ORRT Journal

Introduction

Stargardt disease (STGD) is an autosomal recessive retinal dystrophy, characterized by bilateral progressive central vision loss and subretinal deposition of lipofuscin-like substances [1]. STGD is the most prevalent inherited macular dystrophy and is associated with disease-causing sequence variants in the gene ABCA4 [2]. ABCA4 is the source of biallelic mutations that disrupt the normal function of retinal pigment epithelium cells in the retina [3]. As RPE cells degenerate, they fail to support the overlying photoreceptors, leading to their progressive degeneration and the characteristic central vision loss seen in STGD [4].

STGD progresses slowly during the lifespan and its prevalence is about 1:8000-10,000 [5].  Onset usually occurs in childhood or early adolescence, affecting both males and females [5]. Patients begin presenting with evolving painless bilateral central vision impairment, with visual acuity between 20/20 and 20/400, as well as well-circumscribed central scotoma [6]. Characteristic macular atrophy and yellow–white flecks at the level of the retinal pigment epithelium (RPE) at the posterior pole [2] can be seen during fundoscopy. In its advanced stages, patients affected by this hereditary cone-rod dystrophy end up losing macular vision and can only rely on residual peripheral vision in their daily lives. It has an impact on the quality of life and places a burden on affected individuals and their families [7]. Moreover, vision loss in STGD can lead to difficulties in reading, performing everyday tasks and recognizing faces, which can affect educational and occupational opportunities. STGD affects young individuals in the beginning, thus affected individuals may require long-term support and rehabilitation services.

Lateral geniculate nucleus (LGN) is a small, bilateral structure of the thalamus that receives input from each eye, representing the contralateral half of the visual field. It serves as a relay center from the retina to primary visual cortex [8]. LGN is located superiorly to the hippocampus and medially to the optic radiation [9]. Receptive fields in the LGN are similar to those in the retinal ganglion cell layer in terms of both spatial and temporal characteristics. The structure of LGN consists of six laminae with associated inter-laminar structures that macroscopically segregate the magno-, parvo-, and koniocellular visual streams originating in the anatomically ipsi- and contralateral eyes. The specific contributions of the retina, thalamus, and visual cortex to LGN properties are presently unknown [10]. Inherited retinal dystrophies are progressive in nature, with not only the retina but also downstream visual pathways deteriorating over time [11-13]. Little is known about how degenerative diseases of the outer retina affect the balance of visual processing in the visual pathway. LGN was previously invisible in 1.5T and 3T MRI. Nowadays, thanks to 7T high-field MRI it can be assessed in diseases of the visual pathway, including inherited retinal dystrophies. Therefore, the quantitative assessment of the volume of lateral geniculate nucleus (LGN) using 7 MRI in the presence of the central visual loss due to Stargardt disease (STGD) appears to be interesting and relevant for deepening knowledge about retinal dystrophies [14].

Keywords: Stargardt disease; lateral geniculate nucleus; LGN; thalamus; 7T MRI.