Eye eBook

Question 1

Accessory structures of the eye

These consist of:

Answer 1

 Eyelids
 Eyelashes
 Eyebrows
 Lacrimal apparatus
 Extrinsic eye muscles

Question 2

Eyelids

Answer 2

These are sheets of voluntary muscle with the tarsal plate (connective tissue) at the free edge. The tarsal plate contains a row of sebaceous glands (Meibomian glands) which secrete the lipid layer of the tear film. This delays the evaporation of tears from the eyeball. The upper eyelid is more mobile than the lower. Both eyelids are lined with a mucous membrane, the conjunctiva, which is continuous from the edge of the eyelids onto the eyeball.

Question 3

Eyebrows and eyelashes

Answer 3

Eyebrows are two sets of directional hairs which direct sweat and other moisture away from the eye. The primary function of the eyelashes is to protect the eyeballs from sunlight, sweat and foreign objects. Each eyelash has a sebaceous gland located at the base of each eyelash follicle. These are sebaceous ciliary glands which release fluid to lubricate the eyeball.

Question 4

Lacrimal apparatus

Answer 4

The lacrimal apparatus is responsible for production and distribution of tears. Tear production is stimulated by the parasympathetic fibres of the facial (VII) nerve in response to strong smells, irritants and emotion. Lacrimal overstimulation can fill the nasal cavity with fluid as the excess tears drain down the nasolacrimal duct (this is one reason why you get a runny nose when you cry!).

Question 5

Extrinsic eye muscles

There are six extrinsic eye muscles:

Answer 5

 Superior rectus
 Inferior rectus
 Lateral rectus
 Medial rectus
 Superior oblique
 Inferior oblique

Question 6

The direction of movement of the six extrinsic eye muscles

Answer 6

draw

Question 7

Anatomy of the eyeball

Answer 7

The human eyeball is approximately 2.5cm in diameter and consists of three regions – the fibrous layer (covered by the conjunctiva), the vascular layer (the uvea) and an inner layer. About one sixth of the eyeball is exposed.

Question 8

Fibrous layer (sclera)

Answer 8

The sclera is made up of collagen fibres and fibroblasts and gives shape and rigidity to the eyeball along with its white colour. The anterior sclera (the front portion) is more commonly known as the cornea which is transparent and covers the iris. At the junction of the sclera and the cornea is the Canal of Schlemm which drains aqueous humour from the anterior chamber of the eye.

Question 9

Vascular layer (uvea)

Answer 9

The uvea is a highly vascular choroid layer which lines the sclera. It provides nutrients to the retina and also contains melanocytes. These cells produce melanin to absorb stray light that enters the eye and to maintain the sharpness of the image on the retina. In the anterior portion of the eyeball, the choroid layer becomes the ciliary body which ends in the ciliary processes. These contain capillaries which secrete aqueous humour into the anterior chamber of the eye. There are also suspensory ligaments which hold the lens in place and the ciliary muscle (containing radial and circular smooth muscle) which changes the shape of the lens and hence the focus of the eye.

Question 10

Iris

Answer 10

The iris is a coloured, doughnut shaped arrangement of circular and radial smooth muscle. It is attached to the ciliary processes and so is suspended between the cornea and the lens. Its principal function is to regulate the amount of light entering the eye by changing the size of the pupil.

Question 11

Retina

Answer 11

The retina only covers the posterior segment of the eye. It is highly vascularised, appearing red under examination by light. The edge of the retina where it joins the choroid is pigmented with melanin which absorbs any scattered light that enters the eye.

Question 12

Most of the retina is made up of three layers of neurons:

Answer 12

 Photoreceptor neurons
o Cones (colour vision). These are found at the fovea centralis and are essential
for bright light function.
o Rods (light perception). These are found around the edge of the retina and are
essential for dark function.
 Bipolar neurons
 Ganglion neurons. These cells pass signals from the retina to the optic nerve fibres.

The optic (II) nerve leaves the back of the eye at the optic disc – the so‐called “blind spot” in the eye. The central retinal artery and the central retinal vein both enter and leave at this point.

Question 13

Eye cavities

The eye is made up of two cavities:

Answer 13

1. Anterior (the front of the eye) which consists of the anterior and posterior chambers and contains aqueous humour.
2. Posterior (the back of the eye). This contains vitreous humour.

Question 14

Anterior cavity

Answer 14

The anterior chamber is located between the cornea and the iris. The posterior chamber is located between the iris and the lens. Both are filled with aqueous humour which is secreted by the ciliary body; this aqueous humour is replaced approximately every 90 minutes. The flow of aqueous humour maintains the intraocular pressure (IOP) between 16‐25 mmHg.

Question 15

Posterior cavity

Answer 15

The posterior cavity contains vitreous humour. This is jelly like and its prime function is to hold the retina flush against the choroid. Vitreous humour is made up mainly of water with collagen fibres and hyaluronic acid. It also contains phagocytic cells to remove debris such as dead retinal cells. Vitreous humour is not renewed like aqueous humour and so is stagnant.
“Floaters” may be visible particularly if the patient is looking at a single bright colour for a period of time. Floaters are harmless pieces of debris which cast a shadow onto the cornea. These become more common with increasing age.

Question 16

Eye pathologies

Answer 16

Red eye
Conjunctivitis
Infective conjunctivitis
Allergic conjunctivitis
Sub‐conjunctival haemorrhage
Iritis (anterior uveitis)
Keratitis (corneal ulcer)
Anterior Cavity Pathology – Glaucoma

Question 17

Red eye

Answer 17

Patients presenting with a red eye are some of the most common encounters within community pharmacy. Many conditions causing a red eye are relatively benign and can be treated with non‐prescription medicines and simple advice. However there are some more serious conditions that require immediate referral for specialist medical attention so it is important to be confident in differentiating between these conditions.

Question 18

Conjunctivitis

Answer 18

In conjunctivitis, the affected eyeball is generally diffusely pink or red. In acute bacterial conditions the patient may present with unilateral conjunctivitis; untreated acute infective conjunctivitis may lead to cross infection of the previously unaffected eye. Patients suffering from allergic conjunctivitis generally present with bilateral symptoms. Conjunctivitis is rarely a medical emergency.

Question 19

Infective conjunctivitis

Answer 19

Typically patients will present with unilateral conjunctivitis or bilateral conjunctivitis where one eye became symptomatic before the other. The most common bacterial pathogens are Streptococcus spp. or Haemophilus spp. The most common viral pathogens are adenoviruses or picornaviruses. The eye(s) will feel gritty and possibly itchy, but there is no pain associated with infective conjunctivitis. There may be discharge from the affected eye(s); in bacterial conjunctivitis this is prurulent and in viral conjunctivitis this is clear.
Patients are at their most infectious to others when the eye is red. Chloramphenicol 0.5% eye drops or 1% eye ointment can be recommended over the counter for the treatment of acute bacterial conjunctivitis in adults and children aged over 2 years. Viral conjunctivitis is often accompanied by symptoms of the common cold, is usually self‐limiting and requires no treatment.

Question 20

Allergic conjunctivitis

Answer 20

Patients with allergic conjunctivitis usually present with itchy, watery eyes (the condition is almost always bilateral). There is no pain and no feeling of grittiness which helps to distinguish allergic conjunctivitis from viral conjunctivitis. The patient will nearly always complain of accompanying nasal symptoms, particularly in the case of seasonal allergies such as hayfever. There are several anti‐inflammatory preparations available for the treatment of allergic conjunctivitis (see BNF section 11.3). However only two are available in the non‐prescription environment, namely antazoline (in combination with xylometazoline as Otrivine‐Antistin) and
sodium cromoglicate 2%. As Otrivine‐Antistin contains xylometazoline, a sympathomimetic, it should be used with caution in patients at risk of closed angle glaucoma.

Question 21

Sub‐conjunctival haemorrhage

Answer 21

Also known as a “blood‐shot eye”, a sub‐conjunctival haemorrhage is the result of the bursting of a capillary between the sclera and the conjunctiva, spreading blood across this layer. It is most commonly the result of rubbing the eye concerned but it can happen during severe bouts of coughing. It is a painless condition with no other accompanying symptoms and takes up to 10 days to resolve completely.

Question 22

Iritis (anterior uveitis)

Answer 22

Another condition that presents as a diffuse red eye, iritis requires immediate referral to a more specialist practitioner. Along with the red eye, the patient may report blurred vision, photophobia and pain within the eye. The pupil of the affected eye will be small and fixed. Iritis is associated with autoimmune diseases such as rheumatoid arthritis or ulcerative colitis.

Question 23

Keratitis (corneal ulcer)

Answer 23

Keratitis is inflammation of the cornea which presents as severe pain in the eye, with blurred vision, photophobia and a watery discharge. The patient may also complain of the feeling of a foreign body in the eye. It is commonly associated with soft contact lens use but may also be caused by infections and autoimmune disease.

Question 24

Anterior Cavity Pathology – Glaucoma

Answer 24

Glaucoma is defined as a raised IOP due to a problem with drainage of aqueous humour from the anterior cavity of the eye. There are two types of glaucoma:
 Open angle
 Closed angle
Open angle glaucoma
Open angle glaucoma is the most common form of glaucoma and is due to problems with the trabecular meshwork through which the aqueous humour drains into the Canal of Schlemm. For normal drainage of aqueous humour access to the trabecular meshwork must be completely free. In open angle glaucoma the trabecular meshwork becomes clogged with particles such as red blood cells or iris pigment. Occasionally, tumours may develop and block the meshwork. Open angle glaucoma develops slowly and is often asymptomatic. Attending regular eye tests, particularly as patients get older, often results in early detection of open angle glaucoma.

Closed angle glaucoma
Closed angle glaucoma has two sub types, primary angle closure and secondary angle closure. Primary angle closure most often occurs in patients with a shallow anterior chamber of the eye. Because of this, the iris may temporarily touch the lens and so the papillary outflow of aqueous humour to the anterior chamber becomes blocked. Continuing production of aqueous humour pushes the iris even further out into the lens and thus makes the problem worse. This results in a sudden, dramatic increase in IOP. The symptoms of closed angle glaucoma include:
 Seeing haloes around lights
 ocular congestion
 corneal oedema
 severe pain within the eye (this may be accompanied by nausea and vomiting)
 “acute red eye”.
The last symptom is due to the sudden increase in IOP causing the eyeball to expand which results in the capillaries on the surface of the cornea bursting. Secondary angle closure has many causes including deformation of the iris, tumours and abnormal corneal growth. The symptoms are the same as in primary angle closure. Acute closed angle glaucoma is a medical emergency. Patients who present with symptoms must seek immediate medical attention to reduce the risk of damage to the optic nerve and blindness.

Question 25

Retinal pathology

Answer 25

Detached Retina

Age‐related Macular Degeneration (AMD)

Question 26

Detached Retina

Answer 26

The neural portion of the retina detaches from the pigmented portion. Trauma is the usual cause but other things may precipitate retinal detachment. Once the retina becomes detached fluid seeps between the neural and epithelial layers causing the retina to bulge outwards. This leads to distorted vision (often the first symptom) or blindness. Reattachment of the retina must be done quickly and this is performed using either laser surgery or cryosurgery.

Question 27

Age‐related Macular Degeneration (AMD)

Answer 27

This is a gradual deterioration of the macula lutea and the patient will experience a gradual loss of central vision whilst retaining peripheral vision. “Dry” AMD is a very common condition in elderly patients and there is no treatment. Patients can learn to use their peripheral vision with the use of visual aids such as magnifiers and should be reassured that they will not go blind.
“Wet” AMD occurs when new blood vessels form in the choroid layer. These then leak fluid under the retina causing the retina to deform. Wet AMD is treatable with anti‐vascular endothelial growth factor (anti‐VEGF) in the first instance followed by photodynamic therapy if anti‐VEGF treatment fails. Two anti‐VEGF agents are available namely: ranibizumab (Lucentis) and pegaptanib (Macugen). However, pegaptanib is not recommended by NICE for the treatment of wet AMD.

Question 28

Eyelid pathologies

Answer 28

Stye (hordeolum)
Meibomian cyst (chalazion)
Blepharitis
Ectropion and entropion

Question 29

Stye (hordeolum)

Answer 29

This is the staphylococcal infection of an eyelash follicle. The eyelid margin may become red and inflamed over a number of days culminating in a pustule at the affected follicle. The associated swelling and irritation may be quite painful until the stye resolves. Styes are generally self‐limiting but some relief may be obtained through the application of a warm compress to the eyelid or through the use of dibromopropanidine eye ointment (Brolene, Golden Eye Ointment).

Question 30

Meibomian cyst (chalazion)

Answer 30

The meibomian glands secrete a fluid that prevents the eyelashes sticking together. When one of these glands becomes infected or blocked, a chalazion forms which gradually increases in size. Unlike styes, chalazia are not inflamed and they grow inwards towards the conjunctival surface rather than outward on the eyelid. Meibomian cysts are self‐limiting but may take up to 2 years to resolve. Although painless, the lumps are uncomfortable and can be removed surgically before they resolve.

Question 31

Blepharitis

Answer 31

This is a chronic condition where the eyelids, usually of both eyes, become inflamed. Causes of blepharitis include staphylococcal infection, seborrhoeic dermatitis (often associated with seborrhoea of the scalp and eyelashes) and contact dermatitis (usually from cosmetic use). The eyelid margins are red and inflamed and may appear raw. Patients often complain of burning and/or itching. The cause of blepharitis should be determined before treatment is initiated and non‐prescription remedies may not be very effective.

Question 32

Ectropion and entropion

Answer 32

Both conditions are associated with increasing age. Ectropion is when the lower eyelid sags and turns outwards due to decreased fat and muscle tone below the eye. As a consequence, tears overflow from the eyelid but don’t lubricate the eyeball so the eye becomes dry. The lower eyelid may become chronically infected and scarred.
Entropion is the turning in of the lower eyelid and eyelashes. The eyelashes and eyelid margins then rub against the cornea. The eyelashes may fall out which increases the likelihood of infection of the eyelid margin. Entropion can only be corrected surgically.