with cataract surgery regarded as the most widely performed surgical procedure , a demand exists for continued innovation and technology .
the latest advances evolved through application of well - defined principles to current surgical goals and patient expectations .
for example , femtosecond laser technology emerged after fifty years of employing laser technology in ophthalmology .
theodor scheimpflug described the principle of scheimpflug images in 1904 , but he was actually an austrian army captain who spent his life 's work dedicated to designing methods and tools to create maps depicting aerial photography .
application of these principles to ophthalmology in the last few years has advanced our understanding of corneal biomechanics .
the latest highlights in technology include advances in preoperative and intraoperative diagnostics , femtosecond laser - assisted cataract surgery ( flacs ) , and a new generation of intraocular lenses ( iols ) .
more than ever , patients have the desire to reduce their dependence on spectacles after cataract surgery .
physicians now have access to advanced diagnostics that can better quantify conditions such as dry eye , light scatter , and posterior corneal astigmatism .
mcdonald recently reported that the postoperative prevalence of dry eye related symptoms is approximately 88% .
analysis and optimization of dry eye preoperatively and postoperatively has a beneficial impact on visual outcomes after cataract surgery .
therefore , increased interest among ophthalmologists to utilize objective measurements to assess the ocular surface exists .
the acutarget hd ( visiometrics sl , spain ) assesses the objective scatter index , which can objectively evaluate dry eye disease severity using the degradation of image quality over time ( figure 1 ) .
the keratograph ( oculus , germany ) noninvasively measures tear break up time , tear meniscus height , and meibography , providing a functional and qualitative analysis of the corneal surface and tear film [ 8 , 9 ] .
the tearlab osmolarity system ( tearlab corporation , san diego , california ) uses a small tear sample to measure tear osmolarity using a microelectrode .
compared to other commonly used diagnostic tests for dry eye disease , test results were better at predicting dry eye severity . the lipiflow ( tearscience , morrisville , north carolina ) combines heat and eyelid pressure to treat dry eye disease due to meibomian gland dysfunction .
recent studies showed consistent improvement in meibomian gland function up to 12 months after the treatment .
evaluation of optical quality also aids in decision making between corneal or lens - based procedures .
the c - quant ( oculus , germany , optikgenrate gmbh ) assesses straylight subjectively by utilizing a compensation comparison method .
the acutarget hd ( visiometrics sl , spain ) uses a double pass system to measure point spread function ( psf ) , modulation transfer function ( mtf ) , strehl ratio , and intraocular scattering of the light .
these data allow clinicians to evaluate the quality of a patient 's optical system objectively .
another objective functional diagnostic is the salzburg reading desk ( srd vision , vienna , austria ) , which allows measurement of the variable read print sizes and distances with differences in contrast sensitivity and luminance .
both anterior and posterior corneal astigmatism should be taken into account in iol planning , particularly in patients desiring astigmatic correction .
inaccuracies arise when posterior corneal astigmatism is measured based on the assumption of a fixed - ratio relationship with the anterior curvature .
the cassini corneal shape analyzer ( i - optics bv , the hague , the netherlands ) is a new topographer that uses led ray tracing technology with 700 diode lights to measure anterior and posterior corneal astigmatism .
these advances in cylinder and axis measurement precision can be useful for preoperative planning of toric iol implants and in postrefractive surgery patients [ 1517 ] .
patients with a history of corneal refractive surgery expect reduced dependence on spectacles after cataract surgery .
the optiwave refractive analysis ( ora , alcon , fort worth , tx ) uses wavefront interferometry to produce a fringe pattern , and distortions in this pattern are translated into refractive values and aphakic and pseudophakic readings ( figure 2 ) .
studied mean postoperative residual refractive astigmatism in patients receiving toric iols with power selection aided by intraoperative aberrometry .
surgeons altered cylindrical power 24% of the time and spherical power 35% of the time .
patients were 2.4 times more likely to have less than 0.50  d of residual refractive astigmatism when intraoperative aberrometry was used .
in contrast , huelle et al . published a study where aphakic spherical equivalent- ( se- ) based iol formulas were generated from repeated intraoperative wavefront aphakic measurements of se .
the agreement of repeated aphakic se readings ranged from 0.69 diopters to + 0.66 diopters .
the authors concluded that measurement precision is limiting reliability of intraoperative aberrometry and application to routine cataract surgery .
however , it may be useful in guiding limbal relaxing incision enhancements and has resulted in the need for fewer subsequent laser enhancements .
this technology is particularly useful in postrefractive patients and those with astigmatism uncertainty or other corneal pathology .
other intraoperative inconsistencies include cyclotorsion , variable anterior chamber depth and intraocular pressure , variability in wound hydration , and use of viscoelastic device versus balanced salt solution .
although limitations may exist in quality and measurement precision , the future of this technology is promising .
the use of the electroretinogram ( erg ) has been well described and may have a novel application for refractive cataract surgery .
richard mackool described the use of flash erg testing with office - based electroretinography ( diopsys , pine brook , new jersey ) in preoperative cataract evaluation .
it can provide an objective evaluation of macular function and could be useful in influencing lens selection for patients with conditions such as epiretinal membrane , diabetic retinopathy , and age - related macular degeneration .
more studies evaluating ergs in preoperative cataract assessment need to be done to further assess its value and implications .
noninferiority has been established relative to manual cataract surgery , and some reports have suggested superiority relative to manual methods .
potential advantages include customized corneal incisions and capsulotomy position , precision in shape and size of capsulotomy , custom lens fragmentation patterns , endothelial cell loss reduction , and better refractive stability and predictability .
after the food and drug administration ( fda ) approval of laser - assisted capsulotomy and lens fragmentation in 2010 , five platforms have been released : lensx by alcon ( fort worth , tx ) ; the lensar by lensar ( orlando , fl ) ; the catalys by abbott / optimedica ( north chicago , il ) ; the victus by bausch and lomb ( rochester , ny ) ; and the ldv z8 by ziemer ( port , switzerland ) ( figure 3 ) .
the docking process using the femtosecond laser - eye interface uses a suction ring to stabilize the eye , thereby allowing imaging and laser delivery through a clear optical pathway .
considerations for docking include complete coupling , patient comfort , intraocular pressure elevation , and minimal distortion of anatomy to avoid disruption of the beam path . in a study using alcon 's lensx platform to compare curved direct contact and modified soft interfaces ( softfit by alcon ) , mayer et al .
showed that redocking was unnecessary when a modified soft interface was used , even though some cases resulted in incomplete incisions requiring manual opening .
schultz et al . found significantly fewer intraocular pressure elevations after docking using a liquid interface ( liquid optics interface , catalys precision laser system ) in comparison to flat and curved interfaces . while docking is a necessary step with femtosecond laser technology , laser incisions are optional in flacs .
comparatively analyzed femtosecond laser incisions and manual incisions and cited better tunnel morphology with flacs incisions .
flacs theoretically decreases endothelial cell loss relative to manual techniques by reducing the use of ultrasound energy . however , krarup et al .
compared endothelial cell loss rates between phacoemulsification and flacs and showed there were no differences between both modalities .
published similar findings but did cite a difference in favor of flacs that was limited to the early postoperative period .
they also showed that laser corneal incisions themselves may influence endothelial cells , as there may be a disturbance in the postoperative inflammatory response after laser application [ 3032 ] .
new surgical techniques , in combination with more advanced lens fragmentation patterns , will allow the lens to be extracted through an aspiration mechanism that may reduce endothelial cell loss .
the size , shape , and position of a capsulotomy should theoretically lead to a more predictable lens position by enhancing uniform capsule - optic overlap , thereby reducing the incidence of lens tilt and leading to an overall better effective lens position and visual outcome ( figure 4 ) .
recently , toto and colleagues found no difference in prediction error when comparing traditional phacoemulsification with flacs but did find higher refractive stability and iol centration with flacs .
this similarity in prediction error may be a consequence of unexplored potential with iol calculations and algorithms .
ma approached the prediction of true lens position using an algorithm based on oct anterior segment 3-d reconstruction .
this prediction model could have great potential once there is consistent alliance of oct measurements with flacs to provide more precise outcomes .
this is particularly relevant with premium iols , as there is a lower tolerance threshold for minor unanticipated miscalculation and decentration .
okulix ( tedics peric & joher gbr , dortmund , germany ) is an innovative software program that calculates iol power using ray tracing combined with corneal topography .
evaluated its accuracy in post - lasik eyes in comparison with camellin - calossi , shamas - pl , haigis - l formulas and double - k srk - t method .
they reported that this technology provides sufficient predictability outcomes in postrefractive myopic lasik , even though a small hyperopic shift tendency was noted in the study .
g6 lens professional ( ziemer , port , switzerland ) is an optical biometer that integrates placido rings with a dual rotating scheimpflug camera as well as an optical coherence tomography based a - scan in a single device .
shin et al . compared its accuracy with the lenstar ls 900 ( haag - streit , koeniz , switzerland ) , for intraocular lens ( iol ) power calculation .
they noted that axial length , lens thickness ( lt ) , and white - to - white ( wtw ) values were statistically different .
thus , even though high repeatability was present , and the iol powers were not statistically different between the two devices , the values provided by the galilei g6 were not interchangeable with the lenstar in the clinical setting .
the goal of appropriate iol selection is to provide the best visual outcome that meets a patient 's individualized goals and expectations .
variability in materials , optical properties , and designs are important factors to consider in the patient - specific selection of an iol .
advancements in iol technology aim to improve visual functionality by creating customized iols or modifying optical power postoperatively .
the concept of adjustable iols involves the correction of residual refractive error postoperatively or customization after lens implantation .
this new paradigm in iol manufacturing may be subdivided into two major categories : a modular multicomponent category requiring a separate intraocular procedure and another category where the optic is adjusted postoperatively with a secondary device .
the first category includes multicomponent iols ( clarvista harmoni modular iol system , clarvista medical , aliso viejo , ca ; and omega lens , omega ophthalmics , lexington , ky ) ; infinite vision iol ( infinite vision optics , france ) ; and mechanically adjustable iols ( acritec ar-1 pc / iol , acri.tec , hennigsdorf , germany ) .
the second category includes magnetically adjustable iols ( university of missouri - rolla , rolla , and eggleston adjustable lens , st .
louis , mo ) , light adjustable iols ( calhoun vision , pasadena , ca ) , and the perfect lens ( perfect lens , llc , irvine , ca ) .
the latter is a novel platform , which can be adjusted with the femtosecond laser based on the concept of refractive index shaping .
its mechanism involves the use of infrared light to polymerize photosensitive silicone macromers , which results in changes in lens morphology and optical properties . a new generation of optics with extended depth of focus , multifocal rotational symmetry and asymmetry , and accommodating capabilities offers promising strategies to advance functional vision in refractive cataract surgery .
the tecnis symfony ( amo ) is an extended depth of focus iol that works by correcting chromatic aberration using diffractive optics and reduces glare and halo symptoms classically associated with conventional multifocal iols .
multifocal lenses with bifocal and trifocal designs include the rotationally asymmetric lentis mplus ( topcon europe medical bv , the netherlands ) and the rotationally symmetric finevision ( physiol , liege , belgium ) and at lisa ( zeiss , oberkochen , germany ) .
found that trifocal lenses provide satisfactory intermediate vision without compromising near and far distance visual acuity .
the fluidvision iol ( powervision , belmont , ca ) has silicone oil inside the lens that moves in response to ciliary contraction forces .
an electroactive iol with a liquid crystal that is sensitive to electric current is also in development ( sapphire autofocal iol , elenza , roanoke , va ) .
dual accommodating iols designed for sulcus placement include the dynacurve iol ( nulens , israel ) and the lumina iol ( akkolens , the netherlands ) .
the injectable polymer smartiol ( medennium , irvine , ca ) , which is a thermodynamic , pliable capsule - filling iol , is the only bag filling technology in development .
the future of refractive cataract surgery is exciting ; in time , these new technologies may be the standard of care . with refinements of the latest technology , flacs and other parallel advances will provide surgeons with the potential to perform an even safer , predictable , and effective surgery .
 technology in cataract surgery is constantly evolving to meet the goals of both surgeons and patients . 
 recent major advances in refractive cataract surgery include innovations in preoperative and intraoperative diagnostics , femtosecond laser - assisted cataract surgery ( flacs ) , and a new generation of intraocular lenses ( iols ) . 
 this paper presents the latest technologies in each of these major categories and discusses how these contributions serve to improve cataract surgery outcomes in a safe , effective , and predictable manner . 
1. Introduction
2. Preoperative and Intraoperative Diagnostics
3. Femtosecond Laser-Assisted Cataract Surgery
4. Intraocular Lenses 