Slit lamp I (theory)

Question 1

What are the key components of a slit lamp machine (in the order that they’re placed)?

Answer 1

illumination system, objective lens, galilean telescope, condensing lens, porro-prism, and eyepiece

Question 2

Explain signficance of the objective lens.

Answer 2

Slit lamp biomicroscope is derived from a simple microscope. So the objective lens is replaced with a lower powered lens to:
- increase distance between lens and px
- allows wider depth of focus
- lower powered lens permits a larger lens with more light gathering

The objective lens is the only component that is shared/not doubled in the optical system.

Question 3

Explain the significance of the galilean telescope in the slit lamp.

Answer 3

• In a normal microscope, the magnification is fixed and directly related to object distance. Thus, we add a galilean telescope for a longer working distance.
  
  • This allows us to change the magnification and a tele-microscope fusion.
• Positive objective, negative eye piece lens.

Question 4

Explain the significance of the condensing lens in the slit lamp.

Answer 4

• When galilean telescope is added, there’s no image-plane (image produced). Thus, a condensing lens is added.
• Positive lens, focuses image from the galilean telescope to a point.

Question 5

Explain the significance of the porro-prism in the slit lamp.

Answer 5

• Corrects the image orientation, as previously the image produced was inverted and reversed.
• Flips the image 180 degrees horizontally and vertically
• Has 4x 45˚ reflecting surfaces; 2 for each orientation.

Question 6

Explain the significance of the illumination system in the slit lamp.

Answer 6

Provides light

Question 7

What are the pros and cons of the Haag-streit slit lamp

Answer 7

• light source is above, so less stable.
• easier to use
• Top heavy

Question 8

What are the pros and cons of the Zeiss slit lamp

Answer 8

• Light source is below
• Smaller, more compact
• Lower centre of gravity so is more stable