20D Aspherical Lens
- 1. The silver ring on the lens holder should be held toward the patient's eye during examination, which can ensure the right using direction and may provide for best image quality
- 2. Keep the lens centring on the patients pupil
- 3. Hold the lens far enough from the patient's eye so that the retinal image has the same diameter with the lens
- 4. Keep the illumination sources as dark as possible to minimize reflections and image contrast
- 5. Keep the lens clean to minimize glare from the lens surface.