The Science of NaturalVue® Multifocal

The Science of Natural Vision Meets the Science of NaturalVue® Multifocal

Optics

Depth of focus (DOF) is the range of focus along the visual axis, over which an image is clear, or simply, the range of clear vision. (Figure 1)

Figure 1: Extended Depth of Focus Optics
Figure 1 science of NaturalVue Multifocal
In Figure 1, the range of clear vision where the light rays come together - the image is clear within the range of the extended focus.

Depth of focus (DOF) is relative to aperture. (Figure 2)
• Large aperture, the DOF is narrow;
• Small aperture, the DOF is wider

Figure 2: Extended Depth of Focus – Aperture Size
Figure 2 science of NaturalVue Multifocal
Figure 2 illustrates the difference that the aperture makes to the depth of focus. A larger aperture results in a narrow depth of focus; a smaller aperture results in a wider depth of focus. The aperture can be physical such as an opaque, pinhole occluder, or it can be created optically with a large power shift and be a ‘virtual’ aperture.

Extended depth of focus (EDOF) allows continuous visual correction, from near to distance, across a wider range.

Pinhole Optics

  • A pinhole is an example of an extremely small aperture that creates a large DOF.
  • The pinhole effect creates a virtual aperture that blocks peripheral rays to direct light to the foveal area, decreasing blur.
  • This virtual aperture creates an extended depth of focus and provides clear vision at all distances.

The NaturalVue® (etafilcon A) Multifocal 1 Day Contact Lens uses the Principle of Pinhole Optics in its Design

  • The Neurofocus Optics® technology of the NaturalVue® Multifocal relies on the rapid, continuous, and uninterrupted progression in plus power that creates peripheral blur which generates a virtual aperture effect.1
  • This effect results in an extended depth of focus and a clear and continuous range of vision.
  • Most importantly, this center-distance design provides spectacle-level visual acuity for clear vision at every distance for your patients.2

Neurofocus Optics® technology allows the visual cortex to optimize visual clarity enabling spectacle level stereoacuity for excellent depth perception.2

The high levels of uninterrupted plus power progression in the lens are integral to its performance. We now have a way of describing the lens power profile using customized wavefront software.

The NaturalVue® Multifocal Power Profile

There are two definitions of focal powers used to define lens optics:

  • Sagittal (axial or radial)
  • Instantaneous (tangential)

Both methods of description are useful in creating and describing lens designs, but provide different information and are used for different purposes.

Sagittal Power

  • Also called axial or radial power
  • Common output from wavefront sensors
  • Describes a wavefront as it intersects the optical axis
  • Defined by a normal surface line and its intersection with the optical axis
  • A mathematical construct, easily measured
  • Represents average power of the surface
Figure 3: Sagittal (Axial) Representation
Saggital power

Instantaneous Power

  • Also called tangential power
  • Describes a wavefront that does not fall exactly on the optical axis, such as aspheric surfaces
  • Allows us to assess the “true focus”
  • Not measured directly, but calculated from the measured Sagittal power
 
Figure 4: Instantaneous (Tangential) Representation

The Plot of Instantaneous (Tangential) vs. Sagittal (Axial) Power Profile of the NaturalVue® Multifocal

This graph is a direct output from the NIMO (Lambda-X) wavefront sensor of a -3.00D NaturalVue® Multifocal lens over the central 5mm optic zone.

The Instantaneous profile is shown in red (“Instant”) and the Sagittal profile is show in blue (“Radial”).

NIMO chart
Corneal topographers may also provide both instantaneous and sagittal outputs.

So what does this mean for you and your patients?

The information here should help you better understand the optics of the NaturalVue® Multifocal design. Most importantly, the NaturalVue® Multifocal power profile showcases the large progression in plus power in the lens. That large amount of plus power is key to the clinical performance of the lens and is what differentiates the design.

VTI_practitioner_patient

References:
1. Patents Awarded – MULTIFOCAL OPHTHALMIC LENS WITH INDUCED APERTURE, Canada #2121740, Europe (10 countries) #1381908, Japan #5379945, US #s 7178918, 6474814.
2. VTI data on file, 2015. N=59. Data assessed after 1 week of wear. Preference based on those who expressed a preference among brands tested.

MKT-WVTI-P29 r2