Device interchangeability on anterior chamber depth and white-to-white measurements: a thorough literature review

We have reviewed a set of recently published studies that compared the anterior chamber depth（ACD） and/or white-to-white（WTW） distance obtained by means of different measuring devices.Since some of those studies reached contradictory conclusions regarding device interchangeability,this review was carried out in attempting to clarify which clinical devices can or cannot be considered as interchangeable in clinical practice to measure ACD and/or WTW distance,among these devices：A-scan,ultrasound biomicroscopy,Orbscan and Orbscan Ⅱ（Bausch＆Lomb Surgical Inc.,San Dimas,California,USA）,Pentacam and Pentacam HR（Oculus,Wetzlar,Germany）,Galilei（Ziemer,Switzerland）,Visante optical coherence tomography（Visante OCT,Carl Zeiss Meditec Inc.,Dublin,California,USA）,lOLMaster（Carl Zeiss Meditec,Jena,Germany）,and Lenstar LS 900/Biograph（Haag-Streit AG,Koeniz,Switzerland/Alcon Laboratories Inc.,Ft Worth,Texas,USA）.

Accommodation in human eye models:a comparison between the optical designs of Navarro,Arizona and Liou-Brennan

AIM： To simulate and compare accommodation in accommodative and non-accommodative human eye models.METHODS： Ray tracing and optical design program was used. Three eye models were designed and studied： the Navarro, the Arizona and the Liou-Brennan. In order to make the Navarro and Liou-Brennan models to accommodate, specific geometric parameters of the models were altered with values that were chosen from the literature. For the Arizona model, its’ mathematical functions for accommodation were used for the same accommodative demands. The simulation included four distances of accommodation for each model： at infinity, 3, 1 and 0.5 m.The results were diffraction images of a “letter F” for graphical comparison, spot diagrams on the retinal field and Modulation Transfer Function （MTF） graphs.RESULTS：Zernike coefficients for the aberrations, Airy disk diameter, root mean square （RMS） error diameter and total axial length of the model were provided from the program. These were compared between them in all distances. The Navarro model had the smallest axial length change as a simple model. The Arizona did not change its axial length because it is designed to be accommodative. The Liou-Brennan model had different results concerning the aberrations because of the decentration of the pupil. The MTF graphs showed small differences between the models because of the differences in their designs.CONCLUSION： All the three models are able to simulate accommodation with the expected results. There is no model that can be assumed as the best choice. Accommodation can be simulated in non-accommodativemodels and in customized ones.

Repeatability of in-vitro optical quality measurements of intraocular lenses with a deflectometry technique effect of the toricity

AIM： To evaluate the repeatability of an optical device for measuring the Zernike coefficients of toric intraocular lenses（IOLs） and assess whether its toricity has any impact in its repeatability. METHODS： An experienced technician used the NIMO TR1504 to measure the Zernike coefficients 30 times for an aperture of 4.50 mm for all lenses included. The IOLs included were divided into two group： toric and nontoric ones. The cylindrical powers of the toric lenses included in the present study were 1.00, 1.50, 2.25, 3.00 and 3.75 D. Finally, the repeatability of the NIMO TR1504 was described in terms of within subject standard deviation（Sw） and repeatability limit. RESULTS： The Sw was smaller than 0.011 μm for both lens groups and all Zernike coefficients, and the difference between both groups was smaller than 0.004 μm for all Zernike coefficients. Regarding the repeatability limit, this value was smaller than 0.025 μm for the toric lens group, and smaller than 0.031 μm for the non-toric lens one for all Zernike coefficients. Furthermore, the maximum difference between both lens groups was 0.010 μm. CONCLUSION： The repeatability of the NIMO TR1504 to measure the optical quality is high and independent of the lens toricity. These results reflect that this system is robust and could be used to measure the in-vitro optical quality of either toric or non-toric IOLs.

Evaluation of the iridocorneal angle with accommodation using optical coherence tomography

The changes in the iridocorneal angle structure during accommodation are assessed by means of anterior segment optical coherence tomography.Thirteen right eyes were included in the study.The device used for the measurement was the Visante？omni system.The stimuli were set up at different vergences（0.0 D,-1.5 D,and-3.0 D）.The angle opening distance 500 and 750,the trabecular iris space area 500 and 750,and the scleral spur angle parameters were assessed at the nasal and temporal regions.The results in the iridotrabecular angle comparing the three accommodative states of the eye did not yield any statistically significant difference at nasal or temporal angle sections.In light of our results and in the conditions of our study,the structures of the iridocorneal angle are not significantly changed with accommodation.

Adaptive optics as a tool for controlling the optical signals reaching the retina

The use of adaptive optics systems in ophthalmic research studies has increased in the last years thanks to the development of more accurate devices.Adaptive optics was first introduced in Astronomy for the correction of the effects produced by the turbulences of the Earth’s atmosphere when observing astronomical objects(1,2).Sophisticated deformable mirrors controlled by computers can correct in real time atmospheric disturbances,allowing for much finer details on the images of distance objects.Adaptive optics technology makes it possible to correct many of the aberrations with which the wavefront,i.e.,the geometric envelope of all the rays of light that emerged at the same time of the observed object,arrives.Adaptive optics allows for obtaining sharper images,and thus,with better spatial resolution.