1. INTRODUCTIONRetinal dysplasia (RD) is defined as the abnormal differentiation of the retina.1-5 True RD may result from failure of the inner and outer layers of the optic cup to be in contact during embryogenesis, resulting in retinal detachment.6-8 In dogs, the most common RD form is characterized by multifocal folds and rosettes in retinas that are otherwise mostly attached to the underlying retinal pigment epithelium.9,10 Larger RD lesions are defined as geographic and may develop in regions of partial retinal detachment.4,11,12 Dysplastic changes typically develop in the canine retina at 45-50 days of gestation and generally can be diagnosed before 10 weeks of age, when the retinal layers are fully developed.1-11Retinal dysplasia can be inherited or acquired. For example, Labrador Retrievers and Samoyeds may be affected by oculoskeletal dysplasia (OSD) or dwarfism associated with RD (drd).13,14 This condition is caused by mutations in either COL9A3 (drd1 in the Labrador Retriever) or COL9A2 (drd2 in the Samoyed).13,14Geographic RD-like lesions that develop later than 10 weeks of age were described in some canine breeds, such as Golden Retrievers, German Shepherds, and Labrador Retrievers.11,13 By routine ophthalmoscopy, these cannot be differentiated from true geographic RD, and they are being diagnosed as such.15,16 However, high-resolution imaging in affected Labrador Retrievers, Golden Retrievers, and German Shepherds revealed that at least some of these geographic RD-like lesions consist of inner retinal plaques with tubular rosettes and vesicle-like structures.11,13,17,18 The pathogenesis of these retinal plaques has not been defined; they may be acquired, but a genetic predisposition has not been ruled out.Geographic RD is recognized as an inherited condition in the Cavalier King Charles Spaniel (CKCS).15,16 The breeding recommendations by the Genetics Committee of the American College of Veterinary Ophthalmologists (ACVO) for RD-affected CKCS are similar to most other canine breeds: While dogs with geographic RD should not be bred, dogs with focal/multifocal RD or retinal folds can still be bred (‘breeder option’).15 The Hereditary Eye Diseases (HED) Committee of the European College of Veterinary Ophthalmologists (ECVO) states that breeding is optional for dogs affected by focal/multifocal or geographic RD unless the breed club issues different advice.16 According to the Blue Book on Ocular Disorders Presumed to Be Inherited in Purebred Dogs, published by the ACVO Genetics Committee, of the 17,092 CKCS examined between 2019 and 2023, 1.6% had geographic RD, while 3.2% had retinal folds.15 Even though these prevalences are higher than in the Labrador Retriever with 0.4% geographic RD and 0.9% retinal folds,15 no detailed morphological and clinical reports on geographic RD in the CKCS have been published to the best of our knowledge. It is unknown if these lesions represent true RD or are similar to the inner retinal plaques that develop later than 10 weeks of age in Labrador Retrievers, Golden Retrievers, and German Shepherds.11,13,17,18 To fill this knowledge gap, our retrospective study aims to describe high-resolution imaging of geographic RD in a CKCS using confocal scanning laser ophthalmoscopy (cSLO), optical coherence tomography (OCT), and OCT angiography (OCTA). We compared our findings with the images of a Labrador Retriever with unilateral inner retinal plaques, since this condition has been previously characterized.11,13,17,18