Age-related Macular Degeneration - Ophthalmology _ Fastbleep

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Age-related Macular Degeneration

Written by: Namratha Mathai from Glasgow University,

AGE RELATED MACULAR DEGENERATION

Age-related macular degeneration (ARMD) is a term used to describe a characteristic pattern of

macular change and central visual loss, thought to be associated with the natural ageing

process.

Commonest cause of irreversible visual loss in the developed world

Burden of disease with ARMD likely to increase with an ageing population

PATHOGENESIS

Normal Structure and Function

The relevant layers at the back of the eye are:

Photoreceptor layer: outermost part of the neuroretina, composed of rods (light

perception) and cones (colour perception)

Retinal pigment epithelium (RPE)

Bruch's membrane

Choroid: highly vascular layer providing nutrition to the outer layers of the retina,

including the photoreceptor layer

The RPE is a single layer of cells, with microvilli that project in and around the outersegments

of the photoreceptors i.e. it is in close association with the neuroretina, but is only loosely

attached. The RPE is essential for normal retinal function by carrying out the following tasks:

Phagocytosis of redundant external segments of photoreceptors.

Recycling of vitamin A and therefore helping regeneration of rhodopsin and cone opsin

Absorption of light sc attered by the sc lera to allow better image formation (RPE cells

contain melanin)
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Facilitating nutrient and waste transfer between the retina and choroid (RPE cells are

held together by tight junctions and therefore form part of the blood-retinal barrier)

Bruch's membrane refers to the joint basement membrane of the RPE and the choroid. This

contributes to the diffusion barrier between choroidal blood vessels and the retina.

Pathological changes

The progression from normal macula, to dry ARMD through to wet AMD is variable - only 10%

of patients will develop wet changes in their lifetime. The risk factors involved in determining

progression are as yet uncertain, however the following have been suggested:

Increasing age

Family history

Smoking: single greatest modifiable risk factor in progression

Drusen type: soft drusen (larger >63um, ill-defined borders) is more strongly associated


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Signs:

1. Reduced visual acuity

2. Reduced visual fields: central

scotoma + loss of colour

saturation/contrast perception

3. Amsler grid: this is a useful tool to

quantify and qualify the degree of visual

impairment caused. It refers to a grid of

vertical and horizontal black lines on a

white background, which appear

distorted/blurred/darkened in areas

corresponding to the patient's scotoma.

4. Ophthalmoscopy:

absent foveal reflex

drusen (discrete yellow lesions)

hypo/hyperpigmented areas (atrophic

change)

with progression from ARM to ARMD than hard drusen (small, well-defined). Increasing

number and confluence of drusen also increases risk.

Oxidative stress: some evidence that vitamin/mineral supplementation slows

progression

Cardiovascular risk factors: recent studies have linked poorly controlled hypertension,

sedentary lifestyle, obesity, etc with increased risk of progression to wet ARMD.

CLINICAL PRESENTATION

Classic patient: Elderly, caucasian, positive family history

Smoking history (link to progression)

Changes tend to be bilateral but asymmetrical

Symptoms:

1. Decreased vision: blurred central vision or central scotoma (more advanced). Usually

gradual onset, but may notice more rapid deterioration with wet ARMD (during episodes of

haemorrhage/macular oedema).

2. Metamorphopsia/visual distortion: patients may describe certain parts of their visual

field appearing bigger (macropsia) or smaller (micropsia)

Functionally, as ARMD affects central vision, patients complain of difficulty reading, watching

TV, differentiating colours and recognising faces.


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wet changes: haemorrhages,

neovascularisation

INVESTIGATION

A good hist ory and examination is usually suf fic ient to diagnose ARMD. However, the following

imaging techniques help (1) confirm diagnosis (2) identify early wet changes and (3) act as a

baseline to monitor disease progression and/or response to treatment.

MANAGEMENT

Aims:

(1) preventing progression of disease

(2) minimising functional impairment/improving vision-related quality of life
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Dry ARMD:

Most active interventions for ARMD are only indicated in patients with wet changes. The

mainstay of treatment of dry ARMD is watchful waiting and symptom management (discussed

later).

Observation : 6-24 month follow-up with community optometrists to monitor

changes/progression to wet ARMD. Patients may be given a copy of the Amsler grid for

self-monitoring and asked to report any new visual symptoms developing in between

visits.

Vitamin supplementation (lutein): may be recommended in patients with advanced

dry ARMD who are at high risk of progression to wet ARMD. The evidence base for

effectiveness is currently under debate. Consequently, these have to be purchased

individually by the patient, as they cannot currently be prescribed on the NHS.

Smoking cessation: lowers rate of progression in both dry and wet ARMD.

Wet ARMD

A number of new therapies have been developed to limit neovascular changes. It must be noted

that these do not affect areas of established scarring and fibrosis, so patients may still be left

with residual visual loss.

Visual rehabilitation / Symptom management

The measures described above are aimed at preventing progression of disease. However, a

number of patients will have some degree of irreversible visual loss, that may cause significant

functional impairment. Visual loss may be due to progressive geographic atrophy in dry ARMD,

or complications of wet ARMD including subretinal haemorrhage, retinal detachment and scar

formation. Needs are specific to each patient and must be identified and managed on an

individual basis. Some available options include:

Low vision aids, magnifiers

Training in eccentric focusing (using peripheral vision to carry out tasks like

reading/watching TV that normally involve central vision)

Driving: as peripheral vision is spared, most patients with ARMD can continue to drive.

However, legally they are required to undergo a DVLA-organised visual field assessment

to ensure that the central visual field loss is not severe enough to cause difficulty.

Blind registration: a few patients with advanced disease will require to be registered

blind, particularly those with long-standing progressive changes.

References

Age-related Macular Degeneration - Ophthalmology _ Fastbleep

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