Enhanced Visualization of Retinal Topography
The RHA is designed to enhance visualization of surface and structural changes such as epiretinal membranes, vitreomacular adhesions and macular holes.
This patient has an epiretinal membrane caused by a probable case of 'cat scratch fever' due to an infection with bartonella henselae. Figure 1 (a) below shows the image taken with narrow band green light while (b) shows a red-free traditional fundus photo. By emphasizing the light scattered from the surface, the epiretinal membrane is readily apparent in the RHA image while it is almost invisible in the traditional fundus photo image.
Figure 1 (a)
Figure 1 (b)
Deep Fundus Imaging
The RHA’s extended deep red and infra-red wavelength range provides early detection of RPE changes and pigment distribution, indicative of critical diseases including AMD, allowing for timely monitoring of disease progression and treatment efficacy.
AMD is a leading cause of blindness in persons over 60 years of age in North America, and early detection is critical to preventing vision loss. Scientific research has shown that certain changes, such as thinning, clumping or mottling of the RPE pigment distribution are a precursor to more visible signs and symptoms of AMD. The Annidis RHA is highly sensitive to the RPE structure (Figure 2) and so enables the establishment of baseline characteristics and subsequent monitoring of changes over time.
Deep red wavelength illumination is beyond the significant absorption of hemoglobin and the visual pigments, leaving RPE melanin as the primary absorber. To illustrate the sensitivity of the instrument in detecting small and early changes in the RPE, Figure 3 (a) shows a long red wavelength image while Figure 3 (b) shows an enlarged view of the macula where there is pigment disruption. As the pigment clumps together, adjacent areas are left as micro window defects, appearing white. The importance of multi-spectral imaging is illustrated by a subset of images for this eye, as shown in Figures 3 (c) & (d), where the RPE disruption is barely visible using other wavelengths.
Figure 3 (a)
Figure 3 (b)
Figure 3 (c)
Figure 3 (d)
In advanced AMD, the RPE can become attenuated and atrophic, resulting in geographic atrophy (GA). GA is shown below in Figure 4 (a) and (b). In (b) the boundary of the GA is very clearly highlighted and is seen to have higher pigment content on the edges of the atrophic area. Pigmentation may be predictive of disease progression. Being able to provide patients with objective feedback may make it easier to illustrate the need for lifestyle modification to slow the progression of the disease.
Figure 4 (a)
Figure 4 (b)
Monitoring pigment changes in the RPE is also useful in the case of retinotoxicity which may result from the use of drugs such as hydroxychloroquine (malaria, rheumatoid arthritis) or thioridazine (antipsychotic). An example of RPE damage is shown below in Figure 5, using red light illumination. Visualization of the RPE and detection of the early onset of changes can assist health care professionals in optimally managing patients on such medications.
Figure 5 (a)
Figure 5 (b)