Help! Why are my slit lamp photos blurry?

25.06.26

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.

Gemma’s top five tips for capturing crisp ophthalmic images 

We’ve all been there. The cornea looks perfectly in focus down the eyepieces, but when you go to capture it, the photo on the screen is completely blurry and not even vaguely resembling what you saw through the slit lamp. Here are my top five pieces of advice to ensure your slit lamp photos are focused, well illuminated, and clearly show the pathology of interest.  

1. Check the focus of your eyepieces

This is the most common cause of blurry photographs. While leaving the oculars set to 0 will be fine for an examination, it will not necessarily work for image capture. This is because the camera has a set focal point whereas the human eye can accommodate shifting from one focus point to another. To capture a perfectly focused photo, we must spend some time ensuring that our eyes are focusing on the same point as the camera. This is done using the focusing rod. When the focusing rod is inserted into the slit lamp, it sits at the exact point the camera is focused.

Recommendation

Adjusting one ocular at a time, close one eye and turn the ocular to +5 then back down towards 0 in a smooth turn. Stop turning at the point where you see the texture of the focus rod is sharp. Repeat this with the other optic. Some camera systems have a crosshair in the ocular to help with this fine tuning.

2. Concentrate on the area of interest

When taking a photo using a slit lamp, it can be tempting to try and get as much of the image in focus as possible. While this is good practice, it is not always possible due to the natural curved shape of the eye and the depth of field of the image. Instead, focus specifically on the area of interest.

Recommendation

When photographing the cornea using an optical section, ensure the layers of the cornea are sharp and in focus, and don’t worry about the structures behind the cornea. These structures can be recorded in another image, using a different illumination technique if required. 

3. Select the right shutter speed, aperture & ISO 

Some imaging systems, like the BX 900, give you the option to adjust the shutter speed. This can be useful in low light situations; a reduced shutter speed will increase the brightness of an image. However, if the shutter speed is too slow, it can cause motion to be visible in the image. Another way to adjust the brightness of the image is to use the aperture. A larger aperture will create a brighter image but will also create a shallower depth of field, making it harder to keep all the ocular structures in focus. ISO is how the camera sensor responds to light. Increasing the sensitivity of the ISO will create brighter images but will also introduce a grainy texture to the image.

Recommendation

A shutter speed of 1/125 is generally recommended while reducing shutter speed to less than 1/60 may start to introduce excessive motion blur into images. Keep the aperture small for overview images where depth of field is desired. Increase the size of the aperture when required but be mindful of the reduction in depth of field. The recommended setting for the ISO for general use is 500, but this can be adjusted if required.

4. Magnification matters

Low magnification is useful when capturing an overall image of the eye, as it has greater depth of field and more ocular structures are in focus at one time. Increasing the magnification provides greater visibility of fine ocular structures and is ideal for capturing subtle pathology. Increasing the magnification also ensures that we are using the camera sensor to its full capacity. This tends to give a better result than taking a low magnification image and severely cropping it. However, as the magnification increases, the image will get darker and the depth of field will become shallower, making it more difficult to maintain focus on the structure of interest. 

Recommendation

At high magnifications, compensate for the shallow depth of field by reducing the aperture size, while also increasing illumination to ensure the photo is adequately bright. 

5. Bracketing

If you have tried using the focusing rod and are still struggling with getting sharp images, try bracketing. Bracketing is a photography technique in which several photographs are taken of the same area, with slight changes made to the settings each time.

Recommendation

In this case, we will make changes to the optic. Focusing mainly on the right optic, adjust the optic half a step to the + marker, capture an image. Has it improved? If not go back to the original setting, then move half a marker towards the – sign, capture an image. Has it improved? Using this method, you should be able to narrow down any fine adjusts you require. 

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.