RETINAL LAYER RESPONSE TO RANIBIZUMAB DURING TREATMENT OF DIABETIC MACULAR EDEMA: Thinner is Not Always Better

Correlation of Change in Macular Thickness With Change in Visual Acuity in Diabetic Macular Edema: Post Hoc Analysis of VISTA and VIVID Trials

Purpose: To assess the correlation between the change in central subfield thickness (CST) and change in best-corrected visual acuity (BCVA) in eyes with diabetic macular edema (DME) treated with fixed-dosing intravitreal aflibercept injection (IAI). Methods: This post hoc analysis of the VISTA and VIVID randomized controlled clinical trials, in which 862 eyes with central-involved DME were randomly assigned to IAI 2 mg every 4 weeks (2q4; 290 eyes), IAI 2 mg every 8 weeks after 5 initial monthly doses (2q8; 286 eyes), or macular laser (286 eyes) and followed through 100 weeks. Correlations between the change in CST and change in BCVA from baseline to weeks 12, 52, and 100 were assessed using the Pearson correlation. Results: The respective correlations ( r [95% CI]) at weeks 12, 52, and 100 were −0.39 (−0.49 to −0.29), −0.27 (−0.38 to −0.15), and −0.30 (−0.41 to −0.17) in the 2q4 arm and −0.28 (−0.39 to −0.17), −0.29 (−0.41 to −0.17), and −0.33 (−0.44 to −0.20) in the 2q8 arm. Linear regression analysis of the correlation at week 100, adjusted for relevant baseline factors, showed CST changes accounted for 17% of the variance in BCVA changes; every 100-µm decrease in CST was associated with a 1.2-letter increase in BCVA ( P = .001). Conclusions: Correlations between the change in CST and change in BCVA after 2q4 or 2q8 fixed-dosing IAI for DME were modest. Although a change in CST might be important in determining the need for antivascular endothelial growth factor for DME at follow-up, it was not a good surrogate for VA outcomes.

Correlation of Volume of Macular Edema with Retinal Tomography Features in Diabetic Retinopathy Eyes

Optical coherence tomography (OCT) enables the detection of macular edema, a significant pathological outcome of diabetic retinopathy (DR). The aim of the study was to correlate edema volume with the severity of diabetic retinopathy and response to treatment with intravitreal injections (compared to baseline). Diabetic retinopathy (DR; n = 181) eyes were imaged with OCT (Heidelberg Engineering, Germany). They were grouped as responders (a decrease in thickness after intravitreal injection of Bevacizumab), non-responders (persistent edema or reduced decrease in thickness), recurrent (recurrence of edema after injection), and treatment naïve (no change in edema at follow-up without any injection). The post-treatment imaging of eyes was included for all groups, except for the treatment naïve group. All eyes underwent a 9 × 6 mm raster scan to measure the edema volume (EV). Central foveal thickness (CFT), central foveal volume (CFV), and total retinal volume (TRV) were obtained from the early treatment diabetic retinopathy study (ETDRS) map. The median EV increased with DR severity, with PDR having the greatest EV (4.01 mm³). This correlated positively with TRV (p < 0.001). Median CFV and CFT were the greatest in severe NPDR. Median EV was the greatest in the recurrent eyes (4.675 mm³) and lowest (1.6 mm³) in the treatment naïve group. Responders and non-responders groups had median values of 3.65 and 3.93 mm³, respectively. This trend was not observed with CFV, CFT, and TRV. A linear regression yielded threshold values of CFV (~0.3 mm³), CFT (~386 µm), and TRV (~9.06 mm³), above which EV may be detected by the current scanner. In this study, EV provided a better distinction between the response groups when compared to retinal tomography parameters. The EV increased with disease severity. Thus, EV can be a more precise parameter to identify subclinical edema and aid in better treatment planning.

Impacts of intravitreal anti-VEGF therapy on retinal anatomy and neurophysiology in diabetic macular edema

PURPOSE

To evaluate anatomical and neuroretinal functional aspects in patients with diabetic macular edema (DME) after intravitreal anti-vascular endothelial growth factor (VEGF) therapy, in particular aflibercept.

MATERIALS AND METHODS

This prospective single-centered interventional study was performed at Afyonkarahisar Health Science University Faculty of Medicine, Department of Ophthalmology, where 32 eyes of 32 patients with DME were investigated. All patients received five intravitreal aflibercept injections on a monthly basis and were followed up for ≥ 6 months. After a comprehensive ophthalmological examination, including the measurements of visual acuity and intraocular pressure, and an antero-posterior segment slit-lamp biomicroscopy before and after full pupil dilation, fundus fluorescein angiography and optical coherence tomography were performed at baseline and during the third and sixth months post-therapy. Microperimetry and multifocal electroretinography were also performed at baseline and during the sixth months.

RESULTS

Mean visual acuity increased from 0.73 to 0.57 and 0.33 logarithm of the minimum angle of resolution (logMAR) during the third and sixth months, respectively (p < 0.001). Changes in intraocular pressure were not statistically significant (p = 0.472). There was statistically significantly decreased mean central macular thickness from 390.2 μm to 242.6 and 289.7 μm during the third and sixth months, respectively (p < 0.001). Significantly improved fixation patterns during the sixth month, along with significantly increased macular sensitivity from 8.2 to 14.2 dB (p < 0.001) and significantly decreased local deficit from - 10.3 to 5.5 dB (p < 0.001) were observed. Further, there was a significantly increased N1 amplitude in the first ring and significantly increased P1 amplitude in all rings (p for each parameter < 0.05). There was also significantly decreased N1 wave implicit time in all rings and significantly decreased P1 wave in the second, third, fourth and fifth rings (p for each parameter < 0.05).

CONCLUSIONS

Patients with DME showed profound improvement in the retinal neurophysiological function, which was also accompanied by anatomical and ultrastructural integrity recovery after intravitreal aflibercept therapy. In the pathogenesis of DME, the influence of neurodegeneration has been increasingly gaining significant attention. Consequently, the need to assess neurophysiological effects of anti-VEGF therapy using a variety of diagnostic measures like electrophysiological studies and multimodal imaging technologies is undeniably growing.

Development of a 1-year risk-prediction nomogram for good functional response with anti-VEGF agents in naive diabetic macular oedema

PURPOSE

To develop a risk-prediction nomogram based on baseline variables for good functional response during the 1st year of treatment with anti-VEGF agents in naive diabetic macular oedema (DME).

METHODS

This retrospective study included patients presenting naive-DME treated with anti-VEGF therapy at Dijon University Hospital (France) between 1 February 2012 and 31 March 2015 (derivation cohort). We studied baseline variables that had significant associations with a good functional response to anti-VEGF agents during the 1st year of treatment. We used a program to generate a nomogram based on a binary logistic regression predictive model. Then, this nomogram was tested on data from a separate cohort of naive-DME patients from a multicenter study involving 20 French ophthalmologic centres between January 2014 and June 2015 (validation cohort).

RESULTS

Age, baseline BCVA and ellipsoid zone integrity on spectral-domain optical coherence tomography (SD-OCT) are functional prognostic factors and were used to build a nomogram. The nomogram showed excellent discrimination for good functional responders (area under the curve (AUC) = 0.906, 95% confidence interval (95% CI) = [0.849-0.964], p = 0.004). The discriminative power of this nomogram was tested on the validation cohort data, demonstrating good discrimination of good functional responders (AUC = 0.942, 95% CI = [0.898-0.986], p < 0.001).

CONCLUSION

This nomogram provides a useful estimation of a good functional response in naive-DME patients treated with anti-VEGF agents.

ASSOCIATION BETWEEN EARLY ANATOMIC RESPONSE TO ANTI-VASCULAR ENDOTHELIAL GROWTH FACTOR THERAPY AND LONG-TERM OUTCOME IN DIABETIC MACULAR EDEMA: An Independent Analysis of Protocol i Study Data

This retrospective analysis of Protocol I study data demonstrates a significant positive association between early (Week 12) retinal anatomical response and long-term (1- and 3-year) anatomical response with ranibizumab in center-involved diabetic macular edema. By contrast, early anatomical response was not significantly associated with long-term visual acuity response.

Purpose:

This post hoc analysis explores the relationship between early retinal anatomical response and long-term anatomical and visual outcomes with ranibizumab in center-involved diabetic macular edema.

Methods:

Eyes randomized to the ranibizumab plus prompt laser and ranibizumab plus deferred laser treatment arms in the Protocol I study were categorized according to their proportional reduction (<20 vs. ≥20%) in central retinal thickness (CRT) after 12 weeks. Adjusted and unadjusted analyses assessed the association between early (Week 12) anatomical response and long-term (Weeks 52 and 156) anatomical and best-corrected visual acuity outcomes.

Results:

Of 335 study eyes, 118 showed limited (<20%) and 217 showed strong (≥20%) CRT reduction at Week 12. In unadjusted and adjusted analyses, limited early CRT response was negatively and significantly associated with strong CRT response at Weeks 52 and 156. Sensitivity analyses indicated that this association was robust and unrelated to any “floor effect.” In unadjusted analyses, a strong early CRT response was associated with greater long-term improvement in best-corrected visual acuity; after controlling for confounders, the association lost statistical significance.

Conclusion:

Early CRT response to ranibizumab is a significant prognostic indicator of medium- to long-term anatomical outcome in center-involved diabetic macular edema.

The impact of ganglion cell layer cysts in diabetic macular oedema treated with anti-vascular endothelial growth factor

PURPOSE

To investigate the prevalence and impact of ganglion cell layer cysts (GCLC) in patients with diabetic macular oedema (DME) under continuous anti-vascular endothelial growth factor (VEGF) therapy.

METHODS

The clinical findings and spectral domain optical coherence devices of baseline visits and follow-up after 12-24 and 36 months of DME patients under continuous anti-VEGF therapy were retrospectively collected and analysed for the impact of GCLC cysts. Previously established prognostic parameters were also assessed.

RESULTS

A total of 110 eyes of 110 DME patients (mean age 64 ± 10 years) were included. At baseline, 17% eyes had GCLC. With GCLC, the best-corrected visual acuity (BCVA) improvement was in mean 8.4 ± 2.4 Early-Treatment-Diabetic-Retinopathy-Study (ETDRS) letters less over the course of 36 months compared to the group lacking GCLC (p = 0.0009). Eyes with GCLC showed 68 ± 23.4 μm less central retinal thickness (CRT) decrease than eyes lacking GCLC (p < 0.0001). In the linear mixed effect models including external limiting membrane disruption, disintegration of inner retinal layer and epiretinal membrane, GCLC remained a statistical significant factor for the outcome parameter CRT, but missed statistical significance for BCVA.

CONCLUSION

Ganglion cell layer cysts (GCLC) seem to impact outcome in DME in patients receiving long-term treatment. This prognostic factor warrants further evaluation in the context of already well-established outcome parameters.

Long-term changes in retinal layers in patients undergoing intravitreal ranibizumab for neovascular age-related macular degeneration : Retinal layers after anti-VEGF therapy

PURPOSE

To analyze long-term changes in individual retinal layers (RLs) after intravitreal injections of ranibizumab (IVRs) in patients with neovascular age-related macular degeneration (n-AMD).

METHODS

The patients were treated with 0.5-mg IVRs based on an as-needed protocol after the first three monthly doses over a 12-month follow-up period. Patients underwent optical coherence tomography and best-corrected visual acuity (BCVA) evaluation at each visit. The ETDRS grid with central subfield (R1) (r 0.5 mm) and the inner ring (R2) (r 0.5-1.5 mm) was used for calculation of the mean thickness of each RL. Changes in the thickness of segmented RLs within the R1 and R2 of ETDRS circles at months-3, -6, and -12 were compared to baseline.

RESULTS

The mean age was 72 ± 7.4 years. The mean number of injections was 9.08 (range 6-11). Mean BCVA improved from 49.7 ± 22.1 to 60.1 ± 19.8 letters. Central macular thickness decreased from 390.25 ± 149.6 to 312.74 ± 118.4 μm. Thicknesses of GCL (from 23.93 ± 13.73 to 19.50 ± 9.50 μm in R1; p 0.001, and from 44.5 ± 12.6 to 39.6 ± 10.6 μm in R2; p 0.005), IPL (from 28.90 ± 14.36 to 22.35 ± 6.23 μm in R1; p 0.001, and from 39.34 ± 8.53 to 35.58 ± 7.93 μm in R2; p 0.004), and total inner RL (ILM to ELM) (from 222.93 ± 93.09 to 180 ± 53 μm in R1; p 0.001, and from 255.06 ± 42.74 to 240.25 ± 40.37 μm in R2; p 0.003) in the central and parafoveal rings decreased statistically at month-12. Decrease in INL was limited to month-6 (from 34.80 ± 15.33 to 27.60 ± 12.59 μm in R1; p 0.001), while decreases in total outer RLs (ELM to RPE) (from 128.32 ± 26.92 to 115.54 ± 43.98 μm in R1; p 0.001, and 103.81 ± 16.73 to 96.38 ± 16.22 μm in R2; p 0.014) and RPE (from 39.12 ± 22.33 to 29.70 ± 22.05 μm in R1; p 0.001, and from 31.27 ± 13.11 to 24.40 ± 9.99 μm in R2; p 0.001) were limited to month-3.

CONCLUSIONS

Significant changes were observed in the thickness of the inner RLs after 1-year treatment with IVRs for n-AMD. A significant decrease in RPE thickness confined to the first months disappeared at month-12.

Panretinal Photocoagulation for Diabetic Retinopathy in the RIDE and RISE Trials: Not "1 and Done"

PURPOSE

To evaluate panretinal photocoagulation (PRP) treatment and re-treatment patterns in patients with diabetic retinopathy (DR) and diabetic macular edema (DME).

DESIGN

Post hoc analysis of the phase 3 RIDE (clinicaltrials.gov identifier, NCT00473382) and RISE (clinicaltrials.gov identifier, NCT00473330) clinical trials of ranibizumab for the treatment of DME.

PARTICIPANTS

Seven hundred fifty-nine patients were randomized for treatment.

METHODS

Panretinal photocoagulation treatment patterns and clinical experiences were assessed by baseline PRP treatment status.

MAIN OUTCOME MEASURES

Number and timing of on-study PRP treatment sessions undergone through month 24. Time to new proliferative event (composite end point) was also assessed.

RESULTS

At baseline, approximately 25% of patients in RIDE and RISE had undergone PRP treatment before enrollment (22.2%, 24.4%, and 25.4% of patients in the sham, ranibizumab 0.3 mg, and ranibizumab 0.5 mg arms, respectively). In patients without prior PRP at baseline (n = 577), 9.5% of sham-treated patients underwent 1 or more PRP treatments through month 24, compared with 1.1% and 1.6% of patients receiving ranibizumab 0.3 mg and ranibizumab 0.5 mg, respectively (P < 0.001 for both ranibizumab arms vs. sham). In patients with prior PRP at baseline (n = 182), 19.3% of sham-treated patients underwent 1 or more PRP treatments through month 24. No ranibizumab-treated patients with prior PRP at baseline required additional on-study PRP through month 24 (P < 0.001 for both ranibizumab arms vs. sham). Ranibizumab treatment also significantly reduced clinical DR progression among patients who underwent prior PRP. By month 24 in patients with prior PRP at baseline, the probability of experiencing a new proliferative event was 10.3% and 9.9% in patients receiving ranibizumab 0.3 mg and ranibizumab 0.5 mg treatment, respectively, compared with 39.4% in sham-treated patients (P < 0.0001). Overall, sham-treated patients, including those patients who were PRP naïve at baseline who went on to require PRP, experienced more clinical events than ranibizumab-treated patients.

CONCLUSIONS

In RIDE and RISE, PRP treatment was not a "1 and done" procedure, with on-study PRP re-treatment occurring in patients both with and without prior PRP treatment at baseline. Ranibizumab treatment reduced on-study PRP treatment and DR progression regardless of prior PRP treatment status at baseline.

Correlation of retinal layer changes with vision gain in diabetic macular edema during conbercept treatment

Backgrounds

To assess the changes in individual retinal layer thickness and visual function associated with gains in visual acuity after an intravitreal conbercept injection in the diabetic macular edema (DME) on spectral domain optical coherence tomography (SD-OCT) and microperimetry during 1-year follow-up.

Methods

Retrospective observational study. Twenty patients with clinically significant DME in the study eye were imaged by SD-OCT every 3 months and MP1 microperimeter in the third month while receiving anti-vascular endothelial growth factor (VEGF) (conbercept) treatment. In each patient, seven retinal layers were segmented in 98 scans covering a 6 mm × 6 mm area of the macula at baseline and during 1 year of treatment. An automatic, full-threshold microperimetry of the central field (10° × 10°, 40 stimulated points) with the MP1 microperimeter. Thickness and microperimetry changes were quantitatively measured and evaluated for their correlation with increases in visual acuity.

Results

Although thicknesses of the inner nuclear layer (INL) and the outer nuclear layer (ONL) were reduced the most after treatment (p < 0.05), decreases of the ganglion cell layer (GCL) (r = 0.591, p = 0.006) and inner plexiform layer (IPL) (r = 0.663, p = 0.001) in central subfield area was associated with best-corrected visual acuity (BCVA) gain, and had the best estimation of BCVA gain (adjust R² = 0.544). Mean macular sensitivity in the central subfield was also well correlated with BCVA gain (r = 0.531, p = 0.016).

Conclusions

Neural recovery occurred after the resolution of edema during conbercept treatment, due to the decreases in GCL and IPL associating with gains in vision and improved microperimetry.

Electronic supplementary material

The online version of this article (10.1186/s12886-019-1131-0) contains supplementary material, which is available to authorized users.

Analysis of retinal layer thickness in diabetic macular oedema treated with ranibizumab or triamcinolone

PURPOSE

To evaluate detailed changes in retinal layer thickness in spectral-domain optical coherence tomography (SD-OCT) images during a 1-year follow-up of patients treated for diabetic macula oedema (DME).

METHODS

Post hoc analysis of retinal layer thickness changes applying the automated layer segmentation of SD-OCT images in eyes with DME that were randomly assigned to receive pro re nata (PRN) treatment with either 0.5 mg ranibizumab or 8 mg triamcinolone. In each patient, seven retinal layers were segmented in 49 scans covering a 20° × 20° area of the macula at baseline and after 1 year of treatment. Changes in individual layer thickness were correlated with visual acuity (VA) and compared between treatment arms.

RESULTS

Twenty-five patients (seven female, 60.2 ± 15.1 years) were evaluated. Thickness decrease of retinal nerve fibre layer (RNFL) was associated with a gain in VA over 12 months (r > 0.54; p < 0.05). Decrease in ganglion cell layer (GCL) and GCL+IPL thickness pooled for nasal Early Treatment of Diabetic Retinopathy Study (ETDRS) subfields correlated with VA as follows: ranibizumab r = 0.74 (GCL) and r = 0.63 (GCL+IPL); and triamcinolone r = 0.45 (GCL) and r = 0.46 (GCL+IPL).

CONCLUSION

In DME therapy, reduction in RNFL thickness may have a considerable impact on retinal function, unrelated to the type of pharmacological treatment. Precise morphologic quantification of neurosensory layers by SD OCT offers new insight into disease pathology and therapeutic targets.

Visual acuity loss associated with excessive "dry macula" in exudative age-related macular degeneration

Purpose

To investigate the correlation between visual acuity and central macular thickness (CMT) and choroidal thickness (CCT) in patients with wet age-related macular degeneration (AMD).

Methods

In this retrospective analysis, 14 eyes that received >10 ranibizumab injections (based on pro re nata [PRN] regimen) and maintained initial visual acuity gain were analyzed. The following 5 parameters were measured at the foveal center: CMT (distance from the inner limiting membrane [ILM] to Bruch’s membrane); central retinal thickness (CRT; distance from the ILM to the inner limit of the retinal pigment epithelium or subretinal fluid [SRF]); SRF thickness (SRFT); pigment epithelium detachment thickness (PEDT); and CCT. The correlation between the logarithm of the minimum angle of resolution (logMAR) best-corrected visual acuity (BCVA) and the 5 parameters was examined with generalized estimating equations.

Results

CMT, CRT, and CCT were negatively correlated with logMAR BCVA (P=0.031, 0.023, and 0.036, respectively) when only CMT values less than the thickness that maximized visual acuity for each eye were used for the analysis. Each 100-μm reduction in CMT, CRT, or CCT improved logMAR BCVA by −0.1, −0.08, or −0.07, respectively. SRFT and PEDT were not correlated with BCVA. The median CMT that maximized the visual acuity was 230 μm.

Conclusion

Dry macula with CMT <230 μm was associated with temporary decrease in visual acuity in AMD patients whose visual acuity was maintained with PRN regimen.

Short-term effects of intravitreal ranibizumab therapy on diabetic macular edema

Background

The short-term effects of intravitreal ranibizumab (IVR) on diabetic macular edema (DME) remains unclear. We assessed the short-term effects of IVR on DME.

Methods

Eighteen eyes of 14 patients with DME were enrolled in this prospective interventional case series. After intravitreal ranibizumab was injected into treatment-naïve eyes with DME, we measured the foveal thickness (FT) before and 2 h, 1 day, 1 week, and 1 month later and the best-corrected visual acuity (BCVA) at all times except 2 h and compared the changes to baseline (ΔFT and ΔVA).

Results

The mean FT decreased significantly (p < 0.0001) from 452 ± 77 to 429 ± 65 microns after 2 h. The mean logarithm of the minimum angle of resolution BCVA improved significantly (p = 0.032) after 1 month from 0.41 ± 0.24 to 0.32 ± 0.21 (20/51 to 20/42, Snellen equivalent). The ΔFT after 2 h was significantly (r = 0.53, p = 0.025) correlated with the ΔFT after 1 month. The ΔVA after 1 day was significantly (r = 0.59, p = 0.01) correlated with the ΔVA after 1 month.

Conclusions

The structural effects of IVR for DME occurred within 2 h, whereas the functional effects occurred after 1 month. The short-term effects (within 1 day) of IVR may predict the therapeutic outcome 1 month after IVR in patients with DME.

Trial registration

The trial registration number: UMIN000026118 (Feb/13/2017). Retrospectively registered.

The grey fovea sign of macular oedema or subfoveal fluid on non-stereoscopic fundus photographs

PURPOSE

To describe the grey fovea sign of fovea-involving macular oedema or subretinal fluid accumulation in red-free fundus photography.

METHODS

A test set of 91 digital fundus photographs of good quality from 100 consecutive eyes in 72 patients with diabetic retinopathy or central serous chorioretinopathy was composed by one of the investigators and evaluated by four masked observers. The photographs were graded as to whether a normal dark fovea was present or absent. The reference method was foveal thickness measurement using optical coherence tomography (OCT).

RESULTS

Eyes graded as having a grey fovea on fundus photographs (n = 67) had a median foveal thickness of 279 μm (interquartile range 130 μm), whereas eyes graded as having a normal dark fovea (n = 24) had a median foveal thickness of 238 μm (interquartile range 44.5 μm, p = 0.025).

CONCLUSION

The absence of a dark fovea on red-free greyscale fundus photographs is a sign of foveal thickening or detachment that can be reliably recognized by graders when using OCT as the reference diagnostic method. Awareness of the grey fovea sign may facilitate fundus photographic screening for maculopathy because its absence is a reliable sign that no foveal oedema or detachment is present. Its presence may indicate that such conditions are present, but it can also be induced by various other conditions, for which reason it should prompt further investigations by OCT.

Optical Coherence Tomography Angiography in Mice: Comparison with Confocal Scanning Laser Microscopy and Fluorescein Angiography

PURPOSE

Optical coherence tomography angiography (OCT-A) allows noninvasive visualization of retinal vessels in vivo. OCT-A was used to characterize the vascular network of the mouse retina and was compared with fluorescein angiography (FA) and histology.

METHODS

In the present study, OCT-A based on a Heidelberg Engineering Spectralis system was used to investigate the vascular network in mice. Data was compared with FA and confocal microscopy of flat-mount histology stained with isolectin IB4. For quantitative analysis the National Cancer Institute's AngioTool software was used. Vessel density, the number of vessel junctions, and endpoints were measured and compared between the imaging modalities.

RESULTS

The configuration of the superficial capillary network was comparable with OCT-A and flat-mount histology in BALBc mice. However, vessel density and the number of vessel junctions per region of interest (P = 0.0161 and P = 0.0015, respectively) in the deep vascular network of BALBc mice measured by OCT-A was significantly higher than with flat-mount histology. In C3A.Cg-Pde6b+Prph2Rd2/J mice, where the deep capillary plexus is absent, analysis of the superficial network provided similar results for all three imaging modalities.

CONCLUSION

OCT-A is a helpful imaging tool for noninvasive, in vivo imaging of the vascular plexus in mice. It may offer advantages over FA and confocal microscopy especially for imaging the deep vascular plexus.

TRANSLATIONAL RELEVANCE

The present study shows that OCT-A can be employed for small animal imaging to assess the vascular network and offers advantages over flat-mount histology and FA.