Ординатура / Офтальмология / Учебные материалы / Uveitis Text and Imaging Text and Imaging Text and Imaging 2009

side-effects. Graefes Arch Clin Exp Ophthalmol 1999; 237:289-95.

56.Yang PZ, Wang H, Huang XK, Zhou HY, Zhang Z, Chu LQ, Zhong HH, Xie CF. Quantitative determination of aqueous flare and cells in the eyes of patients with inflammation of the anterior uvea. Zhonghua Yan Ke Za Zhi 2004;40:510-3.

57.Yang P, Fang W, Jin H, Li B, Chen X, Kijlstra A. Clinical features of Chinese patients with Fuchs’ syndrome. Ophthalmology 2006;113:473-80.

58.Fang W, Zhou H, Yang P, Huang X, Wang L, Kijlstra A. Longitudinal quantification of aqueous flare and cells in

Vogt-koyanagi-Harada disease. Br J Ophthalmol 2008;92:182-5.

59.Tugal-TutKun I. Clin Exp Rheumatol 2006;24 (Suppl):S25.

60.Biziorek B, Zarnowski T, Zagorski Z. Evaluation and monitoring of selected inflammation patterns in uveitis using laser tyndallometry. Klin Oczna 2000;102:169-72.

61.Verbraak FD, Schreinemachers MC, Tiller A, van Deventer SJ, de Smet MD. Prevalence of subclinical anterior uveitis in adult patients with inflammatory bowel disease. Br J Ophthalmol 2001;85:219-21.

INTRODUCTION

Imaging of the retina in routine is done by using a monocular retina camera, designed to capture images of the fundus. Fundus photography in uveitis is required to aid diagnosing and monitoring of retinochoroidal inflammation and infections. Digital systems that are being used currently also allow the images to be displayed, stored, modified, manipulated, and archived. A baseline colour fundus photograph serves as a good clinical reference when determining the extent and progression of fundus changes during follow up periods. Fundus colour photography helps in making clinical diagnosis with studies showing a good agreement between retina specialists by interpretation of retinal photographs distinguishing between presumed ocular histoplasmosis and multifocal choroiditis without the need for any ancillary tests.1 Stanford et al reported a good agreement between uveitis experts on the interpretation of retinal photographs of patients with presumed toxoplasmosis retinichoroiditis.2

HISTORICAL PERSPECTIVE

Ophthalmic imaging had its origin in 1850 with the development of the ophthalmoscope by Von Helmhotlz. Five years later, in 1885, an important milestone in ophthalmic imaging was achieved by Jackman and Webster who produced the primitive human fundus photograph of the optic nerve with an exposure time of 20 minutes.3 Fundus photographs, similar to those taken today were made possible follow-

ing the intervention of the reflex-less ophthalmoscope by Thorner in 1899 and perfected by Gullstrand in 1910.3 Dimer published the first book of fundus photography using fundus camera designed with Zeiss. Nordenson and Zeiss using carbon light source developed a modified Gullstrand’s ophthalmoscope. Further modification occurred in 1953 by Hansell and Beeson using a Xenon arc tube for illumination.4 Further, Novotony and Alvis in 1960 upgraded their camera with an electronic flash light source and motorised it to allow rapid and sequential photography that was needed for fluorescein angiography.5 By the late 1980 retinal fundus camera had peaked in their advancement. The major technologic advancement was videography by Destro and Puliafito in the 1980s.6

PRINCIPLE

A camera is the basic photographic equipment unit in the fundus camera. It is modelled after an indirect ophthalmoscope. Traditionally the analog fundus images have been recorded on a photographic film. They are created when the light from the camera is focused on film sensitising silver halide embedded on the surfaces of the film.

Digital systems use these cameras in combination with electronic image sensors and digital archiving system. Digital images are composed of pixels or image elements. Each image is made of an array of pixels. Greater the number of pixels, greater the spatial resolution and accuracy with which the images represent the original. Depending on whether colour or black and white images are necessary, pixel may

be assigned a variety of colours or shades of gray, black and white.

HARDWARE

A fundus camera consists of a main camera unit, base assembly and power supply.

The camera unit has an optical head that houses the aspheric front lens and rear objective lens system, a flash bulb and viewing lamp, filters, mirrors and an eyepiece assembly. A body of 35 mm camera is attached to hold and transport the film since it is used without a lens and does not play any role in the image formation.

The camera unit is attached to a base that is required for patient positioning and camera movement.

The hardware of a digital fundus camera consists of (Figure 1):

1.Forehead rest

2.Chin rest, for reliable fixation of patient’s head

3.Astigmatic compensator

4.Slider for different filters

5.Spigot-end screw to limit swivel range

6.Knurled handle for adjustment of headrest.

7.Knob for field angle adjustments ( 50°, 30° and 20°)

8.Cover of lamp housing

9.Control and flashbulb cable

10.Knurled screw for clamping 35 mm camera to the dovetail mount of the fundus camera

11.Dovetail mount for accommodation of 35 mm camera

12.Cover of top camera port

13.Internal fixation device.

Figure 1: Fundus camera unit (Courtesy of Carl Zeiss India)

A second port is available to connect an additional 35 mm camera or another image recording system via a camera adapter.

TECHNIQUE OF IMAGE ACQUISITION

PREPARING THE FUNDUS CAMERA

Once the camera is switched on, the initial state is automatically set. The patient data is entered. The camera is then pulled, along with the instrument base, away from the patient. The control knob is then adjusted to the desired field angle.

PREPARING THE PATIENT

1.Dilate patient’s pupil

2.Patient sits down with his/her chin on the chinrest and forehead against forehead rest. The knurled handle is turned to bring the patient’s eye level with the eyelevel marks on the headrest.

TECHNIQUE

Once the patient is properly positioned, the fundus camera is moved, with the lens cap still attached, laterally to align the camera to either left or right eye. The lens cap is removed and the patient is made to look either at the external fixation light with the nonexamined eye or with the examined eye to the fixation target of the internal fixation device. The brightness control is turned on and the instrument base moved back and forth until the light ring of the fundus camera is sharply focused on patient’s pupil. The focusing control is then turned to focus onto the fundus and moving the joystick for vertical adjustment, does fine focusing.

The red-free photographs can be acquired by pressing the GREEN key on the control console and the photographs acquired by pressing the release button on the joystick. These red-free photographs deliver high contrast black and white images of the vascular system of the fundus and help in better documentation of nerve fibres and retinal vasculature (Figures 2A and B).

For colour photographs, the images of patient’s eye are recorded in true colours on a 35 mm colour film or data back. This mode is activated by pressing the COLOUR key on the control console and the photo-

Figure 2A: Red-free fundus photograph showing vasculitis along the lower temporal vessels with retinal haemorrhages and cotton wool spot

Figure 2B: Red-free photograph showing optic disc oedema associated with a partial macular star and superficial retinal haemorrhages

graphs acquired by pressing the release button on the joystick. For taking photographs of the mid-peripheral retina, both the patient’s eye and fundus camera may need to be moved, thus allowing the posterior pole, superior, inferior, nasal and temporal retina to be visualised (Figures 3 to 6).

In cases with intermediate uveitis, where one might attempt to photograph the snow banking in the peripheral retina, it is important to know that due to the astigmatism induced by the angle of the fundus camera in relation to the crystalline lens, it is not always possible to get clear pictures when the camera is positioned at an extreme angle. The astigmatic corrector may help reduce the obliquely induced astig-

Figure 3: Showing posterior pole fundus

Figures 4A and B: Fundus photograph of superior retina

matism. This is done by moving the dial until the lesion is clearest and then refocusing the camera if necessary (Figure 7).

Figure 5: Fundus photograph of nasal retina

Figure 6: Fundus photograph of inferior retina

Figure 7: Fundus photograph of inferior retina showing snowbanking in the inferior periphery (inverted)

Figures 8A and B: Red free stereo fundus photographs of left eye showing exudative retinal detachment in Vogt-Koyanagi- Harada disease

Stereo photography (Figures 8A and B): Stereo photographs may be taken in cases with exudative retinal detachment, optic disc oedema, macular and choroidal neovascularisation etc. For taking stereo photographs, the illumination donut is first centered on the patient’s pupil with joystick vertically oriented and the first picture is taken by tilting the joystick first to the left side and then the camera is moved approximately 2 mm laterally by tilting the joystick to the right and second picture is taken. A good 3D representation requires well dilated pupil and stationery eye.

Digital images are captured individually by a computer at the discretion of the photographer who fires fundus camera’s flash lamp. The intensity of light

detected by each pixel while the fundus is illuminated with a flash lamp, is transmitted to the computer where images are stored in a digital format for immediate viewing, manipulation or storage. These digitalised images are then stored into a hard disc.

Images are then sent to a high-resolution monitor for editing and storage. Single frame or multiple images may be viewed in a proof sheet form (Figure 9).

Single image filling the entire screen provides the highest resolution. A resolution of 1024 × 1024 pixels per image is the standard in most of fundus camera systems. Images can be modified (sharpness, magnification and contrast) for better analysis. Images can

also be transmitted to another monitor or centers via a network connection or modem.

SOFTWARE

The software in a digital system generally provides an easy, user-friendly interface that ensures a smooth image capture, display, editing and archiving of the images. It offers following advantages:

I.Instant visualisation and availability of captured images with adjustments in realtime to improve quality.

II. Additional images at minimal cost.

III. Multiple exact duplicates.

IV. Immediate evaluation to determine patient diagnosis, treatment options or to access response to therapy.

V. Comparison of previous images including digital overlays.

VI. Patient education.

VII. Information sharing between physicians by rapid transmission of images through digital imaging and telecommunication.

VIII. Ability to perform ICG.

IX. Data archiving X. Image editing

XI. Precise measurement and mapping of the lesions.

ILLUSTRATIONS SHOWING SOFTWARE UTILITY

The inbuilt software provided in the digital camera gives an option of thumb nailing (Figures 10 and 11), calculations of greatest linear diameter (Figure 12), panorama viewing (Figure 13) and several other options.

Figure 12: Calculation of greatest linear diameter (GDD) and Laser spot size (LSS) in a case of choroidal neovascular membrane is required before planning PDT treatment

Figure 13: Panorama viewing: R/E panorama of a patient with serpiginous choroiditis showing the healed lesions upto midperipheral fundus. The panoramic viewing allows us better display for publication and viewing

Fundus photography is routinely done in all cases of posterior uveitis to document the lesions at the baseline that can be used for comparison to document the progression or healing of the lesions. Few of the conditions where it is done are:

1.Macular oedema

2.Epiretinal membranes

3.Retinitis

4.Choroiditis

5.Parasitic infections like toxocariasis, cysticercosis, onchocerciasis, etc.

6.Retinal vasculitis

7.Masquerade syndromes

8.Helps in assessing media clarity.

ILLUSTRATIONS WHERE CLINICAL

PRESENTATION IS THE MAJOR

CLUE TO THE POSSIBLE DIAGNOSIS

UVEITIC CYSTOID MACULAR OEDEMA

Figure 15: Fundus photograph right eye showing brush fire appearance in a case of CMV retinitis

retinal opacification and haemorrhages (Figure 15).

Uveitic cystoid macular oedema is chacterized by dull foveal reflex. Sometimes cystoid spaces may be appreciated (Figure 14).

CYTOMEGALO VIRUS RETINITIS

Cytomegalo virus (CMV) retinitis has a characteristic brush fire appearance with perivascular

PROGRESSIVE OUTER RETINAL NECROSIS

Progressive outer retinal necrosis (PORN) shows opacificaiton of outer retina (Figure 16).

CONGENITAL TOXOPLASMIC SCAR

Congenital toxoplasmic scar is seen as a central pigmented lesion with scleral show (Figure 17).

Figure 14: Fundus photograph right eye showing vitritis and hazy media with dull foveal reflex due to cystoid macular oedema in a patient with intermediate uveitis

Figure 16: Fundus photograph right eye in progressive outer necrosis

Figure 17: Fundus photograph right eye showing a congenital toxoplasmic chorioretinal scar

Figure 18A: Fundus photograph right eye showing media hazy due to vitritis

ACQUIRED TOXOPLASMIC RETINOCHOROIDITIS WITH HAZY MEDIA

Active toxoplasmic retinochoroiditis with hazy media has a typical “head light in fog” appearance (Figures 18A and B) that resolves after therapy (Figures 18C and D).

INTRAVITREOUS CYSTICERCOSIS

Intravitreous cysticercosis has a characteristic appearance of a cyst with central hyperdense lesion suggestive of scolex (Figure 19).

Figure 18B: Same eye shows a lesion of acquired toxoplasmic retinochoroiditis along the upper temporal vessel

Figure 18C: Same eye after two weeks of antitoxoplasmosis treatment and systemic corticosteroids showing improved media clarity

Figure 18D: The uppertemporal retinochoroiditis lesion shows healing with improved media clarity