Article Text

Download PDFPDF
Near-infrared transillumination photography of intraocular tumours
  1. Jørgen Krohn1,2,
  2. Erlend Ulltang2,
  3. Bård Kjersem2
  1. 1Department of Clinical Medicine, Section of Ophthalmology, University of Bergen, Bergen, Norway
  2. 2Department of Ophthalmology, Haukeland University Hospital, Bergen, Norway
  1. Correspondence to Professor Jørgen Krohn, Department of Ophthalmology, Haukeland University Hospital, Bergen N-5021, Norway; jorgen.krohn{at}helse-bergen.no

Abstract

Purpose To present a technique for near-infrared transillumination imaging of intraocular tumours based on the modifications of a conventional digital slit lamp camera system.

Methods The Haag-Streit Photo-Slit Lamp BX 900 (Haag-Streit AG) was used for transillumination photography by gently pressing the tip of the background illumination cable against the surface of the patient's eye. Thus the light from the flash unit was transmitted into the eye, leading to improved illumination and image resolution. The modification for near-infrared photography was done by replacing the original camera with a Canon EOS 30D (Canon Inc) converted by Advanced Camera Services Ltd. In this camera, the infrared blocking filter was exchanged for a 720 nm long-pass filter, so that the near-infrared part of the spectrum was recorded by the sensor.

Results The technique was applied in eight patients: three with anterior choroidal melanoma, three with ciliary body melanoma and two with ocular pigment alterations. The good diagnostic quality of the photographs made it possible to evaluate the exact location and extent of the lesions in relation to pigmented intraocular landmarks such as the ora serrata and ciliary body. The photographic procedure did not lead to any complications.

Conclusions We recommend near-infrared transillumination photography as a supplementary diagnostic tool for the evaluation and documentation of anteriorly located intraocular tumours.

  • Imaging
  • Neoplasia
  • Pathology
  • Choroid
  • Ciliary body

Statistics from Altmetric.com

Introduction

Transillumination is commonly used for the diagnosis and localisation of uveal melanoma and other intraocular tumours, especially for anteriorly located lesions, which are not visible on slit lamp examination.1 For photographic documentation, however, the technique is less suitable, as the low light intensity usually leads to dark and blurred images. In a recent report, we have described how to modify and use a conventional digital slit lamp camera system for transillumination photography of intraocular tumours.2 The procedure was performed by gently pressing the tip of the background illumination fibre optic cable against the surface of the sclera or the cornea for transocular or transpupillary transillumination, respectively. Due to the high level of illumination delivered by the electronic flash unit and the advanced imaging technology of the system, a significantly improved image resolution was achieved. The new technique made it possible to obtain high-quality photographs suitable to outline the tumours and to evaluate their location and extent in relation to fine landmarks such as conjunctival and episcleral vessels.2 The strong light from the flash also offered the possibility of filtering the transmitted light for observations in the near-infrared spectral region. Except for some studies on infrared transillumination imaging of the iris,3 ,4 we are not aware of previous reports regarding infrared or near-infrared transillumination in the diagnosis of intraocular pathologies. This paper describes the further development of the digital slit lamp camera system, which we have now adapted for near-infrared photography.

Materials and methods

Our technique of transillumination photography has been described in detail elsewhere.2 Briefly, the digital slit lamp camera system Haag-Streit Photo-Slit Lamp BX 900 (Haag-Streit AG, Koeniz, Switzerland) was modified by loosening the locking screw that secures the flexible background illumination cable to its holder, releasing the cable and covering the tip of the fibre optic with sterile and transparent polyethylene drape (figure 1A). After application of topical anaesthesia and insertion of a lid speculum, the patient was positioned at the slit lamp and asked to move the eye in the desired direction. The light fibre was gently pressed perpendicular against the surface of the eye until the flat, smooth end of the fibre tip applanated the scleral or corneal curvature (figure 1B). Then, the slit lamp camera (Canon EOS 20D, Canon Inc, Tokyo, Japan) was fired, delivering the flash through the background illumination fibre cable synchronised with the camera shutter.

Figure 1

(A) Photograph of the distal end of the background illumination fibre optic cable. The fibre tip is covered with a small piece of sterile, adhesive and transparent polyethylene drape. (B) The modified digital slit lamp camera system being in use during near-infrared transillumination photography.

The further modification of the slit lamp camera system was done by simply replacing the original camera body with a Canon EOS 30D (Canon Inc) converted for near-infrared photography by Advanced Camera Services Ltd (ACS, Watton, UK). In this camera, the infrared blocking filter (‘hot mirror’) was exchanged for a 720 nm long-pass filter, so that the near-infrared part of the electromagnetic spectrum up to approximately 1100 nm was recorded by the camera sensor. For photographic documentation, the camera was set to 1600 ISO, the background illumination was maximised and the slit light beam from the slit lamp was switched off. Despite the dim working conditions, the continuous modelling light from the background illumination cable allowed accurate camera focusing and precise placement of the light fibre tip.

We have applied this technique in patients with uveal melanoma and ocular pigment alterations. The study was registered and approved by the Regional Committee for Medical and Health Research Ethics, Western Norway.

Results

Near-infrared transillumination photography was performed in a consecutive series of five women and three men, aged between 43 and 85 years. Two patients had anterior choroidal melanoma, one had anterior choroidal melanoma with ciliary body involvement, three had ciliary body melanoma, one had uveal atrophy after episcleral brachytherapy and one had perilimbal episcleral pigmentation.

The near-infrared transillumination photographs were found to be of good diagnostic quality and well suited for topographic evaluation of the tumours. Pigmented ocular structures were readily visible, making it possible to evaluate the exact location and extent of the tumours in relation to intraocular landmarks such as the ora serrata and the pars plana and pars plicata of the ciliary body. Examples of some of these images are shown in figures 25. In one patient, the photograph was taken 6 years after iodine-125 episcleral brachytherapy for a ciliary body melanoma that had extended anteriorly to the iris and anterior chamber angle. Near-infrared transillumination demonstrated complete tumour regression and radiation-induced atrophy of the uveal tissue in the plaque-treated area (figure 4). In another patient with a patch of perilimbal episcleral pigmentation (figure 5A), the near-infrared transillumination photograph revealed a normal appearance of the ciliary body and there was no evidence of an underlying tumour (figure 5B). The photographic procedures were easy to carry out in clinical practice and did not lead to any negative side effects or complications.

Figure 2

Near-infrared transillumination photograph of an anterior choroidal melanoma located inferiorly in the right eye of a 62-year-old man. The anterior tumour margin can be seen just adjacent to the ora serrata.

Figure 3

Near-infrared transillumination photograph of a ciliary body melanoma located in the lower temporal quadrant of the left eye of a 59-year-old woman. Note the irregular contour of the tumour and its anterior extension.

Figure 4

Transillumination photograph of the right eye of a 54-year-old woman 6 years after episcleral brachytherapy for a ciliary body melanoma that had extended to the iris and anterior chamber angle. The iodine-125 plaque had been positioned between the 7 and 9 o'clock meridians. Note the increased transillumination in the plaque-treated area due to the radiation-induced tumour regression and uveal atrophy.

Figure 5

(A) Conventional slit lamp photograph of the left eye of a 50-year-old man showing a patch of perilimbal episcleral pigmentation at the 11–12 o'clock position. (B) Near-infrared transillumination photograph of the same eye revealing a normal structure of the ciliary body and no evidence of an underlying tumour in the pigmented area.

Discussion

The modification of the slit lamp camera system for near-infrared imaging significantly improved the diagnostic information of transillumination. While the conventional transillumination photographs were useful to define the tumour shadow in relation to conjunctival and episcleral vessels,2 the near-infrared images provided more accurate information on tumour location relative to intraocular landmarks such as the ora serrata and ciliary body. This can be explained by the optical properties of near-infrared radiation, which has a good penetration depth in tissues.5 The attenuation of light within the tissues is well known to be caused by absorption and scattering losses. Natural chromophores, such as haemoglobin, exhibit strong absorption of visible light. The absorption caused by these chromophores decreases at longer wavelengths. In addition, light in the near-infrared region scatter less than light in the visible region. Thus, the absorption and scattering characteristics of the tissues make it easier to penetrate deep into the eye using near-infrared radiation compared with visible light. The near-infrared part of the spectrum is poorly absorbed by haemoglobin, and the relatively stronger absorption by melanin therefore made the pigmented intraocular structures more apparent than blood vessels and vascularised tissues. As the short wavelengths of visible light are scattered more easily than the longer wavelengths, the near-infrared photographs also had a lower tendency of overexposure in the corneal and perilimbal areas. The most posterior margin of a tumour shadow that could be evaluated by our technique depended on several factors, such as the width of the lid fissure and the patient's ability to move the eye in the required direction. In some cases, the posterior tumour border could be visualised close to the equator of the eye. For transpupillary transillumination, however, special care must be taken not to overestimate the posterior extension of thick tumours.1

The technique of using a digital slit lamp camera system for transillumination imaging offers the advantage of improved illumination and image resolution. The further conversion to near-infrared photography is a simple procedure and relatively inexpensive. It also has the potential for improvements, such as filtering the light from the flash so that only near-infrared radiation is delivered through the background illumination cable and into the eye. This will be even more convenient for the patients, as the near-infrared part of the spectrum is invisible to humans.

Transillumination photographs are valuable for the diagnosis of uveal melanoma as well as for the documentation of tumour growth, preoperative planning of plaque placement in episcleral brachytherapy and follow-up after treatment. We recommend near-infrared transillumination photography as a supplemental diagnostic tool for the evaluation and documentation of anteriorly located intraocular tumours.

References

Footnotes

  • Contributors All authors have contributed to the conception and design; acquisition, analysis and interpretation of data; drafting the article or critical revision for important intellectual content and final approval of the version to be published.

  • Competing interests None.

  • Ethics approval Ethics approval was provided by the Regional Committee for Medical and Health Research Ethics, Western Norway.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.