ROLE OF ABERROMETRY

Is performing aberrometry in cataract surgery really necessary? Damien Gatinel MD addressed this question in a session of the 2014 World Ophthalmology Congress in Tokyo.

“The short answer is yes. Aberrometry has a critical role to play both before and after cataract surgery,” said Dr Gatinel, director of anterior and refractive surgery, Rothschild Foundation, Paris, France.

“A major issue with cataract is light scatter. The best tool for preoperative assessment is double pass aberrometry. The Optical Quality Analysis System (OQAS) aberrometer (recently renamed HD Analyzer, Visiometrics) allows you to measure double pass the point spread function, which contains information about scatter. It then converts it into an objective measure, the objective scatter index (OSI). I use it on a daily basis for preoperative objective assessment. It helps to differentiate objectively cataract from clear lens surgery.”

The OSI measures the ratio of scattered light and light in the path of the point spread function. This is particularly helpful when a patient presents with 20/20, but complains about visual symptoms that may be related to cataract. An increase in the OSI signals that it may be time to consider cataract surgery, explained Dr Gatinel.

Cross-sectional study

Dr Gatinel and colleagues conducted a prospective, single-centre, cross-sectional study to evaluate the clinical utility of the OQAS system in 135 patients referred for cataract evaluation (AJO, Vol. 155, Issue 4, 629–63). They found that the objective scatter index, modulation transfer function and visual acuity were correlated with different types of cataract. In patients with good visual acuity and moderate functional symptoms, the OSI values also correlated with the severity of posterior subcapsular cataract.

He cited one case of a patient with subcapsular posterior cataract. The OSI was elevated before surgery, then dropped following implantation of a diffractive IOL. The OSI then increased with the development of posterior capsule opacification (PCO). The OSI returned to normal following YAG capsulotomy.

In another case, an unhappy patient presented asking for explantation of a multifocal IOL. Instead, Dr Gatinel evaluated the eye with corneal topography and the OQAS system, which both suggested a significant amount of corneal astigmatism, given the shape of iterative point spread functions that looked similar to a Sturm conoid on the OQAS. He decided to correct the corneal astigmatism instead, with good visual results for
the patient.

Objective information

“The OQAS/HD Analyzer system is an ideal tool for the evaluation of patient complaints in the postoperative period. It can provide some objective information regarding visual symptoms such as haloes, ghosting, glare and monocular diplopia.”

He described another case of an unhappy refractive multifocal IOL recipient. The OPDscan III (Nidek, Japan) examination revealed that the problem was not really a problem with the multifocal IOL per se, rather the patient was not well corrected for defocus, as was shown on the OPD map, which helps to explore the variation of the local vergence throughout the entrance pupil, when autorefractometer becomes unreliable in such circumstances. The patient underwent LASIK to correct a slight hyperopic error and had a good result.

Another case involved a dramatic toric IOL mislocation resulting in 7 D of error. An exam showed that the IOL was poorly oriented. Subsequent 30° rotation of the IOL led to a good outcome.

Smartphone app

Dr Gatinel also described a new smartphone app he helped to develop. The Toreasy app allows you to take and store oriented pictures of the anterior segment of the eye. The surgeon can use it to find the orientation of natural (limbal vessels) or artificial (ink) marks of the eye for precise positioning of a toric IOL. The app takes advantage of the gravity and horizon tracking functions of the phone. Using the reticule, the surgeon can align the head of the patient, zoom in on the eye and take a snapshot. Using a reference such as a blood vessel or ink mark, the surgeon can then orient the eye properly under the microscope at the time of surgery.

Damien Gatinel: gatinel@gmail.com