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Technological Tools for Refractive Analysis

In an increasingly competitive environment, investment in the latest technology is a crucial way to maintain margins and differentiate your practice.

The more information you have about your patient’s eyes, the better position you are in to prescribe the correct lenses. Zeiss has upped the stakes in technology to provide this information. The i.Profiler Plus, with a four-in-one compact system, provides a detailed visual profile of your patient.

The i.Profiler Plus features a wavefront abberometer, corneal topographer and auto-refractor in one package. The data from the i.Profiler Plus is used to generate i.Scription.

i.Scription is a wavefront-guided refraction that optimises the sphero-cylindrical power based on the interaction between the low-order and high-order aberrations of the entire patients optical system.1 The i.Scription algorithm uses the aberration data to maximise retinal image quality across various pupil sizes and deliver optimal vision under a variety of lighting conditions.

Legitimate differences in prescription sphere and cylinder powers are likely to occur between the i.Scription refraction and the subjective refraction.2 These differences provide an estimate of the potential visual benefit of wavefront-guided refraction under certain lighting conditions.3

Reduced High Order Aberrations

Conventional spectacle prescriptions are intended to correct low-order aberration, sphere and cylinder. With FreeForm Technology by Zeiss,4 high order aberrations can be reduced with i.Scription.

During the subjective refraction the focus of light is restricted to paraxial rays entering the centre of a small pupil. This reduces the influence of high-order aberrations, which reduces the sensitivity of the eye and the patient’s ability to notice small changes in lens power. With larger pupil sizes, the marginal rays of light, near the outer edge of the pupil, will generally differ from the paraxial focus due to high order aberrations. Therefore patients generally notice the biggest difference with i.Scription outside of the exam room, as the benefits of a wavefront guided refraction become more noticeable under low-light conditions.

The impact of high-order aberrations may result in multiple combinations of cylinder power and axis that yield relatively good vision quality. Although the Jackson cross-cylinder technique will isolate one of these local maxima, the technique itself may not necessarily lead to a combination of cylinder power and axis that yields the best vision quality or global maximum.5 The ideal combination may vary considerably depending upon the pupil size (see figure 1).

Binocular Balancing

In order to preserve binocular balancing and similar modifications to the ocular refraction, the i.Scription wavefront refraction is reconciled against the subjective refraction to ensure the spherical equivalent of the final refraction does not deviate more than 0.12 D from the subjective findings. This approach can improve low-light visual acuity, clarity and contrast sensitivity, without compromising visual comfort.

With FreeForm Technology by ZEISS, and i.Profiler Plus Technology, the impact of high order aberrtaions can be minimised with i.Scription.

Andrew Lin is a product manager at Zeiss Vision Care Australasia. He has a keen interest in digital eye strain, myopia control and using new technology to improve eye care and refraction in optometry.

References
1. Lombardo, M; Lombardo, G (Feb 2010). “Wave aberration of human eyes and new descriptors of image optical quality and visual performance” Journal of cataract and refractive surgery 36 (2): p. 313–31.

2. Jinabhai A, O’Donnell C, Radhakrishnan H (2010) “A Comparison between Subjective Refraction and Aberrometry-Derived Refraction in Keratoconus Patients and Control Subjects”. Faculty of Life Sciences, The University of Manchester UK. Vol 35, No. 8: p. 703–714.

3. Thibos LN, Hong X, Bradley A et al (2002) “Statistical variation of aberration structure and image quality in a normal population of healthy eyes”. J. Opt. Soc. Am A Opt. Image Sci. Vis. 19: p. 2329–48

4. US Patent 6,089,713.

5. Simms C, Durham D. The Jackson Cross Cylinder Disproved. Tr. Am Ophth. Soc. 1986, vol. LXXXIV: p. 335–386.

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