Axial biometry of the entire eye using ultra-long scan depth optical coherence tomography

Abstract

Purpose: To assess the repeatability of axial biometry of the entire eye using ultra-long scan depth optical coherence tomography (OCT) and to investigate the agreement with IOLMaster measurements (Carl Zeiss Meditec).

Design: Prospective, observational case series.

Methods: There were 37 adult subjects enrolled in group 1 and 12 adult subjects enrolled in group 2. Using ultra-long scan depth OCT, the left eyes of these groups were measured in 2 separate sessions. The images were processed by a manual method and custom-developed automatic software. A model eye was imaged for verification. The subjects in group 2 were imaged using ultra-long scan depth OCT and using the IOLMaster for axial length measurement comparison.

Results: All measured parameters of the model eye matched the geometric parameters. In group 1, there were no significant differences in all measured parameters using automatic and manual segmentation methods (P > .05, paired t test). The percentage of coefficient of repeatability of segments ranged from 0.3% to 3.9%. The corresponding interclass correlation coefficients ranged from 0.946 to 0.999. The correlation between the results using automatic and manual segmentation methods appeared to be strong (R(2) = 0.999; P < .05). In group 2, the axial length of the eye measured by the IOLMaster matched the results obtained by ultra-long scan depth OCT with the automatic method (R1(2) = 0.987; P < .05) and the manual method (R2(2) = 0.988; P < .05).

Conclusions: Automatic axial biometry using ultra-long scan depth OCT successfully measured each segment of the entire eye with good repeatability. With further development of automatic segmentation, ultra-long scan depth OCT seems to be a promising tool in the axial biometry of the entire eye.

Figure 1

Representative image of axial biometry of the entire eye using ultra-long scan depth optical coherence tomography. The full eye image (left) was obtained from the left eye of a 43-year-old subject with myopia (−1.0 diopter). The right side shows the longitudinal reflectivity profiles produced by the custom-developed software. The profile has peaks from the boundaries of the cornea, crystalline lens and the retina that allows determination of intraocular distances. Bar = 1 mm.

Figure 2

Schematic of model eye (left) used for calibration and it’s engineering drawing (right) was illustrated. The central corneal thickness (Figure 2, A) and the length from the anterior of the cornea to the posterior of the crystalline lens (Figure 2, C) were measured using the digital thickness gauge, the lens thickness (Figure 2, B) was measured using the digital caliper, then the anterior chamber depth was calculated as C- (A+B). The length of the model eye (Figure 2, E) was measured using the digital caliper, the length between the posterior of the model eye and the apex of the retina (Figure 2, D) was measured using the digital thickness gauge, then the axial length was calculated as E minus D. The vitreous length was calculated as E - D. Bar = 10 mm. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness; VL: vitreous length; AL: axial length.

Figure 2

Schematic of model eye (left) used for calibration and it’s engineering drawing (right) was illustrated. The central corneal thickness (Figure 2, A) and the length from the anterior of the cornea to the posterior of the crystalline lens (Figure 2, C) were measured using the digital thickness gauge, the lens thickness (Figure 2, B) was measured using the digital caliper, then the anterior chamber depth was calculated as C- (A+B). The length of the model eye (Figure 2, E) was measured using the digital caliper, the length between the posterior of the model eye and the apex of the retina (Figure 2, D) was measured using the digital thickness gauge, then the axial length was calculated as E minus D. The vitreous length was calculated as E - D. Bar = 10 mm. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness; VL: vitreous length; AL: axial length.

Figure 3

Correlation between the actual parameters of the model eye and the axial biometry of entire eye measured by ultra-long scan depth optical coherence tomography. Correlation was showed strong (R² = 0.999, P<.05). The solid line represents the equality. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness; VL: vitreous length; AL: axial length.

Figure 4

Inter-session variations in automatic (red) and manual (blue) methods of full eye axial biometry in 37 adult subjects. No significances were found among sessions and between the first and second measurement. The results showed strong correlations. Bars = standard deviation. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness; VL: vitreous length; AL: axial length.

Figure 5

Correlation between manual and automatic segmentation methods of full eye axial biometry in 37 adult subjects. Automatically segmented results were compared to the manually segmented results. Both results showed strong correlations (R² = 0.999, P < .05). The solid line represents the equality. Bars = standard deviation. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness; VL: vitreous length; AL: axial length.

Figure 6

Bland–Altman plots of the difference between the two repeated measurements using both automatic (red) and manual method (blue) of full eye axial biometry in 37 adult subjects. The full eye axial biometry included the central corneal thickness, the anterior chamber depth, the lens thickness, the vitreous length and the axial length. Values on the horizontal axis correspond to the mean of the two measurements. Values on the vertical axis correspond to the difference of two measurements. Solid lines and dashed lines indicate mean differences and 95% limits of agreement. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness, VL: vitreous length; AL: axial length.

Figure 6

Bland–Altman plots of the difference between the two repeated measurements using both automatic (red) and manual method (blue) of full eye axial biometry in 37 adult subjects. The full eye axial biometry included the central corneal thickness, the anterior chamber depth, the lens thickness, the vitreous length and the axial length. Values on the horizontal axis correspond to the mean of the two measurements. Values on the vertical axis correspond to the difference of two measurements. Solid lines and dashed lines indicate mean differences and 95% limits of agreement. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness, VL: vitreous length; AL: axial length.

Figure 6

Bland–Altman plots of the difference between the two repeated measurements using both automatic (red) and manual method (blue) of full eye axial biometry in 37 adult subjects. The full eye axial biometry included the central corneal thickness, the anterior chamber depth, the lens thickness, the vitreous length and the axial length. Values on the horizontal axis correspond to the mean of the two measurements. Values on the vertical axis correspond to the difference of two measurements. Solid lines and dashed lines indicate mean differences and 95% limits of agreement. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness, VL: vitreous length; AL: axial length.

Figure 6

Bland–Altman plots of the difference between the two repeated measurements using both automatic (red) and manual method (blue) of full eye axial biometry in 37 adult subjects. The full eye axial biometry included the central corneal thickness, the anterior chamber depth, the lens thickness, the vitreous length and the axial length. Values on the horizontal axis correspond to the mean of the two measurements. Values on the vertical axis correspond to the difference of two measurements. Solid lines and dashed lines indicate mean differences and 95% limits of agreement. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness, VL: vitreous length; AL: axial length.

Figure 6

Bland–Altman plots of the difference between the two repeated measurements using both automatic (red) and manual method (blue) of full eye axial biometry in 37 adult subjects. The full eye axial biometry included the central corneal thickness, the anterior chamber depth, the lens thickness, the vitreous length and the axial length. Values on the horizontal axis correspond to the mean of the two measurements. Values on the vertical axis correspond to the difference of two measurements. Solid lines and dashed lines indicate mean differences and 95% limits of agreement. CCT: central corneal thickness; ACD: anterior chamber depth; LT: lens thickness, VL: vitreous length; AL: axial length.

Figure 7

Correlations of the axial lengths obtained with ultra-long scan depth optical coherence tomography and IOLMaster. The data were obtained from the 12 subjects of Group 2. Strong correlation of axial length was obtained by ultra-long scan depth optical coherence tomography using the automatic method and by IOLMaster (Red, R₁² = 0.987, P < .05). Strong correlation of axial length was obtained by ultra-long scan depth optical coherence tomography using the manual method and by IOLMaster (Blue, R₂² = 0.988, P < .05).