170
E. Gao et al.
analysis further provides the measurement of optic head [3], macular ganglion cells
complex [4], choroidal thickness [5], etc.
However, OCT is not only valuable in providing morphological indices, but also
offers quantitative measurements of local optical intensities (also called optical density or reflectivity) of the underlying normal and/or pathological tissues. It has been
qualitatively observed that OCT optical intensity can provide clues for distinguishing
pathological changes, for example, the optical intensity of inner retina increased in
retinal artery occlusion [6]. In age-related macular degeneration, the optical intensity
increased with development and regression of choroidal neovascularization [7]. In
glaucoma patients, the optical intensity of the retinal nerve fiber layer (RNFL) has
been shown to be lower than that in normal subjects, and decreases with increasing
disease severity [8, 9]. Compared to normal vitreous, exudation lesions show higher
reflectivity, whereas degeneration changes have lower optical intensity [10]. Similarly, optical intensity of pigment epithelial detachment can be used to differentiate
serous, fibrovascular and drusenoid types [11]. In addition, reflectivity of the cystoid
space varies with fluorescein pooling intensity, suggesting that blood—retinal barrier
disruption can lead to content changes in diabetic macular edema [12]. Moreover, loss
of reflectivity in the photoreceptor ellipsoid region has been reported to occur early
and can be detected from the first clinical presentation in patients with idiopathic
perifoveal telangiectasia [13]. These results suggested that the optical intensities of
intraretinal or subretinal spaces can be used as biomarkers and provide clues to the
pathogenesis of retinal diseases.
However, quantitative assessment of OCT optical intensity was much less
reported, compared to the dimension analysis. In 2000, Pons et al. [8] reported
that the internal reflectivity of RNFL was lower in patients with glaucoma compared
to control. It was confirmed in spectral domain OCT recently [14, 15]. A study by
Giani et al. [16], using OCT, shows that quantitative analysis of choroidal neovascularization (CNV) reflectivity can differentiate leaky CNV from that without leakage, providing additional information regarding the fluorescein angiography leakage
status.
There are also lack of the information of normal range and physiological variation of retinal optical intensities. Since application of newly developed parameters
depends on an understanding of normal conditions, it is critical to establish a normative database of specific criteria. To our knowledge, few studies have been carried out
on retinal optical intensity distribution in normal subjects. The effect of determinants
such as sex, age, race, optic disc area, axial length and refractive error [17–19] which
affect retinal thickness measurements on optical intensity remained unknown.
In this chapter, we will introduce a few studies on the OCT optical intensity of
retinal layers based on a validated automatic computer algorithm [20–23]. In the
first study [24], the optical intensities in all retinal layers on spectral domain OCT
was measured, and the variations and relationships among retinal layers’ optical
intensities in normal subjects were investigated. In the second study [25], the retinal
optical intensity distribution of normal subjects was investigated in each retinal layer
and nine macular sectors based on areas defined in the Early Treatment Diabetic
Retinopathy Study (ETDRS) [26]. To collect reference data on the determinants,
E. Gao et al.
analysis further provides the measurement of optic head [3], macular ganglion cells
complex [4], choroidal thickness [5], etc.
However, OCT is not only valuable in providing morphological indices, but also
offers quantitative measurements of local optical intensities (also called optical density or reflectivity) of the underlying normal and/or pathological tissues. It has been
qualitatively observed that OCT optical intensity can provide clues for distinguishing
pathological changes, for example, the optical intensity of inner retina increased in
retinal artery occlusion [6]. In age-related macular degeneration, the optical intensity
increased with development and regression of choroidal neovascularization [7]. In
glaucoma patients, the optical intensity of the retinal nerve fiber layer (RNFL) has
been shown to be lower than that in normal subjects, and decreases with increasing
disease severity [8, 9]. Compared to normal vitreous, exudation lesions show higher
reflectivity, whereas degeneration changes have lower optical intensity [10]. Similarly, optical intensity of pigment epithelial detachment can be used to differentiate
serous, fibrovascular and drusenoid types [11]. In addition, reflectivity of the cystoid
space varies with fluorescein pooling intensity, suggesting that blood—retinal barrier
disruption can lead to content changes in diabetic macular edema [12]. Moreover, loss
of reflectivity in the photoreceptor ellipsoid region has been reported to occur early
and can be detected from the first clinical presentation in patients with idiopathic
perifoveal telangiectasia [13]. These results suggested that the optical intensities of
intraretinal or subretinal spaces can be used as biomarkers and provide clues to the
pathogenesis of retinal diseases.
However, quantitative assessment of OCT optical intensity was much less
reported, compared to the dimension analysis. In 2000, Pons et al. [8] reported
that the internal reflectivity of RNFL was lower in patients with glaucoma compared
to control. It was confirmed in spectral domain OCT recently [14, 15]. A study by
Giani et al. [16], using OCT, shows that quantitative analysis of choroidal neovascularization (CNV) reflectivity can differentiate leaky CNV from that without leakage, providing additional information regarding the fluorescein angiography leakage
status.
There are also lack of the information of normal range and physiological variation of retinal optical intensities. Since application of newly developed parameters
depends on an understanding of normal conditions, it is critical to establish a normative database of specific criteria. To our knowledge, few studies have been carried out
on retinal optical intensity distribution in normal subjects. The effect of determinants
such as sex, age, race, optic disc area, axial length and refractive error [17–19] which
affect retinal thickness measurements on optical intensity remained unknown.
In this chapter, we will introduce a few studies on the OCT optical intensity of
retinal layers based on a validated automatic computer algorithm [20–23]. In the
first study [24], the optical intensities in all retinal layers on spectral domain OCT
was measured, and the variations and relationships among retinal layers’ optical
intensities in normal subjects were investigated. In the second study [25], the retinal
optical intensity distribution of normal subjects was investigated in each retinal layer
and nine macular sectors based on areas defined in the Early Treatment Diabetic
Retinopathy Study (ETDRS) [26]. To collect reference data on the determinants,