BACKGROUND: There are few reports regarding the influence of varying illumination on the compensation effect before and after corneal refractive surgery. We aimed to evaluate the changes in refraction, higher-order aberrations, and aberration compensation between mesopic and photopic illumination before and after small incision lenticule extraction.
METHODS: In this prospective cohort study, only the right eyes of patients who underwent small incision lenticule extraction for the correction of myopia and myopic astigmatism at the Tianjin Eye Hospital were included. Wavefront refraction and higher-order aberrations were measured preoperatively and 3 months postoperatively under mesopic and photopic illumination. Compensation factors were calculated as 1 - (aberration of the whole eye/aberration of the anterior corneal surface).
RESULTS: Forty patients undergoing small incision lenticule extraction were enrolled. All surgeries were completed without postoperative complications. Preoperatively, the eyes only had a statistically significantly higher (t = - 4.589, p < .001) spherical refractive error under mesopic vs. photopic illumination (median [interquartile range], - 6.146 [2.356] vs. - 6.030 [2.619] diopters [D]), whereas postoperatively, the eyes also exhibited statistically significantly higher (t = - 3.013, p = .005) astigmatism (- 0.608 [0.414] vs. - 0.382 [0.319] D). Differences in spherical refraction between the two illuminations were the highest in postoperative eyes (Δ > 0.5 D). Only postoperative eyes exhibited statistically significant elevations (t ≥ 4.081, p < .001) in higher-order aberrations under mesopic illumination, and only preoperative eyes exhibited statistically significantly enhanced (χ2 = 6.373, p = .01 for fourth-order and χ2 = 11.850, p = .001 for primary spherical aberrations) and decreased (χ2 = 13.653, p = .001 for horizontal trefoil) compensation factors under mesopic illumination.
CONCLUSIONS: Exaggerations in higher-order aberrations and myopic shift after small incision lenticule extraction became apparent under mesopic illumination. Slight undercorrection may have an enhanced effect under low illumination and may reduce night vision. The specific changes in compensation effects in preoperative eyes may improve optical quality under mesopic illumination. Postoperative eyes have reduced compensation ability, specifically for spherical aberrations, under mesopic illumination, which may diminish night vision. Further studies that include the measurement of subjective night vision parameters should be conducted.

Digital holographic microscopy is widely used to get the quantitative phase information of transparent cells.
However, the sample phase is superimposed with aberrations. To quantify the phase information, aberrations need to be fully compensated.
We propose a technique to obtain aberration-free phase imaging, using the derivative-based principal component analysis (dPCA).
With dPCA, almost all aberrations can be extracted and compensated without requirements on background segmentation, making it efficient and convenient.
It solves the problem that the conventional principal component analysis (PCA) algorithm cannot compensate the common but intricate higher order cross-term aberrations, such as astigmatism and coma. Moreover, the dPCA strategy proposed here is not only suitable for aberration compensation but also applicable for other cases where there exist cross-terms that cannot be analyzed with the PCA algorithm.

A method for numerical estimation and correction of aberrations of the eye in fundus imaging with optical coherence tomography (OCT) is presented. Aberrations are determined statistically by using the estimate based on likelihood function maximization. The method can be considered as an extension of the phase gradient autofocusing algorithm in synthetic aperture radar imaging to 2D optical aberration correction. The efficacy of the proposed method has been demonstrated in OCT fundus imaging with 6λ aberrations. After correction, single photoreceptors were resolved. It is also shown that wave front distortions with high spatial frequencies can be determined and corrected.

Fluorescence microendoscopy is becoming a standard technique in neuroscience for visualizing neuronal activity in the deep brain. Gradient refractive index (GRIN) lenses are increasingly used for fluorescence microendoscopy; however, they inherently suffer from strong aberrations and distortion. Aspherical lenses change their radius of curvature with distance from the optical axis and can effectively eliminate spherical aberrations. The use of these lenses has not been fully explored in deep brain fluorescence microendoscopy due to technical difficulties in manufacturing miniature aspherical lenses. In this study, we fabricated a novel microendoscope lens assembly comprised two nested pairs of aspherical microlenses made by precision glass molding. This assembly, which was 0.6 mm in diameter and 7.06 mm in length, was assembled in a stainless steel tube of 0.7 mm outer diameter. This assembly exhibited marked improvements in monochromatic and chromatic aberrations compared with a conventional GRIN lens, and is useful for deep brain fluorescence microendoscopy, as demonstrated by two-photon microendoscopic calcium imaging of R-CaMP1.07-labeled mouse hippocampal CA1 neurons. Our aspherical-lens-based approach offers a non-GRIN-lens alternative for fabrication of microendoscopic lenses.

Optical coherence tomography (OCT) catheters for intraluminal imaging are subject to various artifacts due to reference-sample arm dispersion imbalances and sample arm beam astigmatism. The goal of this work was to develop a probe that minimizes such artifacts.
Our probe was fabricated using a single mode fiber at the tip of which a glass spacer and graded index objective lens were spliced to achieve the desired focal distance. The signal was reflected using a curved reflector to correct for astigmatism caused by the thin, protective, transparent sheath that surrounds the optics. The probe design was optimized using Zemax, a commercially available optical design software. Common path interferometric operation was achieved using Fresnel reflection from the tip of the focusing graded index objective lens. The performance of the probe was tested using a custom designed spectrometer-based OCT system.
The probe achieved an axial resolution of 15.6 μm in air, a lateral resolution 33 μm, and a sensitivity of 103 dB. A scattering tissue phantom was imaged to test the performance of the probe for astigmatism correction. Images of the phantom confirmed that this common-path, astigmatism-corrected OCT imaging probe had minimal artifacts in the axial, and lateral dimensions.
In this work, we developed an astigmatism-corrected, common path probe that minimizes artifacts associated with standard OCT probes. This design may be useful for OCT applications that require high axial and lateral resolutions. Lasers Surg. Med. 49:312-318, 2017. © 2016 Wiley Periodicals, Inc.

In structure light measurement systems or 3D printing systems, the errors caused by optical distortion of a digital projector always affect the precision performance and cannot be ignored. Existing methods to calibrate the projection distortion rely on calibration plate and photogrammetry, so the calibration performance is largely affected by the quality of the plate and the imaging system. This paper proposes a new projector calibration approach that makes use of photodiodes to directly detect the light emitted from a digital projector. By analyzing the output sequence of the photoelectric module, the pixel coordinates can be accurately obtained by the curve fitting method. A polynomial distortion representation is employed to reduce the residuals of the traditional distortion representation model. Experimental results and performance evaluation show that the proposed calibration method is able to avoid most of the disadvantages in traditional methods and achieves a higher accuracy. This proposed method is also practically applicable to evaluate the geometric optical performance of other optical projection system.

Recent progress in retinal image acquisition techniques, including optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO), combined with improved performance of adaptive optics (AO) instrumentation, has resulted in improvement in the quality of in vivo images of cellular structures in the human retina. Here, we present a short review of progress on developing AO-OCT instruments. Despite significant progress in imaging speed and resolution, eye movements present during acquisition of a retinal image with OCT introduce motion artifacts into the image, complicating analysis and registration. This effect is especially pronounced in high-resolution datasets acquired with AO-OCT instruments. Several retinal tracking systems have been introduced to correct retinal motion during data acquisition. We present a method for correcting motion artifacts in AO-OCT volume data after acquisition using simultaneously captured adaptive optics-scanning laser ophthalmoscope (AO-SLO) images. We extract transverse eye motion data from the AO-SLO images, assign a motion adjustment vector to each AO-OCT A-scan, and re-sample from the scattered data back onto a regular grid. The corrected volume data improve the accuracy of quantitative analyses of microscopic structures.

Transmitted light holographic microscopy is particularly used for quantitative phase imaging of transparent microscopic objects such as living cells. The study of the cell is based on extraction of the dynamic data on cell behaviour from the time-lapse sequence of the phase images. However, the phase images are affected by the phase aberrations that make the analysis particularly difficult. This is because the phase deformation is prone to change during long-term experiments. Here, we present a novel algorithm for sequential processing of living cells phase images in a time-lapse sequence. The algorithm compensates for the deformation of a phase image using weighted least-squares surface fitting. Moreover, it identifies and segments the individual cells in the phase image. All these procedures are performed automatically and applied immediately after obtaining every single phase image. This property of the algorithm is important for real-time cell quantitative phase imaging and instantaneous control of the course of the experiment by playback of the recorded sequence up to actual time. Such operator\'s intervention is a forerunner of process automation derived from image analysis. The efficiency of the propounded algorithm is demonstrated on images of rat fibrosarcoma cells using an off-axis holographic microscope.