Help! How do I capture a diffused slit lamp image?

02.09.26

The Haag-Streit UK slit lamp ‘Help!’ series has been written by Gemma Edwards, HS-UK Slit Lamp Product Manager. Gemma has worked for Haag-Streit for four years and previously spent 13 years as an NHS Ophthalmic Photographer at Royal Wolverhampton Eye Infirmary.

When is a diffused slit lamp image useful?

While this type of imaging is sometimes considered basic, it is actually very useful for recording large areas of the eye, especially when recording the lids, conjunctiva, or showing variations in colour across the eye.

Mastering the overview image is a good place to begin when starting out with slit lamp imaging. Overview images are captured using low magnification, which has the bonus of creating a good depth of field. The aim of the overview image is to try to reduce harsh lighting and create a soft uniform illumination. This is usually achieved using the diffuser filter attachment, which sits in front of the mirror and can be combined with a pivoting background illumination to help further reduce shadows.

Gemma’s step-by-step guide to capturing the perfect diffused slit lamp image

1. Using the diffuser: optimising the light

The diffuser filter is located in front of the mirror. When engaged, it will scatter the light across the surface of the eye rather than forming the traditional slit of light.

 

Recommendation

To get the best lighting, it is good practice to open up the slit width when using the diffuser, giving you a wider beam of light to scatter. Bear in mind with the wider slit, you may need to reduce the brightness of the beam. You will notice that with the diffuser engaged, the tower cannot be brought into coaxial alignment with the optics as the diffuser will obstruct it. Instead, set the tower to between 30° and 40°.

2. Effective use of background illumination

Haag-Streit has two types of background illumination. One is fixed to the tower, the other can pivot and move independently of the tower. The fixed background will bounce light off the same mirror as the slit beam and will hit the eye at the same angle.

Recommendation

The pivoting illumination moves separately and can be set on the opposite side of the eye to the tower. This works well as an ambient light source and can be used to further reduce shadows. Think of the slit lamp as a camera studio, just in miniature.

3. What if I don’t have a diffuser?

A similar style of image can still be captured without a diffuser.

Recommendation

Open the slit beam to its full height and width, then reduce the brightness of the beam. 

Alternatively, if you have one, use just the background illumination. This will give a similar style of image, but the illumination will still look a little harsher than if you had used a diffuser.

You would also notice that the reflections on the surface of the eye will be more noticeable than if you had used a diffuser. Depending on the magnification used, the full beam may not fully illuminate the eye in the image. Using a higher magnification and careful composition can help.

Top image shows image capture result with no diffuser. Bottom image shows the result when  a diffuser is used.

4. Gemma’s pro tip

Try and keep the illumination tower temporal to the eye (this may not be possible depending on the type of image you are trying to achieve). Keeping the tower temporal will help reduce any shadows cast from the patient’s nose. If you are using a pivoting background illumination, this is often set to the opposite side of the tower. Be aware of where the background illumination is, taking care to avoid bumping the patient’s nose.

Look out for the next post from our slit lamp ‘Help!’ series, coming soon!


Follow us on social media to ensure you see our blog updates.