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(1) Background: Defining the optimum center for laser refractive corrections is difficult, with many of the available approaches having pros and cons. Decentered ablations result in undesirable side effects like halos, glare, monocular diplopia, and a reduction in visual acuity; (2) Methods: The ideal centration in refractive corrections should fulfil three requirements: covering a scotopic pupil; respecting the visual axis; and minimizing tissue removal. The implications of different centration strategies are discussed and shown graphically; (3) Results: Oversized asymmetric offset ablation faces fewer difficulties in registering static cyclotorsion, features less tissue wastage compared to a symmetric offset, and includes a certain amount of coma (and trefoil) in the profile, benefiting eyes with a pupil offset, which typically present with relevant amounts of coma and trefoil corneal aberrations due to decentered optics; (4) Conclusions: There is a need for a flexible choice of centration in refractive procedures to design customized and non-customized treatments optimally. An ideal optical zone covering the pupil with the widest entrance may be as important as a centration reference. [ABSTRACT FROM AUTHOR]

(1) Background: Defining the optimum center for laser refractive corrections is difficult, with many of the available approaches having pros and cons. Decentered ablations result in undesirable side effects like halos, glare, monocular diplopia, and a reduction in visual acuity; (2) Methods: The ideal centration in refractive corrections should fulfil three requirements: covering a scotopic pupil; respecting the visual axis; and minimizing tissue removal. The implications of different centration strategies are discussed and shown graphically; (3) Results: Oversized asymmetric offset ablation faces fewer difficulties in registering static cyclotorsion, features less tissue wastage compared to a symmetric offset, and includes a certain amount of coma (and trefoil) in the profile, benefiting eyes with a pupil offset, which typically present with relevant amounts of coma and trefoil corneal aberrations due to decentered optics; (4) Conclusions: There is a need for a flexible choice of centration in refractive procedures to design customized and non-customized treatments optimally. An ideal optical zone covering the pupil with the widest entrance may be as important as a centration reference.

The problem of 3D gaze estimation can be viewed as inferring the visual axes from eye images. It remains a challenge especially for the head-mounted gaze tracker (HMGT) with a simple camera setup due to the complexity of the human visual system. Although the mainstream regression-based methods could establish the mapping relationship between eye image features and the gaze point to calculate the visual axes, it may lead to inadequate fitting performance and appreciable extrapolation errors. Moreover, regression-based methods suffer from a degraded user experience because of the increased burden in recalibration procedures when slippage occurs between HMGT and head. To address these issues, a high-accuracy 3D gaze estimation method along with an efficient recalibration approach is proposed with head pose tracking in this paper. The two key parameters, eyeball center and camera optical center, are estimated in head frame with geometry-based method, so that a mapping relationship between two direction features is proposed to calculate the direction of the visual axis. As the direction features are formulated with the accurately estimated parameters, the complexity of mapping relationship could be reduced and a better fitting performance can be achieved. To prevent the noticeable extrapolation errors, direction features with uniform angular intervals for fitting the mapping are retrieved over human's field of view. Additionally, an efficient single-point recalibration method is proposed with an updated eyeball coordinate system, which reduces the burden of calibration procedures significantly. Our experiment results show that the calibration and recalibration methods could improve the gaze estimation accuracy by 35 percent (from a mean error of 2.00 degrees to 1.31 degrees) and 30 percent (from a mean error of 2.00 degrees to 1.41 degrees), respectively, compared with the state-of-the-art methods. [ABSTRACT FROM AUTHOR]

AIM: To evaluate the centration of the SBL-3 multifocal intraocular lens, the size of the distant and near power zone in the pupil area and the area of the visual axis using Itrace visual function analyzer. METHODS: Retrospective case study. From January 2018 to January 2019, 51 eyes of 36 patients underwent phacoemulsification cataract combined with regional refraction multifocal intraocular lens implantation at Beijing Aier-Intech Eye Hospital were enrolled. The centration, visual axis, angle α, angle Kappa and the orientation of the intraocular lens measured by Itrace were used to calculate the position of the visual axis in the intraocular lens and the changes in the proportions of the distant and near power zones in the pupil area. RESULTS: The centration(R)of intraocular lens is 0.217±0.09mm. The distribution of the visual axis in the intraocular lens is 0.217±0.09mm. The visual axis is evenly distributed in the distant and near power zones. There was no statistical significance between the two groups with postoperative visual acuity ≥0.8 and 0.05). The size of the angle Kappa is 0.187±0.079mm. The displacement of angle Kappa on the y-axis is 0.10±0.06mm. There was no statistical significance between the changes in the pupil size of distant and near power zones in the pupil area caused by the deviation of the pupil and the postoperative visual acuity ≥0.8 and 0.05). CONCLUSION: The intraocular lens centration and axial data measured by the Itrace visual function analyzer can be used to estimate the area where the visual axis is located and the size of the distant and near power zones in the pupil area, thereby assisting in evaluating the postoperative visual quality of the regional refraction multifocal intraocular lens implanted after cataract surgery.

The perception of individuals to the urban scenes at night is different from that of the day. The previous studies dealt with the subject of the night scene in terms of the effect of artificial lighting in the formation of the night scene and its ability to increase the quality and aesthetics of the scene that designed for night use, but this research deals with other factors. The research problem show itself as: There is a difference in the perception of the viewer at night during the day, where some scenes attract people at night while not attracted by the day and vice versa, while other scenes attract individuals day and night. regardless of the type and efficiency of the lighting used. And the aim of the research, is to study the impact of those characteristics at night where as the people perception differs in the night. The research assumed: the perception of night scene changes according to that visual axes, and the most influential factor in this change is the attraction that result from the presence of a land mark in the axis of motion that changes the characteristics of the visual axis between night and day. And between nightscape and another. The importance of research: is to determine the characteristics that make the scene acceptable to individuals through day and night, and limit some recommendations to hire those characteristics in order to increase the vitality of the urban environment and increase the efficiency of use. In order to achieve this, the research based on a methodology consist of a theoretical base include the explanation of concepts like (urban scene, night scene, visual perception, visual axis) in order to achieve this the research adapt the semantic measurement to measure the people perception of the scene, during the night and day periods of the same scenes, and then compare the results to analyze the differences between them and explore the reasons behind it. Research has found that the characteristics of the axis differ in terms of their impact on the people attraction, as the emergence of the landmarks at the end of the visual axis is the most influential attraction element to people at night. In the night scene people need to see the land marks in compared to the other elements to be able to complete their journey. And that people do not care about the start points as the end points in the journey, in the night compared to the daytime.

The problem of 3D gaze estimation can be viewed as inferring the visual axes from eye images. It remains a challenge especially for the head-mounted gaze tracker (HMGT) with a simple camera setup due to the complexity of the human visual system. Although the mainstream regression-based methods could establish the mapping relationship between eye image features and the gaze point to calculate the visual axes, it may lead to inadequate fitting performance and appreciable extrapolation errors. Moreover, regression-based methods suffer from a degraded user experience because of the increased burden in recalibration procedures when slippage occurs between HMGT and head. To address these issues, a high-accuracy 3D gaze estimation method along with an efficient recalibration approach is proposed with head pose tracking in this paper. The two key parameters, eyeball center and camera optical center, are estimated in head frame with geometry-based method, so that a mapping relationship between two direction features is proposed to calculate the direction of the visual axis. As the direction features are formulated with the accurately estimated parameters, the complexity of mapping relationship could be reduced and a better fitting performance can be achieved. To prevent the noticeable extrapolation errors, direction features with uniform angular intervals for fitting the mapping are retrieved over human’s field of view. Additionally, an efficient single-point recalibration method is proposed with an updated eyeball coordinate system, which reduces the burden of calibration procedures significantly. Our experiment results show that the calibration and recalibration methods could improve the gaze estimation accuracy by 35 percent (from a mean error of 2.00 degrees to 1.31 degrees) and 30 percent (from a mean error of 2.00 degrees to 1.41 degrees), respectively, compared with the state-of-the-art methods.

To evaluate two transducer and needle handling methods, along the visual axis (AL) and across the visual axis (AC), in non-skilled and skilled clinicians. Prospective randomized crossover study. A total of 26 students with no ultrasound locoregional anaesthesia experience (non-skilled group) and six clinicians experienced and familiar with ultrasound locoregional anaesthesia (skilled group) were enrolled. The non-skilled group was asked to perform two tasks: the first on a phantom and the second on canine cadavers, whilst the skilled group performed only the second task. The tasks consisted of guiding the tip of the needle to a target point (simulated nerve on the jelly phantom and sciatic nerve on the cadavers) using two different methods of needle handling—AL or AC. All operators performed each task three times for each method. The time to drive the needle to the target for the two methods was analysed with a paired Student t test, and the number of times the needle was not visualized on the screen between the groups was compared using an unpaired Student t test. Data are presented as mean ± standard deviation. Value of p < 0.05 was considered significant. The AL method, compared with the AC method, resulted in shorter performance time in both skilled (9 ± 5 versus 20 ± 8 seconds for the second task) and non-skilled groups (9 ± 8 versus 17 ± 15 seconds for the first task and 18 ± 11 versus 32 ± 26 seconds for the second task). In both groups, the AL method significantly reduced the time to complete the task. Results from this study indicate that the AL method should be the preferred method for learning/teaching ultrasound-guided regional anaesthesia. [ABSTRACT FROM AUTHOR]

This study aims to describe a new universal method to identify the relative three-dimensional directions of visual, pupillary, and optical axes of the eye and the angles between them using topography elevation data. The method was validated in a large clinical cohort, and ethnical differences were recorded. Topography elevation data were collected from 1992 normal eyes of 966 healthy participants in Italy, Brazil, and China. The three main axes were defined as follows: optical axis (OA) was defined as the optimal path of light that passes through the ocular system without refraction. The pupillary axis (PA) line was defined using X and Y coordinates of the pupil centre with the chamber depth, in addition to the centre of a sphere fitted to the central 3 mm diameter of the cornea. The visual axis (VA) was taken by its best approximation, the coaxially sighted corneal light reflex. The alpha angle was measured between the VA and OA, and the kappa angle between the VA and PA. The average values of kappa and alpha angles were 3.41 ± 2.84 and 6.04 ± 2.43 in the Italian population, 2.6 ± 1.53 and 5.87 ± 2.3 in the Brazilian population, and 2.09 ± 1.22 and 3.85 ± 1.48 in the Chinese population.

Purpose: To identify the relative positions of geometrical and visual axes of the eye and present a method to locate the visual center when the geometrical axis is taken as a reference. Methods: Topography elevation data was collected using a Pentacam HR ® topographer from 2040 normal eyes of 1020 healthy participants in Brazil, China and Italy. A three-dimensional, rotation algorithm, a first-order Zernike polynomial fit and a nonlinear least-squares error function was used within an optimization function to locate the geometrical axis and the visual center of each eye. Results: The right eyes of participants were significantly more tilted than left eyes throughout the topography scanning process (p < 0.001). The visual centers were always located in the nasal-superior quadrant, although the visual centers of fellow eyes were not symmetrically located. Mean distances between the visual center and the geometrical center in right eyes were 0.8 ± 0.29 mm, 0.56 ± 0.18 mm and 0.91 ± 0.34 mm among Brazilian, Chinese and Italian participants, respectively, and located at angular positions of 38.7 ± 24.5°, 23.0 ± 29.8° and 23.1 ± 28.1° from the nasal side. However, in left eyes, mean distances were 0.76 ± 0.33 mm, 0.45 ± 0.12 mm and 0.75 ± 0.33 mm at polar angles from the nasal side of 59.3 ± 29.0°, 50.6 ± 44.5° and 61.8 ± 34.1°, respectively. Conclusions: Fellow eyes do not perform similarly during the fixation process, with right eyes tending to tilt more than left eyes, and the visual centers of the fellow eyes positioned differently relative to the geometrical centers. [ABSTRACT FROM AUTHOR]

Purpose To locate the visual axis of the eye objectively. Method Based on three-beam scanning laser radar microprofilometry, a technique is proposed to objectively locate the visual axis of the eye. The laser beam consists of three components, two of them being shifted relatively to the central one by differing frequencies, filtered in spatially orthogonal directions. The centre of the foveola is defined as the crossing of steepest inclinations determined in the specific beam positions on the trajectory of scanning. The position of the cornea crossing by the visual axis is designated by the optical axis of the measuring instrument. Results Nanometer sensitivity was confirmed in a preliminary test. Conclusions The proposed technique can be incorporated into any clinical wavefront sensing instrument and can be used for centration-sensitive vision correction, as well as for other instances when knowing the exact position of the fovea is important. [ABSTRACT FROM AUTHOR]

We present the case of a 5 year old patient who comes to the II Clinic of Ophthalmology of „Prof. Nicolae Oblu” Clinical Emergency Hospital of Iaşi for correction of the right total unilateral palpebral ptosis Right Eye, 6 months after a palpebral trauma with a sharp object that sectioned a part of the orbicular muscle fibers and the levator muscle of the right upper lid. We mention that the surgical treatment performed was the correction of the palpebral ptosis, by shortening the upper lid levator muscle and reinsertion at its aponeurosis, considering the achievement of a functional and esthetic result. The reducing of the grade IV palpebral ptosis to grade II – I was aimed, letting free the visual axis.

Angle kappa is the difference between the pupillary and visual axis. This measurement is of paramount consideration in refractive surgery, as proper centration is required for optimal results. Angle kappa may contribute to MFIOL decentration and its resultant photic phenomena. Adjusting placement of MFIOLs for angle kappa is not supported by the literature but is likely to help reduce glare and haloes. Centering LASIK in angle kappa patients over the corneal light reflex is safe, efficacious, and recommended. Centering in-between the corneal reflex and the entrance pupil is also safe and efficacious. The literature regarding PRK in patients with an angle kappa is sparse but centering on the corneal reflex is assumed to be similar to centering LASIK on the corneal reflex. Thus, centration of MFIOLs, LASIK, and PRK should be focused on the corneal reflex for patients with a large angle kappa. More research is needed to guide surgeons′ approach to angle kappa.