Acknowledgements: BSC is supported by the Cambridge-Rutherford Memorial Scholarship, awarded by the Royal Society Te Apārangi—Rutherford Foundation and the Cambridge Commonwealth, European & International Trust; and the Bushell Travelling Fellowship in Medicine or the Allied Sciences, awarded by the Royal Australasian College of Physicians (RACP) Foundation. MJG acknowledges funding from the NIHR (CL-2019-18-004), Academy of Medical Sciences (SGL023\1051), Moorfields Eye Charity (GR001207), Eye Research UK (SEE 006) & ProRetina Foundation Deutschland (Pro-Re/Projekt/Gilhooley-Whitehead-Lindner.04-2021). PYWM is supported by an Advanced Fellowship Award (NIHR301696) from the UK National Institute of Health and Care Research (NIHR). PYWM also receives funding from Fight for Sight (UK), the Isaac Newton Trust (UK), Moorfields Eye Charity (GR001376), the Addenbrooke’s Charitable Trust, the National Eye Research Centre (UK), the International Foundation for Optic Nerve Disease (IFOND), the NIHR as part of the Rare Diseases Translational Research Collaboration, the NIHR Cambridge Biomedical Research Centre (BRC-1215-20014), and the NIHR Biomedical Research Centre based at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health.Historically, distinct mitochondrial syndromes were recognised clinically by their ocular features. Due to their predilection for metabolically active tissue, mitochondrial diseases frequently involve the eye, resulting in a range of ophthalmic manifestations including progressive external ophthalmoplegia, retinopathy and optic neuropathy, as well as deficiencies of the retrochiasmal visual pathway. With the wider availability of genetic testing in clinical practice, it is now recognised that genotype-phenotype correlations in mitochondrial diseases can be imprecise: many classic syndromes can be associated with multiple genes and genetic variants, and the same genetic variant can have multiple clinical presentations, including subclinical ophthalmic manifestations in individuals who are otherwise asymptomatic. Previously considered rare diseases with no effective treatments, considerable progress has been made in our understanding of mitochondrial diseases with new therapies emerging, in particular, gene therapy for inherited optic neuropathies
