EP: True Blended Vision – How To Do It Right – Part 2


Mr Alastair Stuart (UK) and Dr Ben LaHood (Australia) explore the advancements in technology that enable modified monovision. The discussion encompasses the utilisation of positive and negative spherical aberration, a comprehensive comparison between enhanced monofocal and trifocal IOLs, and valuable insights for surgeons striving to deliver optimal blended vision to patients who desire reduced reliance on eyeglasses.


Dr Ben LaHood (host)
Dr Ben LaHood, refractive cataract and laser vision correction surgeon from Australia, has gained international recognition for his extensive research on astigmatism management and biometry, which is regularly shared around the world. Additionally, Ben is the host of two widely popular ophthalmology-themed podcasts.

Mr Alastair Stuart (guest)
Mr Alastair Stuart is a Cataract and Refractive Surgeon at Optegra Eye Hospital Hampshire in the UK. He is highly experienced in cataract and lens based surgery, has presented on blended vision at congresses around Europe, and he is also one of just a few surgeons worldwide to have had formal training in refractive surgery.

Key Takeaways:

  • Spherical aberration: Mr Stuart explains the concept of true blended vision or ‘modified monovision’, which incorporates positive spherical aberration into each eye to reduce the associated drawbacks of standard monovision. Spherical aberration converts light from passing through a single focus point to spreading light through the visual axis, which elongates the focal range from far to intermediate. Typically, with this method, the reading vision of an eye that is set at distance (which induces spherical aberration), is a lot better than a cataract patient who has a standard monofocal, as the two eyes work together synergistically, resulting in improved tolerance levels of ~98%.
  • Positive spherical aberration: The total spherical aberration in the eye post-surgery includes what was in the lens, and what was innately in the patient’s cornea – Mr Stuart carries out these measurements prior to performing the lens replacement surgery with RayOne EMV, to predict patient outcomes. The distribution of positive spherical aberration in patient corneas is around 0.2 microns, therefore inducing positive spherical aberration with an IOL moves the patients towards 0.3-0.4, rather than negative which would push towards 0.
  • Practising monovision: Standard monovision involves making one eye better for near vision and the other eye for distance, reported downsides for patients include cross blur, suppression of distance sight, and loss of stereopsis – Mr Stuart explains that some surgeons have been burnt because of these complications. Modified monovision brings some useful near and intermediate vision to the system while helping the distance eye, which improves tolerance and extends emmetropia.
  • Patient adaptation: Mr Stuart uses RayOne EMV in two different ways, either at plano or in a modified monovision set-up. During the adaptation period for patients who undergo the monovision set-up, Mr Stuart offers patients temporary glasses which he advises patients to use sparingly to avoid jeopardising the adaptation process.
  • Refractive accuracy: Mr Stuart and Dr LaHood discuss the RayOne EMV lens and its refractive accuracy, which they agreed 80% of patients achieve within half of the intended target. Mr Stuart explains that when patients are off target, they are typically myopic. Mr Stuart has found that the RayOne EMV lens is more forgiving when implanted at plano. He goes on to explain that he targets the first plus on the biometry for the plano eye and tends to aim for -0.25 D to achieve -1.50D in the refraction. Pushing plus in the refraction gives a hard endpoint, and consistent refractions across clinicians is what Mr Stuart advises is important for auditing data.
  • Segmental refractive IOLs vs RayOne EMV: Mr Stuart has limited experience with segmental refractive IOLs, however feels that more than one focal point poses risk to a drop in distance quality and contrast sensitivity. Modern multifocal technology which works to reduce the diffractive rings to reduce glare, in Mr Stuart’s opinion will only compromise the reading vision. The surgeons agree that there is no such thing as a ‘free lunch’ or a perfect lens, however Mr Stuart explains that he prefers implanting RayOne EMV compared to multifocal IOLs due to the higher patient dissatisfaction rate with the latter.

Connect with Dr Ben LaHood on social:
Dr Ben LaHood (@drbenlahood) | Instagram
Ben LaHood | LinkedIn

Connect with Mr Alastair Stuart on social:
Alastair Stuart | LinkedIn