Posterior Lens Radii Research Articles

Age-related changes in geometry and transparency of human crystalline lens revealed by optical signal discontinuity zones in swept-source OCT images

BackgroundThe shape and microstructure of the human crystalline lens alter with ageing, and this has an effect on the optical properties of the eye. The aim of this study was to characterise the age-related differences in the morphology and transparency of the eye lenses of healthy subjects through the optical signal discontinuity (OSD) zones in optical coherence tomography (OCT) images. We also investigated the association of those changes with the optical quality of the eye and visual function.MethodsOCT images of the anterior segment of 49 eyes of subjects (9–78 years) were acquired, and the OSD zones (nucleus, C1–C4 cortical zones) were identified. Central thickness, curvature and optical density were measured. The eye’s optical quality was evaluated by the objective scatter index (OSI). Contrast sensitivity and visual acuity tests were performed. The correlation between extracted parameters and age was assessed.ResultsThe increase in lens thickness with age was dominated by the thickening of the cortical zone C3 (0.0146 mm/year). The curvature radii of the anterior lens surface and both anterior and posterior nucleo-cortical interfaces decreased with age (− 0.053 mm/year, − 0.013 mm/year and − 0.006 mm/year, respectively), and no change was observed for the posterior lens radius. OCT-based densitometry revealed significant correlations with age for all zones except for C1β, and the highest increase in density was in the C2–C4 zones (R = 0.45, 0.74, 0.56, respectively, P < 0.001). Increase in OSI was associated with the degradation of visual function.ConclusionsOCT enables the identification of OSD zones of the crystalline lens. The most significant age-related changes occur in the C3 zone as it thickens with age at a faster rate and becomes more opaque than other OSD zones. The changes are associated with optical quality deterioration and reduction of visual performance. These findings contribute to a better understanding of the structure–function relationship of the ageing lens and offer insights into both pathological and aging alterations.

Interocular difference in crystalline lens morphology in children and adolescents with unilateral high myopia

PurposeTo investigate the between-eye differences of the crystalline lens in subjects with unilateral high myopia and assess its contribution to the interocular refractive error disparity. MethodsChildren and adolescents with unilateral high myopia, defined as cycloplegic spherical equivalent (SE) ≤ −5D in one eye and ≥ −3D in the other eye, were recruited. Ocular biometric parameters, including axial length (AL) and lens thickness (LT), were measured by IOLMaster 700. Other lens-related parameters, including anterior lens radius of curvature (ALR) and posterior lens radius of curvature (PLR), were measured by CASIA2 swept-source optical coherence tomography. Lens power (LP) was calculated using Bennett’s formula. Paired t-test was used to assess the between-eye difference in biometric parameters, and multiple regression analysis was used to assess factors associated with the between-eye SE difference. ResultsNinety-one participants (6–18 years of age; 52.75% girls) were included. The highly myopic eyes showed significantly lower LP (P < 0.001) and smaller ALR (P < 0.001) than the contralateral eyes, while no significant difference was found in central LT. In both eyes, ALR was significantly related to SE (P = 0.001 and P = 0.006, respectively); while LT was not associated with SE (P = 0.051 and P = 0.052, respectively). Paired-eye analysis showed that the between-eye difference in ALR was the only lenticular parameter significantly associated with the between-eye difference in SE (P = 0.005). ConclusionIn highly myopic eyes, the crystalline lens reduced total power but morphologically changed to a more curved shape without significant lens thinning, suggesting that the LP loss is mainly achieved by reducing its internal power in high myopes.

Lens Biometry in Congenital Lens Deformities: A Swept-Source Anterior Segment OCT Analysis.

Aims: To investigate the lens biometric parameters in congenital lens deformities, using a novel technique of swept-source anterior segment optical coherence tomography (SS-ASOCT).Methods: This prospective study included patients with microspherophakia (MSP), coloboma lentis (CL), and posterior lenticonus (PL). For this cohort, 360-degree high-resolution lens images were obtained using the latest SS-ASOCT (CASIA2, Tomey Corp, Nagoya, Japan). The lens biometric parameters were calculated by the CASIA2 built-in software for anterior lens radius (ALR), posterior lens radius (PLR), anteroposterior distance (APD), anterior chamber depth (ACD), equatorial diameter (Eq Dia), rear projection length (RPL), and maximum diameter of the lesion (MDL).Results: This study included two eyes each with MSP and CL and one eye with PL. The lens of MSP was spherical and posteriorly dislocated, with decreased ALR and PLR, Eq Dia, but increased APD. In patients with CL, the coloboma was isolated, bilateral, inferior, and located toward the maldeveloped ciliary body. High astigmatism was mainly lenticular, and this was calculated by the ALR and PLR. Regarding the site of coloboma, a significant decrease in ALR was observed, while the PLR and APD were not affected. The PL eyes had a cone-shaped protrusion of the posterior lens surface with a subtle cataractous region around the apex. An extremely high posterior surface curvature was observed with a mean PLR of 1.67 mm. The RPL and MDL were about 1.80 and 0.4 mm, respectively, which were homogenous at different sections.Conclusions: The CASIA2 is a valuable option for in vivo crystalline lens measurement for congenital lens deformities, enabling the accurate diagnosis and providing illuminating insights into the pathogenesis of MSP, CL, and PL

Three-dimensional OCT based guinea pig eye model: relating morphology and optics.

Custom Spectral Optical Coherence Tomography (SOCT) provided with automatic quantification and distortion correction algorithms was used to measure the 3-D morphology in guinea pig eyes (n = 8, 30 days; n = 5, 40 days). Animals were measured awake in vivo under cyclopegia. Measurements showed low intraocular variability (<4% in corneal and anterior lens radii and <8% in the posterior lens radii, <1% interocular distances). The repeatability of the surface elevation was less than 2 µm. Surface astigmatism was the individual dominant term in all surfaces. Higher-order RMS surface elevation was largest in the posterior lens. Individual surface elevation Zernike terms correlated significantly across corneal and anterior lens surfaces. Higher-order-aberrations (except spherical aberration) were comparable with those predicted by OCT-based eye models.

Objective measurement of accommodative biometric changes using ultrasound biomicroscopy

To demonstrate that ultrasound biomicroscopy (UBM) can be used for objective quantitative measurements of anterior segment accommodative changes. College of Optometry, University of Houston, Houston, Texas, USA. Prospective cross-sectional study. Anterior segment biometric changes in response to 0 to 6.0 diopters (D) of accommodative stimuli in 1.0 D steps were measured in eyes of human subjects aged 21 to 36 years. Imaging was performed in the left eye using a 35 MHz UBM (Vumax) and an A-scan ultrasound (A-5500) while the right eye viewed the accommodative stimuli. An automated Matlab image-analysis program was developed to measure the biometry parameters from the UBM images. The UBM-measured accommodative changes in anterior chamber depth (ACD), lens thickness, anterior lens radius of curvature, posterior lens radius of curvature, and anterior segment length were statistically significantly linearly correlated with accommodative stimulus demands. Standard deviations of the UBM-measured parameters were independent of the accommodative stimulus demands (ACD: 0.0176 mm; lens thickness: 0.0294 mm; anterior lens radius of curvature: 0.3350 mm; posterior lens radius of curvature: 0.1580 mm; and anterior segment length: 0.0340 mm). The mean difference between the A-scan and UBM measurements was -0.070 mm for ACD and 0.166 mm for lens thickness. Accommodating phakic eyes imaged using UBM allowed visualization of the accommodative response, and automated image analysis of the UBM images allowed reliable, objective, quantitative measurements of the accommodative intraocular biometric changes. Neither author has a financial or proprietary interest in any material or method mentioned.

In vivo human crystalline lens topography

Custom high-resolution high-speed anterior segment spectral domain optical coherence tomography (OCT) was used to characterize three-dimensionally (3-D) the human crystalline lens in vivo. The system was provided with custom algorithms for denoising and segmentation of the images, as well as for fan (scanning) and optical (refraction) distortion correction, to provide fully quantitative images of the anterior and posterior crystalline lens surfaces. The method was tested on an artificial eye with known surfaces geometry and on a human lens in vitro, and demonstrated on three human lenses in vivo. Not correcting for distortion overestimated the anterior lens radius by 25% and the posterior lens radius by more than 65%. In vivo lens surfaces were fitted by biconicoids and Zernike polynomials after distortion correction. The anterior lens radii of curvature ranged from 10.27 to 14.14 mm, and the posterior lens radii of curvature ranged from 6.12 to 7.54 mm. Surface asphericities ranged from −0.04 to −1.96. The lens surfaces were well fitted by quadrics (with variation smaller than 2%, for 5-mm pupils), with low amounts of high order terms. Surface lens astigmatism was significant, with the anterior lens typically showing horizontal astigmatism ( ranging from −11 to −1 µm) and the posterior lens showing vertical astigmatism ( ranging from 6 to 10 µm).

Crystalline lens radii of curvature from Purkinje and Scheimpflug imaging

We present a comparison between measurements of the radius of the anterior and posterior lens surface, which was performed using corrected Scheimpflug imaging and Purkinje imaging in the same group of participants (46 for the anterior lens, and 34 for the posterior lens). Comparisons were also made as a function of accommodation (0 to 7 D) in a subset of 11 eyes. Data were captured and processed using laboratory prototypes and custom processing algorithms [for optical and geometrical distortion correction in the Scheimpflug system and using either equivalent mirror (EM) or merit function (MF) methods for Purkinje]. We found statistically significant differences in 4 of 46 eyes for the anterior lens radius, and 10 of 34 eyes for the posterior radius (using the MF and individual biometric data to process the Purkinje images). For the anterior lens, the agreement increases using individual biometry as opposed to biometric data from a model eye. For the posterior lens, the agreement increases using the MF as opposed to the EM method. For the changes during accommodation, no significant difference between the two techniques was found. In conclusion, the results of the cross-validation using the Scheimpflug and Purkinje imaging technique show that both techniques provide comparable lens radii and similar changes with accommodation. Purkinje tends to overestimate posterior lens radius, whereas pupil size limits the acquisition of posterior lens data with the Scheimpflug camera. Computer simulations using the Scheimpflug data as input show that the consistent slight overestimation of the posterior lens radius using Purkinje imaging can be partly attributed to the asphericity of the lens surface.

The shape of the aging human lens: curvature, equivalent refractive index and the lens paradox

Scheimpflug slit images of the crystalline lens are distorted due to the refracting properties of the cornea and because they are obliquely viewed. We measured the aspheric curvature of the lens of 102 subjects ranging in age between 16 and 65 years and applied correction for these distortions. The procedure was validated by measuring an artificial eye and pseudophakic patients with intraocular lenses of known dimensions. Compared to previous studies using Scheimpflug photography, the decrease of the radius of the anterior lens surface with age was smaller, and the absolute value for the radius of the anterior and posterior lens surface was significantly smaller. A slight decrease of the posterior lens radius with age could be demonstrated. Generally, front and back surfaces were hyperbolic. Axial length was measured of 42 subjects enabling calculation of the equivalent refractive index of the lens, which showed a small, but highly significant decrease with age. These new findings explain the lens paradox and may serve as a basis for modelling the refractive properties of the lens.

Crystalline lens parameters in infancy

Despite the importance of lens power to ocular development, few data are available regarding infant crystalline lens parameters. Lens and corneal radii of curvature were measured in the horizontal meridian using a video-based keratophakometer, and refractive error was measured by cycloplegic retinoscopy in 19 out of 27 infants ranging in age from 3 to 18 months. The median refractive error was +1.50 D, and the median corneal power was 43.5 D. Using previously reported values for axial ocular dimensions, the median anterior and posterior lens radii of curvature were 8.7 and 5.6 mm, respectively, both substantially flatter than infant schematic eye values. The median equivalent refractive index of the lens was 1.49, considerably higher than previous reported schematic values for infants or children. There was a significant reduction in hyperopia with age (r = −0.47, P = 0.043), but no age-related trends in lens or corneal radii of curvature, suggesting that calculated values for lens power and equivalent index may undergo substantial decline with age during early childhood development as axial length increases. Most of the decrease in lens power (75%) may be due to decreases in equivalent index rather than to flattening of the surface radii of curvature. Videophakometry appears to be a feasible and useful technique for documenting the role of the crystalline lens in infant ocular development.

Crystalline lens parameters in infancy

Despite the importance of lens power to ocular development, few data are available regarding infant crystalline lens parameters. Lens and corneal radii of curvature were measured in the horizontal meridian using a video-based keratophakometer, and refractive error was measured by cycloplegic retinoscopy in 19 out of 27 infants ranging in age from 3 to 18 months. The median refractive error was +1.50 D, and the median corneal power was 43.5 D. Using previously reported values for axial ocular dimensions, the median anterior and posterior lens radii of curvature were 8.7 and 5.6 mm, respectively, both substantially flatter than infant schematic eye values. The median equivalent refractive index of the lens was 1.49, considerably higher than previous reported schematic values for infants or children. There was a significant reduction in hyperopia with age (r = -0.47, P = 0.043), but no age-related trends in lens or corneal radii of curvature, suggesting that calculated values for lens power and equivalent index may undergo substantial decline with age during early childhood development as axial length increases. Most of the decrease in lens power (75%) may be due to decreases in equivalent index rather than to flattening of the surface radii of curvature. Videophakometry appears to be a feasible and useful technique for documenting the role of the crystalline lens in infant ocular development.