Fractal analysis of retinal vessel patterns in ophthalmically normal dogs

To study the applicability of the fractal dimension as a parameter for describing retinal vessel patterns in ophthalmically normal dogs. The following strategy was adopted: (i) development of an experimental procedure to obtain digitalized photographs of the fundus; (ii) development of software to segment retinal vessel images and calculate the box-counting and radius of gyration fractal dimensions of the retinal vessels and diffusion-limited aggregation (DLA), a process with similar characteristics to retinal vessel morphology, and (iii) establishment of a standard curve for the fractal dimensions of segmented vessels. Digitalized photographs of the fundus showed an adequate contrast between the vessels and the rest of the fundus for numerical analysis. The software developed produced a binary image of the retinal vessels permitting calculation of the fractal dimension. The mean values of the fractal dimensions calculated by the methods of box-counting and radius of gyration for the DLA were significantly different (t = -40.33, P [almost equal to] 0). The radius of gyration method was found to be more suitable for documenting the dimension of the DLA and, consequently, of the dog's retinal vessels. This methodology may be useful to differentiate between normal and pathologic states of canine retinal vascularization.