Ophthalmology Flashcards
Glaucoma
Glaucoma refers to the optic nerve damage that is caused by a significant rise in intraocular pressure. The raised intraocular pressure is caused by a blockage in aqueous humour trying to escape the eye. There are two types of glaucoma: open-angle and closed-angle.
Basic anatomy and physiology of the eye
The vitreous chamber of the eye is filled with vitreous humour.
The anterior chamber between the cornea and the iris and the posterior chamber between the lens and the iris are filled with aqueous humour that supplies nutrients to the cornea.
The aqueous humour is produced by the ciliary body. The aqueous humour flows from the ciliary body, around the lens and under the iris, through the anterior chamber, through the trabecular meshwork and into the canal of Schlemm. From the canal of Schlemm it eventually enters the general circulation.
The normal intraocular pressure is 10-21 mmHg. This pressure is created by the resistance to flow through the trabecular meshwork into the canal of Schlemm.
Pathophysiology of open-angle glaucoma
In open-angle glaucoma, there is a gradual increase in resistance through the trabecular meshwork. This makes it more difficult for aqueous humour to flow through the meshwork and exit the eye. Therefore the pressure slowly builds within the eye and this gives a slow and chronic onset of glaucoma.
In acute angle-closure glaucoma, the iris bulges forward and seals off the trabecular meshwork from the anterior chamber preventing aqueous humour from being able to drain away. This leads to a continual build-up of pressure. This is an ophthalmology emergency.
Increased pressure in the eye causes cupping of the optic disc. In the centre of a normal optic disc is the optic cup. This is a small indent in the optic disc. It is usually less than half the size of the optic disc. When there is raised intraocular pressure, this indent becomes larger as the pressure in the eye puts pressure on that indent making it wider and deeper. This is called “cupping”. An optic cup greater than 0.5 the size of the optic disc is abnormal.
Risk factors for open-angle glaucoma
Increasing age
Family history
Black ethnic origin
Nearsightedness (myopia)
Presentation of open-angle glaucoma
Often the rise in intraocular pressure is asymptomatic for a long period of time. It is diagnosed by routine screening when attending optometry for an eye check.
Glaucoma affects peripheral vision first. Gradually the peripheral vision closes in until they experience tunnel vision.
It can present with gradual onset of fluctuating pain, headaches, blurred vision and halos appearing around lights, particularly at night time.
Measuring intraocular pressure
Non-contact tonometry is the commonly used machine for estimating intraocular pressure by opticians. It involves shooting a “puff of air” at the cornea and measuring the corneal response to that air. It is less accurate but gives a helpful estimate for general screening purposes.
Goldmann applanation tonometry is the gold standard way to measure intraocular pressure. This involves a special device mounted on a slip lamp that makes contact with the cornea and applies different pressures to the front of the cornea to get an accurate measurement of what the intraocular pressure is.
Diagnosing open-angle glaucoma
Goldmann applanation tonometry can be used to check the intraocular pressure.
Fundoscopy assessment to check for optic disc cupping and optic nerve health.
Visual field assessment to check for peripheral vision loss.
Managing open-angle glaucoma
Management of glaucoma aims to reduce the intraocular pressure. Treatment is usually started at an intraocular pressure of 24 mmHg or above. Patients are followed up closely to assess the response to treatment.
Prostaglandin analogue eye drops (e.g. latanoprost) are first line. These increase uveoscleral outflow. Notable side effects are eyelash growth, eyelid pigmentation and iris pigmentation (browning).
Other options:
Beta-blockers (e.g. timolol) reduce the production of aqueous humour
Carbonic anhydrase inhibitors (e.g. dorzolamide) reduce the production of aqueous humour
Sympathomimetics (e.g. brimonidine) reduce the production of aqueous fluid and increase uveoscleral outflow
Trabeculectomy surgery may be required where eye drops are ineffective. This involves creating a new channel from the anterior chamber, through the sclera to a location under the conjunctiva. It causes a “bleb” under the conjunctiva where the aqueous humour drains. It is then reabsorbed from this bleb into the general circulation.
Acute angle-closure glaucoma
Glaucoma refers to the optic nerve damage that is caused by a significant rise in intraocular pressure. The raised intraocular pressure is caused by a blockage in aqueous humour trying to escape the eye.
Acute angle-closure glaucoma occurs when the iris bulges forward and seals off the trabecular meshwork from the anterior chamber preventing aqueous humour from being able to drain away. This leads to a continual build-up of pressure in the eye. The pressure builds up particularly in the posterior chamber, which causes pressure behind the iris and worsens the closure of the angle.
Acute angle-closure glaucoma is an ophthalmology emergency. Emergency treatment is required to prevent permanent loss of vision.
Risk factors for acute angle-closure glaucoma
The risk factors are slightly different to open-angle glaucoma:
Increasing age
Females are affected around 4 times more often than males
Family history
Chinese and East Asian ethnic origin. Unlike open-angle glaucoma, it is rare in people of black ethnic origin.
Shallow anterior chamber
Certain medications can precipitate acute angle-closure glaucoma:
Adrenergic medications such as noradrenalin
Anticholinergic medications such as oxybutynin and solifenacin
Tricyclic antidepressants such as amitriptyline, which have anticholinergic effects
Presentation of acute angle-closure glaucoma
The patient will generally appear unwell in themselves. They have a short history of:
Severely painful red eye
Blurred vision
Halos around lights
Associated headache, nausea and vomiting
Examination of acute angle-closure glaucoma
Red-eye
Teary
Hazy cornea
Decreased visual acuity
Dilatation of the affected pupil
Fixed pupil size
Firm eyeball on palpation
Initial management of acute angle-closure glaucoma
NICE CKS 2019 say patients with potentially life-threatening causes of red eye should be referred for same-day assessment by an ophthalmologist. If there is a delay in admission, whilst waiting for an ambulance:
Lie patient on their back without a pillow
Give pilocarpine eye drops (2% for blue, 4% for brown eyes)
Give acetazolamide 500 mg orally
Given analgesia and an antiemetic if required
Pilocarpine acts on the muscarinic receptors in the sphincter muscles in the iris and causes constriction of the pupil. Therefore it is a miotic agent. It also causes ciliary muscle contraction. These two effects cause the pathway for the flow of aqueous humour from the ciliary body, around the iris and into the trabecular meshwork to open up.
Acetazolamide is a carbonic anhydrase inhibitor. This reduces the production of aqueous humour.
Secondary care management of acute angle-closure glaucoma
Various medical options can be tried to reduce the pressure:
Pilocarpine
Acetazolamide (oral or IV)
Hyperosmotic agents such as glycerol or mannitol increase the osmotic gradient between the blood and the fluid in the eye
Timolol is a beta-blocker that reduces the production of aqueous humour
Dorzolamide is a carbonic anhydrase inhibitor that reduces the production of aqueous humour
Brimonidine is a sympathomimetic that reduces the production of aqueous fluid and increase uveoscleral outflow
Laser iridotomy is usually required as a definitive treatment. This involves using a laser to make a hole in the iris to allow the aqueous humour to flow from the posterior chamber into the anterior chamber. This relieves pressure that was pushing the iris against the cornea and allows the humour the drain.
Age related macular degeneration
Age-related macular degeneration is a condition where there is degeneration in the macula that cause a progressive deterioration in vision. In the UK it is the most common cause of blindness. A key finding associated with macular degeneration is drusen seen during fundoscopy.
There are two types, wet and dry. 90% of cases are dry and 10% are wet. Wet age-related macular degeneration carries a worse prognosis.
The macula is made of four key layers. At the bottom, there is the choroid layer, which contains blood vessels that provide the blood supply to the macula. Above that is Bruch’s membrane. Above Bruch’s membrane there is the retinal pigment epithelium and above that are the photoreceptors.
Drusen are yellow deposits of proteins and lipids that appear between the retinal pigment epithelium and Bruch’s membrane. Some drusen can be normal. Normal drusen are small (< 63 micrometres) and hard. Larger and greater numbers of drusen can be an early sign of macular degeneration. They are common to both wet and dry AMD.
Other features that are common to wet and dry AMD are:
Atrophy of the retinal pigment epithelium
Degeneration of the photoreceptors
In wet AMD there is the development of new vessels growing from the choroid layer into the retina. These vessels can leak fluid or blood and cause oedema and more rapid loss of vision. A key chemical that stimulates the development of new vessels is vascular endothelial growth factor (VEGF) and this is the target of medications to treat wet AMD.
Risk factors for age related macular degeneration
Age
Smoking
White or Chinese ethnic origin
Family history
Cardiovascular disease
Presentation of age related macular degeneration
There are some key visual changes to remember for spotting AMD in your exams:
Gradual worsening central visual field loss
Reduced visual acuity
Crooked or wavy appearance to straight lines
Wet age-related macular degeneration presents more acutely. It can present with a loss of vision over days and progress to full loss of vision over 2-3 years. It often progresses to bilateral disease.
Examining age related macular degeneration
Reduced acuity using a Snellen chart
Scotoma (a central patch of vision loss)
Amsler grid test can be used to assess the distortion of straight lines
Fundoscopy. Drusen are the key finding.
Slit-lamp biomicroscopic fundus examination by a specialist can be used to diagnose AMD.
Optical coherence tomography is a technique used to gain a cross-sectional view of the layers of the retina. It can be used to diagnose wet AMD.
Fluorescein angiography involves giving a fluorescein contrast and photographing the retina to look in detail at the blood supply to the retina. It is useful to show up any oedema and neovascularisation. It is used second line to diagnose wet AMD if optical coherence tomography does not exclude wet AMD.
Managing dry AMD
There is no specific treatment for dry age-related macular degeneration. Management focuses on lifestyle measure that may slow the progression:
Avoid smoking
Control blood pressure
Vitamin supplementation has some evidence in slowing progression
Managing wet AMD
Anti-VEGF medications are used to treat wet age-related macular degeneration. Vascular endothelial growth factor is involved in the development of new blood vessels in the retina. Medications such as ranibizumab, bevacizumab and pegaptanib block VEGF and slow the development of new vessels. They are injected directly into the vitreous chamber of the eye once a month. They slow and even reverse the progression of the disease. They typically need to be started within 3 months to be beneficial.
Diabetic retinopathy
Diabetic retinopathy is a condition where the blood vessels in the retina are damaged by prolonged exposure to high blood sugar levels (hyperglycaemia) causing a progressive deterioration in the health of the retina.
Pathophysiology of diabetic retinopathy
Hyperglycaemia leads to damage to the retinal small vessels and endothelial cells. Increased vascular permeability leads to leakage from the blood vessels, blot haemorrhages and the formation of hard exudates. Hard exudates are yellow/white deposits of lipids in the retina.
Damage to the blood vessel walls leads to microaneurysms and venous beading. Microaneurysms are where weakness in the wall causes small bulges. Venous beading is where the walls of the veins are no longer straight and parallel and look more like a string of beads or sausages.
Damage to nerve fibres in the retina causes fluffy white patches to form on the retina called cotton wool spots.
Intraretinal microvascular abnormalities (IMRA) is where there are dilated and tortuous capillaries in the retina. These can act as a shunt between the arterial and venous vessels in the retina.
Neovascularisation is when growth factors are released in the retina causing the development of new blood vessels.
Classification of diabetic retinopathy
Diabetic retinopathy can be split into two broad categories: non-proliferative and proliferative depending on whether new blood vessels have developed. Non-proliferative is often called background or pre-proliferative retinopathy as it can develop in to proliferative retinopathy. A condition called diabetic maculopathy also exists separate from non-proliferative and proliferative diabetic retinopathy.
These conditions are classified based on the findings on fundus examination.
Non-proliferative diabetic retinopathy
Mild: microaneurysms
Moderate: microaneurysms, blot haemorhages, hard exudates, cotton wool spots and venous beading
Severe: blot haemorrhages plus microaneurysms in 4 quadrants, venous beading in 2 quadrates, intraretinal microvascular abnormality (IMRA) in any quadrant
Proliferative diabetic retinopathy
Neovascularisation
Vitreous haemorrhage
Diabetic maculopathy
Macular oedema
Ischaemic maculopathy
Complications of diabetic retinopathy
Retinal detachment
Vitreous haemorrhage (bleeding in to the vitreous humour)
Rebeosis iridis (new blood vessel formation in the iris)
Optic neuropathy
Cataracts
Managing diabetic retinopathy
Laser photocoagulation
Anti-VEGF medications such as ranibizumab and bevacizumab
Vitreoretinal surgery (keyhole surgery on the eye) may be required in severe disease
Hypertensive retinopathy
Hypertensive retinopathy describes the damage to the small blood vessels in the retina relating to systemic hypertension. This can be the result of years of chronic hypertension or can develop quickly in response to malignant hypertension. There are a number of signs that occur within the retina in response to the effects of hypertension in these vessels.
Silver wiring or copper wiring is where the walls of the arterioles become thickened and sclerosed causing increased reflection of the light.
Arteriovenous nipping is where the arterioles cause compression of the veins where they cross. This is again due to sclerosis and hardening of the arterioles.
Cotton wool spots are caused by ischaemia and infarction in the retina causing damage to nerve fibres.
Hard exudates are caused by damaged vessels leaking lipids into the retina.
Retinal haemorrhages are caused by damaged vessels rupturing and releasing blood into the retina.
Papilloedema is caused by ischaemia to the optic nerve resulting in optic nerve swelling (oedema) and blurring of the disc margins.
Keith-Wagener classification
Stage 1: Mild narrowing of the arterioles
Stage 2: Focal constriction of blood vessels and AV nicking
Stage 3: Cotton-wool patches, exudates and haemorrhages
Stage 4: Papilloedema
Managing hypertensive retinopathy
Management is focused on controlling the blood pressure and other risk factors such as smoking and blood lipid levels.
Cataracts
Cataracts are where the lens in the eye becomes cloudy and opaque. This reduces visual acuity by reducing the light that enters the eye.
The job of the lens is to focus light coming into the eye onto the retina at the back of the eye. It is held in place by suspensory ligaments attached to the ciliary body. The ciliary body contracts and relaxes to focus the lens. When the ciliary body contracts it releases tension on the suspensory ligaments and the lens thickens. When the ciliary body relaxes it increases the tension in the suspensory ligaments and the lens narrows. The lens is nourished by the surrounding fluid and doesn’t have a blood supply. It grows and develops throughout life.
Most cataracts develop over years with advanced age in the presence of risk factors. Congenital cataracts occur before birth and are screened for using the red reflex during the neonatal examination.
Risk factors for cataracts
Increasing age
Smoking
Alcohol
Diabetes
Steroids
Hypocalcaemia
Presentation of cataracts
Symptoms are usually asymmetrical as both eyes are affected separately. It presents with:
Very slow reduction in vision
Progressive blurring of vision
Change of colour of vision with colours becoming more brown or yellow
“Starbursts” can appear around lights, particularly at night time
A key sign for cataracts is the loss of the red reflex. The lens can appear grey or white when testing the red reflex. This might show up on photographs taken with a flash.
TOM TIP: It is useful in exams to distinguish the causes of visual problems based on the symptoms. Cataracts cause a generalised reduction in visual acuity with starbursts around lights. Glaucoma causes a peripheral loss of vision with halos around lights. Macular degeneration causes a central loss of vision with a crooked or wavy appearance to straight lines.
Managing cataracts
If the symptoms are manageable then no intervention may be necessary.
Cataract surgery involves drilling and breaking the lens into pieces, removing the pieces and then implanting an artificial lens into the eye. This is usually done as a day case under local anaesthetic. It usually gives good results.
It is worth noting that cataracts can prevent the detection of other pathology such as macular degeneration or diabetic retinopathy. Once cataract surgery is performed these conditions may be detected. Therefore, the surgery may treat the cataract but they may still have poor visual acuity due to other causes.
Endophthalmitis
Endophthalmitis is a rare but serious complication of cataract surgery. It is inflammation of the inner contents of the eye, usually caused by infection. It can be treated with intravitreal antibiotics injected into the eye. This can lead to loss of vision and loss of the eye itself.
Pupil constriction
There are circular muscles in the iris that cause pupil constriction. They are stimulated by the parasympathetic nervous system using acetylcholine as a neurotransmitter. The fibres of the parasympathetic system innervating the eye travel along the oculomotor (third cranial) nerve.
Pupil dilation
The dilator muscles of the pupil arranged like spokes on a bicycle wheel travelling straight from the inside to the outside of the iris. They are stimulated by the sympathetic nervous system using adrenalin as a neurotransmitter.
Abnormal pupil shape
Trauma to the sphincter muscles in the iris can cause an irregular pupil. This could be caused by cataract surgery and other eye operations.
Anterior uveitis can cause adhesions (scar tissue) in the iris that make the pupils misshapen.
Acute angle closure glaucoma can cause ischaemic damage to the muscles of the iris causing an abnormal pupil shape, usually a vertical oval.
Rubeosis iridis (neovascularisation in the iris) can distort the shape of the iris and pupil. This is usually associated with poorly controlled diabetes and diabetic retinopathy.
Coloboma is a congenital malformation in the eye. This can cause a hole in the iris causing an irregular pupil shape.
Tadpole pupil is where there is spasm in a segment of the iris causing a misshapen pupil. This is usually temporary and associated with migraines.
Causes of mydriasis (dilated pupil)
Third nerve palsy
Holmes-Adie syndrome
Raised intracranial pressure
Congenital
Trauma
Stimulants such as cocaine
Anticholinergics
Causes of miosis (constricted pupil)
Horners syndrome
Cluster headaches
Argyll-Robertson pupil (in neurosyphilis)
Opiates
Nicotine
Pilocarpine
Third nerve palsy
A third nerve palsy causes:
Ptosis (drooping upper eyelid)
Dilated non-reactive pupil
Divergent strabismus (squint) in the affected eye. It causes a “down and out” position of the eye.
The third cranial nerve is the oculomotor nerve. It supplies all of the extraocular muscles except the lateral rectus and superior oblique. Therefore when these muscles are no longer getting signals from the oculomotor nerve, the eyes moves outward and downward due to the effects of the lateral rectus and superior oblique still functioning without resistance.
It also supplies the levator palpebrae superioris, which is responsible for lifting the upper eyelid. Therefore third nerve palsy causes a ptosis.
The oculomotor nerve also contains parasympathetic fibres that innervate the sphincter muscle of the iris. Therefore third nerve palsy causes a dilated fixed pupil.
The oculomotor nerve travels directly from the brainstem to the eye in a straight line. It travels through the cavernous sinus and close to the posterior communicating artery. Therefore, cavernous sinus thrombosis and a posterior communicating artery aneurysm can cause compression of the nerve and a third nerve palsy.
Causes of a third nerve palsy
Third nerve palsy can be idiopathic, without a clear cause.
A third nerve palsy with sparing of the pupil suggests a microvascular cause as the parasympathetic fibres are spared. This may be due to:
Diabetes
Hypertension
Ischaemia
A full third nerve palsy is caused by compression of the nerve, including the parasympathetic fibres. This is called a “surgical third” due to the physical compression:
Idiopathic
Tumour
Trauma
Cavernous sinus thrombosis
Posterior communicating artery aneurysm
Raised intracranial pressure
Horner syndrome
Horner syndrome is a triad of:
Ptosis
Miosis
Anhidrosis (loss of sweating)
They may also have enopthalmos, which is a sunken eye. Light and accommodation reflexes are not affected.
Horner syndrome is caused by damage to the sympathetic nervous system supplying the face.
The journey of the sympathetic nerves to the head is relevant for the causes of Horner syndrome. The sympathetic nerves arise from the spinal cord in the chest. These are pre-ganglionic nerves. They then enter into the sympathetic ganglion at the base of the neck and exit as post-ganglionic nerves. These post-ganglionic nerves then travel to the head, running alongside the internal carotid artery.
The location of the Horner syndrome can be determined by the anhidrosis. Central lesions cause anhidrosis of the arm and trunk as well as the face. Pre-ganglionic lesions cause anhidrosis of the face. Post-ganglionic lesions do not cause anhidrosis.
Causes of Horner syndrome
The causes can be remembered as the 4 Ss, 4 Ts and 4 Cs. S for Sentral, T for Torso (pre-ganglionic) and C for Cervical (post-ganglionic).
Central lesions (4 Ss):
S – Stroke
S – Multiple Sclerosis
S – Swelling (tumours)
S – Syringomyelia (cyst in the spinal cord)
Pre-ganglionic lesions (4 Ts):
T – Tumour (Pancoast’s tumour)
T – Trauma
T – Thyroidectomy
T – Top rib (a cervical rib growing above the first rib above the clavicle)
Post-ganglionic lesion (4 Cs):
C – Carotid aneurysm
C – Carotid artery dissection
C – Cavernous sinus thrombosis
C – Cluster headache
Testing Horner syndrome
Congenital Horner syndrome is associated with heterochromia, which is a difference in the colour of the iris on the affected side.
Cocaine eye drops can be used to test for Horner syndrome. Cocaine acts on the eye to stop noradrenalin re-uptake at the neuromuscular junction. This causes a normal eye to dilate because there is more noradrenalin stimulating the dilator muscles of the iris. In Horner syndrome, the nerves are not releasing noradrenalin to start with so blocking re-uptake does not make a difference and there is no reaction of the pupil.
Alternatively, a low concentration adrenalin eye drop (0.1%) won’t dilate a normal pupil but will dilate a Horner syndrome pupil.
Holmes Adie Pupil
A Holmes Adie pupil is a unilateral dilated pupil that is sluggish to react to light with slow dilation of the pupil following constriction. Over time the pupil will get smaller. This is caused by damage to the post-ganglionic parasympathetic fibres. The exact cause is unknown but may be viral.
Holmes Adie Syndrome is where there is a Holmes Adie pupil with absent ankle and knee reflexes.
