30 HOW TO TREAT : AGE-RELATED MACULAR DEGENERATION
30 HOW TO TREAT : AGE-RELATED MACULAR DEGENERATION
14 JULY 2023 ausdoc . com . au
PAGE 28 coherence tomography ( OCT ) imaging when the first eye is being treated by an ophthalmologist . If vision is good in the unaffected eye , the patient may not notice a reduction in vision in the affected eye until an event causes them to check the vision in each eye separately .
Figure 4 . Examples of colour fundus photography showing the comparison between atrophic and neovascular AMD .
INVESTIGATIONS
A RANGE of non-invasive and invasive diagnostic tools can help in diagnosis and monitoring .
Optical coherence tomography and OCT angiography
OCT has revolutionised the diagnosis and management of AMD and other retinal disease by allowing non-invasive high-resolution images of the macular anatomy .
In wet AMD , the macular neovascular membrane leaks , leading to an accumulation of fluid within or below the retina . This can be helpful diagnostically . Additionally , the response to treatment can be determined to help guide treatment intervals .
In dry AMD , the characteristic OCT signs of pending or established geographic atrophy can help stage the disease .
OCT angiography ( OCTA ) is a non-invasive approach to assessing the vasculature at the macula ( see figure 3 ). It can be helpful in identifying the presence of a macula neovascular complex and , if confirmatory , avoids the need for invasive fundus fluorescein angiography .
OCTA identifies a branching pattern of new vessels that have entered a location that is normally avascular . This non-invasive imaging confirms a new macular neovascular membrane . Traditional OCT imaging can then identify the extent of associated exudation .
Autofluorescence imaging
This is a non-invasive test that relies on reflectance from lipofuscin present in retinal tissue . The dark areas depict RPE and photoreceptor cell death or geographic atrophy . The brighter areas that often form around these dark lesions are sick RPE that is under considerable stress and at high risk of progressing to geographic atrophy . See case study two as an example .
Colour fundus photography
Colour fundus photography can be helpful to identify macular bleeding associated with neovascular AMD . It can also document changes associated with intermediate AMD and geographic atrophy . Wide-field imaging is now available for colour fundus photography and other retinal imaging modalities . This allows us to identify prognostic factors associated with AMD progression from the more peripheral retina .
The colour fundus images in figure 4 highlight the features suggestive of atrophic or neovascular AMD that would be visible on direct ophthalmoscopy . However , note that more detailed imaging , which is available in ophthalmology or some optometry settings , is required to make a formal diagnosis . For example , not all cases of neovascular AMD have associated intraretinal haemorrhage .
Near-infrared imaging
With different substances — such as oxygenated haemoglobin , melanin ,
Figure 5 . Microperimetry in a patient with bilateral geographic atrophy . This has identified areas of central macula dysfunction .
macular pigment and other macular pathology — all variably absorbing , reflecting or scattering infrared light , images can be obtained in a non-invasive and rapid manner . 15 These are often captured at the same time as OCT imaging .
Microperimetry
Microperimetry is a non-invasive functional test that assesses retinal sensitivity at the macula . By identifying the extent of retinal fixation on a coloured light , the sensitivity loss of both cone and rod photoreceptors can be determined . This can be particularly helpful in understanding the structure – function correlations in patients with AMD ( see figure 5 ). 16 , 17 Microperimetry is mainly used as a research tool , although its use may become more widespread as treatments of atrophic AMD become available .
Fundus fluorescein angiography
Traditionally , the diagnosis of neovascular AMD was made with invasive fundus fluorescein angiography ( FFA ) imaging . This involves the injection of fluorescein dye into a peripheral vein and then serially imaging the fundus and looking for characteristic patterns of macular leakage . The risks of this procedure include allergic reactions to the fluorescein dye ( rare ) and yellow discolouration of urine and skin for a day or two . The diagnosis of neovascular AMD has become less reliant on invasive FFA with the advent of non-invasive OCT and OCTA imaging .
Indocyanine green angiography
This invasive dye test is sometimes carried out at the same time as FFA . Indocyanine green allows better