Slit Lamp Cheatsheet

Cheatsheet Content

### Slit Lamp Definition A slit lamp is a biomicroscope used to examine the anterior segment and posterior segment of the human eye. It provides a magnified, stereoscopic view of the eye's structures, allowing for detailed observation of the cornea, iris, lens, and vitreous humor. ### Types of Slit Lamps Slit lamps are generally classified by the convergence angle of their observation system. #### 1. Parallel (Galilean) System - **Examples:** Haag-Streit, Topcon - **Characteristics:** Provides a wider field of view and higher magnification. The optical paths for each eye are parallel. #### 2. Convergent System - **Examples:** Zeiss, Marco - **Characteristics:** The optical paths converge, offering a more compact design and often a more comfortable viewing experience for some users. #### 3. Portable Slit Lamps - **Characteristics:** Handheld, battery-operated, used for bedside examinations, pediatric patients, or in remote settings. Lower magnification and less detailed examination than tabletop models. #### 4. Digital Slit Lamps - **Characteristics:** Integrated or attachable digital camera for capturing images and videos. Essential for documentation, teaching, and telemedicine. ### Mechanical Design A typical tabletop slit lamp consists of several key components: #### 1. Observation System (Microscope) - **Binocular eyepieces:** Adjustable for interpupillary distance and dioptric correction. - **Magnification changer:** Often a rotating drum (Galilean type) or a zoom system, providing various levels of magnification (e.g., 6x, 10x, 16x, 25x, 40x). #### 2. Illumination System - **Light source:** Typically a high-intensity LED or halogen bulb. - **Slit projector:** Projects a variable-width, variable-length slit of light onto the eye. - **Filters:** - **Blue (Cobalt Blue):** Used with fluorescein dye to detect corneal abrasions, foreign bodies, and fit contact lenses. - **Red-free (Green):** Enhances visualization of blood vessels and nerve fibers. - **Neutral Density:** Reduces light intensity without changing color. - **Heat-absorbing:** Protects the patient from heat. #### 3. Chin Rest and Head Rest - Ensures stable patient positioning and proper alignment with the instrument. #### 4. Joystick - Controls horizontal and vertical movement of the entire instrument base for precise focusing and scanning. #### 5. Instrument Base - Houses the mechanical components and allows for smooth gliding movements. ### Illumination Techniques Proper illumination is crucial for effective examination. #### 1. Diffuse Illumination - **Description:** Wide, low-intensity beam illuminates a broad area. - **Purpose:** General overview of the anterior segment, gross abnormalities. #### 2. Direct Focal Illumination - **Description:** Narrow, intense slit of light focused directly on the structure of interest. - **Purpose:** Detailed examination of corneal layers, aqueous flare, lens opacities. - **Optic Section:** Very narrow slit, used to visualize corneal and lens depth. - **Parallelepiped:** Wider slit, provides a 3D view of a tissue block. #### 3. Indirect Illumination - **Description:** Light is focused adjacent to the area of interest, illuminating it by scattered light. - **Purpose:** Visualizing subtle lesions or structures that are obscured by direct light, such as corneal edema or cysts. #### 4. Retro-illumination - **Description:** Light is reflected off a deeper structure (e.g., iris or retina) to illuminate a more anterior structure from behind. - **Purpose:** Detecting subtle opacities in the cornea or lens, such as cataracts or endothelial changes. #### 5. Specular Reflection - **Description:** The angle of illumination and observation are adjusted so that the reflected light from a smooth surface (e.g., corneal endothelium) is directed into the microscope. - **Purpose:** Examining the corneal endothelial cells, tear film. #### 6. Sclerotic Scatter - **Description:** A broad beam of light is directed at the limbus, and light scatters within the cornea, making opacities visible against the dark background. - **Purpose:** Detecting subtle corneal edema or infiltrates. ### Accessories Various accessories enhance the versatility of the slit lamp. #### 1. Tonometer (e.g., Goldmann Applanation Tonometer) - **Purpose:** Measures intraocular pressure (IOP). #### 2. Fundus Lenses (e.g., 90D, 78D, 60D, 20D) - **Purpose:** Allows examination of the posterior segment (retina, optic nerve) when held in front of the eye. #### 3. Gonioscopy Lenses - **Purpose:** Used to visualize the anterior chamber angle for glaucoma assessment. #### 4. Digital Camera/Video System - **Purpose:** Documentation, patient education, telemedicine. #### 5. Teaching Tubes/Assistant Scopes - **Purpose:** Allows two observers to view simultaneously. #### 6. Pachymeter - **Purpose:** Measures corneal thickness. #### 7. Meibography Adapters - **Purpose:** Imaging of meibomian glands. ### Colour Coding While there isn't a universally standardized "colour coding" for slit lamp components beyond the filters mentioned above, some manufacturers might use colour-coding for: - **Filter Selection:** Different coloured dots or indicators on the filter selection dial. - **Magnification Settings:** Different coloured markings on the magnification drum. - **Joystick Buttons:** For specific functions (e.g., image capture). It's important to consult the specific instrument's manual for any manufacturer-specific colour conventions.