Swept-source OCT biometry for refractive evaluation of both corneal curvatures

Session Details

Session Title: Biometry & Quality of Vision

Session Date/Time: Tuesday 25/09/2018 | 08:00-10:30

Paper Time: 08:12

Venue: Room A2

First Author: : P.Hoffmann GERMANY

Co Author(s): :                        

Abstract Details

Purpose:

To evaluate corneal curvature data delivered by swept source OCT (Zeiss IOLMaster 700) during routine biometry pre cataract surgery.

Setting:

Private eye clinic in Germany

Methods:

At the time of writing (ongoing study), 53 eyes of 32 pseudophacic patients were consecutively measured with the Zeiss IOLMaster 700 as well as the Tomey TMS5, a hybrid Topography/Tomography system. At the time of presentation, more than 200 patients will be included. A new software module (Zeiss IOLMaster 700 version ) not only measured routine parameters, but also posterior radii (PR), posterior astigmatism (ΔPR), a new derived value called “true R” (TR, a derived value) and total corneal astigmatism (ΔTR) =TCA. These results were compared with the TMS5 data as well as subjective refraction for evaluating the astigmatism.

Results:

Mean anterior radii and mean anterior astigmatism did not differ statistically. “TrueR” converted into corneal power using the Zeiss index results in a mean power of 43,25 D as opposed to “RealAvgK” 42,96 D as given by the TMS5 (P<0,01). Using the thick lens formula, total corneal power would be 42,49 for the IOLMaster and 42,29 for the TMS5 (P<0,01). The difference vector betweenTCA as measured by the IOLMaster versus TMS5 was 0,33 D. The centroid of TCA differed by only 0,02 D. The difference vector between subjective cylinder and TCA was 0,25 and 0,23 D respectively.

Conclusions:

The consensus between both machines was very high, especially regarding TCA. The difference vector between TCA and subjective cylinder is close to the limit of subjective refraction and a lot better than standard keratometry allowing for better toric IOL calculation without the need for statistical corrections. IOLMaster posterior radii output seems systematically too flat. The reason might be that the measured value is transformed to match the Gullstrand ratio and keep compatibility with older formulas. PR should not be entered into recent formulas or raytracing software as this will result in a erroneous IOL power calculation (≈ 0,4D too low).

Financial Disclosure:

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