■ Full Question
During examination, when a round halation resembling corneal reflection appears in the iris viewer, the actual blood flow map image also shows a round shadow—sometimes in black, and sometimes in red or yellow as if blood flow were present—overlapping the optic nerve and interfering with measurement. What is the cause?
■ Answer
This is likely not caused by a scratch or defect inside the eyeball, but rather by the speckle-side laser light reflecting off the corneal surface and being captured by the speckle camera. When this round halation is observed, isn't there also a reflection pattern in yellow, red, or similar colors indicating strong reflected light within the light intensity map displayed at the lower left of the measurement screen during blood flow measurement? In such cases, the speckle instrument is not capturing signals from the actual fundus light, resulting in patterns that differ from the actual fundus blood flow pattern, and the expected optic nerve head blood flow map cannot be obtained.
As a solution, this halation must be avoided.
Since the laser light is returning as direct reflection from the corneal surface, try moving the fundus camera slightly to the left or right, or up or down, so that the direct reflected light does not enter the speckle camera, and try deflecting the corneal reflected light causing the halation upward.
Alternatively, applying eye drops to slightly change the condition of the cornea may also help.
However, in this case, to ensure stable measurement, the timing of the eye drop application and the measurement must be coordinated.