Long scan depth optical coherence tomography on imaging accommodation: impact of enhanced axial resolution, signal-to-noise ratio and speed

Background:Spectral domain optical coherence tomography(SD-OCT)was a useful tool to study accommodation in human eye,but the maximum image depth is limited due to the decreased signal-to-noise ratio(SNR).In this study,improving optical resolutions,speeds and the SNR were achieved by custom built SD-OCT,and the evaluation of the impact of the improvement during accommodation was investigated.Methods:Three systems with different spectrometer designs,including two Charge Coupled Device(CCD)cameras and one Complementary Metal-Oxide-Semiconductor Transistor(CMOS)camera,were tested.We measured the point spread functions of a mirror at different positions to obtain the axial resolution and the SNR of three OCT systems powered with a light source with a 50 nm bandwidth,centered at a wavelength of 840 nm.Two normal subjects,aged 26 and 47,respectively,and one 75-year-old patient with an intraocular lens implanted were imaged.Results:The results indicated that spectrometers using cameras with 4096 camera pixels optimized the axial resolutions,due to the use of the full spectrum provided by the light source.The CCD camera system with 4096 pixels had the highest SNR and the best image quality.The system with the CMOS camera with 4096 pixels had the highest speed but had a compromised SNR compared to the CCD camera with 4096 pixels.Conclusions:Using these three OCT systems,we imaged the anterior segment of the human eye before and after accommodation,which showed similar results among the different systems.The system using the CMOS camera with an ultra-long scan depth,high resolution and high scan speed exhibited the best overall performance and therefore was recommended for imaging real-time accommodation.

Modeling of gonioscopic anterior chamber angle grades based on anterior segment optical coherence tomography

Background:To quantitatively assess anterior chamber angle(ACA)structure by anterior segment optical coherence tomography(AS-ocT)and develop a model to evaluate angle width as defined by gonioscopy.Methods:The ACAs of each quadrant were evaluated by gonioscopy,classified by the Scheie grading system,and assigned into one of the three grades:small angle(SA),moderate angle(MA),and large angle(LA).The eyes were imaged by AS-OCT,and ACA structural parameters including angle opening distance at the scleral spur(AODSS)and at 750μm anterior to the scleral spur(AOD750),trabecular-iris space area at 750μm anterior to the scleral spur(TISA750),and a newly defined parameter"light intersection distance"(LID),were measured.The ACA structural data were used to construct an ordered logistic regression model for assignment of ACAs to one of the three angle grades.The validity of the model was then tested.Results:A total of 169 quadrants from 53 subjects were included in the analysis,of which 111 quadrants were included in the modeling data and 58 in the testing data.In pairwise comparisons of SA,MA,and LA by ANOVA,the measured parameters were as follows:AOD750(0.174±0.060 vs.0.249±0.068 vs.0.376±0.114 mm;P<0.001),TISA750(0.075±0.035 vs.0.117±0.036 vs.0.181±0.062 mm^(2);P<0.001),and LID(0.300±0.187 vs.0.085±0.170 vs.0.122±0.156 mm;P<0.001).The ACA grading model based on LID showed a relatively high correction rate of 72.4%,and the model efficiency,calculated using the receiver operating characteristic,showed an area under the curve of 0.740.Weighted kappa statistics showed a good agreement for multiple ACA grades(0.772).Conclusions:The AS-OCT-based multiple ACA grades model was demonstrated as a non-contact approach for ACA assessment with high speed and high spatial resolution,providing guidance for diagnosis of angle closure.

Modeling of gonioscopic anterior chamber angle grades based on anterior segment optical coherence tomography

Background:To quantitatively assess anterior chamber angle(ACA)structure by anterior segment optical coherence tomography(AS-OCT)and develop a model to evaluate angle width as defined by gonioscopy.Methods:The ACAs of each quadrant were evaluated by gonioscopy,classified by the Scheie grading system,and assigned into one of the three grades:small angle(SA),moderate angle(MA),and large angle(LA).The eyes were imaged by AS-OCT,and ACA structural parameters including angle opening distance at the scleral spur(AODSS)and at 750μm anterior to the scleral spur(AOD750),trabecular-iris space area at 750μm anterior to the scleral spur(TISA750),and a newly defined parameter“light intersection distance”(LID),were measured.The ACA structural data were used to construct an ordered logistic regression model for assignment of ACAs to one of the three angle grades.The validity of the model was then tested.Results:A total of 169 quadrants from 53 subjects were included in the analysis,of which 111 quadrants were included in the modeling data and 58 in the testing data.In pairwise comparisons of SA,MA,and LA by ANOVA,the measured parameters were as follows:AOD750(0.174±0.060 vs.0.249±0.068 vs.0.376±0.114 mm;P<0.001),TISA750(0.075±0.035 vs.0.117±0.036 vs.0.181±0.062 mm^(2);P<0.001),and LID(−0.300±0.187 vs.-0.085±0.170 vs.0.122±0.156 mm;P<0.001).The ACA grading model based on LID showed a relatively high correction rate of 72.4%,and the model efficiency,calculated using the receiver operating characteristic,showed an area under the curve of 0.740.Weighted kappa statistics showed a good agreement for multiple ACA grades(0.772).Conclusions:The AS-OCT-based multiple ACA grades model was demonstrated as a non-contact approach for ACA assessment with high speed and high spatial resolution,providing guidance for diagnosis of angle closure.