MOD MACULAR

What is the approximate size of the macula and how much of total VF does it represent?

5.5mm in diameter - represents central 15-20 degrees

What is the fovea and its approximate size?

Shallow depression in the centre of the macula - critical for high resolution image (drives VA) despite occupying just 0.02% of the total retina - approx. 1.5mm in diameter - contains no BV referred to as the Foveal Avascular Zone

What are the percentages of cones and RGC at the fovea?

• 3% of cones total cones (200x greater cone density than the surrounding retina)

• 25% of total RGC

What is the foveola and what is its size?

Found at the centre of the macula - approx. 0.35mm in diameter

• thinnest part of the retina 

• RGC are displaced laterally to minimise image degradation

What is the umbo?

Bottom of the foveolar pit and is the source of the reflex that is visible during fundoscopy 

• Absence of RGC but densely packed cones

Functions of the RPE layer?

• Absorbs any excess light which would otherwise cause glare and reflections

• Form a tight barrier which prevents leakage of fluid from the choroid into the retina

• Removes metabolic waste from retinal tissue via Bruch’s Membrane - 1 RPE cell collects debris from 30 cones

• Provide nutrients to overlying cones via transport from the choroid - outer-blood-retinal layer

What is the function of Bruch's Membrane?

Key role in regulating the transportation of toxic metabolic waste from the retina into the choroidal blood circulation

When assessing the macula what tests should you carry out?

• VA 

• Amsler chart

• Retinal imaging and fundoscopy

Assessing VA, its link to macula disease + pinhole

• Measure both Distance and Near, monocular and binocular

• If macula disease, NEAR VA is often disproportionately impaired

• Use the pinhole test - in px with compromised macula function VA will not improve as the factor limiting VA is non-optical (photoreceptors and RGC function)

• The pinhole could make VA worse as there is a reduce FOV through the pinhole

Amsler Chart

• Sensitive assessment of the 20 degrees visual field

• Test carried out monocularly at 30cm - each square subtends 1 degree of visual angle

• Px need to wear correct reading Rx - NOT varifocals/bifocals

• Px focuses on central dot and reports areas of distortion/scotoma

Retinal imaging/fundoscopy

• Warrants a dilated fundus examination using Volk - allows detection of retinal oedema or elevation

• OCT

Prevalence of AMD in over 75s?, DRY/WET

• Most common cause of irreversible visual impairment in the UK - increases exponentially with age

• 4.8% of over 65 have advanced AMD, rises to 12.2% of over 80s 

• 30% of over 75s are in someway affected by AMD 

• Very rarely detected before 50

• Dry AMD 90% of cases

• WET 10% - typically more acute and severe - may require urgent referral

Is VA affected in the early stages of AMD?

Px may show visible signs associated with AMD but maintain good VA

Risk Factors for AMD

• AGE - strongest RF

• High BMI / History of cardiovascular disease / Hypertension - moderate association

• Caucasians more likely than Africans or Asians

• First degree relative with AMD - 3x more likely 

• Females

• Smoking - Single most powerful modifiable RF - 2x the risk of developing AMD

What protects a px from AMD?

Healthy diet, regular exercise, normal BP and controlled cholesterol levels

How will AMD appear?

• Bilateral, often asymmetric 

• Px with advanced AMD in one eye - 50% chance of advanced AMD in the fellow eye within 5 years

What are the terms used for AMD that describe the development of geographic atrophy?

• Dry

• Non-exudative

• Atrophic

What are the terms used for AMD that are characterised by neovascularization?

• Wet

• Exudative

• Neovascular

Why and How does AMD occur?

Ageing - causes an increase in thickness of Bruch’s membrane which reduces the permeability 

• This inhibits the removal of toxic metabolic waste such as Lipofuscin

• These waste products begin to accumulate between Bruch’s membrane and the RPE (drusen)

SX of AMD

• Bilateral - asymmetric and likely to be asymptomatic in the early stages

• Gradual deterioration of vision - over a number of years

• Advanced AMD - difficulty with visual tasks that require resolution of fine detail e.g reading/recognising faces

• In severe cases a positive central scotoma

SX exclusive to WET AMD

• Painless and sudden onset of blurred or distorted central vision - requires urgent referral - even if no retinal signs

• Initial onset in Px with WET AMD is unilateral BUT 37% develop in 2nd eye within one year

• Vision becomes distorted - metamorphopsia

Why does Metamorphopsia occur?

Due to the disruption of the organisation and orientation of the RPE and PRC by subretinal fluid

Signs of AMD

• Drusen - first visible sign in both forms - typically clustered around the macula

• Geographic Atrophy  - DRY AMD + WET AMD

• Choroidal NV - WET AMD

• Haemorrhages - WET AMD

Summary of Drusen

• Made up of waste products such as lipids and collagen due to build up between RPE and Bruch’s membrane - Cones have exceptionally high metabolic activity = large amount of waste products

• Drusen disrupt the orientation and organisation of RPE cells - end result leading to atrophy

• Drusen associated with depigmentation and hyperpigmentation

What do Drusen indicate?

• They’re a common finding in over 50s so don’t necessarily indicate the presence of AMD!

Positive association between the number + size of drusen and the severity of AMD

Hard Drusen

Small, yellow, well-defined with sharp edges - carry a low risk of visual impairment

Soft Drusen

• Larger, poorly defined fully edges - greater potential to disrupt the structure of the overlying RPE

• Confluent - aggregate together to form a single area of drusen

• Greater risk of visual impairment

What does Drusen do to the retinal layers?

• Elevates the RPE and distorts the structure+organisation of overlying retinal layers

• Due to the above = reduce VA

Geographic Atrophy

• Degeneration of RPE leads to ATROPHY - loss of sensory retina = devastating impact on VA especially if the fovea is affected

• END stage of DRY AMD

• Px can develop a positive central scotoma in the region of the GA

• Areas of GA can be identified by areas of retinal pallor

Signs of RPE degeneration?

Patches of both hypo- (brighter) and hyper- (darker) pigmentation - ‘stippling’ effect

What does GA do to the retina?

Reduces thickness of retinal tissue and exposes underlying BV of choroid and choriocapillaris

What is retinal pallor surrounded by and why does it arise?

• Dense drusen

• Hyper- and hypo- pigmentation - ‘pigment clumping’

• Occurs due to lack of incident light absorption by the absent RPE cells

Choroidal Neovascularization

• Hallmark for WET AMD 

• 10-15% of px with Dry will develop WET AMD - Px with soft drusen and GA are at risk of CNV

• It is possible for CNV without any signs of Dry AMD but very uncommon

Why and How does CNV occur?

• The angiogenic stimulus (trigger for CNV to occur) is ischaemia

• Reduction in permeability of Bruch's Membrane = undersupply of oxygen to retina = new vessels arise from Choroid

• This is supported by the proliferation of the subretinal neovascular membrane which is the tissue underneath the retina - this membrane will appear grey-green-yellow in colour - only in WET

• This extends vessels of the choroid through defects in Bruch’s membrane to the sub-RPE space

• Some vessels breaks through the RPE and grow into the sub-Retinal space

What occurs as a result of CNV

• Leakage of blood = haemorrhaging within the macula region 

• Darker blood = deeper haemorrhages = sub-RPE - due to light absorbing properties of the RPE

• Macula Oedema - driven from exudation of Choroidal BV, not retinal BV which is the case in DR, HTR and post-operative CMO - Sign of ONGOING exudation in AMD

• Oedema is centred on the macula region and may be visible with volk as retinal thickening

Why does Oedema occur?

• ‘macromolecules‘ leaking from BV via an oncotic pressure gradient draws the water component of blood out of the vessel 

• Over time some of that aqueous content is reabsorbed by other vessels OR pumped into the choroid by the RPE

• However the Lipoprotein component of the exudated fluid isn’t reabsorbed and left in the form as hard exudates

What are hard exudates a sign of?

• Some exudated fluid has be reabsorbed but don’t necessarily signify an end to exudation 

• Usually occur in the mid retinal layers rather than sub-retinal space

Management for CNV?

Urgent referral even when haemorrhaging isn’t present as prognosis becomes poor once haemorrhage occurs

What is the end stage of exudative AMD?

• Disciform scar - circular scar around the macular region

• Caused by the proliferation of fibrous tissue which is produced to support CNV

• If extends across fovea = very poor VA e.g hand movements - further vision loss is unlikely

What does a Disciform scar look like?

• Pale white/yellow circular-ish region with relatively well defined margins

• Sub-retinal haemorrhage and oedema may be visible within the scar

• Its surface tends to be irregular and will have differences in elevation throughout the scar

Small number of drusen is classified as?

‘Normal’ no AMD

AMD classification within NICE framework

• DRY AMD - drusen = Early AMD

• AMD - subretinal fluid = ‘Late AMD (indeterminate)’

• DRY AMD - GA = Late AMD DRY 

• WET AMD - CNV = Late AMD (wet active)

• WET AMD - Disciform Scar = Late AMD (wet inactive)

Optometric Management of Dry AMD

• If optometrist confident about diagnosis, px doesn’t require referral but made aware of sx - annual recall

• If not sure about diagnosis of Dry AMD - refer

• Refer if px is symptomatic as likely to need reassurance about their vision loss 

• VA can become severely impaired LVA assessment may be indicated - refer via GP

• Explain that AMD is a progressive condition and vision might start to deteriorate however the rate of progression is very slow - there is variability in different px in the rate of progression 

• Explain it will only impair central vision - they will still be able to navigate their environment

• Explain that it is possible to develop WET AMD at any stage of DRY AMD - make aware of sx of WET - sudden reduction in vision or metamorphopsia 

• Amsler chart for self-monitoring 

• Ask px to regularly compare vision in the LE and RE whilst looking at a regular straight line target

• Explain likely to be some deterioration in vision but isn’t a forgone conclusion - progression may be so slow 

• Make aware of modifiable RF - STOP SMOKING - will be beneficial even after AMD has been diagnosed

What should a px with AMD do if they feel their vision is deteriorating?

• Seek an eye exam - sx are gradual in both WET?? and DRY but CAN be sudden in WET 

• Optom can then decide on referral

What are antioxidants?

• Antioxidants have a protective effect on retinal cells 

• Combat action of free radicals which are produced by oxidative damage associated with incidence of light on the photoreceptors

What role does diet play in the development of AMD?

• Macula has an abundant source of harmful free radicals - increases with AGE

• Macula contains lutein and zeaxanthin - known as carotenoids - have antioxidant properties - causes yellow pigment 

• This pigment absorbs harmful short wavelength(blue) which would otherwise damage the retina - can’t be produced by the body so must be extracted from our diet

• Leafy green vegetables - e.g spinach - good source of carotenoids - can also take supplements such as Viteyes

• Increasing the proportion of antioxidants enhances the retinas ability to withstand harmful effects of free radicals

• This may lead to the control of progression of AMD - does NOT delay or prevent onset of AMD

• Vitamin C, E, and the carotenoids + lutein/zeaxanthin

• Make px aware diet only plays a small role in the clinical procedure of AMD

What would you recommend to dispense AMD px?

UV protection coated lenses can reduce progression of AMD

Optometric Management of WET AMD

• Urgent referral to Ophthalmologist using the Wet AMD ‘fast track’ pathway - aim to be seen within 2/52

• Email the completed referral letter to a dedicated macula clinic - bypasses GP and reduces waiting time

• If unsure of whether Dry/Wet still use the fast track pathway

• If no fast track pathway available then same day phone call to HES

• Last resort be referred to A&E

Ophthalmological management of WET AMD

• Intravitreal injection of anti-VEGF agents - block action of VEGF - occur due to Ischaemia 

• Examples include; Ranibizumab (Lucentis), Bevacizumab (Avastin), Aflibercept (Eylea)

Cystoid Macular Oedema

• Breakdown of inner BRB - pathological response to some form of injury, inflammation or vascular disease

• Leakage of intravascular contents from dilated perifoveal retinal capillaries causes thickening of macula - may reduce macula reflex

• Intraretinal fluid - leads to a flower-petal arrangement - displaces the GC layer 

• Leakage occurs within the INL AND OPL of the retina

What are the causes of CMO?

• Cataract extraction - 20% of cataract surgery px show some form of CMO - only 1% show significant reduction in VA

• Most common cause of unexplained vision loss after surgery - can be termed ‘Irvine-Gass syndrome’ if occurs after cataract extraction

• Other causes include uveitis - posteriorly more common, DR and CRVO/CRAO

Sx of CMO

• Sudden, painless onset of blurred or distorted central vision

• Develops over the course of 1-2 weeks 

• Many px with subtle CMO will be asymptomatic

Optometric Management of CMO

• Same day phone call with Ophthalmologist 

• In cataract induced CMO there will be little to no retinal signs

• If suspicion of uveitis then emergency referral

• If suspicion CRVO/CRAO call HES for advise

Ophthalmological management of CMO

• First line treatment = treat underlying cause e.g stabilise blood glucose in DM

• Carbonic Anhydrase Inhibitors - increase fluid outflow via the RPE 

• Corticosteroids - reduce inflammation

• Laser Photocoagulation 

• Increasingly treated with anti-VEGF drugs - reduce vascular permeability

Central Serous Retinopathy

• Arises due to ingress of fluid from the choroid and breakdown of the outer BRB

• Irregularities of the RPE allow passage of serous fluid from the choroidal space into the sub-RPE space and subsequently into the sub-retinal space

Risk factors for CSR

• Mostly within 20-50 age bracket 

• Males - who are more prone to stress/anxiety - cortisol (hormone) causes changes in choroids structure and function

• Typically unilateral 

• 30% of cases are recurrent episodes

Sx of CSR

Sudden, painless onset of blurred or distorted vision

Signs of CSR

• Serous elevation of macula region (reduces axial length) and reduced VA

• Potentially a positive shift in Rx

Management of CSR

• 70% of cases resolve spontaneously with good recovery of VA

• Ophthalmological opinion is required to confirm diagnosis and rule out CNV

• If confident of diagnosis refer px to HES to be seen within 4/52 - tell px if sx worsen return to Optometrist 

• If in doubt then seek opinion from local AMD fast track or call HES - URGENT

How to differentiate between CSR and CNV?

• Px’s age - younger in CSR

• Asking about px recent stress/anxiety levels 

• OCT will show absence of AMD features such as drusen

Epiretinal Membranes (ERM)

• Disruption of ILM causes Muller cells + other cells to proliferate = epiretinal membrane

• Can occur anywhere but most commonly the macular region  

• ERM are prone to contraction which causes retinal layers to become distorted - ‘bunched up’ appearance on OCT

• Causes include; tractional forces during PVD, posterior uveitis (inflammatory process)

• Most are idiopathic 

• Slow progression - take at least a year to develop

Sx of ERM

Reduced VA, metamorphopsia in severe cases (25%)

Signs of ERM

• Early stage - Reflective, shimmering area around the macula - like the macula of a young px but onset at least 60 years old - referred to as cellophane maculopathy

• VA will be unaffected or limited to a 1 or 2 line drop due to the ‘shiny’ retinal surface

Management of ERM

• Early cases - e.g cellophaning but VA isn’t affected and no sx of distortion - manage routinely with a yearly recall

• Where VA is affected and/or px reports distortion - refer px routinely 

• Ask about duration of sx and whether it was sudden/gradual
  

Macular Hole

• Adhesions between the vitreous and foveal retinal layers are stronger than the layers themselves - macular hole

• Can be thought of as a retinal break that occurs at the macula - limited to the sensory layers of the retina - RPE intact

• Association with PVD - therefore very rare in under 60s 

• More common in males and myopes

• Onset of sx weeks/months

Sx of Macular Hole

• Vision is compromised - reduced VA and metamorphopsia 

• Early MH - VA drops by 1-2 lines with slight distorted vision

How to confirm if a px has a Macular Hole?

• OCT - adhesion attached and raising the macula towards the vitreous

• Can perform ‘WAZKE-ALLEN’

What is Wazke-Allen?

Using a volk lens to make the slit beam 0.5 disc diameter and centered on the macula - ask px to report the perceived shape of the beam - If no macular hole we would expect the beams appearance to match its physical appearance

Signs of early stage MH

• Small diameter lesion - small round red/yellow spot/ring at fovea

• Decreased/absent foveal depression

• Use an OCT to image the break/traction

• 50% improve themselves if the VRT is resolved

Signs of intermediate stage MH

• Moderate diameter lesion

• Significant reduction in VA 

• Distortion likely 

• Fundus signs more visible

• Unlikely to resolve spontaneously 

• If left untreated - permanent loss of central vision is likely to develop

Signs of end stage MH

• Large diameter lesion

• Associated with permanent reduction in VA

• Positive central scotoma 

• Less likely to respond to intervention - success of treatment depends on time elapsed since macular hole onset

Optometric management of MH

• If confident with diagnosis of either early/intermediate MH refer via GP to be seen within 1/12

• End stage MH - routine referral as unlikely to respond to treatment 

• If unsure about diagnosis then refer suspected MH via fast track AMD pathway

• Urgency is a lot lower than RRD as MH can sometimes resolve spontaneously and progression is slower 

• 1 year recall as 15% chance of development of MH in second eye within a 5 year period

Ophthalmological management of MH

• Relieving VRT - 90% of recent onset MH with small diameter can be closed by vitrectomy 

• Intravitreal injection of ocriplasmin - a recombinant protease that helps dissolve the proteins present in the adhesions between vitreous and macular - reduces VRT

Myopic Degeneration

• Retina and choroid thinned - susceptible to atrophy - due to increased axial length

• At the macula - myopic macular degeneration 

• Higher the Rx the greater the risk - uncommon in eyes below -6.00D

Sx of MMD

• Many cases have no sx

• Where they do occur sx similar to dry AMD - gradual, painless onset of blurred central - bilateral (myopia in BE) 

• In rare cases CNV can develop leading to sudden onset of unilateral blurred/distorted vision - stress on Bruch's membrane = breaks = ingress of CNV = affect sub-RPE and sub-retinal space as with WET AMD

Signs of MMD

• PPA

• Thinned retina and choroid particularly at the macula

• Tilting of the Optic disk 

• Regions of pallor - washed out fundus - localised areas of hyperpigmentation - subretinal neovascular membrane

• Similar to end stage dry AMD - GA 

• Minority of cases similar to form of WET AMD - CNV

Management of MMD

• No effective treatment 

• Referral only warranted if signs of CNV - urgent referral via AMD pathway

• VA has dropped to the point it affects quality of life - routine referral via GP - allows LVA assessment

Hereditary Macular Dystrophies

• Stargardt’s disease - most common inherited macular disease

• Pattern Dystrophies - ‘Best disease’ - Large egg yoke lesion @macula - lipofuscin build up between RPE and retina - Vitelliform dystrophy 

• Cone Dystrophy

Cone Dystrophy

• Can be present at birth (stationary) or progressive

•  If progressive presents in older childhood/adulthood

• Sx include reduced VA and CV 

• ERG can be used

• Late stage fundus - Bull’s eye maculopathy - similar appearance to dry AMD - differentiated by age of px (younger) and the symmetry in BE as it is a genetic condition

Management of Hereditary Macular Dystrophies

• If we are unable to ascertain the cause of reduced vision in a child - always refer

• Routine referral via GP

• Ophthalmology will try confirm diagnosis with ERG and will give LVA assessments