Alexandra Benavente-Perez

Ocular blood flow measurements in healthy human myopic eyes

BackgroundTo evaluate the haemodynamic features of young healthy myopes and emmetropes, in order to ascertain the perfusion profile of human myopia and its relationship with axial length prior to reaching a degenerative state.MethodsThe retrobulbar, microretinal and pulsatile ocular blood flow (POBF) of one eye of each of twenty-two high myopes (N = 22, mean spherical equivalent (MSE) ≤−5.00D), low myopes (N = 22, MSE−1.00 to−4.50D) and emmetropes (N = 22, MSE ± 0.50D) was analyzed using color Doppler Imaging, Heidelberg retinal flowmetry and ocular blood flow analyser (OBF) respectively. Intraocular pressure, axial length (AL), systemic blood pressure, and body mass index were measured.ResultsWhen compared to the emmetropes and low myopes, the AL was greater in high myopia (p < 0.0001). High myopes showed higher central retinal artery resistance index (CRA RI) (p = 0.004), higher peak systolic to end diastolic velocities ratio (CRA ratio) and lower end diastolic velocity (CRA EDv) compared to low myopes (p = 0.014, p = 0.037). Compared to emmetropes, high myopes showed lower OBFamplitude (OBFa) (p = 0.016). The POBF correlated significantly with the systolic and diastolic blood velocities of the CRA (p = 0.016, p = 0.036). MSE and AL correlated negatively with OBFa (p = 0.03, p = 0.003), OBF volume (p = 0.02, p < 0.001), POBF (p = 0.01, p < 0.001) and positively with CRA RI (p = 0.007, p = 0.05).ConclusionHigh myopes exhibited significantly reduced pulse amplitude and CRA blood velocity, the first of which may be due to an OBF measurement artefact or real decreased ocular blood flow pulsatility. Axial length and refractive error correlated moderately with the ocular pulse and with the resistance index of the CRA, which in turn correlated amongst themselves. It is hypothesized that the compromised pulsatile and CRA haemodynamics observed in young healthy myopes is an early feature of the decrease in ocular blood flow reported in pathological myopia. Such vascular features would increase the susceptibility for vascular and age-related eye diseases.

Axial eye growth and refractive error development can be modified by exposing the peripheral retina to relative myopic or hyperopic defocus.

PURPOSE Bifocal contact lenses were used to impose hyperopic and myopic defocus on the peripheral retina of marmosets. Eye growth and refractive state were compared with untreated animals and those treated with single-vision or multizone contact lenses from earlier studies. METHODS Thirty juvenile marmosets wore one of three experimental annular bifocal contact lens designs on their right eyes and a plano contact lens on the left eye as a control for 10 weeks from 70 days of age (10 marmosets/group). The experimental designs had plano center zones (1.5 or 3 mm) and +5 diopters [D] or -5 D in the periphery (referred to as +5 D/1.5 mm, +5 D/3 mm and -5 D/3 mm). We measured the central and peripheral mean spherical refractive error (MSE), vitreous chamber depth (VC), pupil diameter (PD), calculated eye growth, and myopia progression rates prior to and during treatment. The results were compared with age-matched untreated (N=25), single-vision positive (N=19), negative (N=16), and +5/-5 D multizone lens-reared marmosets (N=10). RESULTS At the end of treatment, animals in the -5 D/3 mm group had larger (P<0.01) and more myopic eyes (P<0.05) than animals in the +5 D/1.5 mm group. There was a dose-dependent relationship between the peripheral treatment zone area and the treatment-induced changes in eye growth and refractive state. Pretreatment ocular growth rates and baseline peripheral refraction accounted for 40% of the induced refraction and axial growth rate changes. CONCLUSIONS Eye growth and refractive state can be manipulated by altering peripheral retinal defocus. Imposing peripheral hyperopic defocus produces axial myopia, whereas peripheral myopic defocus produces axial hyperopia. The effects are smaller than using single-vision contact lenses that impose full-field defocus, but support the use of bifocal or multifocal contact lenses as an effective treatment for myopia control.

Primary open-angle glaucoma vs normal-tension glaucoma: the vascular perspective.

OBJECTIVE To compare and contrast the presence of ocular and systemic vascular function in patients with newly diagnosed and previously untreated primary open-angle glaucoma (POAG) vs those with normal-tension glaucoma (NTG) and comparable early-stage, functional loss. METHODS The systemic vascular function of 19 patients with POAG, 19 patients with NTG, and 20 healthy individuals serving as controls was assessed using 24-hour ambulatory blood pressure monitoring, peripheral pulse-wave analysis, and carotid intima-media thickness. Retinal vascular reactivity to flicker light was assessed using dynamic retinal vessel analysis (Imedos, GmbH). RESULTS Compared with controls, patients with POAG and those with NTG exhibited similarly increased nocturnal systemic blood pressure variability (P = .01), peripheral arterial stiffness (P = .02), carotid intima-media thickness (P = .04), and reduced ocular perfusion pressure (P < .001). Furthermore, on dynamic retinal vessel analysis, both glaucoma groups exhibited steeper retinal arterial constriction slopes after cessation of flicker (P = .007) and a similarly increased fluctuation in arterial and venous baseline diameter (P = .008 and P = .009, respectively) compared with controls. CONCLUSIONS Patients with POAG or NTG exhibit similar alterations in ocular and systemic circulation in the early stages of their disease process. This finding highlights the importance of considering vascular risk factors in both conditions and raises questions about the current separation of the two conditions into distinct clinical entities.

Reproducibility-repeatability of choroidal thickness calculation using optical coherence tomography.

Purpose. To evaluate the repeatability and reproducibility of subfoveal choroidal thickness (CT) calculations performed manually using optical coherence tomography (OCT). Methods. The CT was imaged in vivo at each of two visits on 11 healthy volunteers (mean age, 35.72 ± 13.19 years) using the spectral domain OCT. CT was manually measured after applying ImageJ processing filters on 15 radial subfoveal scans. Each radial scan was spaced 12° from each other and contained 2500 A-scans. The coefficient of variability, coefficient of repeatability (CoR), coefficient of reproducibility, and intraclass correlation coefficient determined the reproducibility and repeatability of the calculation. Axial length (AL) and mean spherical equivalent refractive error were measured with the IOLMaster and an open view autorefractor to study their potential relationship with CT. Results. The within-visit and between-visit coefficient of variability, CoR, coefficient of reproducibility, and intraclass correlation coefficient were 0.80, 2.97% 2.44%, and 99%, respectively. The subfoveal CT correlated significantly with AL (R = −0.60, p = 0.05). Conclusions. The subfoveal CT could be measured manually in vivo using OCT and the readings obtained from the healthy subjects evaluated were repeatable and reproducible. It is proposed that OCT could be a useful instrument to perform in vivo assessment and monitoring of CT changes in retinal disease. The preliminary results suggest a negative correlation between subfoveal CT and AL in such a way that it decreases with increasing AL but not with refractive error.

Ocular blood-flow hemodynamics before and after application of a laser in situ keratomileusis ring

PURPOSE: To evaluate blood‐flow responses before and after microkeratome application. SETTING: School of Life and Health Sciences, Aston University, Birmingham, United Kingdom. METHODS: Hemodynamic responses were measured in eyes of healthy volunteers before and after transient elevation in intraocular pressure (IOP) resulting from microkeratome application. The IOP was elevated above 85 mm Hg for 90 seconds. Blood‐flow responses were measured using color Doppler imaging, Heidelberg retinal flowmetry, and an ocular blood‐flow analyzer. RESULTS: The study included 10 eyes. There was no difference in ocular‐perfusion measurements before or after IOP elevation using any measurement system. CONCLUSION: In normal healthy eyes, once suction was released, blood‐flow responses returned immediately to normal levels. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Coexistence of macro- and micro-vascular abnormalities in newly diagnosed normal tension glaucoma patients

Purpose:  To investigate the coexistence of ocular microvascular and systemic macrovascular abnormalities in early stage, newly diagnosed and previously untreated normal tension glaucoma patients (NTG).