Ординатура / Офтальмология / Английские материалы / Primary Care Ophthalmology_Palay, Krachmer_2005
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FIGURE 8–2 A, Cross section of the eye in the nonaccommodative state. B, During accommodation to focus on a near object, the ciliary body (1) moves forward, relaxing the zonules, which allows the lens (2) to thicken in the anteroposterior axis. The iris (3) constricts, and the space between the cornea and iris—the anterior chamber (4)—decreases.
•Color perception is reduced.
•With a nuclear cataract, near vision may improve (“second sight”).
•With a posterior subcapsular cataract, near visual acuity decreases.
Signs
• Opacification of the lens is evident.
Workup
•Cataracts are best seen after dilation of the pupil. The examiner looks through the +5 lens of a direct ophthalmoscope held about 6 inches from the patient’s eye.
Treatment
•For early nuclear cataracts, a change in the spectacle prescription may improve vision.
•For small central opacities, pupillary dilation may improve vision.
•Surgical removal of the lens with placement of an intraocular lens implant is performed.
•Cataract surgery is not performed with lasers. A laser may be used, however, if an after-cataract is present (see page 136).
130 CHAPTER 8 • Lens Abnormalities
BOX 8–1 Types of Senile Cataract
Nuclear
•A yellow-brown discoloration of the central part of the lens is observed (Fig. 8–3).
•The nuclear type of cataract usually becomes evident at the age of 50 years and progresses slowly until the entire nucleus is opaque.
Cortical
•Radial or spokelike opacities in the periphery of the lens extend to involve the anterior or posterior lens (Fig. 8–4).
•Patients often are asymptomatic until the lens changes involve the central lens.
FIGURE 8–3 In cases of nuclear cataract,
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the yellow-brown color of the central nucleus (1) is evident.
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FIGURE 8–4 Peripheral spokelike opacities (1) in the cortex are visible in this eye with cortical cataract.
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BOX 8–1 Types of Senile Cataract (Continued)
Posterior subcapsular
•Opacities appear in the most posterior portion of the lens adjacent to the posterior capsule, often forming a plaque (Fig. 8–5).
•Posterior subcapsular cataract most commonly is associated with systemic or topical corticosteroid use.
•Because the visual axis is involved, this type causes a disproportionate number of symptoms for its size.
Dense white
•A white discoloration of the central part of the lens is observed.
•A dense white cataract often is seen in combination with cortical and nuclear cataracts in older patients (Fig. 8–6).
•This type may be severely disabling because of the marked visual loss it produces.
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FIGURE 8–5 The central location of a posterior subcapsular cataract (1).
FIGURE 8–6 Advanced central (nuclear) and peripheral (cortical) opacification is seen in this eye with a dense white cataract.
132 CHAPTER 8 • Lens Abnormalities
Cataract Surgery
Cataract surgery is one of the most frequently performed surgical operations. Greater than 1.5 million cataract surgery procedures are performed annually in the United States. An estimated 5 to 10 million persons in the United States become visually disabled each year because of cataracts.
Indications
Cataract surgery is indicated in the following instances:
• To improve quality of life, which depends on the affected person’s visual needs
•To prevent a secondary glaucoma or uveitis
•To permit visualization of the fundus to monitor patients with diseases of the optic nerve (e.g., glaucoma) or retina (e.g., diabetic retinopathy)
•To permit visualization of the fundus before retinal surgery or laser treatment
Preoperative Considerations
Every patient undergoing cataract surgery needs a complete ophthalmologic examination to rule out an underlying ophthalmic pathologic condition that may contribute to the patient’s visual symptoms. Evaluation of the retina is especially important in patients with diabetes, because diabetic retinopathy can be exacerbated after cataract surgery.
Before cataract surgery, a preoperative exam is required. In many instances the patient is referred back to the primary care provider for a complete history, physical examination, and appropriate laboratory testing. Such testing may include an electrocardiogram, chest radiography, and determinations of hematocrit and potassium level, depending on the patient’s medical status. With newer surgical techniques, however, minimal or no sedation is necessary, and the need for a complete medical evaluation is in question.
Advances in surgical technique also have changed anticoagulation management in the perioperative period. With small incisions, which allow for a “closed system” inside the eye, and the use of topical anesthesia, the risk of bleeding during cataract surgery is minimal, and the great majority of ophthalmologic surgeons do not recommend discontinuing anticoagulation therapy before cataract surgery. In certain procedures that may be performed in conjunction with a cataract extraction, discontinuation of anticoagulants may be warranted. Consultation with the ophthalmologic surgeon performing the operation is recommended before the primary care physician changes a patient’s anticoagulation regimen.
Prognosis and Risks
The prognosis following cataract surgery using current techniques is excellent. Approximately 95% of patients obtain improved vision after cataract surgery.
Potential complications of cataract surgery, as with any ocular surgery, include infection and bleeding that can lead to blindness. The risk of infection is approximately 0.02%. The risk of retrobulbar hemorrhage is 0.1% with retrobulbar anesthe-
Cataract Surgery |
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sia. The risk of intraocular hemorrhage during cataract surgery is 0.06%. Possible late sequelae include retinal detachment and the development of glaucoma.
Anesthesia
In most cases, cataract surgery is performed using topical anesthesia with monitored anesthesia care. Topical anesthetic is placed on the surface of the eye, and a small amount of anesthetic is injected into the anterior chamber after the corneal incision is performed. With this technique, there is no need for retrobulbar anesthesia and therefore no risk of retrobulbar hemorrhage. Some patients require akinesia of the eyelids and eye because of an inability to cooperate or communicate during surgery, which necessitates the use of retrobulbar or peribulbar injections of anesthetic. Some surgeons utilize short-acting intravenous sedatives before performing the injections. General anesthesia is relatively rare in cataract surgery today. It may still be used for patients who are unable to lie still or who have language or hearing problems that may impair communication, potentially compromising the surgeon’s ability to perform the operation safely.
Procedure
Cataract surgery is performed as an outpatient procedure. The procedure takes approximately 10 to 15 minutes to perform. Phacoemulsification is the technique used in nearly all patients undergoing cataract surgery today. Phacoemulsification is the preferred procedure because of the smaller incision size and faster visual rehabilitation. An older technique, extracapsular cataract extraction, is used in rare circumstances.
Phacoemulsification. In phacoemulsification, the surgeon makes a 2- to 4-mm incision (Fig. 8–7) and removes a circular portion of the anterior lens capsule (Fig. 8–8). A phacoemulsification instrument emits ultrasonic vibrations and provides suction for breakup and extraction of the hard nuclear lens material (Fig. 8–9). The surgeon uses
1FIGURE 8–7 Phacoemulsification: A small incision is created in the cornea with a blade (1).
134 CHAPTER 8 • Lens Abnormalities
FIGURE 8–8 Phacoemulsification: Forceps (1) is used to |
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tear a continuous capsulorrhexis in the anterior capsule (2). |
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FIGURE 8–9 Phacoemulsification: The nucleus (1) is removed with the phacoemulsification handpiece (2). A second instrument (3) is used to assist in the procedure.
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a mechanical irrigation and suction instrument to remove the lens cortex (Fig. 8–10) and then places the lens implant in the remaining capsular bag.
Flexible lens implants are now available that can be folded and introduced through a small incision into the eye, where they unfold (Fig. 8–11) and are held in place within the remaining capsular bag (Fig. 8–12). The smaller wounds may be self-sealing or require only a few sutures. This small incision technique can be performed with topical anesthesia.
Extracapsular Cataract Extraction. In extracapsular cataract extraction, the surgeon makes a 10to 11-mm superior sclerocorneal incision and removes the anterior portion of the lens capsule. The entire nucleus is extracted through the incision. The surgeon uses a mechanical irrigation and suction instrument to remove the lens cortex, places the implant in the remaining capsular bag, and sutures the incision. The extracapsular technique is utilized only for very dense cataracts that cannot be removed with the phacoemulsification technique. Retrobulbar or peribulbar anesthesia is required for the extracapsular method.
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FIGURE 8–10 Phacoemulsification: A mechanical irrigation and suction instrument (1) is used to remove the lens cortex (2).
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FIGURE 8–11 Phacoemulsification: The lens (1) is inserted |
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under the anterior capsular surface (2) using a lens inserter |
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FIGURE 8–12 Phacoemulsification: New intraocular lens (1) in proper position in the remaining capsular bag. Note the edge of the anterior capsule (2) and the edge of the intraoc-
1 ular lens (3). Two air bubbles (4) are visible beneath the cornea.
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136 CHAPTER 8 • Lens Abnormalities
Postoperative Care
If cataract removal is performed using local or topical anesthesia, the patient can go home shortly after the surgery. The patient usually is ambulatory on the day of the procedure. The patient is seen in the ophthalmologist’s office for evaluation the following day and often is able to return to work within a day or two. The patient typically is given antibiotic and steroid drops for the first few weeks after surgery. The postoperative course usually is painless; therefore, prescription painkillers are not necessary. An updated spectacle prescription usually is given 3 to 8 weeks after surgery.
After-Cataract (Secondary Membrane/Posterior
Capsular Opacity)
In 10% to 30% of patients who have undergone cataract surgery, the posterior capsule subsequently opacifies (Fig. 8–13), producing significant visual distortion. The opacity usually is noted several months to years after cataract surgery. Treatment involves a noninvasive technique (posterior capsulotomy) using the neodymium:YAG laser to
FIGURE 8–13 Slit lamp view of an opacified posterior
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FIGURE 8–14 After-cataract treatment with |
laser: View of |
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open posterior capsule (1) after the laser procedure. Note the |
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peripheral opacified posterior capsule (2). |
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Cataract Surgery |
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1FIGURE 8–15 After-cataract treatment with laser: Open
central posterior capsule (1) viewed using retroillumination.
2Again, note the peripheral opacified posterior capsule (2).
create a small opening in the center of the opacified posterior capsule (Figs. 8–14 and 8–15). A complication of this procedure is a transient rise in intraocular pressure, which may require medical treatment. The most serious complication is retinal detachment, which may occur weeks to months after the procedure in up to 1% of patients.
CHAPTER 9
Uveitis
TERRY KIM • DOUGLAS M. BLACKMON
Related Anatomy
The uveal tract is a heavily pigmented and highly vascular structure composed of three distinct anatomic components: the iris, ciliary body, and choroid (Fig. 9–1). The iris represents the most anterior portion of the uveal tract and is the only portion that is directly visible by external or slit lamp examination. It is located behind the cornea (with the space between the cornea and iris known as the anterior chamber) and is responsible for giving the eye its color. The central opening of the iris is the pupil, which constricts or dilates, depending on the amount of light entering the eye. The ciliary body is contiguous with the iris and has numerous functions, including aqueous humor production and accommodation. The choroid has a posterior location and lies between the retina and the sclera. Its main role is to provide a blood supply to the outer retina. These three components together form a continuous uveal lining that can be affected by inflammatory conditions within the eye.
Uveitis is a general term used to describe any inflammatory condition involving the uveal tract. Different classifications and terminology are used to denote the specific sites of the uveal tract primarily involved. For the anterior segment of the eye the terms iritis and iridocyclitis describe inflammation of the iris and of the iris–ciliary body complex, respectively. The terms vitritis, retinitis, and choroiditis designate inflammation in the relevant parts of the posterior segment of the eye. In this book, the term anterior uveitis means any inflammation of the iris and/or ciliary body, and the term posterior uveitis denotes any inflammation of the vitreous, retina, and/or choroid.
Identification of the segment of the eye primarily affected by uveitis guides formulation of a differential diagnosis, workup, and treatment. Some disorders appear exclusively as an anterior or a posterior uveitis, although in a few such disorders (e.g., sarcoidosis, Behçet syndrome, syphilis, tuberculosis), the inflammation can be either anterior or posterior. Because of the close anatomic and functional relationships of the vitreous, retina, and choroid, pinpointing the principal site of involvement, especially
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