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Modified 7-Standard Field Color and Angiography Procedure

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Attachment A: Pointers on Photographic Technique

Attachment A

Pointers on Photographic Technique
Prepared by the UW-FPRC


Field Definition

When the modified seven standard stereo fields are taken, the following sequence is recommended: disc (Field 1M), macula (Field 2), temporal to macula (Field 3M), superior temporal (Field 4), superior nasal (Field 6), inferior temporal (Field 5), inferior nasal (Field 7). Stereo Fields 1M, 2 and 3M may be taken on the same horizontal plane.  

The following technique may be used for attaining proper definition of Field 4: (1) move the camera from the center of the disc upwards until the upper edge of the disc meets the bottom of the photographic field, (2) take note of some landmark at the intersection of the cross hairs (e.g., a small vessel or microaneurysms), (3) swing the camera temporally until this landmark is at the nasal border of the photographic field (at this point, the lower edge of the field will fall on the same plane as the upper edge of the disc) -- this is the proper position for Field 4. To locate Field 6, rotate the camera nasally until the landmark is at the temporal edge of the field. A similar approach can be used to obtain Fields 5 and 7.

For further information, please see our Tutorial on Modified 7-Standard Field Photography


Focus/Clarity

Constant attention must be paid to keeping the cross hairs in the camera ocular in focus, otherwise the photos will be out of focus. 

Proper camera-to-eye distance should be maintained to avoid haziness and artifacts.

If it is not possible to get the entire photographic field in crisp focus, the photographer should concentrate on getting the center of the field in focus, sacrificing a bit on the periphery if necessary. This is especially important in Fields 1M and 2. 

When the photographer moves to Field 2, having just taken Field 1M, he/she should refocus on retinal vessels near the center of the field. Failure to do so results in photographs that show the foveal area to be slightly out of focus while the periphery is in focus. 
A common problem is focusing too deep. Photographs which include the disc (Fields 1M and often Field 2) sometimes show clear focus on the bottom of the cup, while the retina is slightly out of focus. It appears that some photographers use the lamina cribrosa (at the bottom of the cup), the disc margin, or the granular pattern of the pigment epithelium for focusing. Instead, it is desirable to focus on fine retinal vessels. Since the depth of focus is greater posterior to the plane of absolute focus than anterior to it, it makes sense to err on the side of focusing slightly up into the vitreous rather than too deep. This should keep both the anterior 
surface of the retina and the pigment epithelial background in focus. Such a strategy is of special importance when macular edema is present.


Stereoscopic Effect

The technique described by Allen1 is used for taking stereo fundus photographs. An Allen stereo separator or manual lateral movement of the camera may be used to obtain the required, non-simultaneous stereo pairs. If the manual method is used, the camera should not be rotated; instead, it should be moved from left to right with the joystick (or by sliding the camera base on its table, if preferred). It is customary to take the left member of the pair first, but this is optional. The first member of the pair is taken as far to one side of the pupil as possible, while maintaining good illumination and a clear image. If the separator is used, it is then flipped to the other side and the second photograph is taken if its quality is good. If the quality is not good, refocusing with spherical or astigmatic correction and/or slight vertical movement of the camera (to avoid lens opacity) may be needed. Such vertical movement will not impair the stereoscopic effect. Somewhat less than optimal focus and clarity is acceptable, if necessary, in the second member of the pair in order to maintain the stereoscopic effect. The same principles apply when the manual technique is used. If the stereo separator is used, it should be set between 2.25 and 2.75mm. About 2mm is the minimum separation between members of the stereo pair to be aimed for when moving the joystick or sliding the camera.

Photographers should monitor their own work

A 4X or 5X magnification stereoscopic viewer for examining stereo fundus photographs is required, so that the photographer can critically examine his/her work and make appropriate corrections in technique. Examples of good stereoscopic photos can be found at the UW-FPRC website, http://eyephoto.ophth.wisc.edu.

What to do if the subject finds the photography procedure unusually difficult

Photography of the photophobic subject can be very challenging for the photographer and uncomfortable for the subject. Minimizing the number of flashes and the length of time the eye is exposed to a bright viewing lamp are two things that can help make the photography procedure more comfortable. We recommend shooting only one set of fundus photographs, copying those fields that you want to retain in your clinic files, to minimize the number of flashes. Additionally, keeping the view lamp as low as possible (maybe even dimming the room lights) can help make the photography procedure more tolerable. For additional help managing difficult photography situations, please contact Michael Neider or Hugh Wabers. 

Questions or Comments

For questions or comments concerning this photography procedure, please contact the UW-FPRC photographic consultants, Michael Neider (608/263-9858; neider@rc.ophth.wisc.edu) or Hugh Wabers (608/263-0740; wabers@rc.ophth.wisc.edu). 

Reference
1. Allen L. Ocular fundus photography. Am J Ophthalmol 1964;57:13-28.

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