09 fundus camera

These lectures has prepared for postgraduate student (Ophthalmology) according to the curriculum of Bangladesh College of Physician and Surgeons (BCPS) and Bangabondhu Sheikh Mujib Medical University (BSMMU) Bangladesh

1. Fundus camera Md Anisur Rahman (Anjum) Professor & Head (Ophthalmology) Dhaka Medical College, Dhaka Contact: 880-1711-832397 [email protected]

2. Optics of fundus camera Source: AAO Vol: 3 Fundus camera captures black-and-white, colour, fluorescein angiographic and indocyanine green angiographic images of the fundus.

3. These cameras employ the same optical principles as the indirect ophthalmoscopes , except that condensing lens is fixed within the camera housing and A flash illumination source is required for the photographic exposur e .

4. As a results, these cameras are relatively large their weight is supported on an adjustable platform similar to that of a slit-lamp microscope.

5. a) forehead rest b) fixation light c) objective lens d) fixation pointer. e ) magnification lever f) camera housing & eyepiece and g) joystick

6. Figure 7-13 Observation system of a fundus camera. As in the observation system of an indirect ophthalmoscope , the condensing lens takes light rays from the illuminated fundus and creates an " aerial“ image . A conventional single-lens reflex camera body, with its microscope eyepiece and ground-glass screen , is then used to focus on the aerial image. When the photograph is taken, a movable mirror flips up , exposing the film or photodetector .

7. For further reading you go through the slide: 9 to end of the power point How Non-mydriatic camera works? Need for wide field imaging Different types of fundus camera

8. As with the indirect ophthalmoscope, the illumination source is projected through the patient’s pupil with a series of condensing lenses and mirrors or beam-splitters. Additionally, a flash lamp for photography is combined into this optical pathway via a beam-splitter. This allows the flash to travel along exactly the same path as the illumination source .

9. Optical filters can be positioned within this optical pathway to restricts the wavelength of light that are used to illuminate the fundus during photography and angiography

10. A fixation pointer is located in the illumination pathway at a position conjugate to the patient’s fundus. The patient sees a sharp outline of the pointer and the shadow of the pointer on the patient’s fundus appears on the photographic film

11. With the fundus illuminated, an aerial image of the fundus is formed by the camera’s objective lens. The image, like that of the indirect ophthalmoscope, is inverted. The viewing system is a camera, often employing a single-lens reflex (SLR) 35 mm camera body or digital camera..

12. The camera lens focuses on the image formed by the condensing lens and projects the image onto the photographic film. As with the indirect ophthalmoscope, the optical pathway of the illumination source and those

13. observation/photography must pass through different areas of the patient’s pupil, otherwise, reflections from the cornea and crystalline lens cause photographic aberrations

14. How Non-mydriatic camera works? Non-mydriatic cameras have been developed to allow fundus photography without the use of dilating eye drops. These cameras use infrared light. The infrared light doesn’t cause pupillary constriction.

15. The first commercially available fundus camera (by CARL ZEISS IN 1926): 20 degree field of view Later standardized 30 degree field of view for fundus camera .

16. Imaging angles greater than 50 degrees is termed as wide field imaging and greater than 100 degrees have been termed as ultra wide field imaging ( DRCR.net) Power of the lens system has direct correlation with the field of view. Focal length of lens system has indirect correlation with the field of view .

17. Need for wide field imaging: The peripheral retina is the site of pathology in many vision- threatening eye diseases. Evaluation of the retinal periphery, therefore, is important for screening, diagnosis, monitoring, and treatment of disease manifestations .

18. Need for wide field imaging: Historically, imaging of the peripheral retina has been limited and difficult to obtain; recent advancements in wide-field photography, however, have dramatically improved the ability to image the anterior retina .

19. Various techniques: CLASSIC fundus camera POMERANTZEFF camera Retcam Panoret Staurenghi lens system Spectralis Optos

20. CLASSIC fundus camera Mechanism: Aspheric objective lens aligned with a 35-mm single lens reflex lens system Degree: 30-60, max 96

21. Retcam Mechanism: Utilizes a contact lens with a fiber optic cable light source connected to a computer monitor to image the peripheral retina in a digital format. 130 degree

22. Heidelberg spectralis hra Uses a noncontact removable lens that attaches onto the camera head of the Heidelberg HRA CSLO which greatly expands the viewing angle capabilities from a previous maximum of 55° to the UWF range Degree 105

23. Optos CSLO based system that utilizes the optics of an ellipsoid mirror to create images of the peripheral retina. An ellipsoid mirror contains two focal points. The laser of the Optos is directed through one of the focal points, while the patient’s eye is positioned so that the second focal point is located inside the patient’s eye.

24. Confocal microscopy, most frequently confocal laser scanning microscopy or laser confocal scanning microscopy, is an optical imaging technique for increasing optical resolution and contrast of a micrograph by means of using a spatial pinhole to block out-of-focus light in image formation

25. CSLO BASED FUNDUS CAMERA Uses confocal optics: A focused low power laser beam is swept across the fundus in a raster pattern. The confocal nature of the optics ensures that the reflectance and fluorescence are derived from the same optical plane. Light originating in the light beam, but out of the focal plane, is greatly suppressed to a large degree. FUNDUS CAMERA: In the absence of confocal optics, the detected fluorescence signal derives from all tissue levels in the light beam with fluorescent properties, and light scattering anterior and posterior to the plane of interest can greatly influence the detected signal.