Published in Non-Clinical

See For Yourself - Pinhole Optics and Presbyopia

Sathi Maiti, OD

Sathi Maiti, OD

Shane Kannarr, OD

Shane Kannarr, OD

This post is sponsored by Allergan, an AbbVie company
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In this talk from Eyes On 2021, Shane Kannarr, OD discusses concepts of looking at the pupil, using the pinhole optics effect, and how the eye’s natural pupil could be used to modulate near vision.

https://fast.wistia.com/embed/medias/3eahrcid2b/swatch

Consider the pinhole

Consider a large dilated pupil. As light passes through it, the light comes to a sharp point on the retina. It’s very clear, but also very small.5 There is no depth of focus. A clear object exists but at a very specific plane. If that object moves at all, clarity is immediately lost. However, if we make the pupil smaller, that results in a larger depth of focus: if an object moves closer we’re still within that depth of focus and can see the object clearly.4
Ideally, a small pupil or pinhole will improve our depth of focus, and if we can find the right balance, maybe we won’t have to compromise peripheral vision.4

Pinholes, planes, and peripherals

Next, we need to think about where to place the pinhole. If we hold it at the spectacle plane like in clinic, the light passing through the pinhole through the center of the pupil is in focus.5 It’s clear and on the retina. But the light further out peripherally will hit the iris and no longer reaches the retina.5 We’ve now lost that part of the image, so there is a huge trade-off in the restriction of peripheral vision. If we move the pinhole to the corneal plane, then we see a little wider peripheral vision, but a significant portion is still blocked.5
How about if we moved even further, into the iris plane? Now no light is blocked, and peripheral vision is still intact.5

Optimal pupil size: there’s no magic number

What is the optimal pupil size we need to reach for our patients? This is a trick question! There is no set optimal size because pupil size will change depending on the environment and a patient’s normal pupil size.6 We need to instead think about what percentage change in pupil size will give the best vision.
Optimal size is a percentage of the patient’s natural pupil and will vary from patient to patient rather than being a single magic number. A graph of pupil size in bright light versus image quality shows that optimal distance and near vision occurs between 40 and 50% of pupil size, and this occurs across all light conditions including mesopic and low light.6
If the pupil isn’t small enough, there won’t be any near vision improvement. If it’s too small, then we’ve lost our distance vision, but if the pinhole isn’t at the iris plane then we impact peripheral vision. Thus, we need to place the pinhole at the iris which will extend our depth of focus without impacting our peripheral vision, and the optimal pupil size needs to be dynamic so we can have maximum image quality at not just near, but also at distance.6

Sources

  1. Chuck RS, Jacobs DS, Lee JK, Afshari NA, Vitale S, Keenan JD. Refractive Errors & Refractive Surgery PPP - 2017. American Academy of Ophthalmology. https://www.aao.org/preferred-practice-pattern/refractive-errors-refractive-surgery-ppp-2017. Published July 9, 2018.
  2. Moarefi MA, Bafna S, Wiley W. A Review of Presbyopia Treatment with Corneal Inlays. Ophthalmology and therapy. https://www.ncbi.nlm.nih.gov/pubmed/28390052. Published April 7, 2017.
  3. Alio del Barrio JL, Vega-Estrada A. Accommodative intraocular lenses: where are we and where we are going. Eye and Vision. https://eandv.biomedcentral.com/articles/10.1186/s40662-017-0077-7. Published June 26, 2017.
  4. Rocha KM, Gouvea L, Waring GO, Haddad J. Static and Dynamic Factors Associated With Extended Depth of Focus in Monofocal Intraocular Lenses. American Journal of Ophthalmology. https://www.sciencedirect.com/science/article/pii/S0002939420301823. Published April 23, 2020.
  5. Charman WN. Correcting presbyopia: the problem of pupil size. Wiley Online Library. https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/opo.12346. Published December 28, 2016.
  6. Xu R, Thibos L, Bradley A. Effect of Target Luminance on Optimum Pupil Diameter for Presbyopic Eyes. November 11, 2016.
UNB145383 04/21
Sathi Maiti, OD
About Sathi Maiti, OD

Sathi Maiti, OD is an ocular surface disease fellow at the Periman Eye Institute and primary care optometrist in Seattle, WA. She is a sub-investigator of a number of clinical trials related to dry eye and ocular surface disease. She graduated from the UC Berkeley School of Optometry in 2014 where she studied endothelial cell traits as a NEI research trainee and taught undergraduates human anatomy as a graduate student instructor. She is passionate about issues regarding social justice and is a member of the Optometric Physicians of Washington’s Diversity, Inclusion, and Access taskforce. She volunteers her optometric skills extensively through local organizations like Public Health Reserve Corp, Uplift Northwest, Seattle/King County Clinic, and VOSH-NW. She particularly values education and mentorship, and mentors local high school students interested in eye care through Project InSight. In her free time, she loves to play with her pup Kali, draw, crochet, and embroider, and share her love for all things eyeball-related on her optometry instagram account, follow her at @dr.maitiseyeballsandstuff!

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Sathi Maiti, OD
Shane Kannarr, OD
About Shane Kannarr, OD

Shane R. Kannarr, OD, grew up in southeast Kansas and graduated from Humboldt High School. He attended Pittsburg State University (PSU), where he received a degree in biology education. During his time at PSU, he met his wife, Amy Askins Kannarr. He earned his Doctorate of Optometry at the University of Missouri-St. Louis. Upon graduation, he practiced in southwest Missouri and Kansas City before returning to Pittsburg. He has practiced in Pittsburg since 2006 and opened Kannarr Eye Care in 2009. Dr. Kannarr is currently on staff at both Via Christi and Girard Medical Center. He treats all types of medical conditions relating to the eye, with specific interests in dry eyes, glaucoma, and diabetic eye disease. Dr. Kannarr has recently added low vision services to his practice to meet the community's needs.

Dr. Kannarr is active in many aspects of optometry. He is very involved in research and is at the forefront of contact lens technology, with experience in toric, bifocal, and contact lenses for dry eyes. His research in contacts and pharmaceuticals is ongoing through extensive studies and state-of-the-art technology. Dr. Kannarr lectures across the country in the areas of ocular disease, ophthalmic medication, contact lenses, and practice management. He enjoys staying at the forefront of eye care and sharing information with colleagues.

More by Shane Kannarr, OD
Shane Kannarr, OD
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