Slit lamp examination is the application of the slit lamp corneal microscope to project light at different angles and widths, focus or diffusion method through the corneal microscope to observe the optical properties of the lens, so as to make a judgment on the position of the lens, the lesion situation. In general, the more proximal the examination, the smaller the angle of projection, such as 15-30 degrees, while the peripheral part can be 45-60 degrees.
Lens slit lamp examination commonly used method 1, diffuse illumination method: the slit lamp light source open wide in a diffuse light spot cast to the corneal lens, through the transparent cornea can see the full picture of the lens. Check whether the lens is displaced, whether there is a clear spot-like or wedge-shaped clouding, whether the lens surface is smooth and consistent, etc.. However, the more subtle changes in the layers of the lens cannot be clarified.
2, direct focus illumination method: the focus of the projected light and the focal point of the corneal microscope to completely one to one, this is an important method to examine the lens, which can be divided into wide band irradiation and narrow band irradiation.
(1) Wide band irradiation: The irradiated light will be in a wide band (e.g., 1-2 mm), which is mainly used to observe the relationship between the peripheral anterior surface of the lens and the position of the pupil. Whether there is a difference in its gap and whether there is fluttering of the iris in front of the corresponding lens. The optical properties of the lens surface and anterior cortex are observed.
(2) Narrow band irradiation: The optical band is adjusted very narrowly (e.g., 0.4 mm), at which time small changes in the optical reflectance band of each layer of the lens can be reflected, and the lesion localization is clearer than in the wide band. Because the lens is 4-5 mm thick, the examination must focus on the anterior capsule of the lens in order to observe the posterior capsule layer by layer. It is also necessary to observe each optical section continuously from the temporal to the nasal side to get a comprehensive impression of the examined lens. In practice, the combination of broad and narrow optical bands can often provide a clear picture of the location, morphology and even nature of the lens lesion.
3, indirect focus oblique illumination method: the focus of the irradiation light on the side of the site to be observed, the use of its indirect light reflection can be seen not completely cloudy but refractive changes in the lesion, such as water gaps, vacuoles and minor clouding.
4, rear reflection irradiation method: irradiation light through the rear of the site to be observed, through the subsequent reflection of light to observe the more subtle direct focus irradiation method is not easy to find changes, such as the lens under the posterior capsule clouding, posterior hair barrier, anterior capsule membrane pigment, micro clouding, etc.
5, specular reflection irradiation method: the lens capsule membrane as a specular reflection area, when the irradiation light projection angle is equal to the reflection angle can be seen when the lens capsule specular reflection. If the lens capsule membrane is not uniformly organized, the specular reflection will be reflected and refracted accordingly. Sharkskin-like reflections can be seen in the anterior capsule of a normal lens, for example.