Distortion Correction of Visante Optical Coherence Tomography Cornea Images

Time-Serial Evaluation of the Development and Treatment of Myopia in Mice Eyes Using OCT and ZEMAX

Myopia is a significant cause of visual impairment which may lead to many complications. However, the understanding of the mechanisms of myopia is still limited. In this paper, in order to investigate the development and the treatment of myopia, we analyzed the biological structure parameters of mice eyes, obtained from optical coherence tomography (OCT), and the optical performance of mice eyes calculated using ZEMAX software (ZEMAX Development Corporation, Kirkland, WA, USA) in which the optical model was built on the segment-by-segment optically corrected OCT 3D-images. Time-serial evaluation of three groups of mice eyes (form-deprivation myopia mice eyes, normal mice eyes, and atropine-treated myopia mice eyes) was performed. In addition to the biological structure parameters, imaging performance with the development of root-mean-square wavefront aberration at six filed angles was compared and analyzed. Results show that the biological structure parameters of the eye are closely related to the development of myopia. The peripheral defocus of the retina has a significant impact on inducing myopia, which verifies the new theory of myopia development. The delaying effect of atropine solution on myopia development is shown to verify the therapeutic effect of the medicine. This study provides technical support for the investigation of the myopia mechanism.

CLEAR - Scleral lenses

Scleral lenses were the first type of contact lens, developed in the late nineteenth century to restore vision and protect the ocular surface. With the advent of rigid corneal lenses in the middle of the twentieth century and soft lenses in the 1970's, the use of scleral lenses diminished; in recent times there has been a resurgence in their use driven by advances in manufacturing and ocular imaging technology. Scleral lenses are often the only viable form of contact lens wear across a range of clinical indications and can potentially delay the need for corneal surgery. This report provides a brief historical review of scleral lenses and a detailed account of contemporary scleral lens practice including common indications and recommended terminology. Recent research on ocular surface shape is presented, in addition to a comprehensive account of modern scleral lens fitting and on-eye evaluation. A range of optical and physiological challenges associated with scleral lenses are presented, including options for the clinical management of a range of ocular conditions. Future applications which take advantage of the stability of scleral lenses are also discussed. In summary, this report presents evidence-based recommendations to optimise patient outcomes in modern scleral lens practice.

Age-related Changes in Crystalline Lens Tilt and Decentration: A Swept-source Optical Coherence Tomography Study

Purpose

To investigate the age-related tilt and decentration of crystalline lenses using a swept-source optical coherence tomography biometer (Casia 2, TOMEY, Japan).

Setting

Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China.

Design

Cross-sectional study.

Methods

The direction and magnitude of the crystalline lens were evaluated in 230 participants with ages ranging from 7 to 90 years using swept-source optical coherence tomography. The participants were divided into four age groups, and the differences among the groups were analyzed. Multiple linear regression was used to investigate the main factors influencing crystalline lens tilt and decentration.

Results

The natural crystalline lens tilted towards the inferotemporal direction with a mean magnitude of 4.3+/-1.5[degrees] (range 0.7-8.95[degrees]). The average decentration toward the superotemporal direction was 0.17+/-0.12 mm (range 0.03-1.15 mm). There was mirror symmetry between the right and left eyes. There were significant differences in the crystalline lens tilt and decentration among the age groups. Multiple linear regression showed that changes in crystalline lens tilt depended on angle [alpha] (p<.01) and anterior chamber depth (ACD; P=.008), while crystalline lens decentration depended on angle [kappa] (P=.003), age (P<.01), and angle [alpha] (P=.002).

Conclusions

Although there was a significant difference in crystalline lens tilt and decentration among age groups, the variation in the crystalline lens position was partially affected by age. The crystalline lens tilt was greater in eyes with wider angle [alpha] and shallower ACD, while crystalline lens decentration was greater in younger eyes with wider angles [kappa] and [alpha].

Detection of refractive photokeratectomy traces during eye banking: impossible with organ culture but possible with an active storage machine: case report

The detection of corneas operated on for refractive surgery [LASIK or photorefractive keratectomy (PRK)] will become a major concern for eye banks in the coming years because this surgery is often forgotten during the interview with the deceased's relatives. We present here 2 corneas operated on with PKR and stored successively in organ culture (OC) and in the active storage machine (ASM) that restores intraocular pressure, restores the cornea to its original shape, respects transparency and incorporates non-invasive controls. The 2 corneas of a 49-year-old donor operated 17 years earlier by PRK for -2 and -3 diopters myopia were stored in OC for 14 days and then placed in ASM for 48 h. Thickness map and OCT topography were performed under the 2 storage conditions, histology and electron microscopy were then performed. Traces of PRK remained unnoticed in OC while they were evident in ASM with central epithelial anomaly, central thinning and flattening of central keratometry shown by OCT. Histology and ultrastructure confirmed the absence of Bowman's membrane in the center. By placing the cornea under physiological conditions, and in particular by triggering its deswelling and by restoring its natural curvature, the ASM allows effective detection of subtle refractive surgery traces like those present after PRK.

Experimental Model of Far Temporal Field Negative Dysphotopsia Generated in Phakic Eyes

Purpose

The axial separation between the iris and the intraocular lens (IOL) in pseudophakic eyes can cause rays originating from the far temporal field to miss the IOL, resulting in negative dysphotopsia (ND). We developed an experimental model to test the hypothesis that obstruction of rays from the far temporal field can generate ND and an accompanying loss of visual sensitivity in the far temporal field.

Methods

The right eyes of 10 phakic subjects were fitted with soft contact lenses containing a 5.50-mm central clear zone and a 12-mm outer diameter opaque annulus. In three of the subjects, eyes were dilated with 1% tropicamide solution, and effective aperture diameters were determined optically (pupil camera) and psychophysically (narrow beam detection). Visual field extent (Goldmann bowl) and temporal and inferotemporal meridian sensitivities (Octopus perimeter) were measured. A wide-angle model was constructed to quantify the impact of the annular opacity on retinal illuminance.

Results

All 10 subjects observed a dark crescent in the far temporal and inferotemporal fields. The opaque annulus reduced effective horizontal pupil diameters from 8 mm to 5.5 mm on-axis and from >2 mm to <1 mm at 90°. Perimetry revealed a 10° reduction in temporal and inferotemporal field extent and increasing loss of sensitivity beyond 70°. The wide-angle model confirmed significant vignetting (>50% beyond 70°), approaching zero retinal illuminance beyond 85°.

Conclusions

Vignetting of rays originating from the far temporal field by axially separated apertures can create symptoms mirroring perceptual reports of negative dysphotopsia in symptomatic pseudophakic patients.

Optical coherence tomography and scleral contact lenses: clinical and research applications

Anterior segment optical coherence tomography (OCT) provides a wealth of opportunities for modern contact lens practice. OCT imaging has numerous clinical and research applications related to the tear film, cornea, conjunctiva, sclera and ocular adnexae, in addition to soft, rigid, and hybrid contact lenses. This review summarises the potential use of OCT imaging in modern scleral contact lens practice including initial lens selection, assessing the scleral contact lens fit with respect to the cornea and sclera, and accurately quantifying the ocular response to lens wear. Recent advances in the understanding of anterior segment metrics including scleral thickness, curvature, toricity, and the anatomy of the corneoscleral limbal junction are also discussed.

Accuracy and Repeatability of an Anterior Segment Swept-Source Optical Coherence Tomographer

OBJECTIVES

To assess accuracy and repeatability of the CASIA swept-source optical coherence tomographer (SS-OCT) in measuring contact lens (CL) radii of curvature and thicknesses compared with verified CL parameters and to investigate intrasession and intersession repeatability of the CASIA SS-OCT in measuring epithelial and total corneal thicknesses.

METHODS

Rigid CLs with varying radii of curvature (front, rf; back, rb) and thicknesses were imaged with the CASIA SS-OCT across two sessions. Contact lens parameters were measured from processed images using an automated MATLAB program and were compared with parameters verified using standard techniques. Central epithelial and total corneal thicknesses of 43 normal subjects were measured to assess intrasession and intersession repeatability of the CASIA SS-OCT.

RESULTS

No significant differences (P>0.05) were found in rigid CL rf and central and peripheral thickness measurements compared with verified CL parameters. However, the rb values obtained from the CASIA SS-OCT were consistently 0.2 mm flatter than the verified rb values (P<0.001) along horizontal and vertical meridians. Bland-Altman analysis revealed excellent intrasession agreement with mean differences of 0.004 and 0.003 mm for rf and rb, 0.000 mm for CL thickness and 0.372 and 0.395 μm for epithelial and total corneal thicknesses, respectively. Similarly, mean intersession differences of 0.020 and 0.000 mm for rf and CL thickness and 0.100 and 0.984 μm for epithelial and total corneal thicknesses were found, respectively. Ninety-five percentage confidence intervals across one or two sessions indicated insignificant undermeasurement or overmeasurement for CL rf, and corneal thicknesses, but significant bias toward overmeasurement for CL rb was found across two sessions.

CONCLUSIONS

The CASIA SS-OCT produces accurate measurements of CL parameters compared with verified values. Inbuilt distortion correction in this instrument necessitated no further correction of scanned images and provided high intrasession and intersession repeatability in measuring both CLs and corneal thicknesses. Further investigation of discrepancies in rb measurements is warranted.

Predicting Accommodative Response Using Paraxial Schematic Eye Models

PURPOSE

Previous ultrasound biomicroscopy (UBM) studies showed that accommodative optical response (AOR) can be predicted from accommodative biometric changes in a young and a pre-presbyopic population from linear relationships between accommodative optical and biometric changes, with a standard deviation of less than 0.55D. Here, paraxial schematic eyes (SE) were constructed from measured accommodative ocular biometry parameters to see if predictions are improved.

METHODS

Measured ocular biometry (OCT, A-scan, and UBM) parameters from 24 young and 24 pre-presbyopic subjects were used to construct paraxial SEs for each individual subject (individual SEs) for three different lens equivalent refractive index methods. Refraction and AOR calculated from the individual SEs were compared with Grand Seiko (GS) autorefractor measured refraction and AOR. Refraction and AOR were also calculated from individual SEs constructed using the average population accommodative change in UBM measured parameters (average SEs).

RESULTS

Schematic eye calculated and GS measured AOR were linearly related (young subjects: slope = 0.77, r = 0.86; pre-presbyopic subjects: slope = 0.64, r = 0.55). The mean difference in AOR (GS - individual SEs) for the young subjects was -0.27D and for the pre-presbyopic subjects was 0.33D. For individual SEs, the mean ± SD of the absolute differences in AOR between the GS and SEs was 0.50 ± 0.39D for the young subjects and 0.50 ± 0.37D for the pre-presbyopic subjects. For average SEs, the mean ± SD of the absolute differences in AOR between the GS and the SEs was 0.77 ± 0.88D for the young subjects and 0.51 ± 0.49D for the pre-presbyopic subjects.

CONCLUSIONS

Individual paraxial SEs predict AOR, on average, with a standard deviation of 0.50D in young and pre-presbyopic subject populations. Although this prediction is only marginally better than from individual linear regressions, it does consider all the ocular biometric parameters.