|Year : 1959 | Volume
| Issue : 4 | Page : 99-102
The new zeiss-made retinal camera
|Date of Web Publication||7-May-2008|
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Noteboom E. The new zeiss-made retinal camera. Indian J Ophthalmol 1959;7:99-102
The Nordenson-type of Retinal Camera produced by the JENA Zeissworks has been for years of valuable assistance to ophthalmic surgeons for diagnostic and therapeutic as well as for academical instruction purposes. However, the photographs required a relatively long exposure time, which in view of the present-day demand for colour photographs would have to be still longer.
For the newly designed camera it was therefore necessary to find a lightsource the luminance of which considerably exceeded that of the former incandescent lamp, since the available luminous surface is restricted by the diameter of the dilated pupil and is not therefore capable of enlargement. On the contrary, the wish has often been expressed that-with the small pupil diameters involved (down to 5 ½ mm.) it should be possible to make perfect photographs.
In the new instrument the film is exposed by an electron-flash discharge in a Xenon-maximum pressure lamp. The extremely short flashing period completely eliminates any blurring of the image attributable to the movements of the patient's eye during exposure. Two pilot-lamps provide adequate illumination for focusing the camera, thus protecting the patient's eye from too long and too excessive an exposure to light.
Since the Xenon lamp is not in continuous operation the instrument does not become warm even if used for extended periods.
[Figure - 1] gives a diagrammatic view of the construction of the instrument. The radiation of the Xenon-flash is utilized in two directions, i.e., by forming an intermediate image (L') and by double reflection, the lightarc L is reproduced in two prisms L" which are located at the right and left of the entrance pupil of the photographic lens and which project their light into the large ophthalmoscope lens O. This, in turn, projects the image of the arc into the patient's pupil (L").
In the same manner also the entrance pupil of the lens system Ob is projected into the patient's pupil; the image Br' of the entrance pupil covering the central part of the patient's pupil, whilst the two arc images L" appear laterally in bean-shaped form. The two lateral images are strictly separated from the central part to prevent the light of the images of the light source reflected from the cornea from entering the lens system and from spoiling the picture [Figure - 2].
The reflex images produced on the surface of the ophthalmoscope lens O are rendered ineffective by a small occluding stop S (0.4 mm in size) in the cemented surface of the lens. This stop was considerably larger in the Nordenson Camera. In highly myopic eyes an image of the occluding stop appears in the center of the field, but while this is unavoidable, it does not in the majority of cases have any disturbing effect.
During the photographic process, i.e., in the reversed optical path, the retina N representing the object is reproduced by the optical system of the eye and of the ophthalmoscope lens O to the point N'. From this intermediate image the lens system Ob projects an image N" into the focal plane of the eye-piece and, during the exposure (after swinging up the mirror Sp) also into the film plane (linear reproduction scale 2.8). A negative lens forming part of the lens system Ob serves for focusing purposes for the different degrees of ametropia. This negative lens can be adjusted in the direction of the axis by means of a button at the right-hand side of the surgeon.
The flash is being released by an electrical contact which also causes the lifting of the mirror Sp. This contact is located at the upper end of the control lever on the compound base and is actuated by the thumb of the left hand which controls the adjusting of the camera relative to the patient's eye. The surgeon is thus free to use both hands for setting and focusing the camera and is accordingly in a position to check the image and the position of the camera up to the moment of exposure, and compensate lateral and depth motions of the eye.
The photographic field coverable in the eye amounts to roughly 28°, thus with a single exposure and with the patient looking in the direct direction both the macula and the papillary region of the retina are embraced. In addition, the viewing direction of the patient can be fixed vertically and laterally by means of a setting device so that also laterally located regions of the retina may be recorded.
By means of a prism attached above the ophthalmoscope lens, the operator can without changing the position of his head, convince himself continuously whether the two images L"' of the coils of the pilot lamp are properly and sharply projected into the patient's pupil [Figure - 2]. Since each lamp is provided with a precentered base, no further centering of the Xenon-flash lamp is necessary.
By actuating the contact, also the pilot lamps are switched off and will not light up again until the film has been moved on for a further exposure with the aid of a button at the left of the surgeon. In this way it is possible automatically to prevent double exposures. The flash gun permits a sequence of flashes of less than io seconds; it is accommodated next to the instrument table.
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]