Remember the first time you viewed the optic disc using stereo slit-lamp biomicroscopy? Seeing the disc in detailed relief immediately made assessment of its structure much easier, more accurate, and less likely to suffer inter-observer variation. The ability to capture this appearance with 3D photography, therefore, is a valuable asset to any glaucoma screening programme, or indeed wherever any three-dimensional structural details needs to be recorded, analysed or transferred for further opinion.
Harper and Spry1 noted that ‘stereoscopic photography is the option of first choice because rim loss may be underestimated and observer agreement reduced when using monoscopic photographs and cup-depth determination is less reliable with the non-simultaneous stereoscopic images’. When they wrote this, the technology allowing you to view stereoimages on a 3D screen was of limited availability and 3D tended to be achieved by convergence of side by side disparate images or by a flicker presentation method.
Advantages of Stereo
The obvious advantage of a stereo image is that it offers an
accurate representation of the actual architecture of the disc, making assessment much more accurate. The image can be maintained for as long as needed for full analysis, not always possible in the live situation, and accuracy of cup and disc parameters, as for example required under the SIGN guidance, easier using dedicated software. Increasingly these days, the onus of disc shape analysis has been pushed towards tomography (firstly HRT and now OCT), but studies have shown stereoimaging to have at least comparable accuracy.2
Not surprisingly, therefore, stereoimaging is included in the protocols of many satellite and primary care supported screening and monitoring schemes, such as the pilot glaucoma schemes set up by Moorfields Eye Hospital3 and others such as that in the Newport area in South Wales.
The ease of capture and transfer of 3D images now makes virtual clinics or telemedicine, where remote workers capture data for central analysis by a specialist, a realistic possibility.4 Indeed, such clinics allow the ophthalmologist to review over three times more patients so representing a significant resource saving that easily counterbalances any initial investment costs in setting up.
Advances in 3D viewing combined with improved camera technology now make stereoimaging of the retina and disc a key technique and the latest camera from Kowa, the nonmyd WX 3D (UK distributor Sense Medical), allows one button press capture of the very highest quality images. I recently tried out the system for myself.
The Kowa nonmyd WX 3D
The WX 3D has a similar footprint and design to most retinal camera, and the simplicity of design is one of its many advantages (figure 1). The unit I used had a dedicated 3D monitor (figure 2) which offered excellent three-dimensional resolution when viewed through the supplied visor.
Figure 2
Apart from the expected initial patient data input, the unit is simplicity itself to operate with really only three buttons that need to be considered (figure 3).
Figure 3
The two on the left set the camera for two-dimensional capture, either normal or small pupil, and operation is then the familiar process of alignment, focusing, and capture giving a retinal image of the resolution and extent of field expected from any modern system (figure 4). The right hand button sets the camera for 3D capture.
Figure 4
One major step forward for this camera is its clever use of two adjacent lenses (figure 5) allowing simultaneous capture rather than serial capture of two disparate images requiring camera movement as is typical of other systems.
Figure 5
This feature means that the image captured is of much greater 3D detail and clarity, the software using vessel details to ensure accurate correspondence of the images taken with each lens (figure 6).
Figure 6
The images of discs that can be captured in 2D were of impressive quality (figures 7a and b) and can still be presented adjacently (figure 7c and d) for 3D viewing using a stereo visor.
Figure 7a
Figure 7b
Figure 7c
Figure 7d
Better, though, was full 3D representation on the stereo screen (figure 8). Though I have tended to focus on glaucoma in this feature, the benefits of such a view in assessing possible papilloedema or disc congestion are obvious.
Figure 8
Analysis
The Kowa software allows a wide range of disc analysis options to be employed. The disc and cup can be outlined using the mouse (figure 9) which then allows full disc interpretation to be calculated (figure 10a and b), a dongle including the Spaeth analysis algorithms5 being supplied with the camera.
Figure 9
During this process, the image shown in figure 9 can be displayed in a flicker fashion which enhances the detection of any changes (see video in online version of this feature). Over repeat appointments, the disc appearance may be shown in seamless succession so offering an accurate way of displaying disc change over time.
Figure 10a
Figure 10b
A detailed report is easily printed or saved at the end of the session (figures 11 and 12) showing disc appearance and numerical values, a thickness map and ‘twin peaks’ style depth map.
Figure 11
Figure 12
Viewpoint
This has to be one of the easiest to operate cameras I have ever come across and one that allows the capture of 3D images of the highest resolution. As stereoimaging becomes an expected part of any screening and monitoring scheme, expect to see the WX 3D in clinics up and down the land.
Further information from www.sensemedical.co.uk
References
1 Harper R, Spry P. Essential glaucoma handbook. 2010. Optician Publications
2 Pahlitzsch M et al. Significance of the disc damage likelihood scale objectively measured by a non-mydriatic fundus camera in preperimetric glaucoma. Clinical Ophthalmology, 2015:9 2147-2158
3 Kotecha A et al. Experiences with developing and implementing a virtual clinic for glaucoma care in an NHS setting. Clinical Ophthalmology, 2015:9 1915-1923
4 Wright H, Diamond J. Service innovation in glaucoma management: using a web-based electronic patient record to facilitate virtual specialist supervision of a shared care glaucoma programme. British Journal of Ophthalmology, 2015;99:313-317
5 Spaeth GL et al. The disc damage likelihood scale: reproducibility of a new method of estimating the amount of optic nerve damage caused by glaucoma. Trans Am Ophthalmol Soc. 2002;100:181-5.
