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How to ensure good / acceptable image quality
How to ensure good / acceptable image quality

How to avoid false positives and negatives and capture fundus photos of acceptable quality for screening and grading

Ganesh Ram avatar
Written by Ganesh Ram
Updated over a week ago


The following article will help you capture good fundus photos; know when a fundus photo needs to be retaken and notice false positives.

When is the quality of a fundus photo good enough?

It is important to ensure good quality of a fundus photo in order for the RetinaLyze algorithms and telemedicine service/Eye-Specialist Backup to make an accurate assessment.

When you discover a sign of poor quality in a fundus photo, simply delete the image and retry. If you do not discover poor image quality before screening the image using RetinaLyze, just retake the photo and rerun the analysis regardless of the result. If there is any doubt, the photo should still be sent to the Eye-Specialist Backup.

A fundus photo can be considered good enough for RetinaLyze when:

  • You can follow all vessels (arteries and veins).

  • You can see the macula and the optic nerve head clearly.

  • The photo is in focus and details are clearly visible.

  • The photo is well-lit, but not over-exposed.

  • The photo is free of any annotations or text.

The following factors can affect the quality of the photo:

  • Shadows

  • Small pupil

  • Over-exposed photo

  • That the client blinks, i.e. eyelashes visible in the photo

  • Grains of dust on the lens of the camera


Photo 1 (left) has a dark shadow in the middle (you can't see the macula) . Photo 2 (right) is generally very dark and you can't follow the veins.

It is important to note that RetinaLyze does not provide an accurate result when there are shadows in the central area of the retina. Try to take the photo again or use small pupil mode (on the fundus camera) if this issue repeats.

Small pupil

If the client has a very small pupil, the fundus camera cannot capture good fundus photos in normal mode. Typically, you will see shadows covering the image or a very dark photo. To resolve this issue, activate the "small pupil"-mode (or similar, if your fundus camera supports it). The camera will then use a stronger flash and other optics that over-expose the photo in the periphery but captures a clear photo of the central area (macula and optic nerve). You can also dim the lights in the room and wait for the patient's pupils to adjust.

Too much light around the client's retinas/over-exposed photo

The image below shows a very over-exposed photo. Over-exposed photos are characterized by the milky-white layer from the periphery and towards the center.

An over-exposed photo does not provide accurate results in both screening and grading scenarios. Capture a new image and try to dim the direct lighting in the room, reduce the amount of flash and/or wait for the patient's pupils to adjust (enlarge) again.

Eye-lashes / Blinking

Sometimes the client will blink at the exact moment when the image is captured. You can clearly see the eyelashes in the top and/or the bottom section of such a fundus photo.

If this happens, the photo just needs to be retaken. Try to audibly count down until the photo is taken so that the client knows when to keep his/her eyes open.

Which factors can result in false positives in RetinaLyze?

A false positive is when the system gives a yellow or red result, even though there are no actual DR- or AMD-related changes detected. These false positives are caused by artifacts appearing as changes.

The following factors can result in false positives in RetinaLyze: 

  • Big reflections in the fundus phot

  • Lively light reflections

  • Fundus laser treatment

  • Degenerative disease

  • Pixel errors

  • Pigment displacement

  • Scaring

  • Laser tracks

  • Tangentially 'cut' vessels, typically in the optic nerve head area

If you discover a false positive, you have to try to retake the photo and then initiate the screening again. If there is any doubt, the photo should be sent to the telemedicine service/Eye-Specialist Backup. The exception is the degenerative disease (and other actual alterations) that naturally has to be sent to the telemedicine service/Eye-Specialist Backup. If in doubt, please use the telemedicine service/Eye-Specialist Backup.

Big reflections

In the image below, there are two very big white areas in the bottom of the fundus photo. These are reflections and will typically not appear in the same location if the photo is retaken. The RetinaLyze algorithms look for the optic nerve to remove it before analyzing the eye background. In this case the system thinks that one of the large reflections is the optic nerve (as the optic nerve typically is the lightest area of a healthy eye background). A false positive created by large reflections is characterized by the system stating that there are DR-related changes present in the optic nerve head area.

If you see such reflections, you just need to retake the photo.

Lively light reflections

Below is a retinal photo of the left eye of a younger person. There will typically be lively light reflections from the flash, especially around the vessels where they can be seen as pearls on a string. When the marking-overlay is hidden, you will see that the small individual sections of the vessel have been marked.

If you see such reflections, you just need to retake the photo. Reflections will typically change location from image to image. If the reflections do not change their location, it's possible that they are not reflections. If in doubt, please use the telemedicine service/Eye-Specialist Backup.

Fundus laser treatment

Certain patient groups have had laser treatment of their retina (e.g. patients treated for Diabetic Retinopathy or Retinal scarring/detachment). The scar tissue of such laser tracks often appear as dark, pigmented spots; often arranged in clusters. 

If the client has had fundus laser treatment (please ask the client), you need to be aware of the fact that RetinaLyze cannot give an accurate response. Here you must instead ask the client to visit an ophthalmologist to have a retinal screening performed, should they wish to do so. Please be aware that a patient treated with fundus laser surgery is likely to already be in cycle of regular care and check-ups by an ophthalmologist or hospital.

Degenerative disease

In certain kinds of retinal diseases the retina undergoes degeneration (decay) and scar tissue is formed in the process. This scar tissue appears as widespread dark spots. 

Please use the telemedicine service/Eye-Specialist Backup, if you encounter this kind of retinal image.

Pixel errors

During the capturing process, errors in the digital fundus camera system can be reflected as localized mergers of smaller to larger pixels that are different than the surroundings and consequently marked by RetinaLyze. They are easily recognizable when the marking-overlay is removed as they are coarse-grained and reproducible in a new photo and will stay in the same location even on other patients.

Please contact your camera manufacturer, if this issue arises.

Pigment displacement and tangentially cut vessels

The degree of pigmentation of the retina varies from one individual to the next. However, "islands" of natural pigmentation may occur in every patient and RetinaLyze can sometimes mark these islands. In addition, vessels show themselves as a "sea serpent over and under the surface", especially near the optic nerve head, may appear segmented and RetinaLyze may mark the individual segments.

If in doubt, please use the telemedicine service/Eye-Specialist Backup.

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