Myopia is the most common refractive error and the subject of interest of various studies assessing ocular blood flow. Increasing refractive error and axial elongation of the eye result in the stretching and thinning of the scleral, choroid, and retinal tissues and the decrease in retinal vessel diameter, disturbing ocular blood flow. Local and systemic factors known to change ocular blood flow include glaucoma, medications and fluctuations in intraocular pressure, and metabolic parameters. Techniques and tools assessing ocular blood flow include, among others, laser Doppler flowmetry (LDF), retinal function imager (RFI), laser speckle contrast imaging (LSCI), magnetic resonance imaging (MRI), optical coherence tomography angiography (OCTA), pulsatile ocular blood flowmeter (POBF), fundus pulsation amplitude (FPA), colour Doppler imaging (CDI), and Doppler optical coherence tomography (DOCT). Many researchers consistently reported lower blood flow parameters in myopic eyes regardless of the used diagnostic method. It is unclear whether this is a primary change that causes secondary thinning of ocular tissues or quite the opposite; that is, the mechanical stretching of the eye wall reduces its thickness and causes a secondary lower demand of tissues for oxygen. This paper presents a review of studies assessing ocular blood flow in myopes.
Purpose To assess pattern electroretinogram (PERG) recordings in patients with axial myopia with a special focus on the correct interpretation of findings. Patients and Methods Sixty patients divided into three groups according to the spherical equivalent of refractive error (group 1, error −3 D to −6 D; group 2, error > −6 D; and controls, error −1 D to +1 D) were examined. Data for the right eye of every patient were considered in the statistical analysis. All patients had a full ophthalmic examination including the measurement of visual acuity, intraocular pressure, degree of refractive error, axial length, biomicroscopic evaluation of the anterior segment, fundoscopy and PERG. The differences of basic parameters and P50 and N95 amplitudes as well as P50 implicit time between groups were studied. Correlations between P50 and N95 amplitudes and P50 implicit time were axial length and refractive error was established. Results The P50 amplitude, N95 amplitude and P50 peak time differed significantly between the groups ( P <0.01). No significant differences were found for the N95/P50 ratio. Significantly lower P50 and N95 amplitudes ( r =−0.42, P <0.01; r =−0.42, P <0.01) and increased P50 peak time ( r =0.64, P <0.01) correlated with elongated axial length. A 1-mm increase in axial length corresponded with a 0.41 µV decrease in the P50 amplitude and 0.55 µV reduction of the N95 amplitude. There was also 1.11 ms increase of P50 wave peak time per 1 mm increase of axial length. Significantly lower amplitudes and longer peak times are associated with increased axial length and increased refractive error. Conclusion According to results observed in this study, the correct interpretation of PERG recordings requires the consideration of axial length.
Purpose This work aims at assessing whether electrophysiological functional changes in the macular region appear in medium myopia, even in the presence of a normal macular OCT scan and how axial length correlates with macular OCT parameters in medium myopia. Methods The study included right eyes of 17 patients with myopia of medium degree (SE < − 6D to > − 3D). Control group consisted of 20 eyes of patients of age and sex that matched healthy controls with normal macular and optic nerve OCT results and normal axial length. Full ophthalmic examination (the distance best-corrected visual acuity, intraocular pressure, refractive error, the anterior and posterior segment of the eye in a slit lamp, the axial length of the eyeball) with OCT of the macular and optic disk and the PERG test were performed in the study and control groups. Only the patients with normal ophthalmic and OCT examination results were qualified. The interview covering questions on risk factors of myopia onset and progression such as prematurity, family history of myopia was carried out in both groups. In myopic group, the question relating to time of near work was also asked. Study and control groups were tested with the use of Shapiro–Wilk, Mann–Whitney, Student’s t test, Pearson and Spearman's rank correlation tests. Results AL was significantly longer in myopia group (p < 0.01), and SE value was lower (p < 0.01). Longer implicit time of P50 was found in the study group, but amplitudes of P50 and N95 waves were not significantly reduced (p < 0.05). AL showed correlations with P50 implicit time (p < 0.05) and with reduction in retinal fiber nerve layer and ganglion cells and inner plexus layer (p < 0.05). Conclusion Patients with myopia of medium degree have a dysfunction of retinal cone system of the macular region even when OCT scans show no abnormalities. Elongation of AL correlates with reduction in retinal fiber nerve layer and ganglion cells and inner plexus layer. Longitudinal follow-up studies may answer the question whether this increase in implicit time may be indicative of a faster myopia progression or of myopic retinal pathology, i.e., whether it may help to determine which patient would benefit from earlier or more intensive management of myopia progression.
Purpose: To assess the thickness of the retinal nerve fiber layer (RNFL), ganglion cell and inner plexus layer (GCIPL) and blood flow parameters in retrobulbar vessels, and to analyze correlations between these parameters in myopes. Methods: The study included forty myopic and 20 healthy eyes. Standard eye examination was supplemented with OCT of the optic nerve and macula (GCIPL, RNFL, RNFL in each quadrant and rim area of the optic nerve) and color Doppler imaging of retrobulbar arteries [peak systolic and end-diastolic velocities, pulsatile index and resistance index (RI) in the ophthalmic (OA), central retinal (CRA), nasal posterior ciliary and temporal posterior ciliary arteries]. Results: Significant correlations were found between blood flow parameters in the CRA, RNFL and GCIPL thickness, and axial length (AL) and spherical equivalent (SE). There were significant positive correlations between RNFL with PSV and EDV in the CRA and negative correlations between RNFL and RI in the CRA. GCIPL was positively correlated with PSV and EDV in the CRA. The decrease in RA was associated with reduced blood flow velocities in the CRA, TPCA and NPCA. Conclusion: The reduced retrobulbar blood flow in healthy young myopes is correlated with increasing AL and refractive value, and thinning of the RNFL and GCIPL. Reduction of the rim-area of the optic disc is associated with vascular and retinal circulatory disorders. These phenomena indicate the vascular basis of the described changes. To the best of our knowledge, this is the first study which correlates ocular circulation with retinal structure.
Krótkowzroczność jest główną przyczyną zaburzeń widzenia, będąc najczęstszą wadą refrakcji. Istnieje wiele podziałów krótkowzroczności uwzględniających wielkość wady refrakcji, dziedziczność, moment pojawienia się wady refrakcji, stan szczegółów dna oka czy długość osiową gałki ocznej. W literaturze istnieje duża niespójność w tym zakresie. Można znaleźć wiele terminów opisowych, jak również klasyfikacji określających rodzaje krótkowzroczności, co prowadzi do trudności przy porównywaniu wyników badań. Celem artykułu jest przedstawienie aktualnej definicji i podziału krótkowzorczności na podstawie przeglądu piśmiennictwa PubMed z ostatnich 5 lat.
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