23 Optical Coherence Tomography for Imaging Anterior-Chamber Inflammatory Reaction in Uveitis


23 Optical Coherence Tomography for Imaging Anterior-Chamber Inflammatory Reaction in Uveitis

Dhivya Ashok Kumar and Amar Agarwal

Anterior chamber (AC) cellular reaction is often clinically observed by slit-lamp biomicroscopy. 1 However, it cannot be performed in eyes with postoperative corneal edema or haze, and the grading ability is also dependent on the experience of the examiner. The existing objective method for AC reaction grading is the flare meter, which is based on the principle of laser photometry. Counting cells by laser flare meter is effective and linear in controlled laboratory situations, but it appears to be less accurate than flare measurements in vivo. 2 Moreover, its reliability in edematous cornea has not been proved so far. Laser flare photometry has been known to be affected by the aqueous humor protein concentration, the mydriatic agent used, and the presence of red blood cells. 2

Optical coherence tomography (OCT) has evolved as a widely used imaging modality in ophthalmology in the last decade. Earlier, we reported a case series on the objective method of diagnosing the AC cells in anterior uveitis with time-domain (TD) anterior-segment OCT. 3 Recently, OCT machines with sophisticated optics with spectral (SD) or Fourier domain (FD), which enabled examination of both the anterior and posterior segment in a single setup, have been developed. 4 ,​ 5 ,​ 6 ,​ 7 ,​ 8 ,​ 9 This development has enabled high-definition scanning of the AC. In this chapter, we discuss the use of OCT, both TD and the FD, in grading AC reaction and the methods of evaluation in uveitis.

23.1 Time-Domain OCT in Anterior-Chamber Cell Detection

Various causes of uveitis, including acute and chronic idiopathic anterior uveitis, postoperative uveitis, panuveitis, herpetic keratouveitis, interstitial keratitis, corneal ulcer, posterior corneal abscess, and endophthalmitis were included in the study. Sixty-two eyes of 45 patients referred to the uvea clinic were studied. Patients not willing to undergo follow-up were excluded. A detailed slit-lamp examination was performed in all patients, and the AC reaction was graded clinically from 0 to 4 using the Standardization of the Uveitis Nomenclature (SUN). 10 Cross-sectional imaging of AC with anterior-segment OCT (Carl Zeiss Meditec, Dublin, CA) was used. Corneal high-resolution single-scan mode (Fig. 23.1) was used. Four images were taken in one axis. The single capture image of the AC included the central cornea to the anterior surface of the lens.

Fig. 23.1 Cross-sectional image of a subject’s anterior chamber (AC) in clinical grade 1 uveitis. (a) Anterior segment time domain optical coherence tomographic (OCT) image showing hyperreflective spots and (b) picture showing the hyperreflective spots as detected in pixel-based candidate object extraction algorithm and (c) picture of the hyperreflective spots counted by the connected component labeling technique using custom MATLAB software (MathWorks, Natick, MA).

23.1.1 Automated Cell Analysis

The hyperreflective spots detected in the AC were counted in nonenhanced image manually and using an automated computer algorithm. The mean numbers of cells were determined by counting the hyperreflective spots from the OCT image (Fig. 23.1). In the automated method, hyperreflective spots were segmented (Fig. 23.2) from the OCT image by a pixel-based candidate object extraction and counted with a connected component-labeling technique using custom MATLAB software version 7.1 (MathWorks, Natick, MA). 3

Fig. 23.2 Graph showing the results of manual and automated method of cell counting in time domain optical coherence tomography, suggesting higher sensitivity of the automated method at higher grades of uveitis.

23.2 Comparison between Manual and Automated Cell-Counting Methods

23.2.1 Anterior Chamber Cells

In the manual counting method, mean hyperreflective spots were 3 ± 1.8 in grade 1, 12 ± 3.5 in grade 2, 33.8 ± 10.2 in grade 3, and 61.4 ± 9.6 in grade 4. The automated method showed mean 3 ± 1.9 hyperreflective spots in grade 1, 12.4 ± 3.6 in grade 2, 33.2 ± 9.6 in grade 3, and 74.8 ± 17 in grade 4. We observed good correlation (Pearson coefficient for grade 1: 0.995, grade 2: 0.948, grade 3: 0.985, and grade 4: 0.893) between automated and manual methods. Except for grade 4 (P = 0.009), there were no significant differences in mean values between the manual and automated method in lower grades. The automated method was more sensitive in grade 4 uveitis and detected a greater number of cells (Fig. 23.2).

23.2.2 Aqueous Flare

Aqueous flare up to grade 3 was not detected in anterior-segment OCT. However, grade 4 aqueous flare, which was characterized by intense fibrinous reaction, was seen by OCT in seven (11.2%) eyes.

23.2.3 Keratic Precipitates

Keratic precipitates were seen as discrete hyperreflective spots attached to the endothelium of the cornea (Fig. 23.3). They were counted similar to AC cells. Keratic precipitates were noted in 12 eyes in the study.

Fig. 23.3 Keratic precipitates (arrow) seen on the endothelium of the cornea in anterior uveitis in time-domain optical coherence tomography. OD, right eye; OS, left eye.

23.2.4 Membrane

Fibrinous membrane was seen in three eyes in the pupillary area and in one eye on the endothelium of the cornea (Fig. 23.4).

Fig. 23.4 Thick fibrinous membrane (arrow) seen on the endothelium of cornea in anterior uveitis in time-domain optical coherence tomography.

23.2.5 Corneal Edema and OCT Cell Counting

Of the 12 eyes with corneal edema, anterior-segment OCT was also able to detect AC cells (Fig. 23.5) in 11 (91.6%) eyes in which slit-lamp grading was not possible because of corneal edema. The central corneal thickness ranged from 702 to 1020 µm (mean, 843± 109 µm). The eyes with postoperative uveitis, endophthalmitis, and corneal infection had corneal edema. The mean number of hyperreflective spots detected in eyes with corneal edema using the manual method was 12.27 ± 12.1 and 12.9 ± 13 using the automated method.

Fig. 23.5 Postoperative uveitis with corneal edema. (a) Slit-lamp picture of an eye with corneal edema and (b) the anterior-segment time-domain optical coherence tomography image of the same eye showing the AC cells and edematous cornea.

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Jun 13, 2020 | Posted by in OPHTHALMOLOGY | Comments Off on 23 Optical Coherence Tomography for Imaging Anterior-Chamber Inflammatory Reaction in Uveitis
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