Figure 1. Progression of dry AMD. (L) Large drusen without pigment changes. (R) Same eye five years later with development of pigment spots indicating increased risk of progression to advanced AMD.
School of Optometry and Vision Science UNSW
Dr Simon Chen
MBBS BSc FRCOphth FRANZCO
Retinal and Cataract Surgeon, Vision Eye Institute, Sydney NSW
Age-related macular degeneration (AMD) is the most common cause of legal blindness in Australia and is divided into dry and neovascular forms.1 Up to 90 per cent of AMD-related blindness is caused by neovascular AMD (nvAMD).
Without treatment, over 50 per cent of patients with nvAMD lose three or more lines of Snellen visual acuity within one year of diagnosis.2 Although vision loss due to nvAMD tends to be rapid, vision may be preserved by timely treatment with intravitreal antivascular endothelial growth factor (anti-VEGF) injections.
Optometrists are well positioned by virtue of their training, equipment and accessibility in the community to identify, educate and monitor patients at risk of nvAMD. They have a critical role in detecting and referring patients suspected of having nvAMD to an ophthalmologist for specialist assessment and treatment.
Figure 2. Fundus autofluorescence (FAF) imaging. (L) Dry AMD with drusen and subtle signs of geographic atrophy. (R) FAF image clearly showing areas of geographic atrophy.
The majority of patients with the dry form of early AMD can be managed by optometrists. The decision regarding whether to refer a patient with dry AMD to an ophthalmologist will depend on the individual optometrist’s personal experience and confidence in managing dry AMD, as well as their access to imaging technology such as retinal photography, fundus autofluorescence and optical coherence tomography (OCT).
Important clinical features of nvAMD that warrant urgent referral to an ophthalmologist include:
• Rapid deterioration of visual acuity
• Recent onset of visual distortion or increased visual distortion
• Retinal haemorrhage, retinal thickening or exudates in the macula
• Suspicious OCT imaging findings: intraretinal fluid, subretinal fluid or pigment epithelial detachment.
Determining the risk of nvAMD
The simplified severity scale for AMD is an evidence-based scale developed using data from the landmark Age Related Eye Disease Study (AREDS). It provides busy optometrists with a quick and easy way to clinically grade patients with AMD, providing a useful prognosis regarding their risk of progression to the potentially blinding advanced forms of AMD. The scale is based on clinical examination and does not require the use of a retinal camera or OCT.3
For each eye, one point is assigned for the presence of one or more large drusen (>/= 125 µm or the width of a large vein at disc margin) and one point for the presence of any pigment abnormality (hyperpigmentation, hypopigmentation, or non-central geographic atrophy) (Figure 1). If no large drusen are present in either eye, the presence of intermediate drusen in both eyes is counted as one point. The points from both eyes are added together to give a total score from 0 to four. The approximate five-year risk of developing advanced AMD (nvAMD or geographic atrophy involving the foveal centre) is based on the total score.
• 0 points = 0.5 per cent
• 1 points = 3 per cent
• 2 points = 12 per cent
• 3 points = 25 per cent
• 4 points = 50 per cent
It should be remembered that the simplified severity scale provides only an approximate guide to prognosis and is not accurate in every patient. In many patients, as AMD progresses, drusen may spontaneously regress, giving the cursory impression that the condition is improving while the risk of losing vision is actually increasing.4,5 Therefore, it is important to assess the changes on retinal photography over time whenever possible.
The increasing availability of fundus autofluorescence (FAF) imaging in optometric practice may lead to better recognition of areas of retinal pigment epithelial pathology and risk of AMD progression. FAF is an indirect measure of the metabolic function of the RPE, with areas of hyperautofluorescence and hypoautofluorescence representing areas of sick or atrophic RPE. For example, in a case where drusen have regressed, FAF may demonstrate AMD related changes to the RPE that are not obvious on fundus examination.5
OCT imaging enables additional risk factors for AMD to be identified. Reticular pseudodrusen (RPD) are yellowish subretinal lesions arranged in a reticular pattern most commonly seen in the superotemporal quadrant of the macula. They are an increasingly recognised risk factor for progression to advanced AMD and often missed on slitlamp examination but visible on OCT as multiple tiny subretinal deposits. RPD may also be often be visualised on FAF or near infra-red photography. In eyes with AMD-related geographic atrophy, up to 62 per cent of eyes show RPD.6
Pigment epithelial detachments (PEDs) are easily seen with OCT imaging and assessing them can present a challenge to the optometrist. PEDs vary in appearance and may be optically clear or hyperreflective.7
The presence of a PED is a risk factor for vision loss with reports that over a 10-year period, up to 25 per cent will develop nvAMD and up to 75 per cent will develop geographic atrophy.8 PEDs may be due to drusen or choroidal neovascular membranes (CNV) and are also a common feature of central serous chorioretinopathy (CSCR). Optometrists should have a low threshold for referring patients with PEDs to an ophthalmologist because fluorescein angiography may be indicated to exclude the presence of CNV and early treatable nvAMD.9
Optometrists should be keenly aware that several retinal conditions can mimic AMD and that misdiagnosis is frequent. The prognosis, management and implications for systemic health associated with each condition can differ significantly from those associated with AMD and therefore, accurate diagnosis is important. Some of these conditions include macular dystrophies (for example, Stargardt’s disease), polypoidal choroidal vasculopathy, central serous chorioretinopathy, acquired vitelliform lesions, retinal vascular occlusions, diabetic retinopathy as well as many others. If in any doubt about the diagnosis, referral to an ophthalmologist is appropriate.
Figure 3. OCT in a patient with nvAMD showing a pigment epithelial detachment and adjacent area of subretinal fluid
Management of nvAMD
When a diagnosis of nvAMD is suspected, urgent referral to an ophthalmologist is indicated for assessment and possible intravitreal anti-VEGF therapy. Fluorescein angiography can be considered the gold standard for identifying CNV and must be used to diagnose nvAMD to access Pharmaceutical Benefits Scheme subsidised anti-VEGF therapy.10
A recent major advance in OCT imaging is the ability to perform OCT angiography (OCT-A) without the need for intravenous dye injection.11 In the future, OCT-A may obviate the need to perform fluorescein angiography in some patients with nvAMD, potentially leading to cheaper, safer and more accessible angiography.
The current standard of care for the treatment of nvAMD is intravitreal anti-VEGF therapy with bevacizumab (Avastin), ranibizumab (Lucentis) or aflibercept (Eylea). These agents have been shown to reduce the risk of severe visual loss by over 90 per cent and are associated with a three-line improvement in visual acuity in more than 30 per cent of patients.12,13
Figure 4. (L) Retinal photo of a patient with nvAMD showing drusen, retinal haemorrhage and exudates. (R) Fluorescein angiogram showing a subfoveal choroidal neovascular membrane.
Neovascular AMD is a common, blinding disease. Identification, education and monitoring by optometrists of patients at risk of developing nvAMD are essential to ensure that those patients do not develop nvAMD. Prompt diagnosis and referral for anti-VEGF treatment of nvAMD can often save sight.
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