Introduction
In ophthalmology, the diagnosis and management of retinal diseases are based on retinal imaging.
The last 30 years have been marked by many innovations in retinal imaging devices:
- First, Fundus cameras allowed the capture of the state of the retina, as color, en-face images.
- SLO (Scanning Laser Ophthalmoscopy) devices use infrared light, en-face images, more contrasted and detailed.
- OCT (Optical Coherence Tomography) devices use a technology similar to echography (light waves instead of sound waves). It provides tomographic sections of the retina to examine the layers of tissue that compose the retina. This achieves a very high resolution in the depth of tissue.
The latter have limitations: the lateral resolution remains insufficient to distinguish the cellular contents of a given layer. Below, we will explore the use of adaptive optics for Ophthalmology to improve imaging.
Adaptive Optics Technology
To address this need, adaptive optics can be used to examine the retina with a level of detail 5x better than conventional SLO or OCT.
AO technology comes from astronomy; it was invented to observe very far stellar objects with large ground-based telescopes. Through the atmosphere and its turbulence, the image of distant stars is of limited quality. The addition of AO in the telescope enables the capture of a sharp image, without sending the telescope into space. They use deformable mirrors and wavefront sensors to compensate for the distortion of the light waves.
Center of our galaxy, Large ground-based telescope
Same telescope with AO
Fig 1: Adaptive optic to correct distortions in light waves caused by atmospheric turbulences
This technique was first applied to retinal imaging 25 years ago by the University of Rochester. Since then, a number of academic research labs have designed AO retinal imaging systems.
Use of AO Kit in Ophthalmology
Fig 2: AO kit EYE
The AO kit EYE is an association of the HASO™4 first wavefront sensor for a simple, precise and reliable measurement of the wavefront. A deformable mirror (mirao™ 52-e or mu-DM™) for a smooth and stable correction, and WaveTune™ AO control software for a total control of the operations.
To use the AO kit to form an image of the retina, light is sent into the eye and the light reflected by the retina is captured by a camera. The eye naturally deforms the light, which limits the level of visible details. This is why a deformable mirror is added; it can change its shape to correct the light distortions. To apply the right shape, a probe light source and a sensor measure distortions. As the deformable mirror applies corrections, the image resolution is enhanced and smaller details become visible.
Rtx1 Retinal Camera
Imagine Eyes’ adaptive optics (AO) components enable AO technology to perform flawlessly when applied to living eyes, and can readily be incorporated in various system configurations.
Imagine Eyes’ products are the most integrated AO components in ophthalmic instruments, including the rtx1, the first adaptive optics retinal camera on the market.
Fig 3: Rtx1 and its imaging system detailed
When using the rtx1 Adaptive Optics Retinal Camera, you can examine the retina at a scale where individual cells are visible. It reveals parafoveal cone photoreceptors as well as other microscopic retinal structures that cannot be seen with conventional techniques, thanks to a 10x better resolution.
Conventional Scanning Laser
Imagine Eyes’
Fig 4: Comparison SLO / AO technology
Image credit : Nippon Medical School Hokusoh Hospital, Chiba, Japan
The rtx1 enables visualization of the microscopic walls of retinal arterioles non-invasively. Focal narrowing, perivascular sheathing, micro-hemorrhages and micro-aneurisms are also visible without using contrast agents.
Conventional color fundus camera
Imagine Eyes’ rtx1TM
Fig 5: Comparison fundus camera / AO technology
Image credit : Nippon Medical School Hokusoh Hospital, Chiba, Japan
The rtx1 stands out as the most widely-used AO imaging device throughout the world. Cleared by regulatory authorities in several countries and adopted by 90 clinical centers, it has become the reference device for cellular-level retinal assessments in clinical research. More than 250 publications illustrate the extensive clinical knowledge and findings that users of the rtx1 AO camera have gained in a large variety of diseases that impact the retina (macular degenerations, diabetic retinopathy, glaucoma, diabetes, arterial hypertension…).
“For the first time, adaptive optics enables us to visualize retinal neurons and offers totally new options to evaluate retinal therapies.”
-Pr. José Sahel, Vision Institute, Paris & University of Pittsburgh Medical Center
In the video « cellular and microvascular retinal alterations » we can see that the rtx1 allows a detailed view of atrophic lesions, a drusen (small yellow deposit under the retina, linked to macular degeneration), the microvascular follow up with the action of an anti-hypertensitive treatment.