interviste

Biometry and success in cataract refractive surgery

The dream of any patient undergoing cataract refractive surgery is a future with no dependence on spectacles for near and far vision.
At the same time the eye surgeon aims at the best quality of vision currently attainable for the patient.
Where we stand and where we are heading to.
Our interview with Giacomo Savini.

To get the utmost of both targets nowadays we have many diagnostic tools, made sharper in these last years by the fast development of refractive cataract.
One of the most important tools is nowadays biometry.
We would like to illustrate the “state of the art” in this complex discipline with a few questions to a skilled specialist, Giacomo Savini MD, who is researcher at the G.B. Bietti Foundation – IRCCS in Rome, Italy.

How much is biometry important in the selection of the patient undergoing cataract refractive surgery with PC-IOLs (Presbyopia-Correcting IOLs)?
G. Savini: The implantation of multifocal IOLs is the highest step of cataract refractive surgery. The achievement of emmetropia is a very important goal, because even 0.50 D error, both hyperopic or myopic, may hinder the satisfaction of the patient who chose this surgery to attain the independence on spectacles. I believe that biometry is as much important as the surgical performance, with a great difference: the surgery performed by an experienced surgeon has little uncertainties while the intraocular lens power calculation is still a source of unforeseeable refractive  surprises. Studies published in the last years reported around 20-25% eyes treated with cataract surgery end with a refractive error higher than 0.5 D. This share cannot be reduced by current calculation formulas and has to be clearly present both to surgeons and patients. For this reason I advise all the patients undergoing the multifocal IOL implantation that a “retouching” with excimer laser might be necessary to correct eventual refractive errors. So, if such event occurs, the patient is not startled and undergoes LASIK or PRK treatments more willingly.

Is there any parameter to correlate the preoperative anatomical parameters to the visual performance after cataract surgery?
G. Savini: Unfortunately at present there is no well definite parameter. It has not been yet systematically studied the influence of the so-called angle K, of the corneal asphericity, of the main high-order aberrations and of other parameters. I hope this subject will be a main focus of my researches in the next years. Indeed we should be able to forecast the visual performance on the basis of the preoperative data, in order to be more confident when we propose the multifocal IOL implantation to the patient. It’d better for all of us to be able to exclude from the use of these IOLs the patients whose preoperative parameters suggest an unsatisfying outcome. A first parameter is anyway coming to light, at least in Literature: the effect of the anterior chamber depth. Our team at G. B. Bietti Foundation in Rome, in co-operation with Kenneth Hoffer, carried out a study that is currently submitted for publication to the Journal of Cataract and Refractive Surgery. This study highlights that the greater is the reading distance for near vision after the surgery, the deeper is the anterior chamber. In other words the farther the IOL is from the cornea, the more the patient must put at distance the object he/she wants to set at focus with near vision. In most cases a deep anterior chamber after the surgery is common in myopic patients, therefore these patients can find greater difficulties in reading at near distance with a multifocal IOL. This circumstance was already reported by Hoffer and Holladay in an article published in 1991 showing that the addition had to be increased in proportion to the anterior chamber depth.

Could you give some advice to the eye surgeons implanting EDOF IOLs to achieve the expected refractive target?
G. Savini: My advice is to follow the rules used for the power calculation of any kind of IOL: 1) measure the axial length with optic or immersion biometry; do not use contact biometry; 2) exclude the patients with corneal astigmatism higher than 0.5 D, taking in account also the posterior corneal surface. For this reason it is essential to have a Scheimpflug camera in order to measure total corneal astigmatism; 3) use the most recent formulas Haigis, Hoffer Q, Holladay 1 and 2, SRK/T. Do not use SRK II; 4) optimize the constants of the used instruments. The technique I usually prefer is immersion biometry, combined with SimK (by Keratron, Optikon 2000topographer). With this combination of instruments, the constants for Mini WELL are 5.64 (Hoffer Q), 1.85 (Holladay 1) and 119.18 (SRK/T). The constants for IOLMaster, according with the calculation by Claudio Carbonara, MD (Rome), are 5.26 (Hoffer Q), 1.48 (Holladay 1) and 118.67 (SRK/T); 5) use Hoffer Q for short eyes (<22 mm), average Hoffer Q, Holladay 1 and  SRK/T for medium eyes (22 – 24.5 mm), Holladay 1 for medium – long eyes (24.5 – 26 mm) and SRK/T for long eyes.

Giacomo Savini
Researcher with an international profile, Giacomo Savini got his university degree in Medicine and started his career in Bologna. Since 2009 he is researcher at the G.B. Bietti Foundation – IRCCS in Rome, Italy.
In clinical practice his activity has been focused on cataract and refractive surgery. As a researcher, his main field of interest is the intraocular lens power calculation
Giacomo Savini is a prolific publisher with more than 100 papers published in peer-reviewed scientific journals.
His studies in biometry led him since 2007 to become a Member of the IOL Power Club (www.iolpowerclub.org), a club gathering the main world experts of biometry (Hoffer, Haigis, Olsen, Shammas and Aramberri).

Read this article in Italian

For further updates see our review about presbyopia surgery:
New IOLs: Tomorrow is already today
New EDOF IOLs for presbyopia correction
New horizons in presbyopia surgery
Presbyopia and economic growth

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Pubblicato il
martedì, 14 luglio 2015
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Area Chirurgica