Around 90% of people have dry age-related macular degeneration and 10% have wet age-related macular degeneration. Most of those with wet age-related macular degeneration started with the dry version which then converted to the wet version. The dry version usually takes many years to cause significant reductions in visual acuity.
The wet version is a condition in which new blood vessels grow in the choroid layer behind the retina. The new vessels are weak, and they leak lipids and blood. These liquids get into the layers of the retina – including the layers of the macula – and can cause reduced visual acuity through disruption of retinal cell structure and scar tissue formation. This damage can take place over a period of a few weeks.
The key point here is that most of the people with the wet, acute version that reduces visual acuity quickly had the dry, chronic version that reduces visual acuity slowly. The quicker the start of the wet version is detected the quicker it can be treated. Speed is of the essence with the wet version.
This is why some eye specialists advise patients with the dry version to home monitor and look for visual changes which can alert them to the start of the dry version. They ask the patient to look out for visual distortion and patches of missing vision. This is achieved through the use of an Amsler grid.
Eye specialists that advise home monitoring with an Amsler grid typically recommend using a black grid on a white background. This is not the proper testing Amsler grid, which consists of a white grid on a black background. The black-on-white-grid is actually the recording sheet which some practitioners have in practice and issue to patients at risk of the wet version for home monitoring. The problem with using the black-on-white version for testing is that some people will see distorted lines even if they don’t have the wet version. A perception of distortion when looking at black lines on a white background is called pattern glare and has nothing to do with the wet version. Distortion due to pattern glare will cause the patient to worry and may lead to a referral and further investigation that is not clinically warranted.
It is far better to print off a white-on-black grid in practice and issue that to the patient or ask them to print a white-on-black grid at home. This will not cause pattern glare to interfere with home monitoring for wet age-related macular degeneration.
See figure 1 for black-on-white Amsler grid recording sheet.
See figure 2 for white-on-black Amsler grid testing sheet.
The following procedure for home testing can be used:
- If the patient wears spectacles for near vision, testing should be done with those being worn.
- In a well-illuminated room, ask the patient to hold the grid around 25 cm away from the face.
- Ask to cover one eye with hand and look directly at the centre black dot.
- While looking directly at the centre dot, observe the grid. If any lines or areas look blurry, wavy, dark or blank consult an eye specialist.
- Follow the same steps with the other eye.
- Always remember to keep the Amsler grid at the same distance from the eyes for each test.
White-on-black Amsler grids for home testing can be found on the internet.