Axial Length Variation Impacts on Superficial Retinal Vessel Density and Foveal Avascular Zone Area Measurements Using Optical Coherence Tomography Angiography

Abstract

Citation: Sampson DM, Gong P, An D, et al. Axial length variation impacts on superficial retinal vessel density and foveal avascular zone area measurements using optical coherence tomography angiography. Invest Ophthalmol Vis Sci. 2017;58:3065-3072. DOI:10.1167/iovs.17-21551 PURPOSE. To evaluate the impact of image magnification correction on superficial retinal vessel density (SRVD) and foveal avascular zone area (FAZA) measurements using optical coherence tomography angiography (OCTA). METHODS.Participants with healthy retinas were recruited for ocular biometry, refraction, and RTVue XR Avanti OCTA imaging with the 3 3 3-mm protocol. The foveal and parafoveal SRVD and FAZA were quantified with custom software before and after correction for magnification error using the Littman and the modified Bennett formulae. Relative changes between corrected and uncorrected SRVD and FAZA were calculated.RESULTS. Forty subjects were enrolled and the median (range) age of the participants was 30 (18-74) years. The mean (range) spherical equivalent refractive error was À1.65 (À8.00 to þ4.88) diopters and mean (range) axial length was 24.42 mm (21.27-28.85). Images from 13 eyes were excluded due to poor image quality leaving 67 for analysis. Relative changes in foveal and parafoveal SRVD and FAZA after correction ranged from À20% to þ10%, À3% to þ2%, and À20% to þ51%, respectively. Image size correction in measurements of foveal SRVD and FAZA was greater than 5% in 51% and 74% of eyes, respectively. In contrast, 100% of eyes had less than 5% correction in measurements of parafoveal SRVD.CONCLUSIONS. Ocular biometry should be performed with OCTA to correct image magnification error induced by axial length variation. We advise caution when interpreting interocular and interindividual comparisons of SRVD and FAZA derived from OCTA without image size correction.

Macular Perfusion Parameters in Different Angiocube Sizes: Does The Size Matter in Quantitative Optical Coherence Tomography Angiography?

“…Moreover, we did not apply any correction of image magnification related to difference into axial length (as proposed by Sampson et al 31 ) because this study was retrospective in its nature and such measurements were not available. In the present study, however, we did not compare the absolute values of macular quantitative parameters between patients with DR and controls, but rather the interscan and intrascan reliabilities.…”

An Optical Coherence Tomography Angiography Study of the Relationship Between Foveal Avascular Zone Size and Retinal Vessel Density

“…34,35 During the measurement of FAZ area and perimeter, Littmann's method was used to correct the ocular magnification by each AL. [34][35][36][37][38] Details of the formula are provided elsewhere. 34,35,37,38 In brief, the relationship between the measured OCTA image diameter, Dm, and the true diameter, Dt, can be formulated as Dt ¼ p*q*Dm, where p and q are the image magnification factor of the imaging system and the eye, respectively.…”

“…[34][35][36][37][38] Details of the formula are provided elsewhere. 34,35,37,38 In brief, the relationship between the measured OCTA image diameter, Dm, and the true diameter, Dt, can be formulated as Dt ¼ p*q*Dm, where p and q are the image magnification factor of the imaging system and the eye, respectively. The p of the OCTA system (Optovue, Inc.) is 3.460, which can be calculated from 1/[0.01306(23.95 À 1.82)], and q can be determined from Bennett's formula, as q ¼ 0.01306*(AL À 1.82), where 1.82 is a constant related to the distance between the corneal apex and the second principal plane.…”

“…The p of the OCTA system (Optovue, Inc.) is 3.460, which can be calculated from 1/[0.01306(23.95 À 1.82)], and q can be determined from Bennett's formula, as q ¼ 0.01306*(AL À 1.82), where 1.82 is a constant related to the distance between the corneal apex and the second principal plane. 34,35,37,38 Thus, AL-related magnification factor can be corrected by Dt ¼ 3.460*0.01306*(AL À 1.82)*Dm. 34,35,37,38 Poor quality OCTA images were excluded from the analysis, including signal strength index (SSI) < 48 (minimum ¼ 1, maximum ¼ 100) 23,25,26,36,[39][40][41][42] ; poor-clarity images due to severe media opacities; motion artifacts or localized weak signal by vitreous floaters; residual motion artifacts visible as irregular vessel patterns or disc boundary on the en face angiogram; images not centered on the fovea for macular OCTA (fixation error); and segmentation failure.…”

Diabeteses kisér-károsodás vizsgálata optikai koherencia tomográfián alapuló angiográfiával

“…Ugyanakkor ezen általános rizikófaktoroknak a hatását a többvál-tozós regressziós modellekben kontroll alatt tartottuk a EREDETI KÖZLEMÉNY szem tengelyhossza mellett, mely szintén befolyásolja az OCT-angiográfiás paraméterek értékét [23,24]. A diabeteses retinopathia kialakulásában központi szerepe van az emelkedett vércukorértéknek, mely oxidatív stresszen keresztül proteinkináz C-aktivációhoz és gliká-ciós végtermékek képződéséhez vezet [25][26][27][28] -ennek következménye a vascularis károsodások kialakulása [29,30].…”