Fractal analysis of retinal vessel patterns in ophthalmically normal dogs

OBJECTIVE: To study the applicability of the fractal dimension as a parameter for describing retinal vessel patterns in ophthalmically normal dogs. PROCEDURES: 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. RESULTS: 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 approximately 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. CONCLUSION: This methodology may be useful to differentiate between normal and pathologic states of canine retinal vascularization.