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EXTENDED DEPTH OF FOCUS OPTICAL DEVICES

The ability to provide good vision at all distances, while minimising ghosting and haloes, is a defining characteristic of extended depth of focus (EDOF) optical devices, which presently includes contact lenses and intraocular lenses.

Brien Holden Vision Institute has incorporated extended depth of focus (EDOF) principles into the design of:
  • Contact lenses to correct presbyopia
  • Contact lenses for myopia management
  • Intraocular lenses (IOLs)
  • And is exploring other applications of this approach, including spectacles.

VISUAL PERFORMANCE COMPARISON

The images and graphs below are representative of the visual performance characteristics of different contact lens designs - single vision; bifocal; and extended depth of focus (EDOF). This includes visual acuity and 'image quality' at distinct viewing distances, as well as through the 'transition' zones between these points. (Click images to enlarge)
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SINGLE VISION

The landscape image above has been modified to demonstrate how someone with presbyopia will see this scene if they are wearing a standard single vision lens.
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The above graph demonstrates how light energy is distributed at the retina after passing through a single vision lens. The resultant light energy distribution is concentrated only in one region offering excellent visual experience at only far visual distance (the area around the mountains).
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BIFOCAL

The landscape image above has been modified to demonstrate how someone with presbyopia will see this scene if they are wearing a standard bifocal lens.
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The above graph demonstrates how light energy is distributed at the retina after passing through a bifocal lens. The resultant light energy distribution is concentrated only in two regions offering optimal visual experience at two corresponding distances: far (the area around the mountains) and near (phone).*
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EDOF

The landscape image above has been modified to demonstrate how someone with presbyopia will see this scene if they are wearing our EDOF lens.
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The above graph demonstrates how light energy is distributed at the retina after passing through an EDOF lens. The resultant light energy distribution is evenly spread on or before the retina to offer optimal visual experience for the corresponding distances: far (the area around the mountains), intermediate (eagle) and near (phone). The resultant through-focus ‘retinal image quality’ offered by an EDOF lens facilitates a smooth transition of vision between the different distances.
In the above plots, the height of the surface in each graph indicates the contrast that can be achieved at the corresponding viewing distance or the respective type of vision correction device. In general, higher contrast provides better vision. The ‘width’ of the surface (front to back along a white line on the blue base) indicates how sharp an image is. A narrower width indicates a sharper image and better visual acuity

*The representation here of bifocal lens performance will hold true for tri- or multifocal contact lenses, except that the power of the lens will be concentrated at near, intermediate and distance. Disclaimer – the images and graphs above are for illustrative purposes only and are designed to represent the general characteristics of different lenses, not the exact nature of them.

CONTACT LENSES FOR PRESBYOPIA

Many commercial multifocal lenses claim to provide simultaneous vision at various visual distances but often this comes at the cost of reduced contrast, increased ghosting (a blurred, shadow-like effect), haloes (rings around bright points of light) and compromised overall vision satisfaction.

Several factors can lead to variability in visual performance, which can occur at one or more distances including:
  • Type of lens design (centre-near, centre-distance multifocal or concentric bifocal),
  • amount of near add power
  • pupil size
  • rate of power change across the optical zone
  • inherent spherical aberrations of the corrected eye
  • contact lens centration on eye
These shortcomings are often exacerbated with low illumination levels. Such visual compromises have been associated with an increase in patient dropout rate and lack of confidence in fitting by practitioners.

Our extended depth-of-focus (EDOF) contact lenses, based on patented technology developed by Brien Holden Vision Institute, are designed to provide optimal visual performance from distance to near. The lenses:
  • Use multiple higher order aberrations to optimise retinal image quality over a wide range of distances from far to near while minimising ghosting and haloes;
  • Perform relatively independently of patients’ natural aberrations and variation in pupil size; and
  • Are designed to meet the vision needs of emerging, moderate and advanced presbyopes.
  • In published clinical studies these EDOF designs have compared very favourably over a range of measures with currently available multifocal lenses.1-5

CONTACT LENSES FOR MYOPIA

Research studies have found that correction strategies that reduce hyperopic defocus or impose myopic defocus can slow myopia progression.

Our EDOF myopia management contact lenses are designed to result in a global retinal image quality (across both central and peripheral retina) that remains invariant for points on and in front of the retina and are degraded for points behind the retina to prevent further axial elongation.6

A shortcoming of current contact lenses and spectacles designed to slow the progression of myopia, is that they can result in compromised visual performance, leading to limited uptake of these lenses and compliance issues.

Subjective variables that may be affected include:
  • Clarity of vision
  • Ghosting for distance, intermediate, and near distances under day- and night-time conditions.
  • Vision stability under day- and night-time conditions
  • Driving vision under day- and night-time conditions
  • Night-time haloes
  • Ocular comfort
  • Overall vision satisfaction
Through manipulation of higher order aberrations our myopia management contact lenses are able to minimise visual disturbances that are characteristic of other myopia management contact lenses.

They provide good vision at all customary viewing distances, minimizing unwelcomed visual compromises like ghosting and haloes commonly associated with conventional simultaneous-image multifocal optical designs.

Visual performance with the EDOF myopia management contact lenses is designed to be relatively pupil neutral and relatively independent of the individual’s inherent ocular aberrations.

Our EDOF lenses have demonstrated improved visual performance over a range of the subjective variables listed above, compared to the traditional bifocal and multifocal alternatives.7 (Click images to enlarge)
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INTRAOCULAR LENSES

Brien Holden Vision Institute is developing a portfolio of technologies designed to improve the through focus visual performance of the eye as a solution for presbyopia, implementable in both contact lenses and IOLs for phakic and pseudophakic eyes.

These products are designed to provide an extended depth of focus (EDOF) range of clear vision, rather than discrete foci at prescribed intermediate and/or near points, as delivered by current bifocal and trifocal lenses. To achieve this EDOF effect, we have developed proprietary technologies, which allow the design of lenses with varying configurations of EDOF to suit differing patient needs.

Our EDOF patent portfolio covers two distinct design approaches to achieve the desired EDOF performance, collectively identified as:
  • Higher order aberration (HOA) Manipulation – which involves deliberate and selective manipulation of HOAs to optimize the retinal image quality over a range of viewing distances.
  • Phase-step – which uses phase modulation to create a stable through focus distribution of light by means of light interference.
Phase-step methodology is especially well-suited for application to lenses immersed in the aqueous environment of the eye and positioned near the eye’s pupil, and as such is ideal for use in IOLs.

We have generated optical designs which provide an EDOF effect over a
2.00D range with little variation in contrast throughout, and image quality equal to or better than the currently available multifocal IOLs’ in that correction range.
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Brien Holden Model Eye System - a custom-designed research instrument
which replicates the parameters of a typical human eye

We have established a range of metrology methods, including a proprietary Model Eye System, which allow both physical and optical measurement of IOL’s fabricated with both HOA manipulation and phase-step technologies.

Optical prototypes have been made and tested them in the Model Eye System, demonstrating a through-focus vision performance which is truly extended depth of focus in nature, a feature that is not observed in commercially available IOLs.

FUTURE EDOF APPLICATIONS

We are exploring further applications of EDOF principles into other optical devices, including spectacle lenses.
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REFERENCES

1. Bakaraju RC, Ehrmann K, Ho A. Extended depth of focus contact lenses vs. two commercial multifocals: Part 1. Optical performance evaluation via computed through-focus retinal image quality metrics. Journal of Optometry (2017), http://dx.doi.org/10.1016/j.optom.2017.04.003

2. Bakaraju RC, Tilia D, Sha J, Diec J, Chung J, Kho D, Delaney S, Munro A, Thomas V, Extended depth of focus contact lenses vs. two commercial multifocals: Part 2. Visual performance after 1 week of lens wear, In Journal of Optometry, 2017, ISSN 1888-4296, https://doi.org/10.1016/j.optom.2017.04.0

3. Sha J; Tilia D; Kho D; Diec J; Thomas V; Bakaraju RC. Comparison of Extended Depth-of-Focus Prototype Contact Lenses with the 1-Day ACUVUE MOIST MULTIFOCAL After One Week of Wear. Eye & Contact Lens: Science & Clinical Practice. Publish Ahead of Print: OCT 2017. DOI: 10.1097/ICL.0000000000000430

4. Tilia D, Bakaraju RC, Chung J, Sha J, Delaney S, Munro A, Thomas V, Ehrmann K and Holden BA, Short-Term Visual Performance of Novel Extended Depth-of-Focus Contact Lenses, Optometry and Vision Science. 93(6):656, June 2016.
5. Tilia D, Munro A, Chung J, Sha J, Delaney S, Kho D, Thomas V, Ehrmann K and Bakarajua RC, Short-term comparison between extended depth-of-focus prototype contact lenses and a commercially-available center-near multifocal, J Optom. 2017 Jan-Mar; 10(1): 14–25.

6. Sankaridurg P, Bakaraju RC, Morgan J, et al. Novel contact lenses designed to slow progress of myopia: 12 month results. Poster presented at: Association for Research in Vision and Ophthalmology (ARVO); May 7–11, 2017; Baltimore, USA. Abstract 2391.

7. Sha J, Tilia D, Diec J, Fedtke C, Yeotikar N, Jong M, Thomas V and Bakaraju RC. Visual Performance of myopia control soft contact lenses in non-presbyopic myopes. Clinical Optometry, 2018:10, 75-86.