Chapter 6
The Lacrimal System and Tear Film
Introduction
The lacrimal system (Fig. 6.1) consists of:
•the lacrimal gland
•the lacrimal drainage system comprising:
the puncta
the canaliculi
the lacrimal sac
the nasolacrimal duct.
The lacrimal gland
The lacrimal gland is situated in the upper, outer quadrant of the orbit, in the lacrimal fossa of the frontal bone. It is almond-shaped and is divided into two lobes by the levator palpebral muscle:
•the superior or orbital lobe
•the inferior or palpebral lobe.
There are 10 to 12 drainage channels leaving the lacrimal gland to convey tears to openings in the upper fornix.
Blood supply
The lacrimal artery and vein supply and drain blood to and from the lacrimal gland.
Nerve supply
Nerve supply to the lacrimal gland is via the lacrimal nerve, the first branch of the ophthalmic division of the trigeminal nerve.
Function of the lacrimal gland
The function of the lacrimal gland is to produce tears in response to stimulation of the trigeminal nerve through, for example, emotion; foreign body
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Lacrimal gland
Lacrimal
ducts
Upper
punctum Superior canaliculus
Lacrimal
sac
Lower punctum
Inferior canaliculus
Nasolacrimal
duct
Fig. 6.1 Lacrimal system. (Reprinted from Darling & Thorpe Ophthalmic Nursing (1981), Fig. 36, p. 144 by permission of the publisher Baillière Tindall Limited, London.)
on the cornea or conjunctiva; or noxious fumes, such as smoke or peeled onions.
The lacrimal drainage system
The puncta
The upper and lower puncta are small round or slightly oval apertures situated on the lid margin on a slight elevation called the lacrimal papilla. This is a pale area, due to the presence of few blood vessels, about 6 mm from the inner canthus. Both puncta are normally turned inwards towards the bulbar conjunctiva so tears can drain into them. Fibres of the orbicularis muscle surround them.
The canaliculi
The upper and lower canaliculi are narrow ducts passing from each puncta vertically for 1.5–2.0 mm, which then turn medially and travel horizontally for 10 mm. They usually unite to form a common canaliculus for about 1 mm before opening out into the lacrimal sac.
The lacrimal sac
The lacrimal sac is situated in the lacrimal fossa of the lacrimal bone. It is blind-ended superiorly, 5 mm wide and 12–14 mm in length. Fibres of the orbicularis and Horner’s muscles surround the sac.
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The nasolacrimal duct
The nasolacrimal duct is a downward continuation of the sac for 12–24 mm before opening into the inferior meatus of the nose beneath the inferior turbinate bone. The valve of Hasner, a mucosal fold, covers part of the opening. All the passages of the lacrimal drainage system are lined with epithelium.
Blood supply
Blood is supplied to the nasolacrimal duct via the nasal artery and the superior and inferior medial palpebral artery. Drainage is via the nasal vein and the superior and inferior medial palpebral veins.
Nerve supply
The infratrochlear nerve, a branch of the nasociliary nerve, which is the third branch of the ophthalmic division of the trigeminal nerve, provides the nerve supply for the nasolacrimal duct.
Lymphatic drainage
Lymph is drained from the nasolacrimal duct via the submaxillary nodes.
The tear film
The tear film is a mixture of secretions from the accessory tear glands of Krause and Wolfring, the goblets cells of the conjunctiva and the Meibomian glands of the eyelids. The tear film is a constant film of fluid bathing the conjunctiva and cornea. The lacrimal gland produces excess tears.
Three layers of the tear film
These layers are illustrated in Fig. 6.2:
(1)Oil: the outer layer, produced by the Meibomian glands of the tarsal plates and also the glands of Moll and Zeis. The oily layer prevents evaporation and spillage of tears over the lid margin.
(2)Aqueous: the middle layer, the ‘tears proper’, produced by the lacrimal gland and the glands of Krause and Wolfring.
(3)Mucin: the inner layer, produced by the goblet cells of the conjunctiva, is a wetting substance for easy spread over the cornea.
Composition of tears
• |
98% |
water |
• |
2–5% |
protein |
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Lipid layer
Aqueous
layer
Mucus |
Micro- |
layer |
villus |
Epithelial cells
Fig. 6.2 Three layers of the tear film. (Reproduced with permission from Vaughan, D.G. & Asbury, T. (1983) General Ophthalmology (10th edn), Appleton & Lange.)
•Glucose
•Urea
•Sodium
•Potassium
•Retinol
•Chloride
•Lysozyme – an antimicrobial enzyme
•Immunoproteins and antimicrobial agents
•Normal pH is between 6.5–7.6 (Forrester et al., 2002).
Function of tears
•Refraction – to provide an optically smooth surface to the cornea.
•Lubrication of the front of the eyeball.
•Cleansing action by washing away dust particles from the eye.
•Protection from infection by secreting the enzyme lysozyme and immunoproteins and antimicrobial agents.
Flow of tears
Tears flow across the front of the eyeball into the lacrimal drainage channels as a result of the following factors:
•Gravity itself assists tear flow.
•Blinking: lid movements assist the flow of tears across the front of the cornea and conjunctiva.
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•Capillary attraction into the puncta and canaliculi.
•The lacrimal pump: the contraction of orbicularis and Horner’s muscles around the puncta and lacrimal sac dilate these structures and draw in the tears.
•Some tears are lost as a result of evaporation into the atmosphere.
Conditions of the lacrimal system
Dacryoadenitis
Dacryoadenitis is a rare acute or chronic inflammation of the lacrimal gland. Causes include:
•Acute:
complication of systemic infections such as: mumps, measles, infectious mononucleosis or influenza
trachoma
herpes zoster
staphylococcal infection
following injury to the lacrimal gland.
•Chronic:
sarcoidosis
tuberculosis
syphilis
lymphatic leukaemia
lymphosarcoma.
Signs and symptoms
Acute:
•Pain: swelling and redness of the upper lid, especially in the upper temporal aspect (Fig. 6.3).
•S-shaped curve to the upper lid.
Patient’s needs
•Relief of pain must be a priority.
•Admission to hospital may be necessary if condition is severe.
•Incision of abscess where necessary.
•Application of warm compresses (as hot as the patient can tolerate without causing heat trauma) can provide some relief.
•Treatment of active infection with appropriate antibiotic.
•Treatment of underlying cause, if possible.
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Fig. 6.3 Dacryoadenitis.
Nursing action
•Admit patient to hospital if condition is severe.
•Give/advise the patient:
to instil antibiotic drops and ointment, usually for 7–10 days
to take any prescribed oral antibiotics for the duration of the course
to take analgesics or apply local heat for pain relief.
•Prepare patient and equipment for incision of abscess.
•Chronic: Normally painless and develops slowly. Treatment is usually with warm compresses and antibiotic therapy.
Dacryocystitis
Dacryocystitis is an acute or chronic inflammation of the lacrimal sac (Fig. 6.4). It is a rare condition but more common than dacryoadenitis. It is usually unilateral and is associated with obstruction to the lacrimal drainage system.
Causes
Acute
•most are unknown
•following chronic dacryocystitis
•causative organisms – Staphylococci, Streptococci, Pneumococci.
Chronic
•following trauma to the lacrimal system
•following chronic conjunctivitis, e.g. trachoma.
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Fig. 6.4 Dacryocystitis.
Infant
Failure of canalisation of lacrimal ducts following birth.
Signs
Adult acute and infant:
•pain
•red, tender swelling over lacrimal sac
•pus regurgitating through punctum
•conjunctivitis
•watering eye (epiphora) which may cause visual disturbance.
Chronic:
•may be swelling over lacrimal sac, which can be recurrent
•pus may emerge from the punctum when pressure is applied to the sac
•epiphora, which may cause visual disturbance.
Patient’s needs
Acute
•relief of pain, which can be severe, with appropriate analgesia; warm compresses can effect some relief of pain
•lid hygiene to address problem of discharge and watering eye.
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Chronic
•relief of watering eye due to blockage of drainage channels
•diagnosis and treatment of obstruction.
Infant
•relief of pain
•lid hygiene to address problem of discharge and watering eye
•admission to hospital for probing of ducts if initial treatment fails.
Nursing action
Acute adult
•Apply/instruct the patient how to apply warm compress to the inflamed area (clean face cloths rinsed under a warm tap can provide some relief).
•Give/instruct him to take the prescribed analgesia and antibiotics, e.g. Augmentin 350 mg three times a day for 7–10 days.
•Clean/instruct him how to clean the eye if sticky and instil prescribed antibiotic drops and ointment, usually Chloramphenicol or Fucithalmic.
Chronic adult
•Perform lacrimal sac washout to detect area of blockage (see p. 41). Note: this is never carried out on a patient with an acute infection of the sac as the inflamed walls are easy to perforate.
•Prepare patient for dacryocystogram. This is an X-ray using radioopaque dye, which is introduced into the lacrimal drainage system to show up any blockage. Warn the patient that it is an uncomfortable procedure and that he should be accompanied home following this test as he may feel unwell.
•Admit and prepare the patient for surgery to correct the blockage. Dacryocystorhinostomy(DCR) is performed to open up a new drainage channel into the nasal cavity. This may be performed using an endoscope or a more traditional external approach through the skin. Sometimes a tube is left in situ (DCR and tubes) for 3–6 months to maintain the patency of the new drainage channels. These tubes should not interfere with the cornea unless they extrude.
Post-operative care
•In the immediate post-operative period, the patient must be monitored carefully for any epistaxis (nosebleed). Blood loss from this can be catastrophic. The haemorrhage may be overt or could be via the back of the throat.
•A pressure dressing will remain in place until the dressing the morning after surgery. This should be observed for signs of haemorrhage.
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•In the case of endoscopic DCR, a nasal pack will be in situ. This too must be observed for haemorrhage. It usually is removed the next day.
•Standard DCR:
Clean the eye and suture line.
Instil antibiotic drops; occasionally antibiotic cream is prescribed to be applied to the suture line. The surgeon may recommend that this is gently massaged in to reduce scarring.
Remove sutures 5–7 days post-operatively (usually in out-patient department).
Instruct the patient not to blow his nose vigorously as this could cause bleeding and will dislodge the tubing.
If a tube is present, it will be removed in the outpatient department. The procedure is relatively painless and does not warrant surgery (see p. 46).
Infant
•Instruct the parent/guardian to instil topical antibiotic drops, e.g. G. Chloramphenicol.
•Instruct the parent/guardian to massage over the lacrimal sac area to remove the accumulated mucus, which may lead to a patent duct.
•Admitting the child to hospital should be considered if these methods fail to open the canaliculus.
•A thorough pre-operative assessment as well as review by the anaesthetist should be completed. Parental or legal guardian’s consent must be obtained.
•Probing of the tear ducts will be done under general anaesthetic.
•Give standard pre-operative care prior to probing of the ducts.
•Give post-operative care: instil antibiotic drops.
Complications
Following acute dacryocystitis, fistula formation may develop. Dacryocystorhinostomy is not always successful in curing the watering eye.
Epiphora
Epiphora is watering of the eye (increased lacrimation).
Causes
Causes include:
•acute or chronic dacryocystitis (see above)
•ectropion (see p. 75)
•a small, tight or absent punctum
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•increased secretion of tears due to reflex stimulation of the lacrimal gland, e.g. by wind, smoke, onions, or a foreign body in the eye
•allergy, e.g. hay fever.
Patient’s needs
•explanation of the condition, its cause and prognosis
•dilation of a small or tight punctum
•removal of causative agent of increased stimulation
•treat hay fever.
Nursing action
•Careful history of the presenting complaint, systematic examination of the eyelids, conjunctiva and the cornea.
•If a foreign body is present, remove this (see p. 36).
•If the cause is a small or tight punctum, this needs to be dilated regularly over a period of several months. This is usually performed every week or so using for example, a Nettleships dilator, holding it in place in the punctum for five minutes.
•Prepare patient and equipment for a one, two or three-snip operation, which will be carried out if the dilation fails. During this procedure, performed under local anaesthetic, snips are made behind the punctum to release the muscle around the punctum.
•Prescribe topical antihistamine drops such as Lodoxamide.
Dry eye syndrome (keratoconjunctivitis sicca)
Dryness of the eye results from any disease associated with deficiency of any of the layers of the tear film as well as lid or corneal surface abnormalities. Its name (dry eyes) implies a non-significant condition. This is not the case. In addition to being very uncomfortable, it has the potential to be sight threatening.
Causes
•lacrimal gland failure
•oil deficiency
•exposure: proptosis, facial palsy
•hot, dry climate/environment
•lid damage
•blepharitis
•meibomianitis
•aqueous deficiency
•Sjögren’s syndrome (arthritis, dry eye, achlorhydria)
•removal/absence of glands
•trachoma
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•chronic dacryoadenitis
•drugs: beta-blockers, diuretics
•old age
•menopause
•mucin deficiency
•chemical burns
•chronic conjunctivitis
•antihistamines
•Stevens-Johnson syndrome
•xerophthalmia.
•other causes: deficient blinking; corneal scarring.
Signs
•Usually a normal-looking eye.
•Damaged epithelial, corneal and conjunctival cells stain with fluorescein drops.
•Breaks in the tear film are seen when stained with G. Fluorescein. The normal tear break-up time is usually over ten seconds.
Patient’s needs
•An adequate explanation of the condition.
•Recognition that it causes ocular disturbance.
•Advice that this is a chronic condition and treatment is about relieving symptoms or preventing symptoms occurring.
•Relief of symptoms that include:
gritty feeling
itching
burning sensation
inability to produce tears
pain around and in the eye
sometimes a red eye
difficulty in opening eyes on waking and moving lids
excessive watering eye (if the outer oil layer of the tear film is deficient, tears will spill over the lower lid margin).
•Investigation and treatment of underlying cause, if possible.
•Treatment with replacement tears.
Nursing action
•Perform tear production test (see p. 38).
•Instruct the patient to use the prescribed artificial tears, e.g. hypromellose. These drops can usually be used as often as the patient requires, keeping the eye feeling comfortable, and will probably need long-term use.
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•Cautery to the punctum or insertion of punctal plugs may be employed to prevent what little tears are produced from draining into the punctum.
Complications
•Chronic conjunctivitis due to loss of the protective function of the tear film and lysozyme.
•Corneal scarring and vascularisation.
•Corneal ulceration, thinning and perforation.
•Eventual loss of the eye through recurrent infections.