الفهرس 
List of contentsOnly 14 pages are availabe for public view
 |  | from | 82 |  |  |
| | | from | 82 | | |
Abstract
Amblyopia is thought to be a disease in which a defect occurs during the critical period of development and maturation of the visual pathway between the retina and the central neurons. It has been believed to have various impacts on different neural levels of the visual pathway; however, the definite site of its influence is still under debates.(83) Some authors stated that functional deficits are first observed at a thalamic level, that of the LGN.(84) On the other hand, different studies have revealed retinal microstructures changes in amblyopic eyes such as decrease in the size and density of parafoveal retinal ganglion cells,(85) a decline in the nucleolar volume in the cytoplasmic area of retinal ganglion cells,(86) thinning in the internal plexiform layer with a decreased number of the bipolar synapses,(87) the outer nuclear layer of the fovea suggesting the possible involvement of the photoreceptors.(83) So, because of all these debates it is interesting to further study of these claimed retinal changes in amblyopia with advanced modalities of imaging as OCT. In this study, 31 patients with unilateral amblyopia were included, and divided into four groups; myopic anisometropia, hypermetropic anisometropia, esotropic strabismus, exotropic strabismus amblyopia. To study OCT parameters changes regarding macular thickness, macular volume, peripapillary RNFLT in amblyopic eye in comparison to its normal fellow eye. We found that; all amblyopic groups had significant higher CST (251.84 ± 44.90 vs. 225.32 ± 53.47 (Um); p= 0.03) but insignificant difference as regard average macular volume (7.84 ± 0.72 vs. 7.94 ± 0.82 (mm3); p= 0.58) in comparison to their normal fellow eyes, Also all groups had insignificant differences as regard peripapillary retinal nerve fiber layer thickness (inferior, nasal, temporal and whole) while amblyopic eyes had significantly lower superior peripapillary RNFLT (101.51 ± 31.18 vs. 117.81 ± 27.04 (mm3); p= 0.03). With especial magnification of these results among the myopic anisometropic group; significantly higher CST in comparison to its normal fellow eye (268.71 ± 53.55 vs. 227.57 ± 51.87; p= 0.03) and significantly lower superior RNFLT (87.71 ± 21.22 vs. 112.42 ± 22.34; p< 0.001) among eyes with anisometropic myopic amblyopia in comparison to its fellow. although It is thought that myopia may affect the normal macular development through the potential apoptosis of the ganglion cell, inner plexiform, and inner nuclear layers in the macular area; this could lead to macular dysplasia,(88) but this association is only in cases of pathological myopia (myopic spherical equivalent >8 diopters) which is excluded in our study.(89) These results are inconsistent with Li et al., (2015)(90), and Rajavi et al., (2018)(88) who stated that the amblyopic process may involve the retina, especially the macula and thicker foveola was found in the amblyopic eyes when compared with visually normal control eyes.(90) Aguirre et al., (2010)(91) also agreed that the macular thickness was significantly higher but in moderate to severe amblyopic eyes compared to their fellow eyes and external controls.(91) Andalib et al., (2013)(92) also reported thicker macula in anisometropic amblyopic eyes, but the increase of macular thickness in strabismic amblyopic eyes was not significant. Retinal involvement was not observed in the peripapillary nerve fiber layer of amblyopic eyes which inconsistent with our study.(92) While Pang et al., (2011)(93) focused on patients with high myopic unilateral amblyopia and found thicker fovea and thinner inner and outer macula in the amblyopic eye with high myopia compared to the normal fellow eye.(93) Altındağ (2016)(94) confound changes in macular thicknesses in strabismic amblyopia and used that as an early diagnostic tool of amblyopia and for early treatment of these cases.(94) Regarding Kasem and Badawi (2017)(95) reported that unilateral amblyopic eyes were prone to have a higher CMT and thicker global RNFL, The exact cause of the increased RNFLT in the amblyopia is unclear, but it may be due to the defect of retinal postnatal maturation with a decrease in the retinal ganglion cells. Which in turn may lead to a similar effect on the normal macular maturation as well, including Henle’s fibers movement from the foveola with a reduction in the foveal diameter and an increase in the measurable foveal thickness.(95) Yen et al., (2004)(6) found that RNFLT may be affected by refractive amblyopia.(6) Yoon et al., (2005)(96) thought that the amblyopic process may involve the peripapillary RNFL, but not the macula.(96) Repka et al., (2006)(97) found a small but not clinically significant difference in RNFLT between amblyopic and sound eye.(97) While Bozkurt et al., (2009)(98) found that there is no difference in RNFLT between the two eyes of cases of unilateral amblyopia by means of scanning laser polarimetry.(98) On the other hand Altintas et al., (2005)(99) had assessed patients with unilateral strabismic amblyopia and found no differences between the two eyes regarding RNFL thickness, macular thickness, and macular volume.(99) In line with that was the results of Kee et al., (2006)(100) who stated that there were no differences in the fovea and the retinal nerve fiber layer thickness found but they had compared amblyopic children with normal ones as external control.(100) The discrepancy between all the mentioned studies may be due the variety in the OCT devices, measurement accuracy, different races, various age groups of the participants, wide range of number of participants, and different types of control group either normal group or the normal sound eye of the same patient. Furthermore, other authors thought that the main detected changes in the amblyopic eye not in the retina itself but it may involve the subfoveal choroid rather than the retinal and peripapillary area.(101)(102)(103) We found that the Axial length was significantly higher among amblyopic eyes (23.59 ± 1.82 vs. 22.81 ± 1.12 (mm); p= 0.04) in comparison to normal eyes. But it could be due to the higher number of myopic patients included in this study, but a direct correlation between axial length and macular parameter and RNFLT couldn’t be detected. Also, we couldn’t find a direct relation between the age of the participants and the retinal parameters changes. This study describes the optical coherence tomography (OCT) findings regarding macular parameters (macular central thickness and macular volume) and peripapillary RNFLT in cases with unilateral amblyopia (either anisometropic or strabismic amblyopia) in comparison to its normal fellow eye as control group. An observational cross-sectional study was employed. Both eyes of participants with unilateral amblyopia were photographed by spectral domain optical coherence tomography (SD-OCT). Quantitative parameters regarding central subfield thickness (CST), macular volume, peripapillary retinal nerve fiber layer thickness (RNFLT) was reported and compared to their sound fellow eyes. Thirty-one participants (20 anisometropic, 11 strabismic amblyopia), with age ranging from 10 to 30. We found that in all amblyopic groups the amblyopic eye had lower BCVA than its fellow eye. And all amblyopic groups had significant higher CST but insignificant difference as regard average macular volume in comparison to their normal fellow eyes, Also, all groups had insignificant differences as regard peripapillary retinal nerve fiber layer thickness (inferior, nasal, temporal and whole) while amblyopic eyes had significantly lower superior peripapillary RNFLT with especial magnification of these results among the myopic anisometropic group. Although it was thought that amblyopia only attributed to anatomical and functional changes in the visual cortex and LGN due abnormal visual stimulation. Recent studies found that the amblyopic eye may involve the visual pathway from retina to visual cortex. In this study we had documented significant increase in central macular thickness and decrease in superior peripapillary RNFLT, and insignificant changes regarding macular volume and inferior, nasal, temporal RNFLT in amblyopic eyes among cases of unilateral amblyopia in comparison to their sound fellow eyes. This in turn could be used as an early diagnostic tool, and prognostic factor for treatment response or resistance. Further studies with large number of cases, and larger strabismic amblyopic group. Wide range of age group may be helpful to find direct correlation between the age of participants and changes in retinal parameters.