138
D. Cabrera DeBuc et al.
Szigeti et al. evaluated the correlation between AL and the thickness of intraretinal
layers in the macula. Their results showed that in the macular area the thickness of the
retina and all intraretinal layers, except for the RNFL, GCC and the RPE, correlated
with AL with an increasing trend towards the outer layers in the peripheral ring which
suggests that the outer layers are elongating or “stretching” with increasing eyeball
length [56] (see Table 6.1). Since the OCT examination was carried out in the macula
in a limited, 6 mm diameter wide retinal area, they did not have the opportunity to
measure the total volume of the retinal layers involving the entire retina to the ora
serrata and thus they were not able to get comparable results to those published by
Németh et al. using ultrasound [48].
Conflicting results were reported in previous studies about the correlation between
AL and thickness of the intraretinal layers. Cheung et al. measured the thickness of
the circumpapillary RNFL and other characteristic parameters of the optic disc (like
the area of the ONH, the area of the rim area, the area of the excavation and the
cup/disc ratio) using spectral domain OCT (SD-OCT) [57]. They found that AL was
significantly and strongly correlated with each examined parameter. Mwanza et al.
examined the effect of AL on the thickness of the GCL+IPL complex in the macula,
also using SD-OCT [58]. Their results indicated that the thickness of the GCL+IPL
complex decreased significantly by the increase in AL. On the contrary, Ooto et al.
did not find the same trend as the above authors for the correlation between AL
and the thickness of any of the intraretinal layers using automatic segmentation and
intraretinal layer thickness measurement on SD-OCT images [53]. It is worth to note
that mild and high myopic eyes were excluded from the study by Ooto et al., while
these were included in the study by Cheung et al. and Mwanza et al. [53, 57, 58].
Therefore, the explanation for the different results could at least in part be that the
standard deviation of the AL of the examined eyes was very low in the study of Ooto
et al., hence the significant deviations which are observable in the case of shorter or
longer eyes did not affect their results.
Szigeti et al. results showed that the weighted mean thickness of the nuclear layers
(GCL+IPL, INL and ONL) correlated with AL after adjustment for age, sex and
image quality, the correlation getting stronger towards the outer layers. Compared to
the above-mentioned studies, in Szigeti et al. study the AL of the eyes was relatively
in a wide range which could also contribute to their results [56].
According to two previous studies using OCT, the total thickness of the central,
1 mm diameter wide area of the macula (the central subfield) and total macular volume
also correlate with AL, although with relatively low coefficients of correlation (r
−0.222 and r 0.308, respectively) [59, 60]. Szigeti et al. results were in line with
these findings as the correlation between total retinal thickness (a derivative of total
macular volume) and AL was somewhat higher (r −0.378) compared to the abovementioned studies [56].
It remains unknown whether thinning in axial myopia occurs equally in all retinal
layers. Abbott et al. studied the changes in retinal thickness (in total and across
layers) in a mammalian animal model (tree shrews, Tupaia belangeri) of high axial
myopia using OCT and histological sections from the same retinal tissue. Analysis
of retinal layers revealed that the IPL, INL, and OPL are showing the most thinning
D. Cabrera DeBuc et al.
Szigeti et al. evaluated the correlation between AL and the thickness of intraretinal
layers in the macula. Their results showed that in the macular area the thickness of the
retina and all intraretinal layers, except for the RNFL, GCC and the RPE, correlated
with AL with an increasing trend towards the outer layers in the peripheral ring which
suggests that the outer layers are elongating or “stretching” with increasing eyeball
length [56] (see Table 6.1). Since the OCT examination was carried out in the macula
in a limited, 6 mm diameter wide retinal area, they did not have the opportunity to
measure the total volume of the retinal layers involving the entire retina to the ora
serrata and thus they were not able to get comparable results to those published by
Németh et al. using ultrasound [48].
Conflicting results were reported in previous studies about the correlation between
AL and thickness of the intraretinal layers. Cheung et al. measured the thickness of
the circumpapillary RNFL and other characteristic parameters of the optic disc (like
the area of the ONH, the area of the rim area, the area of the excavation and the
cup/disc ratio) using spectral domain OCT (SD-OCT) [57]. They found that AL was
significantly and strongly correlated with each examined parameter. Mwanza et al.
examined the effect of AL on the thickness of the GCL+IPL complex in the macula,
also using SD-OCT [58]. Their results indicated that the thickness of the GCL+IPL
complex decreased significantly by the increase in AL. On the contrary, Ooto et al.
did not find the same trend as the above authors for the correlation between AL
and the thickness of any of the intraretinal layers using automatic segmentation and
intraretinal layer thickness measurement on SD-OCT images [53]. It is worth to note
that mild and high myopic eyes were excluded from the study by Ooto et al., while
these were included in the study by Cheung et al. and Mwanza et al. [53, 57, 58].
Therefore, the explanation for the different results could at least in part be that the
standard deviation of the AL of the examined eyes was very low in the study of Ooto
et al., hence the significant deviations which are observable in the case of shorter or
longer eyes did not affect their results.
Szigeti et al. results showed that the weighted mean thickness of the nuclear layers
(GCL+IPL, INL and ONL) correlated with AL after adjustment for age, sex and
image quality, the correlation getting stronger towards the outer layers. Compared to
the above-mentioned studies, in Szigeti et al. study the AL of the eyes was relatively
in a wide range which could also contribute to their results [56].
According to two previous studies using OCT, the total thickness of the central,
1 mm diameter wide area of the macula (the central subfield) and total macular volume
also correlate with AL, although with relatively low coefficients of correlation (r
−0.222 and r 0.308, respectively) [59, 60]. Szigeti et al. results were in line with
these findings as the correlation between total retinal thickness (a derivative of total
macular volume) and AL was somewhat higher (r −0.378) compared to the abovementioned studies [56].
It remains unknown whether thinning in axial myopia occurs equally in all retinal
layers. Abbott et al. studied the changes in retinal thickness (in total and across
layers) in a mammalian animal model (tree shrews, Tupaia belangeri) of high axial
myopia using OCT and histological sections from the same retinal tissue. Analysis
of retinal layers revealed that the IPL, INL, and OPL are showing the most thinning