Table 1

Summary of the current and under development methods for IRD structural evaluation

Imaging modality	Characteristics	Use in inherited retinal diseases (IRD)
Colour fundus photography	Classified based on the use of confocal optics or flash-based systems. Different filters can be employed to enhance particular structures: red light → choroid; green light (red-free) → retinal vasculature, drusen, exudates; blue light → anterior retinal layers.	Fundamental tool that facilitates teaching, documentation, evaluation and monitoring.
Fundus autofluorescence imaging (FAF)	Short wavelength-FAF (SW-FAF): macula appears hypoautofluorescent. Good for evaluation of areas with photoreceptor loss but relatively intact retinal pigment epithelium, and subretinal hyper-reflective material. Near infrared-FAF (NIR-FAF): macula is hyperautofluorescent. It detects geographic atrophy and pigment migration earlier than SW-FAF.	Its property of revealing the retina’s health and metabolism makes it an important tool for diagnosing and monitoring IRD. It also provides valuable insights on disease pathophysiology.
Optical coherence tomography (OCT)	Enables highly detailed qualitative and quantitative assessments of the retinal layers.	Key tool to accurately monitor anatomical changes. Also employed intraoperatively in gene therapy clinical trials.
OCT angiography	Provides tri-dimensional visualisation of the retinal microvasculature and capillary plexi.	Useful to identify choroidal neovascularisation in association with IRD.
Adaptive optics	Two types: (i) confocal is used to resolve the cone and perifoveal rod mosaics; (ii) non-confocal (split detection) identifies cones with abnormal outer segments.	Enables non-invasive cellular imaging. Helpful to increase our understanding of IRD. Also used for monitoring progression and in research settings.
Optoretinography	Allows mapping of stimulus-evoked functional intrinsic optical signal using near infrared light.	May be useful for assessing photoreceptor integrity and dysfunction (still under development).
Laser speckle flowgraphy	Employs the laser speckle phenomenon to quantify in vivo the circulation in the optic nerve head, choroid and retina.	Has been used to correlate blood flow with other structural and functional parameters in IRD.
Retinal oximetry	Measures oxygen metabolism by capturing how haemoglobin absorbs light.	May represent an alternative way to assess outer retinal degeneration in IRD (still under development).
Functional magnetic resonance imaging	Provides high resolution imaging of the brain including the visual cortex.	Useful to assess plasticity and remodelling following visual field defects, congenital visual impairment and/or interventions.