THE PROTECTIVE SYSTEM OF THE EYE

Transcription

1 THE PROTECTIVE SYSTEM OF THE EYE Introduction The eye is offered the same type of protection as the brain being enclosed in a cavity in the skull called the bony orbit (figs1, 2). Fig 1: the bony orbit. Fig 2: the orbital walls. The orbit is a 4-walled cone (roof, floor, medial and lateral walls) opened to the front for the purpose of light entry. In the front protection is taken by the eyelids and the tear film vital for corneal transparency. The orbit communicates with the skull cavity via 2 ports

2 1. The optic canal which transmits the optic nerve out and the ophthalmic artery in. 2. The superior orbital fissure which transmits the 3 rd, 4 th and 6 th cranial nerves, the ophthalmic branch of 5 th nerve, the sympathetic nerves and the superior ophthalmic vein passing to the cavernous sinus (fig3). Fig 3: the superior orbital fissure and optic canal. The orbit is closely related to the paranasal sinuses with the medial wall thinly separated from the ethmoid sinuses, the floor from the maxillary sinus and the roof from the frontal sinus which makes inflammation of the sinuses; sinusitis, the commonest cause of orbital inflammation; orbital cellulitis (fig 4).

3 Fig 4: the relation of the paranasal sinuses to the orbit. Since the orbit is a closed bony space except anteriorly, the most common manifestation of orbital diseases is pushing of the globe forwards; proptosis (fig 5). Fig 5: Forward pushing of the eyes in orbital disease (proptosis). The anterior aspect of the globe is protected by the eyelids; 2 mobile musculocutaneous folds enforced by a strong fibrous sheet called the tarsus (fig 6).

4 Fig 6: A vertical section through the upper eyelid. The upper eyelid is the more mobile one and hence has a larger and stronger tarsus (28x10mm). The lid is opened by the levator palpebrae muscle supplied by the 3 rd cranial nerve and is closed by the orbicularis muscle supplied by the 7 th cranial nerve. The position of the upper eyelid on the globe is rather constant covering the upper 2 mm of the cornea. If the lid covers more of the cornea, the condition is called ptosis of the upper lid, if less it is called lid retraction and is an early manifestation of hyperthyroidism (fig 7).

5 Fig 7: Ptosis (above) and lid retraction (below) On the other hand failure of the eyelid to close, generally because of 7 th nerve palsy is called Lagophthalmos and could easily result in corneal ulceration. The main function of the eyelids is blinking; an act that distributes tears onto the surface of the cornea to keep it moist and transparent. Failure of blinking or deficiency of tears results in rapid deterioration of the optical clarity and function of the cornea; a condition known as dry eye. The third complementary protective mechanism is the tear film and it has 3 distinct components (fig 8): 1. The deep mucin layer; secreted by goblet cells of the conjunctiva (vitamin A is an essential vitamin for proper function). This is the innermost layer directly in contact with the corneal epithelium 2. The middle watery layer; secreted by the main and accessory (conjunctival) lacrimal glands. This forms the main bulk of the tear film and contains necessary nutrients and enzymes (e.g. Lysozyme) to keep the cornea healthy

6 3. The superficial lipid layer; secreted by the tarsal glands (Meibomian glands) mainly to reduce evaporation and prevent spill-over of water at the lid margin. Fig 8: components of the tear film Diseases of the Orbit As mentioned before the main clinical manifestation of orbital disease is forward pushing of the eye called proptosis In order to evaluate a patient with proptosis we need to: 1. Recognize proptosis: we recognize proptosis early by widening of the palpebral fissure and exposure of the sclera above and below the cornea. Now if we place a ruler over the normally eyelids it should just clear the corneal apex (fig 9). The direction of proptosis is important. Sometimes the eye is pushed to one side by an orbital mass which may help in the diagnosis of the type of the mass.

7 Fig 9: a ruler over the eyelids just clears corneal apex 2. Measure proptosis: we measure proptosis by the exophthalmometer, an instrument that measures the distance between the lateral orbital margin and the apex of the cornea (fig 10 A&B). This distance is normally 18-21mm. Fig 10 A&B: Hertel sexophthalmometer

8 3. Identify the cause of proptosis: proptosis has many causes but generally it is classified into inflammatory and non-inflammatory proptosis a. Inflammatory proptosis (fig 11): the 2 common causes are orbital cellulitis and idiopathic orbital inflammation (see red eye). Generally inflammatory proptosis is accompanied by lid edema, conjunctival edema and redness and pain, however pain may be absent in thyroid eye disease and rhabdomyosarcoma in children, which may simulate inflammation. Fig 11: Inflammatory proptosis b. Non-inflammatory proptosis: the most common causes are i. Thyroid eye disease: this is the most common cause of proptosis and will be discussed in some detail in the chapter Eye in systemic disease. ii. Orbital tumors: many benign and malignant tumors can arise in the orbit causing proptosis and pushing the eye to

9 the opposite direction. The more common orbital tumors are: 1. Benign tumors in children : capillary hemangioma and dermoid (fig 12). Fig 12: External angular dermoid. 2. Benign tumors in adults: cavernous hemangioma, neurofibroma. 3. Malignant tumors in children: Rhabdomyosarcoma (fig 13), leukemia. Fig 13: orbital Rhabdomyosarcoma. 4. Malignant tumors in adults: lymphoma, secondaries from breast. 4. Investigate proptosis: a. CT scan and MRI of the orbit are the main tools in investigation of orbital disease (fig 14)

10 Fig 14: CT (left) and MRI (right) of the orbit. b. If TED is suspected thyroid function tests and thyroid antibodies are done c. In case of tumors a surgical biopsy is taken for pathological diagnosis (fig15) Fig 15: biopsy from an embryonal rhabdomyosarcoma of the orbit. Orbital cellulitis: See Red Eye Thyroid Eye Disease (TED): see Eye and systemic disease.

11 Diseases of the Eyelids: When considering the structure (skin, muscle, blood vessels and tarsus) and function of the eyelids (protection, closure, distribution of tears), we can conclude that diseases of the eyelid fall into one of 3 categories 1. Inflammations: a. Acute: Hordeolum externum (stye) and internum (acute chalazion). b. Chronic: Blepharitis and chalazion 2. Malpositions: a. Ptosis. b. Entropion and ectropion. c. Lagophthalmos. 3. Tumors a. Benign: papilloma and nevus (fig 16). b. Malignant: basal cell carcinoma (BCC) (fig 17). Fig 16: upper lid papilloma.

12 Fig 17: BCC of lower lid. Acute Hordeolum Definition: acute inflammation of a hair follicle (externum or stye) or a Meibomian gland (internum or acute chalazion). Causes: the underlying causes are usually eye fatigue from lack of sleep or asthenopia or systemic diseases as diabetes. The direct cause is infection by pus-forming organism as staphylococci. Manifestations: acute inflammation with pain, redness, lid edema and swelling. The stye is near the lid margin, on the skin side and generally smaller, while the acute chalazion is larger, away from the margin and more to the inner (conjunctival) side of the lid (fig 18) Fig 18: Stye (left) pointing near lid margin and acute chalazion (right).

13 Treatment: oral and topical antibiotics and hot foments followed by correction of underlying cause especially in recurrent cases. Chalazion Definition: chronic inflammation of a Meibomian gland with enlargement of the gland/cyst formation. Cause: unknowblockage of the orifices of the meibomian glands some cases result from Blepharitis. Manifestations: there is a localized lid swelling with mild symptoms (fig 19). Treatment: incision and curettage from the conjunctival side. Fig 19: large chalazion. Blepharitis: Definition: chronic inflammation of the lid margin and the Meibomian gland orifices Causes: chronic infection by bacteria and change in composition of Meibomian secretions Types: squamous and ulcerative

14 1. Squamous Blepharitis: characterized by lid margin hyperemia, presence of scaly dandruff-like material between cilia, premature loss of lashes and changes in the character of Meibomian secretion (fig 20). Treatment is by lid hygiene. 2. Ulcerative Blepharitis: infection by Staphylococcus aureusr esulting in ulcers on lid margin with yellow crusts adherent between lashes (fig 21). Meibomian secretion is pus-like. Treatment is by antibiotic ointment and vigorous lid hygiene. Fig 20: squamous Blepharitis. Fig 21: ulcerative Blepharitis.

15 Ptosis Definition: drooping of the upper eyelid below its normal position which covers 2mm of the cornea. Causes: 1. Congenital ptosis is the most common cause and is due to dystrophy of the levator muscle 2. Paralytic ptosis occurs in cases of 3 rd nerve palsy (ptosis + exotropia +/- dilated pupil) 3. Neuromuscular ptosis is characteristically variable and occurs in myasthenia 4. Horner s syndrome: occurs due to sympathetic denervation and is characterized by mild ptosis, miosis and facial anhydrosis. Ptosis is due to paralysis of Muller s muscle, which helps elevate the lid. Miosis is due to paresis of the dilator pupillae muscle. Acute Horner syndrome in a patient with acute chest pain is diagnostic of aortic dissection. 5. Involutional (aponeurotic ptosis): occurs in old age but may occur with trauma or following cataract surgery due to weak or stretched levator aponeurosis. Examination: 1. Degree of ptosis: is judged by the lid margin-corneal reflex distance (MRD), normally 4-5mm 2. Levator action: is measured by the difference in the width of the palpebral fissure between extreme downgaze and upgaze, normally it is 12mm (fig 22)

16 Fig 22: Estimation of levator function. 3. Other extraocular muscles are examined to exclude 3 rd nerve palsy 4. Some clinical tests are useful in diagnosis of the cause a. Apraclonidine test for Horner syndrome: apraclonidine eye drops do not dilate the pupil except in Horner s syndrome. b. Tensilon test or Ice-pack test for myasthenia: ptosis improves in minutes. Management: ptosis, except in myasthenia and temporary causes as diabetic 3 rd nerve palsy or some mechanical ptosis (e.g. inflammatory) is generally treated surgically. If there is good levator action the treatment is by levator muscle resection. If the ptosis is severe and the levator action is poor, a frontalis suspension surgery is done (fig 23).

17 Fig 23: frontalis suspension by autologous fascia lata for severe congenital ptosis. Entropion and ectropion (fig 24) Definition: rolling of the lid margin either inwards (towards the eye; entropion) or outwards (away from the globe; ectropion) Fig 24: Entropion and ectropion Causes: most cases are involutional (age-related) or cicatricial. In involutional cases the underlying cause is horizontal laxity of lid tissues and ligaments with age and the direction of rolling is determined by whether the globe is sunken

18 (entropion happens) or bulging (ectropion happens) in the orbit. In cicatricial entropion there is conjunctival fibrosis as in trachoma (fig 24) or chemical injuries of the eye and in cicatricial ectropion there is fibrosis or shortening of the skin (fig 25) as in burns or following surgery (blepharoplasty). Treatment: Involutional causes are managed by horizontal tightening of the lid laxity surgically. Cicatricial cases are managed by replacing the shortened conjunctiva in entropion by a mucus membrane graft and in ectropion the shortened skin is replaced by a skin graft from behind the ear. Lagophthalmos Definition: incomplete closure of the palpebral fissure when blinking or during sleep. Causes: most cases are due to facial nerve palsy (VII) causing weakness of the orbicularis muscle. The commonest cause is idiopathic (Bell s palsy) but some cases result from parotid gland inflammation (Sarcoidosis) and tumors. Manifestations: as a result of incomplete blink and corneal exposure during sleep, corneal ulcer may occur. The ulcer tends to affect the lower cornea because the eyes usually roll-up during sleep (Bell s phenomenon). Treatment: wetting of the cornea is the main line of treatment. Artificial tears achieve this by day and ointment by night. In severe or

19 prolonged cases a lateral tarsorrhaphy is done until the nerve recovers (fig 26). Fig 26: right Lagophthalmos: note rolling-up of cornea (Bell s phenomenon). Lid Edema Swelling of the eyelids is rather common. Any inflammation not only of the lids as acute Hordeolum but also of the nearby face or scalp can cause lid edema by spread of fluid due to the loose subcutaneous structure of lid spaces. Non-inflammatory edema is commonly seen in systemic allergic reactions as atopy or anaphylaxis. Bilateral lid edema is also a common manifestation of generalized edema seen in renal disease and heart failure. Diseases of the Lacrimal System Tear components are secreted by various eye structures as previously mentioned. Any disturbance of tear secretion or component results in one form of DryEye; a term used to describe the

20 manifestations of ocular surface disease resulting from tear deficiency or abnormality. Excess tears carrying various wastes are also drained into the inferior meatus of the nose via the lacrimal excretory system consisting of (fig 27): 1. A small punctum on the upper and lower lid margins. 2. A short canaliculus which opens into a lacrimal sac under the medial palpebral ligament 3. A nasolacrimal duct that extends from the sac to the nose Fig 27: lacrimal drainage system Any obstruction in the lacrimal excretory system results in epiphora. The common causes of obstruction are: 1. Congenital nasolacrimal obstruction: discussed with eye diseases of infants 2. Acquired nasolacrimal obstruction which affects females in their 50 s and older (postmenopausal females). It results in chronic inflammation of the lacrimal sac (chronic

21 Dacryocystitis but could lead to acute exacerbations with abscess formation; acute Dacryocystitis. Generally any obstruction of the drainage system has to be managed surgically. The most common surgical procedures are: probing in infants and dacryocystorhinostomy (DCR) in adults. Epiphora Definition: it is the overflow of tears outside the lids due to failure of drainage (excess tearing is called lacrimation). Causes: any obstruction in the lacrimal drainage system e.g. 1) Puncti: congenital absence or fibrosis 2) Canaliculi: congenital atresia or inflammation 3) Nasolacrimal duct obstruction: a. Congenital nasolacrimal obstruction: discussed with eye diseases of infants b. Acquired nasolacrimal obstruction which affects females in their 50 s and older (postmenopausal females). It results in chronic inflammation of the lacrimal sac (chronic Dacryocystitis but could lead to acute exacerbations with abscess formation; acute Dacryocystitis. 4) Nose: polyps and deviated septum.

22 Diagnosis: 1. Fluorescein dye disappearance test: a drop of fluorescein dye is put in the conjunctival sac and the patient is re-examined after 5 min. Normally most of the fluorescein should disappear into the nose within 5 min. both eyes are compared 2. Lacrimal syringing: the puncta are irrigated with a salty or sugary solution. Failure to perceive the taste in the throat is suggestive of obstruction. Management: most cases of epiphora are managed surgically 1. Punctal occlusion is snipped. 2. Canalicular obstruction is dilated and a temporary nasolacrimal tube inserted (fig 28) 3. Congenital nasolacrimal duct (NLD) obstruction by probing 4. Acquired NLD obstruction by dacryocystorhinostomy DCR Fig 28: nasolacrimal tube (left), passed through upper and lower puncta (right).

23 Chronic Dacryocystitis Definition: chronic inflammation of the lacrimal sac secondary to nasolacrimal duct obstruction Symptoms: the main symptom is epiphora with recurrent mucoid discharge Sign: positive regurge (fig 29) is the diagnostic hallmark of the disease (pressure on the lacrimal sac causes extrusion of discharge through the lacrimal punctum) Fig 29: Regurge test for chronic dacryocystitis. Complications: 1. Problem of epiphora 2. Recurrent conjunctivitis 3. Acute dacryocystitis 4. Endophthalmitis following cataract surgery Treatment: surgical; the standard procedure is DCR.

24 Acute Dacryocystitis (fig 30) Acute exacerbation of chronic Dacryocystitis caused by infection with virulent organisms as Staphylococcus aureus or Streptococcus. The sac is swollen, red and very painful. Regurge is absent. Treatment is by antibiotics, hot foments and sometimes incision and drainage. Fig 30: acute dacryocystitis DCR: Is the most common operation to treat nasolacrimation obstruction in older children and adults. It can be done from the skin side of from the nose. The bone separating the lacrimal sac and the nasal mucosa is removed and an ostium is created connecting the cavity of the sac to the cavity of the nose at the middle meatus. Dry Eye A collective term that describes the clinical condition in which there is deficient tear function The 2 most common forms are 1. Deficiency of aqueous tears (also known as Keratoconjunctivitis sicca): the most common causes are collagen diseases as rheumatoid arthritis and idiopathic form in

25 postmenopausal females. Treatment is by artificial tears 2. Mucin deficiency: occurs when there is widespread loss of Goblet cells of the conjunctiva as in severe vitamin A deficiency, chronic trachoma and ocular cicatricial pemphigoid. The severe forms are called ocular Xerosis. Treatment is difficult.