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）.

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.

Effect of even and odd-order aberrations on the accommodation response

AIM： To investigate the potential effect that odd and even-order monochromatic aberrations may have on the accommodation response of the human eye. METHODS： Eight healthy subjects with astigmatism below 1 D, best corrected visual acuity 20/20 or better and normal findings in an ophthalmic examination were enrolled. An adaptive optics system was used in order to measure the accommodation response of the subjects＇ eyes under different conditions： with the natural aber- rations being present, and with the odd and even-order aberrations being corrected. Three measurements of accommodation response were monocularly acquired at accommodation demands ranging from 0 to 4 D （0.5 D step）. RESULTS： The accommodative lag was greater for the accommodate demands of 1.5, 3, 3.5 and 4 D for the condition in which the even-order aberrations were corrected, in comparison to that obtained for the natural aberrations and corrected odd-order aberrations for the same accommodation demands. No statistically significant differences were found between the accommodation responses under the three conditions. CONCLUSION： The odd and even-order aberrations are not helping the visual system to accommodate, because their partial correction do not affect the accommodation performance.

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.

Anterior segment imaging using non-invasive high-resolution optical coherence tomography

One of the most important developments in the ophthalmology and visual sciences field has been the application of new techniques for imaging the anterior and posterior segment of the eye with non-contact devices.These techniques have been developed quickly considering that are non-invasive and provide high-resolution images of the different parts of the human eye.Definitely,the most spread and used technique for non-contact imaging of the human eye is the optical coherence tomography(OCT).OCT technique was first demonstrated in 1991 by Huang et al.(1).

In vivo optical quality of posterior-chamber phakic implantable collamer lenses with a central port

Background: The aim of this review is to summarize the optical quality results in patients following theimplantation of the V4c implantable collamer lens with a central port (ICL, STAAR Surgical Inc.).Main text: A literature search in several databases was carried out to identify those publications, both prospective,retrospective and/or comparative with other refractive surgery procedures, reporting optical outcomes of patientswho were implanted with the V4c ICL model. A total of 17 clinical studies published between 2012 and 2021 wereincluded in this review. A detailed analysis of the available data was performed including number of eyes, follow-upand preoperative spherical equivalent. Specifically, the review focused on several optical parameters includinghigher-order aberrations (HOAs), modulation transfer function (MTF) cut-off frequency and Strehl ratio. This reviewencompassed a total of 817 eyes measured using different optical devices based on Hartmann-Shack, retinal imagequality measurement and ray-tracing technologies at different follow-ups.Conclusions: The outcomes found in this review lead us to conclude that the ICL V4c model provides good opticalquality, by means of different metrics, when implanted.

In vivo optical quality of posterior-chamber phakic implantable collamer lenses with a central port

Background:The aim of this review is to summarize the optical quality results in patients following the implantation of the V4c implantable collamer lens with a central port(ICL,STAAR Surgical Inc.).Main text:A literature search in several databases was carried out to identify those publications,both prospective,retrospective and/or comparative with other refractive surgery procedures,reporting optical outcomes of patients who were implanted with the V4c ICL model.A total of 17 clinical studies published between 2012 and 2021 were included in this review.A detailed analysis of the available data was performed including number of eyes,follow-up and preoperative spherical equivalent.Specifically,the review focused on several optical parameters including higher-order aberrations(HOAs),modulation transfer function(MTF)cut-off frequency and Strehl ratio.This review encompassed a total of 817 eyes measured using different optical devices based on Hartmann-Shack,retinal image quality measurement and ray-tracing technologies at different follow-ups.Conclusions:The outcomes found in this review lead us to conclude that the ICL V4c model provides good optical quality,by means of different metrics,when implanted.

Angle-to-angle and spur-to-spur distance analysis with high-resolution optical coherence tomography

Background:To measure angle-to-angle(ATA)and spur-to-spur(STS)distances along six meridians using highresolution swept-source optical coherence tomography(SS-OCT)and to compare those values with horizontal white-to-white(WTW)distance.Methods:68 eyes from 68 patients were quantitatively assessed with the Anterion SS-OCT(Heidelberg Engineering,Heidelberg,Germany).ATA and STS distances were measured with the SS-OCT’s B-Scan in six cross-sectional images corresponding to the vertical(6-12 o’clock),1-7 o’clock,2-8 o’clock,horizontal(3-9 o’clock),4-10 o’clock and 5-11 o’clock meridians.WTW was measured horizontally with the device’s infrared camera.A Pearson correlation analysis was carried out to compare ATA and STS distances with WTW.Results:The largest values were found for the vertical meridian and the shortest for the 2-8 o’clock meridian,both for ATA and STS distances.No statistically significant differences were found between WTW,ATA and STS along the horizontal meridian(p>0.1).However,ATA and STS showed statistically significant differences elsewhere,except for the horizontal and the 2-8 o’clock meridians(p>0.05).Moreover,we found that ATA and STS varied significantly depending on the meridian being assessed,except for ATA at 4-10 versus 3-9 o’clock and for STS at 4-10 versus 3-9 o’clock and at 3-9 versus 2-8 o’clock(p>0.1).R^(2) values ranged from 0.49 to 0.75 for ATA and STS at the different meridians,showing the best correlation at 3-9 o’clock meridian(0.64 and 0.75,respectively)and the worst at 6-12 o’clock meridian(R^(2)=0.49 for both ATA and STS).Conclusions:ATA and STS distances vary radially,thus showing that the anterior chamber is vertically oval.Therefore,it is advisable to measure these two distances along the meridian to be used.