Eye, Ear, Nose, and Throat Diseases

Corneal Pathology and Systemic Disease

A vast spectrum of conditions may be associated with corneal pathology ( Box 1-2 ). Associated inflammatory diseases include rheumatoid arthritis, Reiter's syndrome, Behçet's syndrome, and sarcoidosis. Connective tissue disorders such as ankylosing spondylosis, scleroderma, Sjögren's syndrome, and Wegener's granulomatosis have been associated with corneal disturbances. Associated metabolic diseases include cystinosis, disorders of carbohydrate metabolism, gout, hyperlipidemia, and Wilson's disease. Also, such conditions as Graves' hyperthyroid disease, leprosy, chronic renal failure, and tuberculosis may have associated corneal disease. Even skin diseases such as erythema multiforme and pemphigus have corneal manifestations (see Chapter 10 ). Finally, mandibulo-oculofacial dyscephaly (Hallermann-Streiff syndrome) is of interest to anesthesiologists because of anticipated difficulty with intubation.

Lens Pathology and Systemic Disease

A cataract is defined as a clouding of the normally clear crystalline lens of the eye. The different types of cataracts include nuclear-sclerotic, cortical, posterior subcapsular, and mixed. Each type has its own location in the lens and risk factors for development, with nuclear-sclerotic cataracts being the most common type of age-related cataract. The leading cause of blindness worldwide, cataracts affect more than 6 million individuals annually. Indeed, cataract surgery is the most frequently performed surgical procedure in the United States, with more than 1.5 million operations annually. More than half the population older than 65 develop age-related cataracts with associated visual disability. Despite extensive research into the pathogenesis and pharmacologic prevention of cataracts, however, there are no proven means to prevent age-related cataracts.

Although age-related cataracts are most frequently encountered, cataracts may be associated with dermatologic diseases such as incontinentia pigmenti, exogenous substances, genetic diseases, hematologic diseases, infections, and metabolic perturbations ( Box 1-3 ).

Exogenous substances that can trigger cataracts include corticosteroids, phenothiazines, naphthalene, ergot, parachlorobenzene, and alcohol. Metabolic conditions associated with cataracts include diabetes mellitus, Fabry's disease, galactosemia, hepatolenticular degeneration (Wilson's disease), hypoparathyroidism, hypothyroidism, phenylketonuria, Refsum's disease, and xanthomatosis. Another metabolic disorder important in the differential diagnosis of congenital cataracts is Lowe's (oculocerebrorenal) syndrome. In this X-linked disorder, cataract is frequently the presenting sign, with other abnormalities appearing later. These anomalies include mental and growth retardation, hypotonia, renal acidosis, aminoaciduria, proteinuria, and renal rickets, requiring calcium and vitamin D therapy. Other concomitants include osteoporosis and a distinctive facies (long with frontal bossing). Although lens changes may also be seen in heterozygous female children, affected male children usually have obvious, dense, bilateral cataracts at birth. They may also be afflicted with associated glaucoma. Interestingly, carrier females in their second decade of life have significantly higher numbers of lens opacities than age-related controls; however, absence of opacities is no guarantee that an individual is not a carrier. Anesthetic management includes careful attention to acid-base balance and to serum levels of calcium and electrolytes. Renal involvement of oculocerebrorenal syndrome of Lowe comprises tubular dysfunction characterized by proteinuria and generalized aminoaciduria progressing to the renal Fanconi's syndrome. Bicarbonate wasting and hyperkaluria result from a proximal tubule transport defect, with later glomerular disease. The administration of drugs excreted by the kidney should be observed carefully and nephrotoxins avoided. The patient with osteoporosis should be positioned on the operating table gently and carefully.

Infectious causes of cataracts include herpesvirus, influenza, mumps, polio, rubella, toxoplasmosis, vaccinia, and varicella-zoster virus. Chromosomal anomalies associated with cataracts include trisomy 13 (Patau's syndrome), trisomy 18 (Edward's syndrome), and trisomy 21 (Down syndrome). In Patau's and Edward's syndromes, congenital cataracts frequently occur in conjunction with other ocular anomalies, such as coloboma and microphthalmia. Cataracts have also been reported with Turner's syndrome (XO).

An additional type of lens abnormality that can be associated with major systemic disease is ectopia lentis ( Fig. 1-1 and Box 1-4 ). Displacement of the lens can be classified topographically as subluxation or luxation. Luxation denotes a lens that is dislocated either posteriorly into the vitreous cavity or, less often, anteriorly into the anterior chamber. In subluxation, some zonular attachments remain, and the lens stays in its plane posterior to the iris, but tilted. The most common cause of lens displacement is trauma, although ectopia lentis may also result from other ocular disease, such as intraocular tumor, congenital glaucoma, uveitis, aniridia, syphilis, or high myopia. Inherited defects and serious systemic diseases, such as Marfan's syndrome, homocystinuria, Weill-Marchesani syndrome, hyperlysinemia, and sulfite oxidase deficiency, are also associated with ectopia lentis. Indeed, lens displacement occurs in approximately 80% of patients with Marfan's syndrome (see later discussion).

Glaucoma and Systemic Disease

Glaucoma is a condition characterized by elevated intraocular pressure (IOP), resulting in impairment of capillary blood flow to the optic nerve and eventual loss of optic nerve tissue and function. Two different anatomic types of glaucoma exist: open-angle (or chronic simple) glaucoma and closed-angle (or acute) glaucoma. (Other variations of these processes occur but are not especially germane to anesthetic management. Glaucoma is actually many diseases, not one.)

With open-angle glaucoma, the elevated IOP exists in conjunction with an anatomically patent anterior chamber angle. Sclerosis of trabecular tissue is thought to produce impaired aqueous filtration and drainage. Treatment consists of medication to produce miosis and trabecular stretching. Common eyedrops include epinephrine, echothiophate iodide, timolol, dipivefrin, and betaxolol. Carbonic anhydrase inhibitors such as acetazolamide can also be administered by various routes to reduce IOP by interfering with the production of aqueous humor. All these drugs are systemically absorbed and thus can have anticipated side effects.

It is important to appreciate that maintenance of IOP is determined primarily by the rate of aqueous formation and the rate of aqueous outflow. The most important influence on formation of aqueous humor is the difference in osmotic pressure between aqueous and plasma, as illustrated by the following equation:

where K = coefficient of outflow, OPaq = osmotic pressure of aqueous humor, OPpl = osmotic pressure of plasma, and CP = capillary pressure. Because a small change in solute concentration of plasma can dramatically affect the formation of aqueous humor and thus IOP, hypertonic solutions such as mannitol are administered to reduce IOP.

Fluctuations in aqueous outflow can also greatly change IOP. The primary factor controlling aqueous humor outflow is the diameter of Fontana's spaces, as illustrated by the following equation:

where A = volume of aqueous outflow per unit of time, r = radius of Fontana's spaces, Piop = IOP, Pv = venous pressure, η = viscosity, and L = length of Fontana's spaces. When the pupil dilates, Fontana's spaces narrow, resistance to outflow is increased, and IOP rises. Because mydriasis is undesirable in both closed-angle and open-angle glaucoma, miotics such as pilocarpine are applied to the conjunctiva in patients with glaucoma.

The previous equation describing the volume of aqueous outflow per unit of time clearly underscores that outflow is exquisitely sensitive to fluctuations in venous pressure. Because an elevation in venous pressure results in an increased volume of ocular blood as well as decreased aqueous outflow, IOP increases considerably with any maneuver that increases venous pressure. Therefore, in addition to preoperative instillation of miotics, other anesthetic objectives for the patient with glaucoma include perioperative avoidance of venous congestion and of overhydration. Furthermore, hypotensive episodes should be avoided because these patients are purportedly vulnerable to retinal vascular thrombosis.

Although glaucoma usually occurs as an isolated disease, it may also be associated with such conditions as Sturge-Weber syndrome and von Recklinghausen's disease (neurofibromatosis) ( Box 1-5 ). Ocular trauma, corticosteroid therapy, sarcoidosis, some forms of arthritis with uveitis, and pseudoexfoliation syndrome can also be associated with secondary glaucoma.