TNOA Journal of Ophthalmic Science and Research

: 2022  |  Volume : 60  |  Issue : 2  |  Page : 137--141

How to take a good slit lamp photograph?

Naveen Radhakrishnan, N Ventakesh Prajna 
 Department of Cornea and Refractive Services, Aravind Eye Hospital, Madurai, Tamil Nadu, India

Correspondence Address:
Naveen Radhakrishnan
Consultant, Department of Cornea and Refractive Services, Aravind Eye Hospital, 1, Anna Nagar, Madurai - 625 020, Tamil Nadu

How to cite this article:
Radhakrishnan N, Prajna N V. How to take a good slit lamp photograph?.TNOA J Ophthalmic Sci Res 2022;60:137-141

How to cite this URL:
Radhakrishnan N, Prajna N V. How to take a good slit lamp photograph?. TNOA J Ophthalmic Sci Res [serial online] 2022 [cited 2022 Sep 25 ];60:137-141
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About the author

Dr Naveen Radhakrishnan completed his under graduation in JIPMER medical college and Residency in Ophthalmology in Regional Institute of Ophthalmology, Chennai under Dr K Vasantha. He finished his Cornea fellowship in Aravind Eye Hospital Madurai under the mentorship of Dr N Venkatesh Prajna who is the Academic director of Aravind Eye Care System, Madurai. Dr Naveen Radhakrishnan is currently working as a Consultant in Cornea and Refractive services in Aravind Eye Hospital, Madurai. He is also the Joint Editor of TJOSR and has numerous peer reviewed, indexed publications to his credit.

The author has published two Ophthalmology cover images, one on the cover page of the prestigious Eye journal and another on the Ophthalmology Glaucoma Cover page and has won numerous awards in national and regional conferences for slit lamp photography.

Slit lamp photography is useful technique for capturing anterior segment pathologies. It is used for documentation, education, sharing knowledge and in tele-ophthalmology.[1],[2] Though newer advances in anterior segment imaging with mobile phone attachments and digital add-ons to slit lamp are on the raise, a traditional photo slit lamp is still ideal for documentation of anterior segment pathologies especially in teaching institutions.[3],[4] A photo slit lamp is a combination of a biomicroscope, an illumination system and a camera. The illumination system in addition has a flash unit and a fill light for background illumination.[5] The flashlight is delivered simultaneously with the camera shutter to optimise exposure. The fill light or the background light is used to illuminate the background structures to provide a context in techniques like direct focal illumination. The light from the right ocular is usually split with the help of a beam splitter or a mirror housing unit to the camera for simultaneous capture of the image while viewing it.[5] The different illumination techniques and their uses are described below.

 Types of Illumination

1. Diffuse Illumination:

It provides an overview of the anterior segment in low magnification and serves as an introduction to demonstrate the general condition of the eye. The slit beam is opened fully, with the light diffuser on. The background illumination is also kept to the maximum. Both the illumination systems are kept at an angle of 45-60' to the ocular. This provides a shadow free illumination with two light reflexes as artefacts [Figure 1]. The angle of the light source can be altered to prevent the light reflexes from falling on the area of interest. One can also take a diffuse illumination image with just the background fill light to capture the details of Iris lesions by improving the contrast. Conjunctival lesions may require reduction of the illumination to avoid artefacts due to reflections from conjunctiva. These are commonly used as an introductory image of the eye being examined. Conjunctival mass lesions and dense large corneal opacities are seen well with diffuse illumination.{Figure 1}

2. Direct Focal Illumination:

In this illumination technique, the area of interest is illuminated directly by the slit beam. There are two types of direct focal illumination, namely, broad beam illumination and narrow beam illumination.

Broad Beam Illumination:

A broad slit beam of 2-4 mm width is used to illuminate the pathology. The beam size is varied as per the size of the lesion. The slit beam is kept at an angle of 45-60' to the ocular. Fill light is usually switched off or kept to a minimum [Figure 2]. Flash intensity is reduced to prevent over-illumination of the lesion. This technique is mainly used for anterior or surface lesions of cornea (corneal epithelial irregularities, superficial punctuate keratitis, anterior stromal opacities, epithelial dystrophies and Bowman's layer dystrophies) and anterior or surface lesions of the lens (Pseudoexfoliation of lens, anterior lens capsule calcification, etc.). For iris lesions, the slit beam is kept as oblique as possible to the ocular to increase the contrast and get a silhouette of the margins.{Figure 2}

Narrow Beam Illumination/Optical Section:

A slit beam as thin as possible is made to create an optical section of the cornea and lens. It is used to locate the depth of the pathology in the cornea and lens [Figure 3], [Figure 4], [Figure 5]. This illumination technique is difficult to capture due to insufficient light from the narrow slit beam and requires a high intensity flash to compensate for the same. The slit beam is usually kept at 45' to the ocular. A low intensity fill light is necessary to illuminate the background area for a better context. The intensity of the slit beam is usually increased to four times intensity of the fill light to increase the quality of the image. Due to the problems associated with depth of focus, the entirety of the lens cannot be captured in a single image and the anterior and posterior aspect of lens has to be focussed and captured separately.{Figure 3}{Figure 4}{Figure 5}

3. Indirect Illumination:

In this technique, the area adjacent to the pathology is illuminated. All forms of indirect illumination require decentration of the slit beam from its normal isocentric position to maintain focus and centration of the lesion. Fill light is usually switched off or kept to a minimum in all forms of indirect illumination. This technique includes proximal illumination, direct and indirect retroillumination from iris, retroillumination from fundus and sclerotic scatter.

Proximal Illumination:

A decentered broad slit beam is focussed just adjacent to the area of pathology. This technique is commonly used for conjunctival and lid lesions where the surface specular reflections from direct focal illumination can produce significant artefacts. In proximal illumination, retroillumination of the light from the deeper layers of the same tissue is utilised to delineate the pathology [Figure 6].{Figure 6}

Direct and Indirect Retroillumination from Iris:

In these illumination techniques, a decentered broad slit beam is used to illuminate the iris and the pathology is visualised against the light reflected back from the iris. The part of cornea illuminated by the light reflected from iris is focussed in direct retroillumination and the part of cornea adjacent to the illuminated section is focussed in indirect retroillumination. Direct retroillumination is used for opaque corneal lesions like intrastromal foreign bodies and indirect retroillumination is used for refractile lesions like Lattice Dystrophy, Descemets folds, etc. Direct and indirect retroillumination are used together to get maximum information [Figure 5], [Figure 7], [Figure 8].{Figure 7}{Figure 8}

Retroillumination from Fundus:

Light reflected from the retina is used to highlight the corneal and lens opacities. A small rectangular or a semicircular slit beam is used coaxially or nearly coaxially to the ocular, to illuminate the retina. Decentration of the slit beam is required to maintain focus of the lesion. Fill light is usually switched off. A large dilated pupil is required for better imaging. Mapdot fingerprint corneal dystrophy, lattice dystrophy, pseudoexfoliation of lens, posterior subscapsular cataract are the common abnormalities imaged with this technique [Figure 9], [Figure 10].{Figure 9}{Figure 10}

Sclerotic Scatter

In this illumination technique, a large part of cornea is illuminated against a dark background. A decentered moderate slit beam of high intensity is focussed at the limbus. Light traverses the cornea via total internal reflection and the small refractile/opaque lesions are seen against a dark background. A normal cornea appears dark in sclerotic scatter. This illumination is used mainly for corneal foreign bodies, granular dystrophy, corneal edema, keratic precipitates, cornea verticillata, etc., To produce better results the peripheral light artefacts can be cropped. Dilation of pupil provides a better contrast by increasing the dark background.

4. Tyndall Light for Aqueous Flare and Cells:

A small circular beam of high intensity light is projected tangentially through the anterior chamber to view the cells and protein in aqueous in high magnification. To get a better image, the light is focussed in a dark background of a dilated pupil.

5. Specular Reflection:

The ocular and illumination system are kept at 45' on either side of the centre of the cornea. A small high intensity moderate slit beam is focussed in 40X magnification to capture the specular reflection from the endothelium which is seen adjacent to the specular reflections from the tear film. The cellular details of the endothelium can be appreciated with this technique. Abnormalities of the endothelium like guttae can produce off-axis reflections and interrupt the homogeneity of specular reflection.

6. Vital Dyes

Imaging with vital dyes should be performed at the end of the examination after completion of different techniques of illumination described above. Pooling of excess dye should be removed before imaging. A diffuse illumination or a broad beam illumination with normal light is used for Rosebengal and Lissamine green dyes. For Fluorescein staining, the blue exciter filter is used for better imaging [Figure 11], [Figure 12].{Figure 11}{Figure 12}

 Tips for Better Slit-Lamp Photography

To begin with, one should make the patient comfortable and gain the trust of the patient. Explaining clearly to the patient that this is a non-contact, painless procedure can increase his/her cooperation. A drop of local anaesthetic along with topical cycloplegic to relieve the discomfort of patients with painful conditions can improve patient cooperation dramatically.Practising the different illumination techniques with different angles and magnification in non-inflammatory anterior segment lesions, can help the examiner to get acclimatised with the different settings of the slit-lamp photography.Adjusting the eyepiece for the refractive error of the examiner will improve the focus. Most slit-lamp photography captures the image seen in the right eye. Training to see with the examiner's left eye closed can help in better centration of the lesion especially for different modes of indirect illumination.All forms of indirect illumination will require decentration of slit beam. Background light is usually switched off to increase the contrast in indirect illumination.Young children, patients with severe nystagmus, patients with significant photophobia (Gelatinous droplet dystrophy) are better suited for external photography than slit-lamp imaging.The view through the ocular of the slit lamp is circular. Whereas the image captured in the camera is rectangular. Lesions in the extreme periphery of the view focussed may not be captured in the camera.Before closing the session, reassessment of the images taken should be done to ensure completeness of imaging.

To conclude slit-lamp photography is a useful technique for documenting anterior segment pathologies. Understanding the various illumination techniques can help us in capturing better images of anterior segment.

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Conflicts of interest

There are no conflicts of interest.


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