Ophthalmology Dept, Flinders Medical Centre, Bedford Park, Australia
Purpose: Serial slit lamp photography is the process of producing images of the same eye at different moments in time. The interval between images may range from minutes to years. The aim is to impart information about change in the eye over time to the clinician in support of patient care. To best illustrate change occurring in the eye, images need to be consistent and comparable. There are a number of variables which can adversely affect image repeatability which the photographer needs to be aware of. In this presentation some cases with serial imaging will be examined in order to highlight the various parameters, discuss how to control these and show that the longer the period of time spanned by the imaging, the greater the scope for image variability.
Results: Sequential photographs of a case of iris melanoma over a period spanning 38 years showed differences in lighting, colour temperature, magnification, pupil size and resolution. The change in parameters contributing to these differences included; the slit lamp used, the camera back used on the slit lamp ie. initially film, then successively upgraded digital camera backs, the settings used on the camera back ie. ISO, white balance and colour space, the post processing of the image, the photographer, the use of dilating drops and the age of the flash tube.
Conclusion: Every patient should be regarded as a potential candidate for serial photography. A systematic approach which includes establishing standardised techniques is recommended in order to replicate previous eye imaging. A simple and important step, often overlooked, in the process is to review patient photographs from the most recent visit prior to commencing repeat photography. Colour variation in existing series of images can be improved using specialised image editing software such as the “colour match” feature in Adobe Photoshop.