Imaging and full-length biometry of the eye during accommodation using spectral domain OCT with an optical switch.

An optical switch was implemented in the reference arm of an extended depth SD-OCT system to sequentially acquire OCT images at different depths into the eye ranging from the cornea to the retina. A custom-made accommodation module was coupled with the delivery of the OCT system to provide controlled step stimuli of accommodation and disaccommodation that preserve ocular alignment. The changes in the lens shape were imaged and ocular distances were dynamically measured during accommodation and disaccommodation. The system is capable of dynamic in vivo imaging of the entire anterior segment and eye-length measurement during accommodation in real-time.

Postnatal elongation of eye size in DBA/2J mice compared with C57BL/6J mice: in vivo analysis with whole-eye OCT.

PURPOSE: To characterize postnatal changes in eye size in glaucomatous DBA/2J (D2) mice and in nonglaucomatous C57BL/6J mice (B6) in vivo by means of whole-eye optical coherence tomography (OCT). METHODS: D2 (n = 32) and B6 (n = 36) mice were tested between 2 and 20 months of age in eight age bins. A custom time-domain OCT system with a center wavelength of 825 nm and an axial scan length of 7.1 mm produced axial A-scan interferograms at a rate of 20 A-lines/s with a resolution of 8 µm. Axial length (AL), corneal thickness (CT), anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and retinal thickness (RT) were measured in the optical axis and adjusted with corresponding refractive indices. Corneal curvature (CC) and IOP were also measured. RESULTS: AL increased (P < 0.001) more in the D2 (21%) than in the B6 (9%) mice. There was an interaction effect (two-way ANOVA, P < 0.001) between age and strain for AL, CT, ACD, and VCD. In the D2 mice, the lens became dislocated posteriorly. Multiple regression analysis in the D2 mice revealed an independent effect of age and IOP (P ≤ 0.01) on axial length. CC steepened in the older D2 mice, whereas it flattened in the B6 mice. CONCLUSIONS: In D2 mice, postnatal elongation of AL is larger than that in B6 mice and is associated with a greater increase in ACD and IOP, which seems to be a causal factor. The ease of use, short acquisition time, and noninvasiveness of whole-eye OCT make it suitable for routine use in longitudinal studies of mouse models.

Intraoperative OCT of a full-thickness macular hole before and after internal limiting membrane peeling.

A child with a traumatic full-thickness macular hole was imaged perioperatively using spectral-domain optical coherence tomography (SD-OCT). Intraoperative imaging using a portable SD-OCT device equipped with a handheld probe demonstrated the full-thickness macular hole to be nearly completely closed following vitrectomy and internal limiting membrane peeling. Air was used as a tamponade agent and prone positioning was used postoperatively for 2 days. SD-OCT imaging confirmed closure of the full-thickness macular hole 5 days and 1 month postoperatively.

Refractive index measurement of the isolated crystalline lens using optical coherence tomography.

An optical coherence tomography system has been developed that was designed specifically for imaging the isolated crystalline lens. Cross-sectional OCT images were recorded on 40 lenses from 32 human donors with an age range of 6-82 years. A method has been developed to measure the axial thickness and average refractive index of the lens from a single recorded image. The measured average group refractive index at the measurement wavelength of 825 nm was converted to the average phase refractive index at 589 nm using lens dispersion data from the literature. The average refractive index for all lenses measured was 1.408+/-0.005 which agrees well with recent MRI measurements of the lens index gradient. A linear regression of the data resulted in a statistically significant decrease in the average refractive index with age, but a simple linear model was insufficient to explain the age dependence. The results presented here suggest that the peak refractive index in the nucleus is closer to 1.420, rather than the previously accepted value of 1.406.

Simultaneous fundus imaging and optical coherence tomography of the mouse retina.

PURPOSE: To develop a retinal imaging system suitable for routine examination or screening of mouse models and to demonstrate the feasibility of simultaneously acquiring fundus and optical coherence tomography (OCT) images. METHODS: The imaging system is composed of a photographic slit lamp for biomicroscopic examination of the fundus, an OCT interferometer, an OCT beam delivery system designed for the mouse eye, and a mouse positioning stage. Image acquisition was controlled with software that displays the fundus and OCT images in real time, and allows the user to control the position of the OCT beam spot on the fundus image display. The anesthetized mouse was placed in a cylindrical holder on the positioning stage, and a single operator adjusted the position of mouse. RESULTS: Fundus images and OCT scans were successfully acquired in both eyes of 8 C57BL/6 mice. Once the animal is anesthetized and placed in the holder, a typical imaging experiment takes less than 2 minutes. The retinal vasculature, pigmentation, nerve fiber arrangement, and optic nerve head were clearly visible on the fundus images. The quality of the OCT images was sufficient to allow measurement of the total, inner, and outer retinal thicknesses and to visualize the optic nerve head excavation. CONCLUSIONS: The study demonstrates the feasibility of acquiring simultaneous fundus and OCT images of the mouse retina, by a single operator, in a manner suitable for routine evaluation of mouse models of retinal disease.

Noncontact optical measurement of lens capsule thickness in human, monkey, and rabbit postmortem eyes.

PURPOSE: To measure interspecies thickness differences in the central anterior and posterior capsules of postmortem crystalline lenses, by a technique that maintains the anatomic integrity of the lens. METHODS: Central capsule thickness was measured with a custom-built, noncontact optical system, using a focus detection technique. Anterior and posterior lens capsule thickness measurements were performed on 22 human, 29 monkey, and 34 New Zealand White rabbit intact postmortem lenses in situ. Eyes were prepared for optical measurements by bonding a PMMA ring to the sclera in the region of the ciliary body after the conjunctiva, adipose, and muscle tissues were removed. The posterior pole was removed by making a circumferential incision through the sclera approximately 7 mm posterior to the limbus. Excess vitreous was removed to expose the posterior capsule surface, and the eye assembly was placed on a Teflon slide. The cornea and iris were sectioned to expose the anterior capsule surface. After the experiments, the lenses were excised, placed in 10% buffered formalin, and prepared for histology. Lens capsule thickness was measured from the histologic slides and compared to the optical RESULTS: results. Central anterior lens capsule thickness was 8.2 +/- 5.5 (human), 7.5 +/- 4.4 (monkey), and 10.7 +/- 4.2 (rabbit) microm optically and 12.4 +/- 2.5 (human), 10.7 +/- 3.7 (monkey), and 10.4 +/- 2.0 (rabbit) microm histologically. Central posterior capsule thickness was 6.3 +/- 2.2 (human), 5.9 +/- 1.7 (monkey), and 7.8 +/- 2.3 (rabbit) microm optically and 4.1 +/- 1.5 (human), 3.5 +/- 1.6 (monkey), and 4.7 +/- 2.5 (rabbit) microm histologically. CONCLUSIONS: The central anterior and posterior lens capsule thicknesses do not appear to vary considerably among human, rabbit, and monkey eyes. There were significant differences between optical in situ measurements and histology, which indicates that histologic preparation may affect lens capsule thickness.