Fig. 11.15: Fluorescein stain photography
Fig. 11.16: Anterior segment fluorescein angiogram
with an internal timer that is critical for fluores- cein studies requiring dynamic flow analysis (Fig. 11.16). Black and white films ISO 400 or instant type (polaroid or Fuji) film can be used and processed in a similar way as for retinal angiography.
Optical System of Fundus Camera
Fundus camera’s optical system can be compared to the Galilean type telescope and is characteristic by incorporating an internal co-axial type illumination and electronic flash. The lightemitted through the objective of the camera lens is a ring-shaped image. The distance from this ring to the surface of objective lens is referred to as the working distance and is of great importance in taking good artifact-free fundus photographs. The actual position of this ring- shaped light can be best observed by looking from the side of the fundus camera. To keep this relative position constant is one of the most important and basic points in fundus photo- graphy to insure good color saturation and artifact-free photography (Fig. 11.17).
agent to achieve best possible pupillary dilation (optimally a pupillary dilation of over 8 mm is desirable). The objective lens should be clean and free from dust and smear. Any dust particles must be carefully removed with a manual blower while smear should be removed with lens cleaning paper. Check that the film is correctly loaded and flash intensity control is properly set according to the film sensitivity as well as the retinal pigmentation. Also adjust the eyepiece diopter scale to match the operator’s diopteric correction (Fig. 11.18). Adjust the height of the motorized camera table as well as the operator’s and patient’s stool so both may be as comfortable as possible in front of the fundus camera (Fig. 11.19).
Fig. 11.17: Working distance
Fig. 11.18: Diopteric correction
Fundus Photography Preparatory Operations
Prior to starting the photographic session, the patient’s eye must be dilated with a mydriatic
Fig. 11.19: Comfortable position
Operational Procedures
The patient rests his/her chin on the chin rest and presses his/her forehead lightly against the forehead bar. Adjust the patient’s lateral canthus with the head rest of the fundus camera and align the patient’s eye with the illumination beam and optical pathway of the fundus camera. If necessary, adjust the optical table for optimal patient comfort.
Looking through the viewfinder of the fundus camera, focus the camera until you obtain a sharp image of the posterior segment of the eye. Slightly adjust the joystick (left-right-forward and backward) to set the camera to a position in which the subject’s eye is evenly illuminated. It should be free from flares and reflections. One should try to achieve maximum color saturation. Ask the patient to gaze at the fixation target until you have the desired area of the fundus in your viewfinder. It is important for operator to ask the patient to keep both eyes open throughout the entire photographic session. Also make certain that the eyelids as well as eyelashes should not obstruct the light passage. The light
Fig. 11.20: Beam pathway
beam should be projected entirely into the pupil to avoid artifacts to be recorded on the film (Fig. 11.20).
If pictures are taken before the above conditions are fully satisfied, reflections and/ or artifacts will be produced and it will result in a lower picture quality and poor contrast. Once all these conditions have been fully satisfied, capture the image with a minimum delay, otherwise the patient may be tired and lose fixation and concentration. When the patient is asked to keep his eye open for over 30 seconds, the tear film starts breaking and cornea gets dry causing a low contrast photograph. It is important to always keep in mind that the patient’s comfort and well-being is critical in order to achieve good photo-documentation. Speak slowly and clearly explain the photographic procedure to the patient in order to lessen his or her anxiety.
Fluorescein Angiography
Ophthalmic photography is unique because the medical photographers also perform dynamic flow studies of the iris, retina or choroid using dyes such as sodium fluorescein or indocyanine green. These studies provide a vital piece of information needed by the treating ophthalmo- logist in order to understand the vision problems of a patient. Fluorescein angiography (FA) is often more complex than conventional color retinal photography. This, however, is not the case, the main differences between color retinal photo- graphy and angiography are a set of filters (usually a set of exciter and barrier filter) and remembering the correct sequence of the flow study (area to be photographed in the early, mid or late phase that are usually recorded with a timer).
Principle of Sodium Fluorescein Angiography
Sodium fluorescein is mainly used to perform dynamic flow studies of the integrity of retinal vessels (in some cases, sodium fluorescein may also be used in the study of the vascular integrity of the anterior segment). Once the pupils are sufficiently dilated, a solution with a concen- tration of 10% (2.5 cc of volume) or 25% (1 cc of volume) of sodium fluorescein is injected in the patient’s vein. Injection volume should be carefully controlled in children or patients weighing less than 100 pounds. When using a concentration of 10% of sodium fluorescein, a recommended dose of 0.066 cc per kg should be used. It not only avoids adverse reactions but gives a good fluorescence standard in the dynamic flow study. The dye travels throughout the body’s circulatory system (first throughout the veins) including the retinal vessels. When observing the retina with a cobalt blue light (referred to as the exciter light set at about
490 nm), sodium fluorescein reflects a green fluorescence towards the film plane of the retinal camera. Before arriving to the film plane, that green fluorescence passes through a yellow barrier filter (referred as the barrier filter) that removes all unwanted blue light that may inter- fere with the true appearance of the fluorescence found at about 520 nm. These exciter filters (cobalt blue set at 490 nm) and the barrier filter (sharp cut-off filter set at 520 nm) must be matched perfectly in order to render true fluorescence images of the retinal vessels (Fig. 11.21). Film Type and Development
The amount of fluorescence perceived by the film when properly excited by cobalt blue illumination is somewhat low; therefore, a highly sensitive black and white film such as ISO 400 film should be used. When processing this black and white film (in total darkness), use a medium to high contrast fresh developer in conjunction with an extended processing time in a solution set at 20°C/68°F. Push process is a technique that is used in angiography to see more detail on the film produced by the fluorescence; this technique consists of processing the exposed sensitive film for an extended period of time (50 to 100% longer) or to process the film in a warmer solution say 2 to 4 degrees centigrade higher.
Photographic Procedures
Fluorescein angiographic study consists of several phases based on time sequence. Depending on the particular ocular disease, dynamic flow studies vary between 3 and 15 minutes. Fluorescein angiography has following phases:
1. Preinjection or control photograph: It is a photograph in which both the exciter and
barrier filters are in place and a photograph
is taken without the presence of sodium fluorescein. This is usually done to determine the presence of pseudo-fluorescence or auto- fluorescence such as in the case of drusens.
Fig. 11.22: Arterial/venous phase of FA
2. Arterial and venous phase: This is the early phase of the angiogram study usually within 14 to 30 seconds after injection of sodium fluorescein (Fig. 11.22).
3. Mid-phase: When all retinal vessels have been filled (stained) with sodium fluorescein (from 30 seconds to 120 seconds).
4. Late phase: This is the last phase and varies in duration depending on the disease of the patient. In diabetic retinopathy, this phase may vary from 3 to 5 minutes, whereas in some ocular tumors, it may last as long as 15 to 20 minutes (Fig. 11.23).
Fig. 11.23: Late phase of FA
The fluorescein angiography helps in understanding various retinal diseases and abnormalities. One needs to study carefully the retinal drawing of the patient’s chart and look for notes or direction from the retina specialist to understand the areas of interest and the main phase of the study (early, mid or late). It is critical to follow precisely the retina specialist’s notes to understand the diseased eye to be first studied (right or left eye). How soon the retina specialist needs to evaluate the results of the angiogram? Does the retina specialist need to treat the patient with laser immediately after the angiographic study? This is referred to as a STAT angiogram. A good practice is to carefully study the diseased retinal areas when performing color photo- graphy, usually done prior to an angiography. Once you understand the ocular disease, you can start the angiographic procedure with a good plan. Number of images in each phase, early, mid and late phases as well as area of interest, are dependant on a particular study. It is, however, important to get different results from what were initially anticipated. In fact, at times, angiographic pattern may be completely different from what was anticipated, a retinal vessel that was thought to be leaking may be intact and
a normal one may be found leaking. Anticipating the unexpected findings comes with years of angiographic experience and a good set of standardized angiographic protocol.
Monochromatic Fundus Photography Various monochromatic wavelengths penetrate at different layers of the eye revealing specific structures as well as foreign bodies in those layers. With the appropriate monochromatic wavelength filter (cobalt blue filter), it is possible to isolate the first layer of the retina where you can find the nerve fiber layers (Fig. 11.24). This
may be very useful while documenting a patient with glaucoma to demonstrate nerve fiber dropout. A green filter (referred to as red-free) will cut out all red-light making those areas black (red is seen as black) creating a nice high contrast image of the posterior pole. Red filters will allow the longer wavelengths of the visible spectrum to penetrate deep into the ocular structures to reveal the choroidal vascular pattern (choroidal vessels appear as white while retinal vessels will appear as black Fig. 11.25) and a choroidal nevus or melanoma (Fig. 11.26). These photo- graphs, in particular those taken with red-free light, are very suitable for printing use. Anterior Segment Photography with Photo Slit-lamp
The anterior segment is usually photographed with a photo slit-lamp biomicroscope (Fig. 11.27). It is similar to the clinical slit-lamp biomicroscope that is used in our daily work; with the exception that it incorporates a camera (static or motion such as video) and an electronic flash light. Needless to say, photographers need a good understanding of the clinical instrument before they can become skillful in capturing clinically useful images of the anterior segment (Fig. 11.28). Fig. 11.24: Nerve fiber layer with blue filter
Fig. 11.25: Red-free photography
Fig. 11.27: Photo slit-lamp Fig. 11.28: Slit-lamp photograph of lens with various nuclei
Different from fundus photography, photo slit- lamp biomicroscopy is perhaps the most challenging type of photography in the field of ophthalmology. It requires a good understanding of the ocular structures; disease process as well as illumination techniques to illustrate the area of interest to the clinician. The illumination is of key importance.
Since pathology varies greatly and may appear differently for each case, simple changes of slit-width, height angle of the illumination tower or even the use of diffuser, the same pathology may show itself quite differently in the final picture. It becomes essential to select most suitable lighting technique for each situation. This challenge is perhaps what gives the photographer greatest pleasure in taking pictures of best area of interest.
In observing through the slit-lamp the reflections from the cornea and lens are not so offensive. However, same reflections may become disturbing and even harmful in hiding areas of interest when taking photographs. Adjust the illumination tower angle to avoid unwanted reflections. When using auxiliary light (often
referred to as fill light), it is necessary to pay attention to avoid the reflection that light may produce on the cornea. Carefully place the area of interest in the field to be photographed while making certain that you are using the best possible form of illumination. Use appropriate magnification to ensure that not only the area of interest is captured but you leave enough room to have a point of reference for follow-up photo- graphic sessions (for example, in photographing an iris melanoma; use of medium magnification would allow for a portion of the iris to be seen for identification that the mass is located at 12, 3, 6 or 9 o’clock and provides an idea about the size of the mass.
Bibliography
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