Vision loss Flashcards
What is your diagnostic approach to someone presented with visual loss?
Visual loss can be divided into:
- Acute visual loss
- Persistent
- Red eye
- Examine anterior segment for any pathologies
- Orbital cellulitis
- Scleritis
- Endophthalmitis
- Trauma and/or spontaneous hyphema
- Herptic keratitis
- Bacterial keratitis
- Anterior uveitis
- Acute angle-closure glaucoma
- Examine anterior segment for any pathologies
- Painful eye
- Examine anterior segment for any pathologies (mentioned above)
- Test RAPD to assess retina and optic nerve/ disc function
- If RAPD +
-
Abnormal optic disc - can be caused by:
-
Arteritic AIOH
- Due to to vasculitis e.g. GCA. This type of AIOH causes pain e.g. headache, jaw claudication, scalp tenderness
- Optic neuritis
-
Arteritic AIOH
-
Abnormal optic disc - can be caused by:
- If RAPD +
- Painless (no red eye)
- Test RAPD and examine posterior segment to assess retina and optic nerve/ disc function
- If RAPD + and posterior segment abnormal (either abnormal optic disc or abnormal retina)
-
Abnormal optic disc - can be caused by:
-
Non-arteritic AIOH
- Due to microvascular disease e.g. diabetes, HTN. This type of AIOH does NOT cause pain
- Optic neuritis (tho usually painful)
-
Non-arteritic AIOH
-
Abnormal retina
- Vitreous haemorrhage
- Retinal detachment
- CRAO
- CRVO
-
Abnormal optic disc - can be caused by:
- If RAPD + but posterior segment normal (i.e. normal optic disc and retina), the likely pathology is in the posterior optic nerve or brain
-
Check visual field loss to localise the lesion
- Inferior altitudinal field defect –> Posterior Ischaemic Optic Neuropathy (PION)
- Bitemporal hemianoptia –> Optic chiasm lesion e.g. pituitary adenoma
- Homonymous hemianopia –> a brain lesion (e.g. tumour) in the contralateral optic tract or occipital lobe
- Inferior quadrantanopia –> parietal lobe lesion
- Superior quadrantanopia –> temporal lobe lesion
-
Check visual field loss to localise the lesion
- If RAPD + and posterior segment abnormal (either abnormal optic disc or abnormal retina)
- Test RAPD and examine posterior segment to assess retina and optic nerve/ disc function
- Red eye
- Transient (amaurosis fugax)
- TIA
- Migraine with aura
- Seizures with aura
- Hypoglycaemia
- Persistent
- Chronic (gradual) visual loss
- Refractive errors
- Cataract
- Primary open angle glaucoma
- Age-related macular degeneration (AMD)
- Diabetic retinopathy
- Corneal blindness - e.g. trachoma, keratitis that cause corneal opacification
- Drug toxicity e.g. hydroxychloroquine, ethmabutol
(Remember that RAPD suggests a pathology from the retina all the way to the pretectal area)
Please see below the image illustrating the dual blood supply of the macula
See image
The eye can be split into anterior and posterior segments.
What structures make up the anterior and posterior segments?
Anterior segment:
- Cornea, iris, ciliary body, lens
- Both anterior and posterior chambers
- Anterior chamber - between cornea and iris
- Posterior chamber - between iris and vitreous humor
Posterior segment:
- Vitreous humor, retina, choroid, optic nerve disc/ head
What is anterior ischaemic optic neuropathy (AION)?
AION refers to ischaemia of the optic nerve which results in optic disc swelling (papilloedema). If the optic nerve ischaemia is present without optic disc swelling, it’s referred to as posterior ischaemic optic neuropathy (PION)
(Note that ischaemia of the optic nerve can occur at different anatomical locations. If it affects the inferior nerve fibres of the retina/ optic nerve, you get superior altitudinal field defect. If it affects the superior nerve fibres, you can inferior altitudinal field defect instead)
There are 2 types of AION. What are they?
What are the causes of each type?
Arteritic AION
- Due to GCA which causes inflammation of the temporal arteries and subsequent thrombosis of the short posterior ciliary arteries (branch from the ophthlamic artery, which arises from the ICA)–> ischaemia of optic disc and optic nerve
- Inflammation damages the lining of affected blood vessels, causing narrowing and thrombosis (think about Virchow’s triad: venous stasis, endothelial damage, hypercoagulability)
- Loss of proteins (albumin) from arteries result in optic disc swelling
Non-arteritic AION (more common + better prognosis)
- Due to microvascular (non-inflammatory) disease of small blood vessels (short posterior ciliary arteries) that supply the optic nerve, such as diabetes, HTN, atherosclerosis
What are the risk factors for arteritic AION and non-arteritic AION?
Risk factors for arteritic AION (GCA):
- Age > 50 yrs old
- Female
- Whites (European)
- PMHx of polymyalgia rheumatica
Risk factors for non-arteritic AION:
- Age > 50 (tho typically younger than that of GCA at presentation)
- Cardiovascular risk factors e.g. HTN, diabetes, hyperlipidaemia and smoking
- Anaemia
What are the clinical features of AION?
Presentations:
- Arteritic AION (features of GCA)
- Symptoms
- Typically affects patients > 50 yrs old
- Rapid onset
- Temporal headache - often localised, unilateral, boring or stabbing in quality over the temple
- Scalp tenderness e.g. when combing hair
-
Jaw claudication upon mastication –> difficulty eating –> weight loss
- “Angina” of the jaw muscles - the pain comes on gradually during chewing
-
Acute painful loss of vision (amaurosis fugax) in one eye
- May take weeks-months to develop after onset of other symptoms
- If left untreated, the 2nd eye may become affected in 1-2 weeks
-
Diplopia - due to CN3, 4 and 6 palsy
- In GCA, inflammation can cause narrowing of the ophthalmic artery, which supplies blood to your extraocular muscles
-
Polymyalgia rheumatica in 50% of patients
- Bilateral pain, tenderness and morning stiffness in proximal limbs, shoulders, hips and neck
- Systemic symptoms e.g. fever, anorexia, night sweats, depression, fatigue
- Signs
- On palpation of the temporal artery –> tender, pulseless, beaded, enlarged
- Fundoscopy shows papilloedema + pale optic disc (indicating optic atrophy) - see image
- RAPD
- Reduced visual acuity (more profound compared to non-arteritic AION) and colour vision
- Symptoms
- Non-arteritic AION
- Symptoms
-
Acute painless loss of vision in one eye (often described as blurring or cloudiness)
- Patients often become aware of vision loss upon waking in the morning
-
Acute painless loss of vision in one eye (often described as blurring or cloudiness)
- Signs
- Reduced visual acuity (less profound compared to GCA) and colour vision
- Fundoscopy shows papilloedema + pale optic disc + splinter haemorrhages
- RAPD
- Inferior altitudinal field defect
- Symptoms
What does the image (the one on the right) below show?
Splinter haemorrhage
(splinter = a small thin sharp piece)
This is different from flames haemorrhages which look bigger (see the image on the left)
What investigations would you consider in someone with suspected AION?
Ix:
- Bedside investigations
- Visual acuity assessment - reduced in AION
- Colour vision assessment - reduced in AION
- Blood pressure - as HTN is a risk factor of non-arteritic AION
- Laboratory investigations for arteritic AION:
- FBC - normochromic anaemia and raised plt count
- CRP - raised in GCA
- ESR >/= 50 mm/h
- LFTs - mild elevation of ALP, ALT and AST
- Laboratory investigations for non-arteritic AION:
- Glucose, HbA1c - diabetes mellitus is a risk factor
- Lipid profile - hyperlipidaemia is a risk factor
- Vasculitis screen - if patient < 50 yrs old (patients with non-arteritic AION typically present younger than that of GCA at presentation)
- Other investigations
- Temporal artery biopsy - shows mononuclear cell infiltration or granulomatous inflammation with multinucleate giant cells - gold standard
- Duplex USS of temporal artery - shows halo sign (due to oedema of vessel) if positive for GCA
What is the management of AION?
Mx:
- Arteritic AION (GCA)
- High-dose prednisolone
- Urgent same-day referral to an ophthalmologist or rheumatologist
- Non-arteritic AION
- Treatment aims at optimising risk factors e.g. better control of HTN, diabetes and hyperlipidaemia to prevent progression
Compare and contrast arteritic AION and non-arteritic AION
Epidemiology:
- Arteritic AION - less common (1/100,000)
- Non-arteritic AION - more common (10/100,000)
Risk factors:
- Arteritic AION - age, female, PMHx of polymyalgia rheumatica
- Non-arteritic AION - age, diabetes, HTN, hyperlipidaemia, smoking, anaemia
Age
- Arteritic AION - 70 yrs old
- Non-arteritic AION - 60 yrs old (typically presents younger than arteritic)
Visual acuity and visual field defect
- Arteritic AION - usually < 6/60 (worse visual acuity)
- Non-arteritic AION - usually > 6/60 (better visual acuity), often have an altitudinal field loss
Associated symptoms
- Arteritic AION - scalp tenderness, jaw claudication, headache
- Non-arteritic AION - usually none
Optic disc
- Arteritic AION - pale (optic atrophy) and swollen optic disc (papilloedema)
- Non-arteritic AION - pale and swollen optic disc with splinter haemorrhages
ESR, CRP, Plt count
- Arteritic AION - raised
- Non-arteritic AION - normal
Prognosis
- Arteritic AION - 15% improve
- Non-arteritic AION - 40% improve
What are the causes of unilateral papilloedema?
Young people –> optic neuritis (MS)
Old people –> microvascular (atherosclerosis)
What are the causes of bilateral papilloedema?
Raised ICP, HTN
What is retinal artery occlusion?
An ocular emergency caused by blockage of blood supply to the retina of one eye, causing sudden painless loss of vision. If not treated promptly, infarction of the retina occurs after 90 minutes of oxygen deprivation resulting in permanent visual loss in that eye
It’s essentially a type of stroke that affects the retinal artery
What are the different types of retinal artery occlusion?
2 types of retinal artery occlusion:
- Central retinal artery occlusion (CRAO)
- Branch retinal artery occlusion (BRAO)
Describe the course of ICA and how it enters the brain to give rise to central retinal artery and its branches
Common carotid artery –> ICA + ECA –> ICA enters temporal cranial fossa through the carotid canal within the petrous part of the temporal bone –> goes over the foramen lacerum –> pass anteriorly through the cavernous sinus –> once the ICA is distal to the cavernous sinus, it gives rise to:
- Ophthalmic artery
- Posterior communicating artery
- Anterior choroidal artery
- Anterior cerebral artery
The ICA then continues as the middle cerebral artery
The ophthalmic artery passes through the optic canal with and inferolaterally to the optic nerve to enter the orbit. The ophthalmic artery gives off central retinal artery (the first to branch) along with other branches such as supraorbital and supratrochlear arteries (supply scalp), anterior and posterior ethmoidal arteries (supply the Kiesselbach area), short and long posterior ciliary arteries
The central retinal artery supplies the optic nerve and inner retina!
Upon entering the nerve fibre layer of the retina, the central retinal artery divides into two branches; the superior branch and the inferior branch. These both further subdivide into temporal and nasal terminal arterioles, resulting in 4 terminal arterioles. Each of the arterioles supplies one quadrant of the eye. They are named according to their quadrant: superior nasal, inferior nasal, superior temporal, and inferior temporal arterioles. Each arteriole supplies its respective quadrant exclusively and there are no anastomoses between the 4 of them, which is why they are called functional end-arteries (this means that if one of these 4 arterioles is blocked, you get ischaemia and infarction of that quadrant of the retina –> branch retinal artery occlusion)
What are the causes of retinal artery occlusion?
Older patients: thromboembolism (from atherosclerosis and stroke) - most common
Younger patients: vasculitis (e.g. temporal arteritis) or artery dissection
a) . How common is CRAO?
b) . What age group of people does it affect the most?
a) . CRAO is rare
b) . More commonly seen in patients with cardiovascular risk factors e.g. diabetes, HTN, smoking, hence more likely in elderly patients (60-65 yrs old)
Give 5 risk factors of retinal artery occlusion
- Things that promote atherosclerosis and embolism (stroke) - HTN, diabetes, hyperlipidaemia, smoking, _*AF_
- Haematological - antiphospholipid syndrome (increases risk of blood clots), malignancy (e.g. myeloma, leukaemia, lymphoma), sickle cell anaemia
- Vascular - carotid artery dissection (if extension into the ICA or retinal artery), fibromuscular dysplasia (narrowing of the arterial lumen due to arterial wall abnormalities that are non-inflammatory, non-atherosclerotic)
- Inflammatory - GCA, SLE, granulomatosis with polyangiitis (GPA)
- Infective - toxoplasmosis, syphilis, lyme disease
-
Pharmacological - COCP, recreative drug use (e.g. cocaine)
- Cocaine increases risk of blood clots
- Others (rare) - complications of ophthalmic surgery, fat/ amniotic fluid embolism
What are the clinical features of central retinal artery occlusion?
Presentations:
- Sudden unilateral painless visual loss or reduced visual acuity
- Severity depends on the site of occlusion
- Proximal ophthalmic occulsion (CRAO) –> significant visual loss
- Occlusion to a branch/ distal portion of the retinal artery (BRAO) –> less profound visual loss
- Note that in 25% of people who develop CRAO have an extra artery called a cilioretinal artery (arises from the short posterior ciliary artery) in their eyes, giving additional supply to the macula. In these patients, having a cilioretinal artery can greatly lower the chances of damage to the central vision, as long as the cilioretinal artery is not affected. Therefore, CRAO may present with central visual sparing in these patients
- In BRAO, rather than losing vision in the entire eye, patients often present with a loss of a section of the visual field, usually the inferior part (respecting the horizontal midline) –> Inferior altitudinal field defect (blockage in the superior nasal and superior temporal branches of the central retinal artery)
- Severity depends on the site of occlusion
- RAPD
- Fundoscopy shows:
- Narrowing of retinal arteries/ veins
-
Pale retina (due to ischaemia)
- In BRAO, the area of ischaemia (retinal pallor) is typically sectoral - which means it typically affects either superior nasal, inferior nasal, superior temporal or inferior temporal part of the retina
-
Cherry-red spot
- The cherry red spot appears in the fovea because the fovea is the thinnest part of the retina, so when the retina becomes ischaemic and pale, you can see the underlying vascularised choroid (appears red) through the fovea
- Note that the cherry red spot is not observed in those with a cilioretinal artery
- Retinal emboli
-
Neovascularisation of the optic disc, fundus or iris (chronic ischaemia)
- The concept is the same as having collateral vessels in ischaemia (due to VEGF)
- Raised IOP
- Other features:
- Arrhythmias e.g. AF –> thrombus formation in atrium –> dislodge to the brain then to the retina
- Heart murmurs - indicative of valvular heart disease or infective endocarditis
-
Carotid bruits - suggests the presence of carotid artery stenosis
- Carotid stenosis can cause stroke in 2 ways:
- The plaque lodged in the carotid arteries comes loose and goes downstream into the blood vessels in the brain (embolism)
- The carotid artery blockage becomes so severe that it actually slows down the blood flow to the brain
- Carotid stenosis can cause stroke in 2 ways:
- Temporal artery tenderness - associated with CRAO
Patients present to you with acute visual loss. On examination of the fundoscopy, you see this. What does the image show? and what diagnosis does it indicate?
Branch retinal artery occlusion (BRAO)
In this case, the superior temporal area of the retina is ischaemic, which means the superior branch of the central retinal artery is affected!
What investigations would you carry out for retinal artery occlusion?
Ix:
CRAO is usually a clinical diagnosis - based on clinical features, fundoscopy findings and the presence of cardiovascular risk factors
If needed, the diagnosis can be confirmed using fluorescein angiography. A fluorescent dye is injected intravenously, the retinal vessels are then assessed through imaging to look for evidence of slowed flow or a filling defect
- Bedside investigations
- Visual acuity
- Colour vision
- RAPD
- BP - as HTN is a risk factor
- ECG - as AF can cause embolus to lodge in retinal artery
- Laboratory investigations
- FBC
- ESR, CRP - to exclude GCA (esp in older patients > 50 yrs old)
- Coagulation screen - conditions such as antiphospholipid syndrome, malignancy, sickle cell anaemia and thrombophilia increase the risk of blood clot formation
- Glucose - as diabetes is a risk factor
- Lipid profile - as hyperlipidaemia is a risk factor
- If the patient is < 50 yrs old (where atherosclerosis is less likely), include:
- Vasculitis screen: ANA, ANCA, dsDNA, RF, Anti-GBM, serum immunoglobulins
- Serum protein electrophoresis (myeloma)
- Infection screen (serology) for toxoplasmosis, syphilis
- Thrombophilia screen
- Syphilis serology
- TFT - hyperthyroidism can cause AF
- Imaging
- Carotid artery doppler - to evaluate the presence of carotid stenosis
- CXR - to detect sarcoidosis and TB (in patients < 50)
- Echocardiography - if there is a PMHx of rheumatic fever, valvular heart disease or IVDU
What is the management of CRAO?
Mx of CRAO:
Urgent referral to the stroke team and ophthalmology
Treatment should be administered within 6 hrs of onset, except if it’s GCA where immediate management is needed
- If GCA –> urgent high-dose steroids (IV methylprednisolone)
Intra-arterial thrombolysis - for patients without complications who present within the appropriate time frame
- This refers to catheter-directed delivery of recombinant tissue plasminogen activator (tPA) via the ophthalmic artery
- Systemic thrombolysis is avoided as it has more side effects e.g. intracerebral haemorrhage
Surgical intervention - for patients who are not suitable for thrombolysis but still present within a reasonable timeframe from onset
- Anterior chamber paracentesis - reduce IOP to try to dislodge the embolus
Other interventions - for those not suitable for thrombolysis or surgical intervention
-
Ocular massage (rarely successful)
- Apply direct pressure to the affected eye over a closed eyelid every 10 seconds with 5 second breaks
- External pressure to the eye increases IOP, which causes reflexive dilatation of retinal arterioles. A sudden drop in IOP with release increases the volume of flow, dislodging the embolus
-
Hyperbaric oxygen therapy
- It increases the amount of oxygen the choroid vessels can provide to the inner retina via diffusion
- Reducing IOP with IV acetazolamide, mannitol and topical agents
- Vasodilator therapies - pentoxifylline and nitroglycerin to dilate arterial vessels
Long term management:
- Optimise cardiovascular risk factors
- Lifestyle advice, aspirin, statin, antihypertensives, metformin, smoking cessation, beta-blocker for AF
- Ix underlying cause:
- Carotid artery disease - carotid duplex USS or CT angiography. Carotid endarterectomy maybe needed
- Exclusion of GCA - ESR, CRP, temporal artery biopsy
- Cardioembolic sources - echo, 24 hr tape and ECG
- Thrombophilia testing - esp in young patients
Mx of BRAO:
- Supportive Mx mostly due to a high chance of spontaneous recovery
- Urgent referral to an ophthalmologist for same-day assessment if presenting within 24 hrs
- Ix underlying cause + optimise cardiovascular risk factors
What are the complications of retinal artery occlusion?
- Permanent vision loss
- Insufficient retinal perfusion results in the production of VEGF which results in the development of new vessels on the retina (neovascularisation of the optic disc and fundus). These new vessels are brittle, hence they rupture easily causing recurrent vitreous haemorrhage
- Neovascularisation of the iris (rubeosis iridis) - the new blood vessels grow on the iris and can occlude the drainage angle –> raised IOP –> neovascular glaucoma
What is the treatment for neovascularisation?
Pan-retinal photocoagulation
(note that this is not just for treating neovascularisation from proliferative diabetic retinopathy, it’s for treating neovascularisation of any cause)
Prognosis of CRAO:
What is the prognosis of CRAO?
Severely affected patients are usually left with only a small island of temporal vision that can detect counting fingers at best without intervention. Those with branch occlusion usually recover normal vision completely (~80%)
Describe how retinal veins drains blood from the retina
Each quadrant of the retina (ST, SN, IT, IN) is drained by multiple minor retinal veins which coalesce to form a main retinal vein. The confluence of the superotemporal and superonasal main retinal veins forms the superior papillary vein, while the confluence of the two inferior main retinal veins forms the inferior papillary vein. The superior and inferior papillary veins converge creating the central retinal vein, which drains the retina and the optic nerve
The central retinal vein exits the eye globe via the lamina cribrosa, and courses in the centre of the optic nerve alongside the central retinal artery
What is the pathophysiology of central retinal vein occlusion (CRVO)?
Pathophysiology:
The central retinal artery and vein share a common adventitial sheath as they exit the optic nerve head and pass through a narrow opening in the lamina cribrosa. Because of this narrow entry in the lamina cribrosa, the vessels are in a tight compartment with limited space for displacement.
Atherosclerotic changes in the central retinal artery transform the artery into a rigid structure and impinge on the pliable central retinal vein, causing haemodynamic disturbances (slowing of venous blood flow), endothelial damage, and thrombus formation (Virchow’s triad) in the central retinal vein! This mechanism explains the fact that there maybe an associated arterial disease with CRVO. However, this association has not be proven consistently
Thrombotic occlusion in the central retinal vein not only can be caused by atherosclerosis in the central retinal artery, it can also be caused by compression of the vein (mechanical pressure due to structural changes in lamina cribrosa e.g. glaucomatous cupping, inflammatory swelling in optic nerve, orbital disorders); haemodynamic disturbances (associated with hyperdynamic or sluggish circulation); vessel wall changes (e.g. vasculitis); and changes in the blood (e.g. deficiency of thrombolytic factors, increase in clotting factors)
- Think about the Virchow’s triad - hypercoagulability, venous stasis, endothelial damage
Thrombotic occlusion of the central retinal vein leads to the backup of blood in the retinal venous system and increased resistance to venous blood flow. This increased resistance causes stagnation of the arterial blood and ischaemic damage to the retina. Ischaemic damage to the retina stimulates increased production of VEGF in the vitreous cavity. VEGF stimulates neovascularisation of the anterior and posterior segment, increasing the risk of secondary complications e.g. recurrent vitreous haemorrhage and neovascular glaucoma in CRVO. In addition, VEGF causes increased capillary permeability (more leaky), which together with increased capillary hydrostatic pressure (from thrombotic occlusion of the central retinal vein), leading to cystoid macula oedema which is the leading cause of visual loss in both ischaemic CRVO and non-ischaemic CRVO
Retinal ischaemia also causes direct endothelial damage to retinal blood vessels, causing extravasation of blood –> haemorrhages
(**Central retinal vein occlusion occurs secondary to atherosclerotic thickening of the central retinal artery compressing the central retinal vein at a common crossing point)
What is the pathophysiology of branch retinal vein occlusion (BRVO)?
Pathophysiology of BRVO:
- Common adventitia binds the branch retinal artery and the branch retinal vein together at the arteriovenous crossing. The artery lies anterior to the affected vein in 99% of eyes with BRVO
- Thickening of the arterial wall compresses the vein underneath resulting in turbulence of flow, endothelial damage and thrombotic occlusion
- > 50% of BRVO cases occurs in the superotemporal quadrant
What are the 2 types of CRVO?
Which type is the most common?
Non-ischaemic CRVO (more common; 75% of cases) - a milder type characterised by leaky retinal vessels with macular oedema
Ischaemic CRVO (25% of cases) - a more severe type with closed-off small retinal blood vessels
Give 5 risk factors of central retinal vein occlusion
Risk factors of CRVO:
- Old age - > 50% of cases occur in patients > 65 yrs old
- Cardiovascular disease - diabetes mellitus, HTN, hyperlipidaemia, smoking, alcohol - more common in elderly
- Hypercoagulable state - thrombophilia, malignancy (myeloma, leukaemia), antiphospholipid syndrome, previous DVT, polycythaemia
- Autoimmune disease e.g. SLE, sarcoidosis - more common in those < 50 yrs old
- Ophthalmic disease e.g. glaucoma
- Infections e.g. syphilis
- Drugs - COCP
What are the clinical features of CRVO?
Presentations:
- Sudden unilateral painless visual loss or reduced visual acuity (a lot worse in ischaemic type)
- RAPD
- Fundoscopy shows:
-
Retinal haemorrhage - dot/blot and flame-shaped haemorrhages
- Central retinal vein occlusion has a haemorrhage in all 4 quadrants (widespread) while in branch retinal vein occlusion it’s more localised (e.g. affects one particular quadrant)
- The retinal veins are less expandable compared to arteries, so they can rupture easily
- Dilated tortuous retinal veins
- Papilloedema (optic disc swelling)
-
Cystoid macula oedema - usually seen at late presentation
- Often observed in Optical Coherence Tomography (OCT)
- In addition to the above, findings suggestive of ischaemic CRVO include:
- Cotton wool spots
- Neovascularisation of the optic disc, fundus and iris as a result of chronic ischaemia –> recurrent vitreous haemorrhage + neovascular glaucoma
-
Retinal haemorrhage - dot/blot and flame-shaped haemorrhages
What does the Optical Coherence Tomography show?
The image on the left is a normal OCT
The one of the right shows macula oedema
What investigations would you carry out in someone with suspected CRVO?
Ix:
- CRVO is usually a clinical diagnosis - based on clinical features, fundoscopy findings and the presence of cardiovascular risk factors
- If needed, the diagnosis can be confirmed using fluorescein angiography. A fluorescent dye is injected intravenously, the retinal vessels are then assessed through imaging to look for evidence of slowed flow or a filling defect
- Bedside Ix:
- Visual acuity
- Colour vision
- Test RAPD
- Ocular tonometry to determine IOP - as glucoma is a risk factor
- BP - as HTN is a risk factor
- ECG - to rule out AF, ACS
- AF can cause central retinal artery occlusion which in turn causes central retinal vein occlusion
- Laboratory Ix:
- FBC, ESR, CRP
- Random blood glucose - as diabetes is a risk factor
- Lipid profile - as hyperlipidaemia is a risk factor
- Coagulation screen - as thrombophilia, polycythaemia, malignancy, antiphospholipid syndrome
- Serum protein electrophoresis to rule out myeloma
- Laboratory Ix for those < 50 yrs old (where atherosclerosis is less likely) include:
- Serum ACE to rule out sarcoidosis
- Anticardiolipin, Lupus anticoagulant (LAC) - both are to rule out antiphospholipid syndrome
- Autoantibodies: RF, ANA, ANCA, dsDNA
- Thrombophilia screen: protein C and S, and factor V Laiden
- Syphilis serology
- Imaging
- Not usually needed unless the patient has an atypical presentation or is < 50 yrs old
- CXR to look for sarcoidosis
- Not usually needed unless the patient has an atypical presentation or is < 50 yrs old
How would you manage this patient with CRVO?
Mx:
- Treat underlying cause + optimise risk factors
- Anti-VEGF injections to treat macular oedema
- Laser therapy to treat neovascularisation of the fundus or iris
Give 2 complications of CRVO
Permanent visual loss
Cystoid macula oedema
Recurrent vitreous haemorrhage
Neovascular glaucoma
Before learning what retinal detachment is, it’s important to understand the anatomy of the retina first.
What are the different layers of the retina? (must remember!) and what does each layer consist of?
Retinal layers:
There are 10 distinct layers of the retina! From closest to farthest from the vitreous body
-
Inner limiting membrane
- Basement membrane spanned by Muller cells (retinal glial cells)
-
Nerve fibre layer
- Contains axons of ganglion cell bodies (= optic nerve fibres)
-
Ganglion cell layer
- Contains cell bodies of ganglion cells, the axons of which become the optic nerve fibres , and some amacrine cells (inhibitory interneurons)
-
Inner plexiform layer
- Contains the synapse between the bipolar cell axons and the dendrites of the ganglion and amacrine cells
-
Inner nuclear layer
- Contains the cell bodies of the bipolar cells, amacrine cells and horizontal cells
-
Outer plexiform layer
- Contains projections of rods and cones. They form synapses with the dendrites of the bipolar cells and horizontal cells
- In the macular region, this layer of the retina is known as the Fibre layer of Henle
-
Outer nuclear layer
- Contains cell bodies of rods and cones
-
External limiting membrane
- A layer that separates the inner segment portions of the photoreceptors from their cell bodies
-
Inner segment/ outer segment layer
- Inner segments and outer segments (contains light-sensing apparatus) of rods and cones
-
Retinal pigment epithelium
- A single layer of cuboidal epithelial cells
- This layer is closest to the choroid, and provides nourishment and supportive funvtions to the neural retina
- Contains melanin (hence it’s a “pigmented” layer) which is a black pigment that prevents light reflection throughout the eyeball - very important for clear vision
In pre-clinical years, we were taught that the retina only has 2 layers - the inner neural layer and the outer pigmented layer. The outer pigmented layer is essentially the retinal pigment epithelium, and the inner neural layer includes all other layers except for the retinal pigment epithelium!
What are the 3 key cells (neurons) that help conduct signals from the photoreceptors to the optic nerve fibres?
Remember, the retina is part of the CNS (part of the brain), and whenever information is delivered, it has to go through 3 neurons:
Light hits: Photoreceptors (rods + cones) –> bipolar cells –> ganglion cells
The axons of the ganglion cells converge to form the optic nerve. The axons coming from the nasal side of the retina (nasal fibres) decussate in the optic chiasm
Please label each of the respective layers on this optic coherence tomography (OCT)
See image!
What is retinal detachment?
Retinal detachment is an ophthalmic emergency caused by separation of the inner neurosensory retina from the underlying retinal pigment epithelium, which allows vitreous fluid to accumulate in the subretinal space. If left untreated, the fluid accumulation will cause further progressive retinal detachment, resulting in progressive loss of vision in the affected eye. If the retina in the macula starts detaching, you will start to lose central vision as well
The retina is constantly supplied with blood by the choroid layer, so if it’s not reattached ASAP, ischaemia of the retina occurs and subsequently infarction –> permanent visual loss in the affected eye
What are the causes/ types of retinal detachment?
There are 3 main types of retinal detachment:
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Rhegmatogenous (most common) - your vitreous shrinks (becomes liquidifed) as part of the normal aging process. When it does that, it can pull the retina along with it, causing a retinal tear or break. Continued traction by the vitreous on the retina allows fluid to enter the subretinal space, causing retinal detachment
- Most gradual posterior vitreous detachment (PVD) does not result in retinal detachment. However, in acute form the vitreous can suddenly come away from the retina causing retinal detachment!
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Tractional
- Most commonly seen in people with proliferative diabetic retinopathy
- Diabetic retinopathy can result in fibrous scar tissue forming inside the vitreous and on the retinal surface. This scar tissue can then pull on the retina (traction) causing a retinal detachment!
- Unlike the rhegmatogenous form, there is no retinal break!
- Other causes include:
- CRVO
- Proliferative sickle cell retinopathy
- Exudative (rare)
- This is caused by leakage of fluid from the choroid vessels lying behind the retina into the subretinal space
- Often due to inflammation of the choroid (posterior uveitis), malignancy (e.g. choroidal melanoma or ocular metastases), hypertensive choroidopathy, or iatrogenic (e.g. vitrectomy or laser treatment)
- There are no hole or tear present
What does the image below show?
What diagnosis does it indicate?
Detached retinal fold –> large retinal detachment (macula is spared)
What does the fundoscopy image below show?
Retinal tear!
Patients complain of seeing floaters more frequently. He is 74 yrs old. What does the image below show?
Weiss ring–> posterior vitreous detachment!
What does the image show?
Tobacco dust –> retinal detachment
What are the different types of age-related macular degeneration?
What are the characteristics of each type of AMD?
2 types:
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Dry macular degeneration (most common but better prognosis, 80% cases)
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Non-exudative + Geographic atrophy
- Geographic atrophy refers to regions of the retina where cells waste away and die. Sometimes these regions of atrophy look like a map to the doctor who is examining the retina with a fundoscope, hence the term geographic atrophy)
- Characterised by the presence of drusen (hard/ soft), which are yellow round spots found between the RPE and the Bruch’s membrane
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Non-exudative + Geographic atrophy
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Wet macular degeneration (less common but worst prognosis, 20% cases)
- Exudative + neovascularisation
- Characterised by choroidal neovascularisation
- These new blood vessels extend through the Bruch’s membrane and invade the space between the RPE and the Bruch’s membrane, and also through the RPE into the subretinal space
- These vessels are leaky and brittle –> leakage of serous fluid and blood into the potential spaces –> further separation between the RPE and Bruch’s membrane, and further separation between the neural layer of the retina and the RPE –> rapid vision loss
(**Wet AMD almost always arise from dry AMD, so patients usually get dry AMD first before progressing to wet AMD)
What’s the pathophysiology of AMD?
In summary, the imbalance between the production of damaged cellular components and degradation leads to the accumulation of harmful products, for example, intracellular lipofuscin and extracellular drusen
The retina is the most oxygen-consuming tissue in the body with a consumption level of 50% higher than the brain or kidneys. Most of this oxygen consumption occurs in photoreceptors (rods + cones) which are most abundant in the macula and fovea. This results in the accumulation of oxidative and photo-oxidative damage in the photoreceptors (esp in the macula)
To get rid of the damaged parts, photoreceptors continuously renew their outer segment by shedding membranous disks (the portion that captures light in cone cells) in RPE. This daily cycle of renewal and shedding places a heavy metabolic burden on the underlying RPE cells, so over time, the phagolysosomes of RPE cells become overwhelmed and are unable to fully degrade these molecular debris, resulting in accumulation of sacs of molecular debris inside the RPE cells. These debris form lipid-protein aggregates called lipofuscin.
As the person ages, more and more of these functionless lipofuscin residues accumulate, causing progressive engorgement of the RPE cells. This causes the RPE cells to excrete these aberrant materials into a potential space located between the Bruch’s membrane and the RPE layer in the form of drusen (hard/ soft yellow deposits)
- Hard drusen - small, hard, solid deposits
- Soft drusen - larger soft deposits
(Lipofuscin is intracellular while drusen is extracellular, both are made of the same materials)
Dry AMD:
As drusen builds up, they ‘lift’ the RPE away from the Bruch’s membrane, causing hypoxia of the RPE and inflammation. Hypoxia of the RPE results in atrophy of choriocapillaries, RPE and photoreceptors, and also hypo/ hyper-pigmentation of the RPE
- In advanced dry AMD, you get advanced map-like area of atrophy extends to foveal centre - this is called “geographic atrophy”
Wet AMD:
Inflammation attracts monocytes/ macrophages which releases VEGF-A. The VEGF-A, in turn, causes choroidal neovascularisation, which is the growth of new blood vessels that originate from the choroid through a break in the Bruch membrane into the sub-retinal pigment epithelium (sub-RPE). The presence of choroidal neovascularisation = wet AMD
These new vessels are leaky and brittle, this causes fluid and blood to leak beneath and into the retina –> exudation and haemorrhage –> ischaemia and infarction of the macula –> disciform scar formation over the macula –> central vision loss (a scotoma)
What are the fundoscopic signs of pre-proliferative diabetic retinopathy?
Multiple microaneurysms
Dot and blot haemorrhages
Hard exudates
Evidence of retinal ischaemia such as cotton wool spots, venous beading/ looping, arteriolar narrowing, and intraretinal microvascular abnormalities (IRMAs)
What are the fundoscopic signs of proliferative diabetic retinopathy?
Neovascularisation - new vessels on the disc (NVD) and/or new vessels elsewhere (NVE)
Vitreous haemorrhage
Tractional retinal detachment (due to fibrous tissues forming in the vitreous and on the retinal surface)
*Proliferative diabetic retinopathy is more common in T1DM, with 50% of patients going blind in 5 yrs
How do you manage diabetic retinopathy?
Mx:
- Medical management
- Glycaemic control - ensure blood sugar levels are well controlled will delay the progression of diabetic retinopathy. Aim for a HbA1c between 48-58 mmol/mol
- BP control - aim to stabilise BP to < 140/80 mmHg to help prevent progression of diabetic retinopathy
- Diet, exercise and smoking cessation
- Advise that they may not be able to drive or play sports
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Photocoagulation to manage proliferative diabetic retinopathy and in some cases, severe non-proliferative diabetic retinopathy
- Involves the use of a laser to create burns in the retina, thus destroying the photoreceptors. With fewer photoreceptors, oxygen demand in the retina decreases so endothelial cells release less VEGF, delaying the progression of diabetic retinopathy
- 2 different methods of photocoagulation (see image)
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Focal/ grid photocoagulation
- Focal photocoagulation targets a specific point of leakage around the macula with laser, while grid photocoagulation targets more diffuse retinal thickening and oedema with no obvious point of leakage around the macula.
- Complications - decreased acuity of central vision, paracentral scotoma, DMO may worsen
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Pan-retinal photocoagulation (PRP) - more commonly used
- The periphery of the retina is targeted with the aim of achieving a global reduction in oxygen demand. The macula (centre) is not treated
- Complications - restricted peripheral vision, reduced night vision, eye pain, DMO may worsen
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Focal/ grid photocoagulation
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Intravitreal anti-VEGF/ corticosteroid injections
- Aim at minimising neovascularisation and thus are used in proliferative diabetic retinopathy
- Complications - cataract, raised IOP
- Anti-VEGF injections are contraindicated in patients who have had a stroke or MI in the last 3 months
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Vitrectomy if persistent vitreous haemorrhage or in central, sight-threatening tractional retinal detachment
- Proliferative diabetic retinopathy can cause bleeding into the vitreous humour (vitreous haemorrhage), which further increases the risk of retinal detachment. In most cases, waiting for the haemorrhage to settle can allow sufficient view to perform laser therapy. However, in persistent haemorrhage, a vitrectomy maybe performed. This allows the vitreous to be removed and repairing of any scarring/ retinal detachment
Another image comparing different methods of photocoagulation!
See image
Microaneurysms of the eye
Dot and blot haemorrhages
What does the image show?
Cotton wool spots, seen in pre-proliferative diabetic retinopathy
Neovascularisation
See image
What do the fundoscopy and the OCT show?
Diabetic macular oedema - you see hard exudates (waxy yellow lesions with relatively distinct margins arranged in clumps or rings, often surrounding leaking microaneurysms)
What does the OCT show?
Diabetic macular oedema (DMO)
What does the fundoscopy show?
Pan-retinal photocoagulation (PRP)
What is the lens made of and what are its functions?
The lens is made of the capsule, epithelium, cortex and nucleus (see image). It has 2 functions primarily: refraction and accommodation reflex
