clinical staging of senile cataract is based largely on the visual acuity of the patient. A patient who cannot read better than 20/200 on the visual acuity chart is said to have a mature cataract. If the patient can distinguish letters at lines better than 20/200, then the cataract is described as being immature. An incipient cataract is found in a patient who can still read at 20/20 but possesses a lens opacity as confirmed by slit lamp examination.

Treatment
No time-tested and proven medical treatment exists to delay, prevent, or reverse the development of cataracts. Aldose reductase inhibitors, which are believed to inhibit the conversion of glucose to sorbitol, have shown promising results in preventing sugar cataracts in animals. Other anticataract medications being investigated include sorbitol- lowering agents, aspirin, glutathione-raising agents, and antioxidant vitamins C and E.

The definitive management for cataract is lens extraction. Over the years, various surgical techniques have evolved from the ancient method of couching to the present-day technique of phacoemulsification. Almost parallel is the evolution of the IOLs being used, which vary in ocular location, material, and manner of implantation. Depending on the integrity of the posterior lens capsule, the 2 main types of lens surgery are the intracapsular cataract extraction (ICCE) and the extracapsular cataract extraction (ECCE). Below is a general description of the 3 commonly used surgical procedures in cataract extraction namely ICCE, standard ECCE, and phacoemulsification.

Prior to the onset of more modern microsurgical instruments and better IOL, ICCE was the preferred method for cataract removal. It involves extraction of the entire lens, including the posterior capsule. In performing this technique, there is no need to worry about subsequent development and management of capsular opacity. The technique can be performed with less sophisticated equipment and in areas where operating microscopes and irrigating systems are not available. However, a number of disadvantages and postoperative complications accompany ICCE. The larger limbal incision, often 160-180°, is associated with the following risks: delayed healing, delayed visual rehabilitation, significant against-the-rule astigmatism, iris incarceration, postoperative wound leaks, and vitreous incarceration. Corneal edema is a common intraoperative and immediate postoperative complication. Furthermore, endothelial cell loss is greater in ICCE than in ECCE. The same is true about the incidence of postoperative cystoid macular edema (CME) and retinal detachment. The broken integrity of the vitreous can lead to postoperative complications even after a seemingly uneventful operation. Finally, because the posterior capsule is not intact, the IOL to be implanted must either be placed in the anterior chamber or sutured to the posterior chamber. Both techniques are more difficult to perform than simply placing an IOL in the capsular bag and are associated with postoperative complications, the most notorious of which is pseudophakic bullous keratopathy. Although the myriad of postoperative complications has led to the decline in popularity and use of ICCE, it still can be used in cases where zonular integrity is impaired severely to allow successful lens removal and IOL implantation in ECCE. Furthermore, ICCE can be performed in remote areas where more sophisticated equipment is not available. ICCE is contraindicated absolutely in children and young adults with cataracts and cases with traumatic capsular rupture. Relative contraindications include high myopia, Marfan syndrome, morgagnian cataracts, and vitreous presenting in the anterior chamber.

In contrast to ICCE, ECCE involves the removal of the lens nucleus through an opening in the anterior capsule with retention of the integrity of the posterior capsule. ECCE possesses a number of advantages over ICCE most of which are related to an intact posterior capsule, as follows: A smaller incision is required in ECCE and, as such, less trauma to the corneal endothelium is expected. Short and long- term complications of vitreous adherence to the cornea, iris, and incision is minimized or eliminated. A better anatomic placement of the IOL is achieved with an intact posterior capsule. An intact posterior capsule also (1) reduces the iris and vitreous mobility that occurs with saccadic movements (e.g.: endophthalmodonesis), (2) provides a barrier restricting the exchange of some molecules between the aqueous and vitreous, and (3) reduces the incidence of CME, retinal detachment, and corneal edema. Conversely, an intact capsule prevents bacteria and other microorganisms inadvertently introduced into the anterior chamber during surgery from gaining access to the posterior vitreous cavity and causing endophthalmitis. Secondary IOL implantation, filtration surgery, corneal transplantation, and wound repairs are performed more easily with a higher degree of safety with an intact posterior capsule. The main requirement for a successful ECCE and posterior capsule IOL implantation is zonular integrity. As such, when zonular support is insufficient or appears suspect to allow a safe removal of the cataract via ECCE, ICCE, or pars plana lensectomy should be considered.

Standard ECCE and phacoemulsification are similar in that extraction of the lens nucleus is performed through an opening in the anterior capsule or anterior capsulotomy. Both techniques also require mechanisms to irrigate and aspirate fluid and cortical material during surgery. Finally, both procedures place the IOL in the posterior capsular bag that is more anatomical than the anteriorly placed IOL. It should be noted that there are significant differences between the 2 techniques. Removal of the lens nucleus in ECCE can be performed manually in standard ECCE or with an ultrasonically driven needle to fragment the nucleus of the cataract and aspirate the lens substrate through a needle port in a process termed phacoemulsification. The more modern of the 2 techniques, phacoemulsification offers the advantage of using smaller incisions, minimizing complications arising from improper wound closure and affording more rapid wound healing, and faster visual rehabilitation. Furthermore, it uses a relatively closed system during both phacoemulsification and aspiration with better control of intraocular pressure during surgery, providing safeguards against positive vitreous pressure and choroidal hemorrhage. However, more sophisticated machines and instruments are required to perform phacoemulsification.

Ultimately, the choice of which of the 2 procedures to use in cataract extraction depends on the patient, the type of cataract, the availability of the proper instruments, and the degree at which the surgeon is comfortable and proficient in performing standard ECCE or phacoemulsification.

During the postoperative period, the patient is prescribed topical 1% prednisolone acetate, which is applied every hour for the first day, then tapered depending on the inflammatory state of the eye. Recent studies have shown that topical ketorolac tromethamine provides adequate postoperative control of intraocular inflammation without the risk of increased intraocular pressure, which may be associated with steroid use. A broad-spectrum topical antibiotic also is given 4-6 times a day for 1-2 weeks.

Complications
The following are the major intraoperative complications encountered during cataract surgery: Shallow or flat anterior chamber, Capsular rupture, Corneal edema, Suprachoroidal hemorrhage or effusion, Expulsive choroidal hemorrhage, Retained lens material, Vitreous disruption and incarceration into wound, Iridodialysis.

The following are the major immediate postoperative complications encountered during cataract surgery often seen within a few days or weeks after the operation: Flat or shallow anterior chamber due to wound leak, Choroidal detachment, Pupillary block, Ciliary block, Suprachoroidal hemorrhage, Stromal and epithelial edema, Hypotony, Brown-McLean syndrome (peripheral corneal edema with a clear central cornea most frequently seen following ICCE), Vitreocorneal adherence and persistent corneal edema, Delayed choroidal hemorrhage, Hyphema, Elevated intraocular pressure (often due to retained viscoelastic), Cystoid macular edema, Retinal detachment, Acute endophthalmitis, Uveitis- glaucoma-hyphema (UGH) syndrome.

The following are the major late postoperative complications seen weeks or months after cataract surgery: Suture-induced astigmatism, Pupillary capture, Decentration and dislocation of the IOL, Corneal edema and pseudophakic bullous keratopathy, Chronic uveitis, Chronic endophthalmitis.

At any stage of the postoperative recovery of the eye, a risk of noninfectious endophthalmitis and infectious endophthalmitis exists. Noninfectious endophthalmitis is believed to be a multifactorial process or an interindividual variable response to a common factor as a hypersensitivity reaction. Treatment may range from the use of topical, transseptal, or oral steroids to the explantation of the intraocular lens. Ultimately, this may lead to infectious endophthalmitis. Of late, a significant increase in the incidence of gram-positive bacteria in bacterial isolates from postoperative eyes suspected of having endophthalmitis has been observed. Furthermore, a significant increase in resistance to ciprofloxacin has occurred. Seemingly, the spectrum of bacteria causing postcataract endophthalmitis is changing partly because of increased resistance to mainstay antibiotics in the treatment of endophthalmitis.

Medical-Legal Considerations
The onset of office setting phacoemulsification under topical anesthesia performed in less than 30 minutes ironically has turned the art of cataract surgery into an industry and has increased the risk of medical malpractice actions. Proper surgical technique is necessary to avoid litigation. Sterile conditions, prevention of infection, and documentation of known complications will help to avoid litigation.