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Comprehensive Ophthalmology Free Papers 5. Bechmann M, Thiel MJ, Roesen B, et. al. Central corneal thickness determined with optical coherence tomography in various types of glaucoma. Br J. Ophthalmol 2000;84:1233–7. 6. Fishman GR, Pons ME, Seedor JA, Liebmann JM, Ritch R. Assessment of central corneal thickness using optical coherence tomography. J. Cataract Refract Surg. 2005;31:707–11. 7. Leung DY, Lam DK, Yeung BY, Lam DS. Comparison between central corneal thickness measurements by ultrasound pachymetry and optical coherence tomography. Clin Experiment Ophthalmol 2006;34:751–4. 8. Zhao PS, Wong TY, Wong W-L, et. al. Comparison of central corneal thickness measurements by Visante anterior segment optical coherence tomography with ultrasound pachymetry. Am J Ophthalmol 2007;143:1047–9. 9. Kim HY, Budenz DL, Lee PS, Feuer WJ, Barton K. Comparison of Central Corneal Thickness using Anterior Segment Optical Coherence Tomography vs Ultrasound Pachymetry. Am J Ophthalmol 2008;145:228–32. Photographic and Digital Documentation of The Anterior Segment using Compact Digital Camera Dr. Susil Kumar Pani The aim of the study is to simplify the process of documentation of the diseases of the anterior segment of the eye by the use of easily available compact digital camera. METHODS AND MATERIALS Every eye care professional uses a slit lamp bio-microscope to examine the anterior segment of the eye. To document, the slit lamp needs to have a standard beam splitter, image capturing device or a digital camera back fitting on to the beam splitter, video, audio interface, all connected to a standard desktop computer. Most of them come with proprietary software to capture and edit the photograph. The whole system other than slit lamp costs minimum of Rs 100,000 from the Indian companies and more than Rs 300,000 from abroad. I have tried to use the ordinary digital camera which is easily available in market from standard known companies available from Rs 5000 to Rs 10,000 very easily. In my study I have used Sony compact camera model DSC W520. This camera is a 14 MP camera costing about Rs 8000 at the beginning of study. I will describe the camera controls to be used in documenting the slit lamp photography. The routine method used by me is to place the compact camera tightly against the eye piece of the slit lamp while the bio-microscope and the light are already sharply focused on the area to be photographed. One will be able to see the live picture on the screen of the camera before capturing the image. 475
70th AIOC Proceedings, Cochin 2012 Camera Controls ISO: The ISO represents the sensitivity of the film or sensor to light. Normally the option given is auto ISO, 100, 200, 400, 800, 1600 and rarely 3200 or more. The higher the number, the more sensitive is the ability to capture the image. As you increase the ISO, pictures can be taken at low light conditions. This will produce a graininess of the picture. Hence for slit lamp photography set the ISO always 100 or 200 or maximum at 400. White Balance This feature deals with the type of light used for lighting the object photographed. To be more precise it means the color temperature of the light falling on the object. The options available in a compact digital camera is auto white balance, day light, cloudy, fluorescent under natural white light, incandescent light and flash. In auto white balance setting the camera tries to recognize the color temperature of the light falling on the object and sets the white balance. Incandescent white balance is when the light source is an ordinary bulb or a Halogen light. As most of the slit lamps use the Halogen bulb as the light source, this is the white balance to be used for slit lamp photography. Flash can be used for gross photography of the eye and the face. Otherwise while taking photos, the slit lamp is used as the source of the light and magnification, hence the white balance to be used is always incandescent light. Focus The compact digital cameras give option of multiple auto focus points and central auto focus point. In the multi auto focus points the camera tries to focus on the entire exposed screen. In case of central auto focus the camera focuses only at the centre of the object in front of the camera. In case of slit lamp photography it is better to use the central auto focus mode keeping the area of interest right at the centre of the frame. In case of taking general photograph of eye or face one can use multi auto focus mode. Metering Mode Most compact digital cameras provide at least 3 metering modes. Metering mode means the exposure time to capture the image. This exposure time is decided by two main factors, the shutter speed and aperture. Three to be precise, the ISO, shutter speed and aperture. The shutter speed is the amount of time the aperture remains open to capture the image. The lower the shutter speed the more is the exposure, faster the shutter speed lesser is the exposure. Aperture is the size of the opening through which the light reaches the film or the sensor. The aperture is otherwise called F stop. The larger the aperture the more the exposure, the smaller the aperture the less is the exposure. The aperture is designated as 1.2, 1.8, 2.8, 3, 3.5, 4….22. The lower the number is the larger aperture and the larger the number the narrower the aperture. The 476
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