Fourier domain optical coherence tomography to assess the iridocorneal angle and correlation study in a large Caucasian population

Abstract

BackgroundRecently, novel anatomic parameters that can be measured by optical coherence tomography (OCT), have been identified as a more objective and accurate method of defining the iridocorneal angle. The aim of the present study is to measure the iridocorneal angle by Fourier domain (FD) OCT and to identify correlations between angle measurements and subject factors in a large healthy Caucasian population.MethodsA cross sectional study was performed in 989 left eyes of 989 healthy subjects. The iridocorneal angle measurements: trabecular-iris angle (TIA), angle opening distance (AOD500) and trabecular-iris space area (TISA500) 500 μm from the scleral spur, were made using the FD-OCT RTVue®. Iris thickness was also measured. Correlations were examined between angle measurements and demographic and ocular factors. The main determinants of angle width were identified by multivariate linear regression.ResultsTIA could be measured in 94 % of the eyes, and AOD500 and TISA500 in 92 %. The means recorded were TIA 35.8 ± 12.2 degrees (range 1.5 to 76.1), AOD500 542.6 ± 285.4 μm (range 15 to 1755), and TISA500 0.195 ± 0.104 mm2 (range 0.02 to 0.62). The correlation between the temporal and nasal quadrant was R = 0.902 for TIA. The reproducibility of measurements was excellent (intraclass correlation coefficient >0.947). Mean angle width measurements were smaller in women (p = 0.02). Correlation was detected between angle means and anterior chamber volume (ACV; R = 0.848), anterior chamber depth (ACD; R = 0.818), spherical error (R = -0.619) and age (R = -0.487), while no correlation was observed with Intraocular pressure (R = -0.052). ACV emerged as the main determinant of TIA (R2 = 0.705; p < 0.001).ConclusionsIn this Caucasian population, strong correlation was detected between FD-OCT anterior angle measurements and ACV, ACD, spherical refractive error and sex, emerging the ACV as the main determinant of TIA.

Update on the usefulness of optical coherence tomography in assessing the iridocorneal angle

“…It has been observed that AOD values vary according to race and measuring device. Thus, in a healthy Asian population Leung et al 37 found AOD 500 = 527 ± 249 m with OCT Visante, a reading similar to that observed by Fernandez-Vigo et al 4 Fourier domain OCT RTVue an AOD 500 = 537 ± 292 m in a Caucasian population, whereas in patients with angle closure Mansouri et al 33 found a markedly diminished AOD (AOD 500 = 210 ± 16 m).…”

“…TIA was described in 2005 by Radhakrishnan et al 34 who carried out a study to classify potentially occludable angles comparing OCT with Ernie Oscar B and UBM. In a population of 989 subjects, Fernández-Vigo et al 4 were able to measure TIA in 94% of cases with OCT RTVue, obtaining a mean value of 35.8 ± 13.2 degrees. In addition, said authors observed a correlation between refractive defect and TIA, with angle opening remaining stable between −9 and −3 diopters (D) with a mean angle of 46 • .…”

“…A mean TISA 500 of 0.193 ± 0.102 mm 2 by means of OCT-Visante was found in the Leung et al study, 37 whereas said parameter was 0.195 ± 0.103 mm 2 in the Fernández-Vigo et al study with RTVue. 4 Even though TISA is a parameter that was proposed to represent the effective filtering area of TM, a range of population studies have not found a correlation with IOP. 35 Index of trabecular-iris contact [TIC]): this term was introduced after a semiautomatic analysis with the CASIA device (Tomey Corporation, Nagoya, Japan) that assessed the percentage of 360-degree trabecular-iris contact (Fig.…”

“…OCT technology developments in capture speed and image resolution has allowed this technology to become an essential examination tool in ophthalmological practices. [1][2][3][4][5][6][7][8][9][10][11][12] Different OCT devices enable the assessment of the angular region (Table 1). Some of the main advantages of AS−OCT include the possibility of identifying the structures that comprise the angle, objectively measuring the angle region, exploring the angle in pediatric patients or those exhibiting traumatism because it is a noncontact examination which does not require anesthesia.…”

“…1,2 In addition, OCT technology exhibits excellent reproducibility (intraclass correlation coefficient of >0.9) for measuring angle parameters utilizing different devices. 3,4 However, even though various studies have found a good match between angle measures obtained with different OCT devices, 5 absolute values are not interchangeable. 6…”