Laser Scar Detection in Retinal Images

Laser is an important tool for theraputic treatment of retinapothy, but powerful laser beams can cause severe damage to the retina. A shallow yellowish spot appears in retinal image after it is exposed to the laser beam (see Figure 1). The purpose of laser scar detection is to detect and track laser scars based on before-and-after image comparison.

Figure 1. Laser scar (left) and the manually marked positions (right).

Our system consists of four major steps:

1. Image quality checking

There are three kinds of unqualified images: underexposed, overexposed and unbalanced exposed (see Figure 2). The


Good exposure	Under exposure	Over exposure	Unbalanced exposure

                                 

2. Blood vessel mapping


3. Image registration
   Blood vessels on two images are registered using their bifurcation points. The ratio between number of "matched" pixels and number of all pixels in the common area is called "registration score".
   

   
   

4. Background extraction, image subtraction and post-processing
   Background of each image is extracted by a morphological opening operation. And then the difference between two is used to determine the the brighter laser scar spots.

Experiment Results

Pre-surgery	Post-surgery	Result

Number of laser scars found: 11