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) |
| 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. |