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Table 2 Main tests for visual assessment in ALMS

From: Consensus clinical management guidelines for Alström syndrome

Refraction status (mandatory) It often shows a hyperopia (ranging from + 3.5 up to + 12) and astigmatism. Myopia is not common. Full corrective glasses must be prescribed as long as some vision is still present.
Visual acuity (mandatory) Visual acuity is often very low early on (less than 1/10 with Decimal test or 6/60 with 6 m Snellen test) evolving to residual light perception around the age of 10. However, some cases have shown a later and milder onset with higher values of vision.
Slit lamp examination (mandatory) The fundus examination varies according to age and among individuals independently from the genetic status or the extra ocular status. Chronologically the fundus examination can reveal: near normal appearance, attenuated vessels, hypo-pigmented appearance to the retina with increased visibility of the choroidal vessels, macula pigmentary changes, pale optic discs and /or papillary drüsen often observed. Later global pigment mottling and local clumps can appear whereas classical “bone spicules” are seldom reported. Crystalline deposits have been observed [21].
Electroretinography (ERG)
The usual characterization is an early onset severe cone-rod dystrophy and confirmation must be made by a full-field ERG. ERG shows very early and usually profound alteration of the light adapted photopic responses due to severe alteration of the cones. The follow up highlights a rapid evolution with diminishing dark-adapted rod responses. Before the end of the first decade, the ERG become un recordable and shows extinguished cone and rod responses (absent responses using any type of stimuli).
Goldman visual field (Optional) Goldman or Humphrey Visual fields are often unrecordable. Exceptionally more or less pronounced visual field constriction have been reported and even very exceptionally with some preservation [20, 21].
Optic Coherence Tomography (OCT)
The OCT findings are scarcely reported [21,22,23,24], because the recording is difficult to achieve especially in young children with nystagmus, photophobia and need for sedation. Thinning of the macula and immature retina with persistence of the foveal inner retinal layer were reported [22, 23] but this was challenged by further reports that showed mild central macular changes in the first decade followed by loss of photoreceptors and pigment epithelium that correlated with the low vision [21, 24]. The OCT images in adults show general atrophy of both inner and outer retinal layers. Thinning of the outer nuclear layer and the outer plexiform layer outside the fovea is a constant finding [21].
Fundus Auto Fluorescence (FAF)
FAF is seldom reported with hyper autofluorescent parafoveal ring in two patients and small areas of hypo and hyperfluorescent zones outside or inside the arcades [21].