Ординатура / Офтальмология / Английские материалы / Clinical Ocular Pharmacology 5th edition_Bartlett, Jaanus_2008

408 CHAPTER 23 Diseases of the Eyelids

twitching sensation, often with no observable eyelid signs.The condition tends to be unilateral and affects the lower lid most often.

Etiology

The etiology remains unknown; however, various psychosocial factors may play a role: fatigue, stress, tension, anxiety, lack of sleep, smoking, and alcohol or caffeine consumption. In the past topical instillation of anticholinesterase agents or the use of oral fluphenazine and haloperidol has been reported to cause isolated lid myokymia; no firm data exist to confirm these claims. Isolated lid myokymia has not been related to any serious underlying neurologic conditions; however, in at least one reported case there were abnormal electrophysiologic results suggesting perhaps an underlying stable neurologic disease.

Eyelid myokymia does not progress to other parts of the face. When myokymia involves the other facial muscles, it is a sign of an underlying neurologic problem that needs further evaluation and referral.

Diagnosis

The diagnosis of isolated eyelid myokymia can usually be made after the case history. Affected patients often complain that the eyelid “jumps” or “quivers”; however, gross external examination and slit-lamp assessment may fail to uncover any abnormality. Neuroimaging studies are generally not warranted in the absence of any other clinical signs, symptoms, or neurologic findings unless the condition persists for months to years.

Management

Most cases of isolated eyelid myokymia can be managed conservatively with patient reassurance, rest, and elimination or reduction of alcohol, cigarette, and caffeine use. Most cases of eyelid myokymia spontaneously resolve in a few days to weeks, with an occasional case lasting many months. When eyelid fasciculations are isolated and severe or chronic (>3 months duration), further intervention may be necessary. Topically administered antihistamines, such as antazoline or pheniramine, are often effective and may give significant relief within 15 to 20 minutes. Antihistaminic therapy relaxes the spasming orbicularis muscle by prolonging its refractory time.The topical medication should be used every 4 hours as needed to abolish symptoms. If this is ineffective, 12.5 to 25.0 mg of promethazine can be administered orally one to three times daily, or 25 to 75 mg of tripelennamine can be administered orally four times daily. For recalcitrant cases oral quinine, 200 to 300 mg, may be administered one to two times daily either alone or in combination with oral antihistamine therapy. Quinine relaxes the orbicularis muscle by a curari-like action, but it must be avoided in pregnant women. Quinine should be discontinued if the

patient experiences tinnitus or visual disturbances.When these measures do not relieve the symptoms, a botulinum toxin injection into the affected muscle may be used or, for very severe cases, a referral for a surgical myectomy is warranted.

CYANOACRYLATE TARSORRHAPHY

Cyanoacrylate adhesives (Krazy glue, Super glue) are common household products.They are packaged similar to topical ocular preparations and therefore have accidentally been instilled into the eye.Although these adhesives typically do not cause serious harm, they can and are the cause of significant anxiety when accidents occur.

Etiology

Once the glue is instilled into the eye, it causes an instantaneous tarsorrhaphy, total or partial, due to the apposition of the upper and lower eyelashes or, less commonly, a total ankyloblepharon. Corneal abrasion, SPK, eyelash loss, skin excoriation, and conjunctivitis can also occur, and immediate irrigation is indicated if possible.

Management

Initial conservative management includes the application of wateror mineral oil–soaked eye pads to the lids and/or the copious application of a broad-spectrum antibiotic ointment over the area along with a light pressure dressing. Within 24 hours the glue should soften enough to be easily removed with forceps. Careful application of acetone to the lid margins, using a cotton-tipped swab, may also prove useful in breaking the tarsorrhaphy; care must be taken not to use this preparation if a penetrating injury is suspected. Other means of manual separation of the lids include forceps, a Jameson muscle hook, or scissors. Any retained glue fragments must be removed from the eye to prevent further complications such as infection, inflammation, keratitis, or cataracts. In the event the patient is uncooperative, sedation may be required. Oral analgesics may be helpful and patient education and reassurance is always warranted. Continued topical antibiotics may be necessary to treat corneal abrasions or keratitis. In the event the corneal abrasion is large, bandage contact lenses may also be indicated.The use of topical steroids is contraindicated, because fungal and viral contamination cannot be excluded and because they can mask the symptoms of infection.

SURGICAL TREATMENT OF THE LIDS

Neuroanatomy of the Eyelids

To perform a surgical procedure on or around the eyelids, it is most often necessary to give an injection of local anesthetic to ensure the patient’s comfort during the procedure and to lessen the likelihood of surgical

bleeding and/or weeping. Keep in mind that the entire upper eyelid is innervated from above (the lacrimal nerve in the outer canthus, the supraorbital nerve centrally, and the supratrochlear and infratrochlear nerves in the inner canthal area), whereas the entire lower eyelid is innervated from below (infraorbital nerve for the entire lower eyelid). Hence, to ensure local anesthesia of the area of a lesion on the eyelid, the injection site is proximal to the origin of the nerve (inject between the nerve origin and the lesion). Therefore if the lesion is on the upper eyelid the injection of anesthetic is placed superior to the lesion, and if the lesion is on the lower eyelid the injection is placed inferior to the lesion.

Rhytids (Eyelid and Facial Wrinkles

and Folds)

It is extremely important to respect the natural folds and wrinkles of the face and eyelids when making an incision in the surrounding tissue so as not to create an undesirable healing outcome. When making an incision through the skin, always make the incision parallel to, or within, the rhytid (fold) of the skin.When this is done correctly,the incision will close in upon itself at the conclusion of the procedure and no closure (suturing) will be necessary. A small butterfly bandage or Steri-Strip may be all that is needed for the closure of surgical wounds that require it. Also, if a thin lineate scar results from the incision, it will be hidden in the rhytid and will not be perceivable. Study the area of the lesion and first determine the orientation of the incision before starting the procedure. If an incision is made contrary to the folds of the skin, the surgical wound probably will require suturing at the completion of the procedure, and the healing will result in an undesirable bunching of tissue.

Procedures

There are a number of surgical techniques and procedures used to treat eyelid and periocular lesions and anomalies. These techniques include chemical and thermal cautery, used to destroy tissue; incision, used to cut into and/or separate tissue; and excision, used to remove tissue.

Chemical Cautery

Chemical cautery uses dichloroacetic acid to treat verrucae, xanthelasma, dermatosa papulosa nigra, keratoacanthoma, and solar keratosis. The area of the lesion is swabbed with alcohol and a thin layer of petrolatum jelly is spread in the area surrounding the lesion to protect the adjacent normal skin.The cauterant (dichloroacetic acid) is then judiciously and carefully applied to the lesion in small amounts with a sharpened wooden applicator. The patient is forewarned regarding a stinging sensation that will seem to escalate, then level off, and finally subside. During and immediately after the application of the cauterant, the lesion turns a milky white. After a few

hours the lesion darkens to a blackish coloration. In a day or 2 an eschar (scab) forms. On small lesions the eschar falls off in 7 to 10 days. Larger lesions may require a second application of cauterant 2 weeks after the initial application. When the eschar eventually falls off, the underlying skin is pinkish or lighter than the surrounding normal skin. With time this skin area assumes normal skin coloration as melanin migrates to the area. Care should be taken with darkly pigmented individuals, especially AfricanAmericans, who may have a tendency to form keloids. A keloid is formed when healing is achieved by secondary intention and results in excessive scar formation. Simply questioning the patient about previous trauma to the skin will determine if the individual is a keloid former. Alternatively, a single small lesion in an inconspicuous area can be treated and followed for untoward effects. If the healing results are desirable, then other lesions can be safely treated.

Thermal Cautery

Thermal cautery uses heat to destroy tissue. A similar technique, called fulguration, uses electric current to destroy tissue. Heat cautery is performed using a disposable heat cautery unit and is used to stop bleeding during surgical procedures and to remove skin tags, cutaneous horns, and pedunculated verrucae. It can also be used to occlude a punctum, reposition an ectopic punctum with resultant epiphora, and alleviate trichiasis as a result of spastic entropion.

To remove a pedunculated lesion, swab the area with alcohol, anesthetize the area of the lesion with a 14⁄ to 12⁄ cc shallow subcutaneous injection of 2% lidocaine with epinephrine, and grasp the tip of the lesion with a mousetooth forceps. Pull the lesion away from the skin and sever the base of the lesion with the hot tip of the cautery unit.The tip removes the lesion and cauterizes the blood vessels at the same time. An eschar forms and falls off in 7 to 10 days.

To occlude a punctum with heat cautery, a 14⁄ to 12⁄ cc subconjunctival injection of 2% lidocaine with epinephrine is given below the punctum and the vertical arm of the canaliculus in the everted lid. After the patient compresses the in situ lid to compress the bullous of lidocaine, the punctum is dilated. The lid is then put on stretch by pulling on the lid at the outer canthus. This stabilizes the lid and makes it easier to insert the tip of the heat cautery unit. Before the tip is inserted, the unit is turned on to sanitize and clean the tip. The unit is then turned off and allowed to cool before inserting it into the punctum. It is inserted cold then turned on when it is in the punctum. A blanching of the tissue surrounding the punctum is noted. The tip is removed with the unit still turned on. It will be retrieved easily, and a darkened charred area of the punctum is noted in the center of the blanched area. Prophylactic antibiotic ointment is applied four times a day for 3 days.

Warning: If one tries to remove the cautery tip from the punctum after the area is cauterized and the unit is

410 CHAPTER 23 Diseases of the Eyelids

turned off the tissue will adhere to the tip and a tug of war will ensue. Always remove the tip before the unit is turned off.

To treat an ectopic punctum of the lower lid with secondary epiphora, first evert the lower lid at the inner canthus and subconjunctivally inject 14⁄ to 12⁄ cc of 2% lidocaine with epinephrine below the punctum and vertical arm of the canaliculus. Have the patient compress the in situ lower lid with a folded 2 2 gauze sponge for 5 minutes.This flattens the bullous of lidocaine and anesthetizes the area. The lower lid is again everted and, respecting the anatomy of the nasolacrimal drainage system, a double row of three to four cautery burns is placed horizontally 4 mm below the punctum. The spot of each cautery burn blanches out around a central blackened charred area.The destruction of conjunctival tissue causes fibrosis that shrinks and pulls the tissue tight,repositioning the punctum in the lacrimal lake.Antibiotic ointment applied four times a day for 3 days is ordered as a prophylactic measure. This technique works nicely for ectopic puncta but will not correct a frank ectropion.

To correct spastic entropion of the lower lid, one or several shallow subcutaneous injections are given the entire length of the lower lid in the fold at the border of the anatomically inferior tarsal plate. The patient compresses the bullous of lidocaine to expose the area to be cauterized.A drop of 12⁄ % proparacaine is inserted onto the eye and a Jaeger plate (Figure 23-35) is inserted between the globe and the lower lid. The Jaeger plate protects the globe and, when pulled toward the clinician, pulls the lid tight and stabilizes it for the procedure.The clinician now proceeds to place a line of cautery burns at the junction of the tarsal orbicularis oculi muscle and the preseptal orbicularis oculi muscle the entire length of the

Figure 23-35 Plastic and metal Jaeger plates.

lower lid. With the cautery tip turned on each cautery burn pierces the skin, the orbicularis oculi muscle, and into the tarsal plate. The burns destroy tissue and cause fibrosis, which pulls the tissue tight and away from the globe, preventing the lower lid folding back onto the globe.The resulting wounds form an elongated eschar that will fall off in a week or two.The area is prophylactically treated with antibiotic ointment four times a day for 3 days.

Incisional Surgical Procedures

Stab Incision. A stab incision is done with a no. 11 disposable scalpel. It is performed to provide an outlet for pus such as with an external hordeolum or an acute dacryocystitis. Pus, under pressure, needs to be released. The area is first cleansed with an alcohol swab or Betadine. A subcutaneous injection of lidocaine may not be beneficial as the injection itself is painful because the space-occupying bolus of anesthetic creates pressure in an already tender area.Also, the pH of the infection site is acidic,which neutralizes the alkaline anesthetic,rendering it less effective. A quick stab of the abscess causes the contents to spill out. Once this occurs the tenderness of the area is immediately relieved as the pressure within the abscess is eliminated.The wound area can be treated with topical antibiotic ointment four times a day for 3 days. In the case of an acute dacryocystitis, the patient ideally should be taking oral antibiotics for several days before the procedure.Topical and oral antibiotics are also prescribed after the procedure. Draining an acute dacryocystitis is necessary to relieve the often severe pain and to prevent a fistula formation in which the body creates its own passageway to drain the pus. Once the stab incision is made through the overlying skin and into the nasolacrimal sac, pressure is created over the sac with cottontipped applicators to express the pus through the wound of the stab incision. Copious amounts of pus are usually evacuated from the infected area, and this material should be cultured and sent for identification and sensitivity.

Lineate Incision. A lineate incision starts with a stab incision with a no. 11 disposable scalpel and is continued until the desired incision length is achieved.The incision through the skin should always be in or parallel to the rhytids (folds) of the skin.A single lineate incision parallel to the lid margin through the skin and into the tarsal plate is used when an anteriorly pointing chalazion is to be treated by incision and curettage. The lineate incision is also the basis for the removal of hydrocystomas (sudoriferous cysts, cyst of an eccrine sweat gland) when combined with snip excisions. The combination of the two techniques is referred to as an exenteration procedure (Figure 23-36). A lineate incision is also used to cut through the skin immediately overlying a cyst to be excised (such as a subcutaneous sebaceous cyst). The technique of excising a subcutaneous cyst by creating an incision into but without removing skin is known as a marsupialization technique. A double lineate incision,

made at right angles to and crossing each other, is known as a cruxiate (cross) incision.A cruxiate incision is made through a posteriorly pointing chalazion on the conjunctival side of the lid. The incisions are made through the conjunctiva and into the tarsal plate. One incision is parallel to the lid margin and the other crosses the first perpendicular to the lid margin. Once the two lineate incisions are made, the corners of the cuts unfurl like the opening of the petals of a flower bud. After curettage, these four corners are then removed with snip excisions.

Incision and Curettage. This procedure is used to treat anterior pointing chalazia (the chalazion is pushing out or has erupted through the tarsal plate on the skin side of the lid). Usually, two lidocaine injections are given before this procedure is done.The first is a ring block technique injection proximal to the origin of the enervating nerve. Therefore if the chalazion is on the upper lid the first injection of 12⁄ to 1 cc of 2% lidocaine with epinephrine is given subcutaneously superior and around the sides of the chalazion.Then, a second deep peribulbar injection is given above the chalazion site. The patient compresses the injection site for 5 to 10 minutes.When the clinician is ready to proceed, the area to be operated on is tested for sensitivity by pricking the area with a sharp object (e.g., the end of the needle used to inject the lidocaine). Be sure to also test an area of the eyelid and face that is not anesthetized so the patient can differentiate between a sensitive (unanesthetized) area with a nonsensitive (anesthetized) area.When the clinician is convinced that

the area in question is numb, a drop of 12⁄ % proparacaine is introduced onto the globe,and a chalazion clamp of the appropriate size is placed with the slightly concave flat solid jaw of the clamp between the globe and the posterior surface of the eyelid. The ring side of the clamp is positioned centrally over the lump on the skin side of the eyelid so that the chalazion is centered in the ring. The clamp is tightened significantly on the lid and a 3- to 4-mm lineate incision is made parallel to the lid margin through the skin, into the orbicularis oculi muscle, and into the tarsal plate in the area of the chalazion.The incision through the orbicularis oculi merely separates the fibers and does not sever them, ensuring no functional impairment after the procedure. Pressure on either side of the incision with a cotton-tipped applicator causes the typical grayish gelatinous inflammatory material of a chalazion to ooze out of the wound. Vigorous curettage with a curette follows, making sure that all recesses of the chalazion capsule are probed. After each curettage, the scoop of the curette is wiped clean with a gauze sponge and curettage is repeated until no more material is extracted. The tip of a sterile cotton-tipped applicator is introduced into the wound to remove any tenacious material.Finally,the wound is irrigated with sterile saline to rinse out any loose material.After drying the eyelid of excessive saline, the clamp is loosened but not removed. A drop of blood will appear in the wound at which point the clamp is retightened.After several minutes the blood droplet coagulates and the clamp can be removed. An alternative method is to simply remove the clamp at the end of the

412 CHAPTER 23 Diseases of the Eyelids

procedure and have the patient compress the area with his or her hand using a folded 4 4 gauze pad or an eye pad.

The eyelids are very vascular and are very forgiving, and secondary infection after an eyelid procedure is rare. However, an application of antibiotic ointment is gently applied to the area and is prescribed four times a day for 3 days. It is important to inform the patient that the eyelid is going to look worse immediately after the procedure than it did before the procedure. The trauma created by the injections, the clamp tightening, and the incision and curettage make the lid appear swollen. By the next day the lid will be markedly improved in appearance. There should be total resolution of the lesion within 2 to 3 weeks with no evidence of the procedure. Pain after the procedure and after the anesthetic wears off is virtually nonexistent. If there is discomfort, ibuprofen is prescribed for pain control.

Excision

Excision is the removal of tissue utilizing a number of different techniques. A snip excision using a pair of Wescott surgical scissors can be used to remove or excise any pedunculated lesions such as skin tags or stalked verrucae.A shave excision, using a no. 15 scalpel, is used to remove a lesion or a section of a lesion. It is often used to take a tissue sample for a biopsy.

Excision and Curettage

For posterior pointing chalazia (on the conjunctival side) a somewhat different approach is needed. The lid is everted and a 14⁄ to 12⁄ cc subconjunctival injection of lidocaine is given proximal to the enervating nerve origin. The lid is returned to its normal position and a deep peribulbar injection is given below the chalazion. The patient applies pressure with a folded gauze sponge over the closed eye after which the conjunctival area of the chalazion is probed to determine sensitivity. Once the area is anesthetized a chalazion clamp is applied, with the ring of the clamp centering the chalazion on the conjunctival side of the lid. Once the clamp is tightened and the eyelid everted, a lineate incision is made through the chalazion perpendicular to the lid margin. If any inflammatory material oozes out, the chalazion capsule should be curetted. A second lineate incision is made parallel to the lid margin bisecting the first incision. When both incisions are made, the four edges of the incised tissue will bulge up. After curetting the chalazion capsule each of these flaps needs to be excised by grasping the tip of the flap with a mouse-toothed forceps and the base of the flap is cut with Wescott scissors.When all four flaps are removed, a divot remains. Again, the clamp is loosened, a drop of blood is permitted to enter the wound, and then the clamp is retightened. After the blood droplet coagulates, the clamp is removed and antibiotic ointment is prescribed four times a day for 3 days. If needed, ibruprofen is used for pain control. The wound will fill in by secondary intention and will appear milky white as

fibrosis results. The wound will be fully healed in 2 to 3 weeks.

Patient Management

Many patients present to eye care practitioners with any number of eyelid and/or periocular lesions. Most of these lesions are benign and are of no consequence except for their unsightly appearance. A large, long-standing, centrally located chalazion of the upper lid can induce mechanical with-the-rule astigmatism. Its removal can be considered a therapeutic intervention because it eliminates the induced astigmatism. Similarly, a viral lesion on the lid margin or close to the globe, such as a verruca or molluscum contagiosum, can create eye symptoms of irritation, epiphora, and/or burning. Removal of the offending lesion relieves the symptoms and can also be considered a therapeutic intervention. However, for the most part, the only reason to remove many lesions of the eyelid and periocular area is for cosmetic considerations. Even after informing the patient that a lesion is benign and is of no cause for concern, she or he may still want to have it removed. These patients are extremely grateful and appreciative of a successful outcome. In fact, often these patients have consulted their family practitioner about these lesions and are told not to worry about them because they pose no threat to the health or well-being of the patient. However, the patient is still conscious of and often embarrassed by the appearance of these lesions. Many of these lesions are a result of aging skin and are unavoidable in the susceptible individual. As the general population continues to gray, more and more aging patients will present with these lesions.

If a patient is interested in treatment of an eyelid lesion, it is very important to first explain to the patient what the lesion is and then to explain in lay terms exactly what procedure will be performed to treat or remove the lesion. Once the patient understands the procedure and the sensations experienced during the procedure, what course the healing process will take,and what the desired outcome is as well as any possible untoward side effects, let the patient make his or her own decision as to whether to have the procedure done. If the patient decides to have it done, have him or her sign an informed consent form which explains all of the above in lay terms. It is also important to have a witness to the patient’s agreement to the procedure, and the witness’s signature should also appear on the informed consent form.

Before starting any procedure needing local anesthesia, ask the patient if he or she has any allergies to anesthetics.Also inquire if the patient is on any anticoagulant medications (e.g., aspirin, Coumadin, and heparin) that could create bleeding problems.

During the procedure the clinician should keep a constant ongoing communication with the patient. Occasionally ask the patient if he or she is alright.Above all, speak in a calm, confident, and reassuring manner.

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Diseases and disorders involving the lacrimal system are among the more common conditions experienced by ophthalmic patients, with as many as 25% complaining of dry eye symptoms alone.The lacrimal system is most easily considered as having three components—the secretory system, the distribution system, and the excretory or drainage system.These components must work in harmony to support a healthy, moist, and comfortable ocular surface.

Although the components are anatomically separate, if a disruption in any subcomponent of the lacrimal system occurs, patients report strikingly similar symptoms. For example, tearing is a common complaint and can be caused by disorders within the secretory, distribution, or excretory system.An increase in tear secretion as a result of ocular surface irritation (pseudoepiphora), poor lid apposition interfering with the distribution system, and obstruction of the lacrimal excretory system (true epiphora) may all cause tearing. Other common lacrimal system-based symptoms include general irritation, discomfort, burning, foreign body sensation, redness, or dryness. To further complicate matters, some complaints reported by patients with lacrimal disease can mimic symptoms associated with infectious and inflammatory diseases not directly involving the lacrimal system. As an example, a red irritated eye with mucopurulent discharge may initially appear as a bacterial conjunctival infection but may in fact be an infection associated with a blockage within the lacrimal drainage system.

A healthy lacrimal system is necessary for ocular comfort, resistance to disease and exposure, corneal oxygenation, and optimal visual function.A careful patient history and examination is necessary to arrive at an accurate diagnosis, which directs appropriate management.

CLINICAL ANATOMY AND PHYSIOLOGY OF THE LACRIMAL SYSTEM

Secretory System

Recently, clinicians have begun to better appreciate the importance of the interrelationship among the various

components within the lacrimal secretory and distribution systems. The concept of a lacrimal “functional unit,” comprising the lacrimal gland, the ocular surface, and the sensory/autonomic neural reflex loop that is the communication network between the ocular surface and the lacrimal gland, provides a useful model to examine the etiology of dry eye disease (Figure 24-1).

The lacrimal gland is approximately the size and shape of a shelled almond and consists of main and accessory portions separated by the aponeurosis of the levator muscle into the orbital and palpebral portions. The lacrimal gland is primarily responsible for reflex secretion, which is caused by irritation of the trigeminal nerve endings in the cornea, conjunctiva, and proximal structures or by bright light stimulation of the retina. Emotional impulses from the frontal cortex, basal ganglion, thalamus, and hypothalamus also contribute to reflex secretion. Primary neuronal control of the lacrimal gland is through parasympathetic nerve fibers traveling in the seventh cranial nerve. Androgens (male hormones) have been shown to help regulate the normal functioning of the lacrimal gland. Disease or inflammation of the lacrimal gland has an adverse effect on its output, thereby reducing the secretion to the ocular surface. As tear secretion decreases, ocular surface sensitivity also decreases, providing an impaired feedback loop from the ocular surface to the lacrimal gland.

The ocular surface, including the cornea, conjunctiva, accessory lacrimal glands, and meibomian glands, is the second critical component of the functional unit. Irritation of the cornea or conjunctiva, whether from infection, contact lens overwear, allergic reaction, mechanical or environmental irritation, or from dry eye itself, causes trigeminal stimulation and abnormal neural feedback to the lacrimal gland.This in turn causes a modification of lacrimal gland output. The accessory lacrimal glands of Krause (embedded in the conjunctival fornices) and Wolfring (located along the upper border of the tarsal plate) are thought to be the main contributors to the aqueous component of the tear film under normal conditions. The meibomian glands, within the tarsal plates,

secrete an oily substance that helps limit evaporative loss of the aqueous component of the tear film. Although the mechanism is not completely understood, androgens likely play a role in the maintenance of the structure and function of these glands, with a reduction in androgens having a deleterious effect on the functional unit.

Disruption in either the lacrimal gland or any part of the ocular surface results in abnormal neural activity. This disruption initiates and perpetuates an inflammatorybased cyclic feedback loop including reduced lacrimal output, reduced sensitivity at the ocular surface, further ocular surface inflammation, and a reduced ability of the ocular surface to respond to environmental challenges. This inflammatory loop results in chronic neurosensory fatigue and is the currently accepted model for most dry eye syndrome diagnoses.

The tear film is a dynamic fluid layer with lipid, aqueous, and mucin components that interact with each other

and with the ocular surface.The bulk of the tear film layer is aqueous, secreted by the glands of Wolfring and Krause. Historically, the tear film has been described as a trilayered structure, with mucin at the ocular surface, aqueous in the “middle,” and a lipid layer superficially. It may be more accurate to conceptualize these three layers as being somewhat integrated, in that the tear film’s “resting state” assumes the configuration of a bilayer (Figure 24-2). According to this model, there is a lipid layer superficially and a mucin–aqueous layer comprising the rest of the tear film. Regardless of whether the three components are fully stratified or somewhat “blended,” the origins and functions of the various components are well established. The lipid layer serves to thicken, stabilize, and prevent premature evaporation of the aqueous component of the tears and is the product of secretions of the meibomian glands with additional contributions from the glands of Zeis (sebaceous) and Moll (apocrine), both of which are

TEAR FILM STRUCTURE

Lipid(oily) layer

Aqueouswithsolublemucins

Membraneadherent mucins

Corneal surface cells

Figure 24-2 The tear film layer. (From http://www. systane. com/consumer/What_are_Tears.asp; Copyright 2006,Alcon, Inc.)

located at the eyelid margin in close proximity to the cilia follicles. A layer of mucin, made up of large highly glycosylated glycoproteins, serves to make the normally hydrophobic ocular surface more favorable for the aque- ous-based tears to inhabit. The mucin layer is secreted primarily by the goblet cells within the conjunctiva. Soluble mucin is secreted by the lacrimal gland epithelial cells and is thought to be mixed within the aqueous layer. These mucins in the tear film are more active than previously thought; inadequate mucins may significantly contribute to ocular surface disease (Figure 24-3).

Tears also contain a number of proteins, enzymes, metabolites, and electrolytes (Table 24-1). These components,although present in very small quantities,serve critical functions,including maintaining tear film structural integrity, contributing to immunoprotection, providing trace nutrients to the ocular surface, maintaining tear osmolarity, and maintaining the pH level of tears at approximately 7.45.

Distribution System

The lacrimal distribution system incorporates the opening and closing of the eyelids and the fluid dynamics of

the tear film. Eyelid closure is under the muscular control of the orbicularis oculi muscle, which is innervated by cranial nerve VII. Eyelid opening is achieved through contraction of the levator palpebrae superioris muscle, innervated by cranial nerve III, with secondary elevation activity provided by Müller’s muscle, which receives sympathetic innervation.

Under normal conditions the various components of the tear film are continually produced in sufficient quantity, not only to cover the ocular surface but also to supply a reservoir of tears that is stored at the margin of the upper and lower eyelids. The movement of the upper eyelid distributes this reservoir, called the tear river or tear meniscus, during blinking or voluntary lid closure. As the tear film thins and “breaks up,” the blink reflex is stimulated. The down-phase of each blink compresses the superficial lipid layer, and the up-phase redistributes the lipid layer, which remains in a fairly dynamic state well after the completion of the blink. Each time the eyelid reopens, a new tear film layer is spread across the ocular surface. The blink itself may also augment meibomian gland expression.

Excretory System

The action of the blink also facilitates tear drainage (see Figure 24-1). The eyelids direct the lacrimal fluid along a channel formed by the globe and the plica semilunaris toward the inner canthi for drainage into the puncta.

The puncta are located on the posterior margins of the upper and lower eyelids, at the nasal end of the tarsus, approximately 6 mm from the nasal canthus. Each punctal opening measures 0.2 to 0.3 mm in diameter and is surrounded by a connective tissue ring. The four puncta point toward the globe, so that under normal conditions they are not directly visible without lid manipulation. Normally, when the eyelids are closed, the upper and lower puncta are directly opposed to one another.

Except for the punctum, the remainder of the lacrimal drainage system is hidden from direct observation. After tears enter the punctum, they flow through a 2-mm vertical segment of each canaliculus. The upper and lower canaliculi then turn toward the nose, run a horizontal course of approximately 8 mm, and join together as the common canaliculus at the entrance to the lacrimal sac. This structure is approximately 10 to 12 mm in vertical dimension, the top one-third of which balloons above the common canaliculus (Figures 24-4 and 24-5).The lacrimal sac is housed within the bony lacrimal fossa.

The lacrimal sac is normally collapsed when the eyelids are open. As the eyelids close, tears are squeezed into the sac, aided by the negative pressure within the sac (see Figure 24-5). A valve-like structure at the opening to the lacrimal sac helps to retain tears within the sac and prevent their backflow into the canaliculus. The nasolacrimal duct (NLD) is continuous with the lacrimal sac inferiorly. The NLD extends 15 to 20 mm caudally,

418 CHAPTER 24 Diseases of the Lacrimal System

Excretory duct

Glands of Krause

Conjunctiva

Wolfring’s glands

Crypts of Henle

Meibomian glands

Glands of Zeis

Cilia

Glands of Moll

Lacrimal gland

Glands of Manz

narrows, and finally opens into the inferior meatus, which is a space located under the inferior turbinate bone in the outer wall of the nasopharynx. Tears are then drained toward the back of the throat to be swallowed. Regurgitation of tears from the nasopharynx into the nasolacrimal system is prevented by the negative pressure within the drainage apparatus and by a membranous valve at the end of the NLD, termed the valve of Hasner.

Approximately 90% of the tears are drained in this manner, with the remainder being lost to evaporation.To facilitate normal drainage of tears, the entire nasolacrimal drainage system must be properly positioned and patent. Blockages anywhere along the way generally result in epiphora and may create an environment that is conducive to infection and inflammation.

DIAGNOSIS AND MANAGEMENT OF DISORDERS OF THE SECRETORY AND DISTRIBUTION SYSTEMS

History

As in most ocular conditions, a well-conducted patient interview assists greatly in the diagnosis of disorders of any subcomponent of the lacrimal system, even before any clinical tests are performed (Box 24-1). Social and demographic factors such as the patient’s gender, age, occupation, and environment may influence differential diagnostic considerations between secretory and excretory abnormalities. For example, infants who present with tearing are more likely to suffer from a drainage