A case of acute syphilitic posterior placoid chorioretinitis showing improved choroidal blood flow after treatment

Purpose

Acute syphilitic posterior placoid chorioretinitis (ASPPC) is a rare form of ocular syphilis. However, its pathophysiology is not fully understood. Laser speckle flowgraphy (LSFG) can facilitate the non-invasive evaluation of blood flow and allow investigations into the effects of treatments in various ocular diseases. We report a case of ASPPC that presented with symptoms only in the right eye but showed bilateral disease in LSFG.

Observations

A 54-year-old man presented with decreased vision and visual field defects in the right eye 2 days prior to the initial visit. Fundoscopy images showed a typical yellowish placoid lesion in the macular area, and optical coherence tomography showed disruption of the outer retinal layers and nodular appearance of the retinal pigment epithelium. Fluorescence angiography showed excessive leakage of the placoid lesion characterized by hypofluorescent dots in the inner area ("leopard spotting"). The patient was diagnosed with unilateral ASPPC based on multiple imaging and serological tests. Penicillin was administered for 2 weeks, and the patient showed improvement in symptoms and restoration of the retinal structure. The mean blur rate of the right/left eye was 2.1/5.9 arbitrary units (AU) before treatment and increased to 4.5/9.3 AU 6 months after treatment.

Conclusions and importance

Despite the absence of typical imaging signs and symptoms in the left eye, both eyes may have been affected with different degrees of severity. Thus, LSFG may facilitate the evaluation of treatment effects and the prediction of ocular inflammatory diseases in the early stages.

Long-term changes of choroidal blood flow velocity in Vogt-Koyanagi-Harada disease

PURPOSE

To evaluate changes in choroidal blood flow in patients with Vogt-Koyanagi-Harada (VKH) disease after initiation of corticosteroid treatment.

METHODS

Fourteen patients (10 men and 4 women) with acute VKH disease followed for 2 years were retrospectively reviewed; only right eyes were included in the analysis. Mean blur rate (MBR) in the macula was measured by laser speckle flowgraphy (LSFG) and central choroidal thickness (CCT) was measured by optical coherence tomography (OCT), both prior to treatment and over 2 years after initiation of corticosteroid treatment.

RESULTS

Of 14 patients included in this study, 13 received initial treatment consisting of intravenous corticosteroid pulse therapy and one patient was treated using bilateral sub-Tenon injections of triamcinolone acetonide. Mean percentage change in MBR was significantly increased after initiation of treatment compared to pretreatment values (P < 0.001). Mean CCTs were significantly decreased after initiation of treatment, compared to pretreatment thicknesses (P < 0.001). There was no significant change in either MBR change or CCT at 1 month after initiation of treatment through 2 years of follow-up. The mean MBR percentage change was significantly higher in eyes with sunset glow fundus (SGF) compared to eyes without SGF at 1 year.

CONCLUSION

With initiation of corticosteroid treatment in VKH disease patients, choroidal blood flow improved and was maintained for 2 years. However, the presence of SGF should be taken into consideration when interpreting MBR results in VKH disease patients.

Imbalanced choroidal circulation in eyes with asymmetric dilated vortex vein

PURPOSE

Asymmetric dilated vortex vein (ADVV) observed in eyes with pachychoroid spectrum diseases is thought to be due to congestion of choroidal blood flow. The purpose of this study was to quantitatively investigate the blood flow velocity of ADVV using laser speckle flowgraphy (LSFG).

STUDY DESIGN

Retrospective case series.

METHODS

This was a retrospective case series with 23 eyes of 18 patients with ADVV on en-face OCT. A pair of choroidal veins from ADVV side (defined as ADVV vein) and non-ADVV side (defined as non-ADVV vein) was selected in each eye under the following criteria: (i) equivalent proximity to the deviated watershed, (ii) does not overlap with retinal blood vessels in the en-face OCT image, (iii) has approximately the same blood vessel diameter. Rubber bands were placed on the selected choroidal veins on the LSFG color map. Mean blur rate (MBR) values of ADVV and non-ADVV veins were statistically compared.

RESULTS

The average MBR was 10.11 ± 1.9 in the ADVV veins and 13.49 ± 6.2 in the non-ADVV veins, showing significantly lower values in the ADVV veins (P = 0.03). The blood vessel diameter of the ADVV was 10.26 ± 3.0 and in the non-ADVV veins, 10.63 ± 2.9 pixels; not significantly different (P = 0.66). The distance from the deviated watershed to the ADVV was 53.3 ± 24.8 and to the non-ADVV veins, 46.80 ± 20.3 pixels; not significantly different (P = 0.41).

CONCLUSION

In eyes with ADVV, the blood flow velocity in the ADVV veins was lower than in the non-ADVV veins, suggesting anatomical congestion of ADVV.

Alteration in choroidal microvasculature determined by optical coherence tomography angiography in patients with acromegaly

AIM

We aimed to investigate the retinal layers and macular capillary structure using optical coherence tomography angiography (OCTA) with acromegaly patients and determine the relationship between OCTA parameters and disease duration, Growth hormone (GH) and Insuline growth factor (IGF - 1) levels.

PATIENTS AND METHOD

Twenty-two patients with acromegaly who were followed up in the endocrinology outpatient clinic of Sisli Hamidiye Etfal Health Training and Research Hospital, were recruited into the study. Healthy control group was consisted of 22 age and gender matched subjects. Complete opthalmological examination including best visual acuity (BCVA), axial lenght, intraocular pressure (IOP) measurement, anterior segment and fundus examination, central corneal thickness with pachymetry and OCTA measurement were performed in the patients and healthy control group. Foveal avascular zone (FAZ), foveal vascular density (FVD), parafoveal vascular density (PFVD), choroidal flow (CF), foveal thickness (FT) and choroidal thickness (CT) were compared beetwen groups. Correlation between disease duration, GH and IGF-1 levels and OCTA parameters were evaluated.

RESULTS

There was no statistically significant difference between the groups in terms of BCVA, axial length, IOP, FT, FAZ, FD and PFVD. Choroidal thickness and CF was significantly high in the patients group compared to healthy controls (respectively, p = 0.003, p = 0.022). The mean follow-up period in patients with acromegaly was 90±50.2 months. There was a significant correlation between GH and subfoveal choroidal thickness in the patient group (p < 0.001, r = 0.52), a significant correlation was determined between disease duration and corneal thickness (p = 0.01, r = 0.41). In addition, an inverse correlation was detected between the IGF-1 level and the FAZ domain (p = 0.022, r= -0.34).

CONCLUSION

In patients with acromegaly, choroidal vasculature seems to be more affected than the retinal vasculature.

Decrease in choroidal blood flow after half and one-third dose verteporfin photodynamic therapy for chronic central serous chorioretinopathy

Background

The effect of various reduced doses of verteporfin photodynamic therapy (PDT) on choroidal blood flow in chronic central serous chorioretinopathy (CSC) remains unclear. Therefore, this study aimed to evaluate choroidal blood flow after half-dose PDT (1/2PDT) and one-third dose PDT (1/3PDT) with verteporfin for chronic CSC using laser speckle flowgraphy and spectral-domain optical coherence tomography.

Methods

Twenty-seven eyes of 27 patients with serous retinal detachment (SRD) caused by chronic CSC for more than 6 months were included in this study. Patients were divided into the 1/2PDT (n = 12; January 2018 to July 2019) and 1/3PDT (n = 15; August 2016 to December 2017) groups based on the treatment period. The best-corrected visual acuity (BCVA), central retinal thickness (CRT), central choroidal thickness (CCT), and mean blur rate in the macular area (m-MBR) and optic nerve head (ONH-MBR) were obtained using laser speckle flowgraphy and evaluated at baseline (pre-treatment), and 2 weeks, 1 month, 3 months, and 6 months after treatment.

Results

We found that SRD disappeared after 1 month in 92 and 93% of patients’ eyes in the 1/2PDT and 1/3PDT groups, respectively. Recurrence of SRD was observed in one eye at the 6-month follow-up after 1/2PDT and two eyes at the 3-month follow-up after 1/3PDT. No significant improvement was observed in baseline BCVA in the 1/3PDT and 1/2PDT groups. The average m-MBR against baseline significantly decreased at 2 weeks and 1, 3, and 6 months in the 1/2PDT group. The average m-MBR against baseline decreased significantly only at the 2 weeks follow-up in the 1/3PDT group. The average rate of change in the CCT against baseline decreased significantly throughout for up to 6 months in the 1/2PDT group and for up to 3 months in the 1/3PDT group. No significant fluctuation was observed in the ONH-MBR.

Conclusions: Here, PDT significantly affected choroidal blood flow depending on the verteporfin dose in chronic CSC.

Trial registration

This trial was retrospectively registered (UMIN000026850; Approval date 03/04/2017).

Changes in choroidal circulation and pulse waveform in a case of pregnancy-induced hypertension with serous retinal detachment

Purpose

We aimed to examine the changes in choroidal blood flow (CBF), choroidal pulse waveform, and central choroidal thickness (CCT) in a case of pregnancy-induced hypertension (PIH) using laser speckle flowgraphy (LSFG) and enhanced depth imaging optical coherence tomography (EDI-OCT) before and after treatment with antihypertensive drugs.

Observations

A 24-year-old Japanese woman diagnosed with PIH presented with complaints of worsening and blurred vision in the right eye. Funduscopic findings at the initial visit showed serous retinal detachment (SRD), retinal hemorrhage, and arterial tortuosity. The LSFG color map showed a warm color. Macular mean blur rate (MBR), which is an index of relative blood flow velocity, in both eyes was high, along with choroidal thickening. Blowout time (BOT), which indicates the rate of time in which the MBR is greater than half the amplitude during one heartbeat, was low and acceleration time index (ATI), which represents the time-to-peak of MBR, was high. Several weeks after treatment with antihypertensive drugs, the CBF and ATI gradually decreased with regression of the SRD and thinning of the CCT. On the other hand, BOT gradually increased after treatment, showing a significant decrease in vascular resistance. Ocular perfusion pressure decreased after treatment because of the reduction in blood pressure.

Conclusions and Importance

LSFG might reveal choroidal overperfusion and increased vascular resistance, along with SRD and choroidal thickening, in a patient with PIH with reversal after treatment with antihypertensive drugs. These findings demonstrate the importance of evaluation of ocular blood flow and vascular resistance in women with PIH in order to routinely assess the clinical and systemic condition.

Neural control of choroidal blood flow

The choroid is richly innervated by parasympathetic, sympathetic and trigeminal sensory nerve fibers that regulate choroidal blood flow in birds and mammals, and presumably other vertebrate classes as well. The parasympathetic innervation has been shown to vasodilate and increase choroidal blood flow, the sympathetic input has been shown to vasoconstrict and decrease choroidal blood flow, and the sensory input has been shown to both convey pain and thermal information centrally and act locally to vasodilate and increase choroidal blood flow. As the choroid lies behind the retina and cannot respond readily to retinal metabolic signals, its innervation is important for adjustments in flow required by either retinal activity, by fluctuations in the systemic blood pressure driving choroidal perfusion, and possibly by retinal temperature. The former two appear to be mediated by the sympathetic and parasympathetic nervous systems, via central circuits responsive to retinal activity and systemic blood pressure, but adjustments for ocular perfusion pressure also appear to be influenced by local autoregulatory myogenic mechanisms. Adaptive choroidal responses to temperature may be mediated by trigeminal sensory fibers. Impairments in the neural control of choroidal blood flow occur with aging, and various ocular or systemic diseases such as glaucoma, age-related macular degeneration (AMD), hypertension, and diabetes, and may contribute to retinal pathology and dysfunction in these conditions, or in the case of AMD be a precondition. The present manuscript reviews findings in birds and mammals that contribute to the above-summarized understanding of the roles of the autonomic and sensory innervation of the choroid in controlling choroidal blood flow, and in the importance of such regulation for maintaining retinal health.

Effects of intravitreal injection of ranibizumab on choroidal structure and blood flow in eyes with diabetic macular edema

PURPOSE

To determine the effects of an intravitreal injection of ranibizumab (IVR) on the choroidal structure and blood flow in eyes with diabetic macular edema (DME).

METHODS

Twenty-eight consecutive patients with DME who received an IVR and 20 non-diabetic, age-matched controls were followed for 1 month. The eyes with DME were divided into those with prior panretinal photocoagulation (PRP, n = 16) and those without prior PRP (no-PRP, n = 12). The enhanced depth imaging optical coherence tomography (EDI-OCT) scans and Niblack's image binarization were performed to determine the choroidal structure. The choroidal blood flow was determined by laser speckle flowgraphy.

RESULTS

The subfoveal choroidal thickness at the baseline was significantly thicker in the no-PRP group than in the PRP-treated group. After IVR, the best-corrected visual acuity (BCVA) and central retinal thickness in eyes with DME were significantly improved compared to the baseline values. There were significant differences in the choroidal thickness, total choroidal area, and choroidal vascularity index between the groups after IVR. Choroidal vascular index and choroidal blood flow were significantly reduced only in the no-PRP group and not in the PRP-treated group. In addition, the correlation between the central retinal thickness and the choroidal blood flow was significant in the no-PRP group (r = 0.47, P < 0.05).

CONCLUSIONS

A single IVR will reduce the central retinal thickness and improve the BCVA in eyes with DME in both the no-PRP and PRP-treated group. IVR affected the choroidal vasculature and blood flow significantly, and a significant correlation was found between the central retinal thickness and the choroidal blood flow in eyes without PRP.

Macular choroidal thickness after vitreoretinal surgery: Long-term effect of pars plana vitrectomy with and without encircling scleral buckling surgery

PURPOSE

To evaluate the macular choroidal thickness (CT) of eyes subjected to pars plana vitrectomy (PPV) whether or not combined with encircling scleral buckling (ESB) surgery for primary rhegmatogenous retinal detachment repair at 6 months or more after surgery.

METHODS

This observational study included: 15 eyes (15 patients) submitted to combined ESB+PPV; 15 eyes submitted to PPV and their respective 30 normal fellow eyes (FE). Two 6mm lineal perpendicular optical coherence tomography B-scans centred on the fovea with enhanced depth imaging were performed on each eye. CT was measured at several macular locations: subfoveal (SF-CT) and at a radius of 1, 2, and 3mm from the fovea. CTs of the eyes in the CE+PPV group were compared to CT in the PPV group and the CTs of all operated eyes were compared to the CTs of their FE.

RESULTS

SF-CT of the eyes in the ESB+PPV group was significantly increased compared to their FE (P=.001). CT at a radius of 1, 2, and 3mm from the fovea of the ESB+PPV group were significantly increased (P=.001, P=.005, and P=.001, respectively). The SF-CT of the PPV group was similar to their FE (P=.691). The SF-CT of the ESB+PPV group was significantly increased compared to SF-CT of the PPV group (P=.019).

CONCLUSIONS

The CT of the eyes subjected to combined ESB and PPV was significantly increased at 6 months or more after surgery compared to the CT of their FE and to the CT of the eyes subjected to PPV alone, which could be explained by a venous engorgement caused by the ESB.

Changes in choroidal blood flow and choroidal thickness after treatment in two cases of pediatric anisohypermetropic amblyopia

Purpose

We aimed to examine the changes in choroidal blood flow (CBF) and central choroidal thickness (CCT) in children with anisohypermetropic amblyopia using laser speckle flowgraphy (LSFG) and enhanced depth imaging optical coherence tomography (EDI-OCT).

Observations

The patients were both 6-year-old Japanese male children with complaints of worsening right visual acuity and were diagnosed with anisohypermetropic amblyopia. The decimal best-corrected visual acuities (BCVAs) in cases 1 and 2 were both 0.5. In both cases, LSFG results demonstrated CBF impairment in amblyopic eyes compared with fellow eyes. EDI-OCT results also showed that the CCTs of amblyopic eyes were greater than those of fellow eyes at the initial visit. Several months after the first visit, the decimal BCVAs in both cases had improved to 1.0 because of treatment. Further, the CBF gradually increased along with a decrease in the CCT of the amblyopic eye. The axial lengths and spherical powers of the amblyopic eyes in the two cases were not different during follow-up.

Conclusions and importance

We have determined the changes in CBF and CCT in two children with anisohypermetropic amblyopia for the first time. CBF impairments may be involved in the pathogenesis of anisohypermetropic amblyopia, and LSFG may be useful in examining CBF in pediatric anisohypermetropic amblyopia.

Comparison of Choriocapillaris Flow Measurements between Two Optical Coherence Tomography Angiography Devices

PURPOSE

To evaluate choriocapillaris (CC) perfusion in healthy subjects using 2 different optical coherence tomography angiography (OCT-A) devices.

PROCEDURES

Macular OCT-A imaging (36 eyes of 36 subjects) was performed using Optovue AngioVue and Zeiss AngioPlex devices. CC decorrelation signal index was assessed, and CC data were analyzed regarding intra-device variability, inter-device correlation, age, signal strength, and fields of view.

RESULTS

The intra-device variability of CC measurements in the 3 × 3 mm2 field was 5.3 and 2.6% (Angiovue and Angioplex, coefficients of variation; 6 × 6 mm2: 8.0 and 2.8%, respectively). Mean CC decorrelation signal index in 3 × 3 mm2 was 104.3 ± 6.7 (Angiovue) and 81.3 ± 9.2 (Angioplex) (6 × 6 mm2: 95.6 ± 8.1, 81.1 ± 6.5) with high correlation between both devices (3 × 3 mm2: p = 0.0053; 6 × 6 mm2: p = 0.0139). CC decorrelation signal index in 3 × 3 mm2 was significantly higher in subjects aged ≤58 years compared to subjects aged ≥59 years (Angiovue: 107.3 ± 3.6, 101.3 ± 7.7, p = 0.0156; Angioplex: 84.6 ± 7.6, 78.0 ± 9.5, p = 0.0371). Signal strength was 64.6 ± 8.9 (Angiovue) and 9.5 ± 0.8 (Angioplex).

CONCLUSION

Both devices showed low intra-device variability and a high inter-device correlation. CC decorrelation signal index was negatively correlated with advancing age.

Disinhibition of neurons of the nucleus of solitary tract that project to the superior salivatory nucleus causes choroidal vasodilation: Implications for mechanisms underlying choroidal baroregulation

Preganglionic neurons in the superior salivatory nucleus (SSN) that mediate parasympathetic vasodilation of choroidal blood vessels receive a major excitatory input from the baroresponsive part of the nucleus of the solitary tract (NTS). This input appears likely to mediate choroidal vasodilation during systemic hypotension, which prevents decreases in choroidal blood flow (ChBF) due to reduced perfusion pressure. It is uncertain, however, how low blood pressure signals to NTS from the aortic depressor nerve (ADN), which fires at a low rate during systemic hypotension, could yield increased firing in the NTS output to SSN. The simplest hypothesis is that SSN-projecting NTS neurons are under the inhibitory control of ADN-receptive GABAergic NTS neurons. As part of evaluating this hypothesis, we assessed if SSN-projecting NTS neurons, in fact, receive prominent inhibitory input and if blocking GABAergic modulation of them increases ChBF. We found that SSN-projecting NTS neuronal perikarya identified by retrograde labeling are densely coated with GABAergic terminals, but lightly coated with excitatory terminals. We also found that, infusion of the GABA-A receptor antagonist GABAzine into NTS increased ChBF. Our results are consistent with the possibility that low blood pressure signals from the ADN produce vasodilation in choroid by causing diminished activity in ADN-receptive NTS neurons that tonically suppress SSN-projecting NTS neurons.

Choroidal blood flow impairment demonstrated using laser speckle flowgraphy in a case of commotio retinae

Purpose

To report the time course of choroidal blood flow (CBF) in a commotio retinae case using laser speckle flowgraphy (LSFG).

Observations

A 58-year-old Japanese man with complaints of worsening left visual acuity after blunt eye trauma was diagnosed with commotio retinae. A funduscopic examination showed macular opacity, and LSFG results demonstrated CBF impairment in the affected eye.

Optical coherence tomography also showed disruption of the photoreceptor outer segment. Seven months after the initial visit, CBF was significantly increased, along with improvement in the photoreceptor outer segment.

Conclusion

and importance: We revealed CBF impairment in a case of commotio retinae for the first time. CBF impairment may be involved in the pathogenesis of commotio retinae, and LSFG may be useful for examining CBF in commotio retinae.

Type-specific photoreceptor loss in pigeons after disruption of parasympathetic control of choroidal blood flow by the medial subdivision of the nucleus of Edinger-Westphal

The medial part of the nucleus of Edinger–Westphal (EWM) in birds mediates light-regulated adaptive increases in choroidal blood flow (ChBF). We sought to characterize the effect of loss of EWM-mediated ChBF regulation on photoreceptor health in pigeons housed in either moderate intensity diurnal or constant light (CL). Photoreceptor abundance following complete EWM destruction was compared to that following a lesion in the pupil control circuit (as a control for spread of EWM lesions to the nearby pupil-controlling lateral EW) or following no EW damage. Birds were housed post-lesion in a 12 h 400 lux light/12 h dark light cycle for up to 16.5 months, or in constant 400 lux light for up to 3 weeks. Paraformaldehyde–glutaraldehyde fixed eyes were embedded in plastic, sectioned, slide-mounted, and stained with toluidine blue/azure II. Blinded analysis of photoreceptor outer segment abundance was performed, with outer segment types distinguished by oil droplet tint and laminar position. Brains were examined histologically to assess lesion accuracy. Disruption of pupil control had no adverse effect on photoreceptor outer segment abundance in either diurnal light or CL, but EWM destruction led to 50–60% loss of blue/violet cone outer segments in both light conditions, and a 42% loss of principal cone outer segments in CL. The findings indicate that adaptive regulation of ChBF by the EWM circuit plays a role in maintaining photoreceptor health and mitigates the harmful effect of light on photoreceptors, especially short wavelength-sensitive cone photoreceptors.

Effect of Resveratrol-Based Nutritional Supplement on Choroidal Thickness: A Pilot Study

PURPOSE

The effect of an oral trans-resveratrol-based supplement (Longevinex^®) on choroidal thickness, measured using optical coherence tomography (OCT) enhanced depth imaging, was investigated in a prospective study.

MATERIALS AND METHODS

34 young, healthy participants were randomly divided into two age- and gender-matched groups. They were then assigned in a randomized fashion to treat with either a trans-resveratrol-based group (Longevinex^®, Las Vegas) or placebo. All participants underwent ocular imaging with spectral domain (SD)-OCT (Spectralis; Heidelberg Engineering, Heidelberg) at the baseline and then again 1 h following treatment. The choroidal thickness was measured in a masked fashion at the fovea and at four additional points, located at 500 μm and 1000 μm nasal to the fovea and 500 μm and 1000 μm temporal to the fovea.

RESULTS

In the resveratrol group, the foveal choroidal thickness at the baseline was 267.73 ± 84.19 μm (mean ± SD); it increased to 284.57 ± 92.39 μm 1 h after drug treatment (p = 0.033). The mean choroidal thickness was also significantly increased at each of the four extrafoveal points (all p < 0.05). In the control group, the mean baseline choroidal thickness at the fovea was 269.73 ± 71.40 μm (mean ± SD) and it was 268.43 ± 70.15 μm (mean ± SD) 1 h after the placebo was administered (p = 0.183); there were also no significant differences in choroidal thickness at the four additional points (all p > 0.05) Conclusion: A significant increase in choroidal thickness following oral administration of a trans-resveratrol-based supplement was observed. There was no change in choroidal thickness in the placebo-treated control group. We speculate that the increased choroidal thickness is the result of choroidal vessel vasodilation.

Choroidal Blood Flow Change in Eyes with High Myopia

Purpose

To evaluate choroidal blood flow changes in eyes with high myopia according to the pulsatile components of ocular blood flow analysis.

Methods

A total of 104 subjects (52 males and 52 females) were included in this study. One eye of each participant was randomly selected and assigned to one of four refractive groups, designated as, hyperopes (n = 20; refractive error, ≥+1.00 diopter [D]), emmetropes (n = 28; refractive error, ±0.75 D), lower myopes (n = 33; refractive error, -1.00 to -4.75 D), and high myopes (n = 23; refractive error, ≤-5.00 D). Components of pulse amplitude (OBFa), pulse volume (OBFv), pulse rate (OBFr), and pulsatile ocular blood flow (POBF) were analyzed using a blood flow analyzer. Intraocular pressure and axial length were measured.

Results

Pulsatile components of OBFa, OBFv, and POBF showed positive correlations with refractive error and showed negative correlations with axial length (r = 0.729, r = 0.772, r = 0.781, respectively, all p < 0.001; r = -0.727, r = -0.762, r = -0.771, respectively, all p < 0.001). The correlations of refractive error and axial length with OBFr were irrelevant (r = -0.157, p = 0.113; r = 0.123, p = 0.213). High myopes showed significantly lower OBFa, OBFv, and POBF than the other groups (all p < 0.001).

Conclusions

Axial length changes in high myopes potentially influence choroidal blood flow, assuming the changes are caused by narrowing of the choroidal vessel diameter and increasing rigidity of the choroidal vessel wall. These finding explains the influence of axial length on OBFa, OBFv, and POBF, but not on OBFr. Thus, changes in axial length and the possible influence of these changes on the physical properties of choroidal vessels is the mechanism believed to be responsible for putting high myopes at risk for ocular vascular diseases.