Opthalmology Flashcards
What do you need to do for opthalmoscopy ?
dilate pupil by relaxing sphincter muscles
-Eg Atropine
[Tropicamide /
Cyclopentolate ]
Things to describe in the optic disk
Colour
Contour
Cup
Circulation
Name 3 causes of retinal haem
diabetic retinopathy, SAH, vasalva haemorrhage, hypertensive retinopathy,
What would a bright yellow ring around a central leak in opthamoscopy indicate ? mx if near macula?
fluid leakage
laser
What are cotton wool spots -
micro infarcts
What are drusen?
pale, round and grey. Seen at the macula in the elderly
-> sign of age-related macula degeneration
spidery black pigmentation in peripheral retina?
Retinitis pigmentosa
-inherited retinal degeneration
What is a scotoma
Cause of a central?
blind spot
lesion in the optic nerve between nerve head and chiasm
-Eg optic neuritis, MS
Macular degeneration leads to a central scotoma
/Users/eleanorpatterson/Desktop/The-illustration-of-the-location-of-central-scotoma-simulation-on-the-goggle.png
What is meant by congruity?
refers to the agreement of shape of the defect.
The closer to the visual cortex - the more congruous
What is a junctional scotoma
Lesion at junction of optic nerve and chiasm
->contralateral nasal fibres compressed because the nasal fibres dip into the optic nerve before travelling down the optic tract.
/Users/eleanorpatterson/Desktop/Simplified-diagram-of-the-anterior-visual-pathways-and-chiasmal-decussation-A-bundle.png
What is a slit lamp used for
examining the anterior segment of the eye (i.e. infront of the vitreous body)
Small depression in centre of macula
fovea
Central/thickest part of retina, high concentration of cones
macula
Central retina, colour vision and acuity
Cones
Outer retina, night vision
rods
Highly pigmented and vascular layer below RPE, provides O2 req of outer retina
Choroid
How can you test acuity
snellen chart
What is a cataract
Any opacity or clouding of the lens, progressive over years, usually bilat
Name 3 rfs of cataract
Sunlight, age, smoking, alcohol, corticosteroid, DM
What is meant by ‘the angle’ in open angle glaucoma
Space between posterior surface of cornea and anterior surface of iris.
Where the aqueous humour leaves the eye.
Where is aqueous humour produced?
what does it do?
Ciliary body, circulates and nourishes lens.
What is chronic open angle glaucoma? (its the most common)
O/E?
Chronic, progressive, optic neuropathy with characteristic changes in optic nerve head and corresponding visual field loss
3 THINGS:
- enlargement of optic disc cup (loss of neurones)
- Progressive visual field loss -> tunnel vision
- raised intraocular pressure (>21) - however this is not always present because some people can have normal pressure glaucoma
Triad of glaucoma
Raised IOP (>21mmHg) - not always present
Abnormal disc - cup:disc ratio - (cup gets bigger ) asymmetry, disc haemorrhage etc
VF defect - tunnel vision
3 Ix in screening of chronic open angle glaucoma
IOP - low specificity, high FPR
VF test - high FPR
Fundoscopy - cupping - high FPR
Drops for open angle glaucoma
Beta blockers - timolol
[reduces aqueous production] - B for BLOCK production
Prostaglandin analogue - latanoprost
[increases outflow]
If drops dont work / lack of compliance what can you do for glaucoma ?
Post these mx?
Laser therapy (trabeculoplasty)
/
Surgery (trabeculotomy)
-> Dexamethasone (can’t find this in nice guidelines)
what 3 things is visual acuity dependent on?
Functional photoreceptors (rods/cones)
Healthy retinal pigment epithelium (RPE)
Perfusion of choroid (capillary layer)
First thing you develop in macular degeneration
drusen
Seen on opthalmoscope of dry macular degeneration?
visual field loss?
On opthalmoscope
- Atrophy of RPE (visible choroidal arteries)
- drusen
Visual field loss
Central scotoma with preserved peripheral vision
Seen on opthalmoscopy of wet macular degeneration? Visual field loss?
Choroidal neovascular membrane (CNVM)
Leaking vessels below retina
Exudates and haemorrhage and scarring
distorted central vision (objects distorted or appear smaller) and eventually central scotoma
Mx of wet MD
Anti-VEGF injections
DDx of sudden visual loss
vascular - occlusions of vein/artery
Inflammatory - optic neuritis (MS)
Retinal detachment
presentation of retinal artery occlusion ? Key single thing O/E
Sudden, total loss of vision (central retinal artery)
or sudden latitudinal (top half or bottom half) loss (branch retinal artery)
RAPD - swinging flashlight
Name 3 Ix in retinal emboli
Carotid artery doppler
fasting serum lipids
\+/- ECG (+ ECHO if young and calcific embolus) FBC EST CT head Clotting screen
What is amaurosis fungax
Loss of vision for 30 mins (ocular TIA)
Exam q
Cherry red spot at fovea + retinal oedema
Why do you see the cherry red spot?
central retinal artery occlusion
The cherry red spot is seen because the layer of retina is thinnest at the fovea, so when this layer starts to die you can see the dense vascular choroidal vessels below which appears red.
What is ocular ischaemic syndrome?
What is the presentation?
Name 3 signs of ocular ischaemic syndrome
It is a chronic condition affecting the anterior and posterior compartments of the eye as well as other structures supplied by the ophthalmic artery. It may occur due to due to hypoperfusion as a result of carotid stenosis.
Presentation:
- gradual or sudden visual loss
Signs:
Anterior signs:
- Rubeosis (abnormal vessel growth on iris)
- Dilated episcleral vessels
- Corneal oedema
Posterior signs:
- Blot haemorrhages (peripheral/midperipheral)
- Microaneurysms
- Dilated veins
What Ix do you have to do with microaneurysms and why ?
fluorescein angiography to check for perfusion and leak
microaneurysms are often watch and wait but if there it is leaking and fovea is threatened what mx? Ix?
Laser around margin
Ix
HTN, lipids, source of emboli, consider aspiirn
Name 2 things seen on opthamoscopy of branch retinal vein occlusion
Flame haemorrhages
Leaking veins
Intact arteries
What do you need to do with branch retinal vein occlusion ix?
Must establish integrity of foveal arcade!
= fluorescein angiography
1st / 2nd line mx for branch retinal vein occlusion? What is it that you are treating?
The treatment is needed to reduce macular oedema secondary to branch retinal vein occlusion.
THE NEW GUIDELINES:
- first line is anti-VEGF injections e.g. Ranibiumab. to prevent neovascularisation
- second line is modified grid laser photocoagulation
How do you identify retinal non perfusion
RAPD
Extensive blots and microinfarcts
Fluorescein angiography
name 2 things seen on ophthalmoscopy of central retinal vein occlusion?
Widespread flame haemorrhages
swollen optic disc
dilated tortuous veins
extensive blot haemorrhages worse centrally
macular oedema - this is what we are treating because it leads to blindness!!!
mx of central retinal vein occlusion
Anti-VEGF injections e.g. Ranibizimab
What is rubeosis? Mx/
new vessles forming on iris
Immediate AGGRESSIVE PRP (panretinal photocoagulation) +/- vitrectomy
What is AION?
Usual association with Anterior ischaemic optic neuropathy
It is sudden visual loss due to disruption of the blood supply to the head of the optic nerve.
GCA - this arteritis reduces blood supply to the optic nerve
Optic neuritis key assoc?
MS
Usual cause of retinal detachement? what happens? what does it lead to?
Name 2 sx
When can these symptoms be normal?
Retinal tear
Potential space between photoreceptors and RPE fills with fluid
Retina lifted or detached which leads to a field defect.
flashes -> retinal traction
floaters -> vitreous haemorrhage
field loss -> detached retina
Flashes and floaters can occur with age as your vitreous volume shrinks. This leads to posterior vitreous detachment which doesn’t cause problems in most people.
Mx of retinal detachment
Surgery
What is hypersensitive retinopathy? Name 3 features of hypertenisive retinopathy
Management?
HR = HTN leading to damage of the retinal blood vessels.
Arteriolar changes = Arteriovenous crossing change (nipping) - vein disappears under artery as arterial wall is thickened, atherosclerosis of arteries, Heightened reflex on artery (silver wiring)
Advanced changes = Microinfarcts (cotton wool spots), Flame haemorrhages
Mx = manage BP!
Name 2 comps of hypertensive retinopathy
Retinal vein occlusion (B/C) (due to compression from atherosclerotic arteries)
Retinal artery occlusion (due to atherosclerosis)
AION - Anterior ischemic optic neuropathy
Exacerbation of diabetic retinopathy
Retinal macroaneurysms
Whats the issue with dropping BP too quick in accelerated hypertension
may lead to ischaemic optic neuropathy and blindness
2 parts of diabetic retinopathy causing damage?
microvascular leakage
occlusion
stages getting worse of diabetic retiopathy and features of each
Background - balloon-like swellings are growing (micro aneurysms) on the retinal vessels.
- Dots, blots (<3), hard exudates
Pre-proliferative - the vessels nourishing the retina swell and can become blocked, encouraging the formation of new vessels via VEGF
- Cotton wool spots (ischaemic nerve fibres), blots 4+, venous beading
Proliferative - VEGF being released to create new blood vessels but these are immature only with a lamina propria so they leak more and more!
Neovascularisation - vitreous haemorrhage
Dots and blots are ruptured microaneurysms in the retinal layer!
Visual loss in diabetic retinopathy
PATCHY VISUAL LOSS (like cow spots)
Name 2 sign on opthalmoscopy of diabetic macular oedema
Retinal thickening
Exudates approaching fovea
Microaneurysms close to the fovea
Increasing levels of Mx of diabetic retinopathy
Optimise glycaemic control and BP +
Observation
Background = No treatment! observation plus glycemic control
Pre-proliferative = Regular slit lamp to look for evidence of retinal ischaemia. Consider pan-retinal photocoagulation as approaches proliferative
Proliferative = pan-retinal photocoagulation, if further advanced then vitrectomy
Mx of diabetic retinopathy not responding to treatment? SE of this?
Vitrectomy
SE - haemorrhage, cataract
How often monitor diabetic retinopathy ?
in preg?
12 months
every trimester
red flags of red eye
Impaired vision
Pain/photophobia
Lack of ocular discharge
What is Blepharitis, how does it present?
inflamation of eye lid
Gritty, irritable eyes
Watery discharge
Foreign body sensation eyelid
What is a stye
infection of lash follicle
Mx of blepharitis
lubricants
hygeine + topical abx
hot spoon bathing
removal of any debris from eye
Sx of herpes zoster in eye
Severe corneal inflammation (keratitis)
Vascularisation
Corneal clouding
Corneal thinning
LOOKS LIKE A ZOMBIE FUCKER
Usual cause malposition of eye lid (in/out turned) ?
mX?
Lid laxity in elderly
Surgical
Key feature of sub-conjunctival haemorrhage ?
Sudden onset, bright red (stays bright red as Hb is easily oxygenated from atmosphere),
Mx sub conjunctival haemorrhage
No treatment required BUT if following trauma check for orbital/ocular injury
Sx of conjunctivitis? visual change?
Red eye, discharge, swollen eyelid
vision unaffected
Usual cause of viral conjunctivitis?
mx?
adenovirus (although many others)
self limiting
Name 1 cause of bacterial conjunctivitis and mx?
staphylococcus, streptococcus, haemophilus, neisseria
Chloramphenicol / fusidic acid eye drops
What might you query if recurrent conjunctivitis?
nasolacrimal duct obstruction
Which conjunctivitis is important in neonates
Chlamydial -> neonatal -> risk of chlamydial pneumonitis
Starts in one eye and spreads to other
Chlamydial conjunctivitis - spread? most important comp?
flies
conjunctival scarring
Mx of adult conjunctival infection with GU sx
Must identify and treat underlying GUI
Treatment is systemic erythromycin
How to remember the 4 types of hypersentitivity
ACDE
1 - Allergic, Anaphylaxis, Atopy
2 - antiBody
3- immune Complex
4- Delayed
Mx of allergic conjunctivitis
topical steroids
how does allergic conjunctivitis present?
V. swollen conjunctiva
V. itchy eyes
Usually unilateral! Different to non-allergic conjunctivitis
How can you check for corneal abrasions
fluorescein dye
What is the 3rd main cause of keratitis (corneal infection) other than viral / bacterial
Acanthamoeba
What is keratitis?
Dx of viral keratitis organism? Ix?
Sx?
Keratitis = inflammation of the cornea
Herpes simplex
Characteristic shape (dendrite) that stains with fluorescein
Foreign body sensation, *photophobia, watery discharge
Mx of viral keratitis? What should you not use
Topical aciclovir
NO Topical steroid as leads to enlarging dendritic ulcer caller amoeboid ulcer
Should you use steroids for a red eye?
DON’T USE STEROIDS FOR A RED EYE WITHOUT SPECIALIST OPINION
Risk of enlarging dendritic ulcer caller amoeboid ulcer
Bacterial keratitis is rare but what Sx? Sign? Mx?
Painful red eye + loss of vision
Hazy cornea with central abscess
REQUIRES SPECIALIST
Intense dual ABX
[cef + gent]
Iritis (acute anterior uveitis) has acouple key associations…name 2
Sero-neg arthropathies (HLA-B27)
- IBD
- Psoriatic arthritis
- Ankylosing spondylitis
Granulomatous disease
- Sarcoidosis
- Syphilis
Behcet’s disease (multisyst, mouth ulc)
Q - Someone has Acute anterior uveitis and mouth ulcers ? mx?
behcet’s
Steroids
Mydriatics - eg atropine
Immunosupression Eg ciclosporin / azathioprine
Mx of iritis (acute anterior uveitis)>
atropine - dilates
steroid eye drops - eg dexamethasone
Refer to ophthalmology
Unilateral, painful, red eye with profound loss of vision + nausea + vomiting
Photophobia
Often in elderly
Acute angle-closure glaucoma
Very high IOP (normal range = 10-21mmHg)
Sx of acute angle-closure glaucoma ?
Mech?
Very red eye
Corneal oedema
Mid-dilated pupil
Poor vision
Aqueous is produced in ciliary body. The aqueous has to travel between the lens and cornea to get to the anterior chamber. When the lens comes into contact with the iris it cannot get though and the fluid builds up in the posterior chamber. This causes the iris to bulge and close the space between the iris and cornea which then blocks the exit of fluid from the eye. This occurs when the pupil is mid-dilated
- > iris is pushed against cornea and angle closes
- > rapid build up of pressure
Name 2 Ix in Acute angle-closure glaucoma
Gonioscopy (examination anterior angle) - trabecular meshwork not visible
Slit-lamp - shallow anterior chamber, signs of glaucoma (large cup + nerve fibre loss)
/Users/eleanorpatterson/Desktop/Screenshot 2019-08-31 at 18.25.32.png
Static perimetry - VF loss
2 parts of acute Mx of Acute angle-closure glaucoma
Lower the pressure
-Topical carbonic anhydrase inhibitors
(Acetazolamide ‘Diamox’)
-topical beta-blockers
Constrict the pupil
Pilocarpine drops
How can you prevent recurrence of Acute angle-closure glaucoma
Laser ± surgery
Laser iridotomy
Are you more worried about bilat or unilat red eye
Bilateral red eye is less serious than unilateral (conjunctivitis, blepharitis)
Name 2 Asx eye conditions in early disease
Chronic glaucoma
Diabetic retinopathy
HTN
Papilloedema
Name and DDx of small bilateral pupils
miosis
Opiates, pontine haemorrhage, topical pilocarpine (pressure - glaucoma)
Name and DDx of bilatreal large pupils
mydriasis
Sympathomimetics (amphetamine, cocaine), anticholinergics, topical mydriatics
Seen in horners
Miosis (check with poor dilation on dark), anhidrosis, partial ptosis (paralysis of miller’s muscle - superior tarsal muscle)
What are you thinking horners might be caused by? Ix/
brainstem stroke/carotid dissection/Pancoast’s tumour
CT/MRI head, neck and thorax
CNIII palsy sx? DDx? Mx?
blown pupil, ptosis, down and out pupil
aneurysm of posterior communicating artery
uncal herniation post trauma
neurosurgery immediately
Pupil sparing CNIII palsy usually is
diabetes / vascular disease
3 pupil reflexes?
Reaction to light (constriction-miosis)
Direct
Consensual
Reaction to dark (dilatation-mydriasis)
Reaction to near
Miosis
Convergence
Accommodation (focussing by ciliary muscle)
Light response when R side CNII optic nerve damage
Right sided afferent pupillary defect.
Neither pupil responds when affected eye stimulated.
Both pupils respond when light shone into L.
[https://www.youtube.com/watch?v=WwB2jyj2lYM]
light response response when R side CNIII oculomotor damage
Right sided efferent pupillary defect. [Resting anisocoria]
Light in R - no direct response, normal consensual.
Light in L - normal direct response, no consensual response
[https://www.youtube.com/watch?v=WwB2jyj2lYM]
2 DDx cause of RAPD
large retinal lesions
(retinal detachment, central retinal artery occlusion, ischaemic central vein occlusion)
optic neuropathies
advanced glaucoma, optic neuritis, anterior ischaemic optic neuropathy)
3 things that happen with a normal near response
convergence, miosis and accommodation
VF loss in retinal problems
Uniocular defects, mirroring problem.
E.g. superior temporal detachment -> inferior nasal field defect
superior retinal artery occlusion -> inferior altitudinal (bottom half) defect
VF loss in macular pathology
central scotoma
VF loss in optic nerve pathology
central scotoma
VF loss in optic neuritis
Reduced acuity, central scotoma, loss of colour vision, RAPD
VF loss in early vs late glaucoma
Early = arcuate, nasal step
advanced = tunnel vision
VF loss in chiasmal compression? 2 causes and slight difference?
Classically bitemporal hemianopia (nasal crossing fibres)
Pit tumour compresses from below (inferior fibres) = bitemporal upper quadrantanopia
Craniopharyngioma compresses from above = bitemporal lower quadrantanopita
Junctional scotoma VF loss
Pit tumour may compress Optic nerve and chiasm
-> central scotoma in one eye and superior temporal defect in other
WHat happens in retinitis pigmentosa ?
Presentation?
Age of onset?
Hereditary, progressive dystrophy of photoreceptorsin retina and RPE
ring scotoma and night vision problems
(Loss of peipheral vision)
10-30 yrs
Mx of retinitis pigmentosa
Refer to ophthalmology + genetic counselling
Screen complications (cataracts, glaucoma, macular oedema)
Inform DVLA + wear sunglasses
Vitamin A/beta-carotene, acetazolamide (oral carbonic anhydrase inhibitor)
Name 2 key DDx of wet eyes
Blockage at punctum/lacrimal duct
[Test with injection of sterile saline]
Reflex lacrimation due to dry eye
[Prescribe lubricating eye drops]
Dacryocystitis
Inflammation of lacrimal sac due to infection
Name 2 causes of dry eyes
Aging
Medication (diuretics, antidep, antihist, beta blockers)
Systemic illness (RA, SLE, Sjogren’s - hyposecretive)
Blepharitis (decreased tear production)
Allergic conjunctivitis (decreased tear production)
Increased evaporation (low humidity, low blink rate, allergic conjunctivitis)
Ix in dry eyes
Slit-lamp
Schirmer’s test
assessment of corneal damage (Fluorescein stain)
Viral vs bac vs allergic conjunctivitis
viral
gritty feeling
watery discharge
lymph nodes
Bac
Gritty
purulent
lymph nodes
Allergic Itchy stringy No lymph nodes - usually unilateral
45y female happened to notice redness on the lateral part of her eye. There was a bit of discomfort associated, but no pain, watering or discharge. No loss of vision.
The redness was confined to the lateral globe, and the blood vessels in the affected area were slightly dilated but not obscured by the redness.
Likely Diagnosis?
Treatment?
Episcleritis
NSAIDS - Diclofenac (topical)
NSAIDS - oral useful in (rare) severe disease
[Acute or gradual onset
Often unilateral, localized eye redness
+/- discomfort, photophobia, tenderness ]
How is scleritis different from episcleritis?
more severe than episcleritis
may be associated with connective tissue disease (rheumatoid arthritis, polyarteritis nodosa, SLE)
Scleritis symptoms
Intense Pain
Blurred vision
Swollen sclera
Choroidal effusions (if affecting posterior part of globe)
Mx of scleritis
Referral to Ophthalmology
Steroids (high dose, systemic Indomethacin)
Cytotoxic therapy (in severe disease)
Name 2 Scleritis complications
Scleral thinning (scleromalacia) Scleral perforation Keratitis Uveitis Cataract formation Glaucoma
2 rfs for bacterial keratitis
contact lens
dry eyes
prolonged use of topical steroids
Key Ix for bacerial keratitis
Scrapes
gram-staining and culture
A 56-year-old lady presents with photophobia, redness of the eye and blurred vision. She has no previous eye history. She has been diagnosed with sarcoidosis and is currently on systemic prednisolone
OE
Diffuse Redness
Abnormal Pupil
Photosensitivity & Pain on accommodation
White spots in the cornea
Dx?
Sx?
Signs?
Uveitis
Symptoms PPRP Pain (less in posterior uveitis) Photophobia Redness of eye Poor vision
Anterior Uveitis: Keratitic Precipitates Hypopyon dilated Iris vessels Posterior synechiae
What is the key organism causing uveitis should be aware of
TB
A 78-year-old hypermetropic lady presents to the main casualty unit one evening with severe pain in her right eye which came on suddenly, associated with N&V. It feels like she’s looking through frozen glass and notices glaring rings around bright lights. OE injected eye dilated pupil blurred vision
Likely Diagnosis?
Treatment?
Closed Angle Glaucoma
Immediately
Acetazolamide ‘Diamox’ (IV then Oral)
Pilocarpine (topical) x3 every 5m
β-blockers (topical)
Surgery (YAG laser)
Iridotomy or Iridectomy
second eye treated Prophylactically
Name 3 sx of closed angle glaucoma
Raised intra-ocular pressure Red eye Rainbow halos around lights Photophobia Pain (and headache) Discharge (watery) Blurred vision
Systemically upset:
Nausea
Abdominal Pain
70 year old woman presentes with sudden loss of vision in her right eye. She has noted increasing headaches and funny sensation over her scalp when she combs her hair. She complains of jaw pain when she eats.
O/E: VA CF, RAPD +ve, optic disc swollen. Left eye normal.
What is the likely diagnosis?
Treatment?
How would you confirm?
Precautions with mx?
What is the likely diagnosis?
Giant Cell Arteritis causing ischaemic neuropathy
Treatment?
IV steroids prior to any Ix
How would you confirm?
ESR, CRP, Temporal Artery Bx
Precautions? Latent TB (CXR), BP, BMs, Bone and PPI
80 year-old lady sudden vision loss in her left eye described “a curtain came down over her eye” vision came back within 12 hours. PMHx of IHD & poorly managed hypertension. She also suffered a TIA a year ago OE Retinal exam – to left Acuity 6/12 in left eye, 6/6 in right Carotid bruit
Dx?
Amaurosis fugax
Amaurosis fugax mx of cause
Embolic
Carotid Stenosis
Hypercoagulability
Vasculitis (GCA)
Vasospasm
Embolic
Aspirin (75mg/day)
Carotid Stenosis Carotid Endarterectomy (if >70% carotid stenosis)
Hypercoagulability
Warfarin
Vasculitis (GCA)
Steroids
Vasospasm
Nifedipine
36 yeard old patient presents with 3-day history of floaters, flashing lights and then a dense, curtain-like field loss in his left eye. He’s known to be myopic, but has no other PMHx.
OE
Visual Acuity left eye 6/60, right eye 6/9
Dx?
2 Rfs?
Management?
Retinal Detachment
Risk Factors Myopia Cataract surgery recent severe eye Trauma previous Detachment in other eye
Refer to ophthalmology for surgical opinion
Name 2 uses of Acetazolamide - what type of drug is it?
Carbonic anhydrase inhibitor
Retinitis pigmentosa
Acute glaucoma
What is uveitis?
Inflammation of the uvea: iris, ciliary bodies, choroid
anterior = iritis middle = cyclists posterior = choroiditis
Mostly these are non-infective - related to something going on in the rest of the body
Differentials of a red, painful eye.
Which ones are emergencies?
Keratitis Conjuctivitis Uveitis Scleritis Episcleritis Close angle glaucoma
Emergencies:
- closed angle glaucoma
- keratitis
- uveitis
Can you regain the sight in central retinal artery occlusion?
NO
Can you regain sign in central retinal vein occlusion?
Ischaemic - no
Non-ischaemic - yes
What is a corneal ulcer vs abrasion?
Abrasion is a break in the basement membrane. Ulcer occurs when this becomes infected and tunnels into the stroma.
When do you get a red optic disc?
When do you get a white optic disc?
When it is congested or inflamed - papilloedema, optic neuritis and vein occlusion.
Optic atrophy!
What is the red reflex? When can it be absent?
Examining for any blockages in the media. The media is the line that passes from the anterior top of the eye (cornea) all the way to the macula. The structures in between this area are the cornea, sclera, anterior chamber, lens, vitreous humour, and the macula.
Blockage can occur at any level e.g. cataract on the lens, ulcer on the cornea, haemorrhage in the vitreous compartment. The larger the absent portion of the red reflex, the more important.
