Foreword –
TRIUMF, self described to be “pushing the frontiers in research to advance science, medicine, and business” is a particle accelerator centre in Vancouver that was founded by The University of British Columbia, Simon Fraser University, and The University of Victoria. The centre has a variety of programs focused around research and education, and sharing the latest science with the community. Their mission includes the hunt for the smallest nano-particles in the universe and the next generation of medical isotopes. I was recently fortunate enough to be invited give a presentation to an audience interested in all things science at their Public Saturday Morning Lecture Series, read below and watch the video to learn all about the use of physics in an eye exam and optometry!
Into – Physics in an Eye Exam
It’s no secret that optometry is a field that relies heavily on physics during an eye exam. From using lasers to measure refractive errors to diagnosing and prescribing treatments for various eye conditions, doctors of optometry must be comfortable with using mathematical formulas and principles to understand how the eye works. In this post, we’ll take a look at some of the key uses of physics in eye exams and optometric care. We’ll also explore some of the exciting new technologies being developed in this area. So if you’re curious about what goes on behind the scenes during an eye exam, read on!
Ocular Anatomy and the Eye Exam
The eye is an amazing structure that has evolved over many years to allow us to see and perceive the world we live in. In order for us to see clearly, a very specific and precise structure and anatomy must be present. And a very large number of extremely complex physiological steps are required to transform a blip of light into what we see and perceive as an object.
The cornea is the most anterior structure of the eye that is responsible for the majority of the eye’s refracting power. It is formed by collagen, proteins, and a variety of other cells that are very precisely aligned in order to not only have some structural rigidity, but to also maintain perfect clarity.
Another vital part of the eye that light bends through is the lens. The natural lens found in the eye is a bi-convex structure whose main responsibility is to bend and focus light in a more precise manner to a specific spot on the back of the retina. In order for us to see clearly, this structure must also be perfectly clear. As the proteins in the lens start to degrade, we develop what many people know as a cataract. The lens is controlled by muscles that have the ability to change the shape of the lens, which subsequently allows us to focus light, particularly during near work.
Focusing light is great and all, but in order for us to process light and actually see, the eye must have a way to interpret the light as information and send it back to the brain. The posterior portion of the eye is a structure that we call the retina. The retina is a comprised of cells referred to as photoreceptors, the two main types being rods and cones. Rods and cones have the ability to get triggered by even the smallest stimuli of light. The stimuli starts a physiological cascade that transforms a blip of light into an electrical physiochemical signal, which produces a gross electrical potential relative to the brains visual processing centre.
Physics terms used in an eye exam
20/20 vision during your eye exam
Everyone has heard the term 20/20, but very few people actually know what it means. 20/20 is what your optometrists use as the “gold standard” of the size of letter we would like you to be able to see. It is technically referred to as the Snellen fraction, named after a Dutch eye doctor, named Dr Herman Snellen. The Snellen fraction is in fact a ratio; the numerator is the testing distance (20 feet in our case), and the denominator is the letter. Therefor someone with 20/40 vision can only see a letter that is twice as big at 20 feet as someone with 20/20 vision.
Discovering nearsightedness and farsightedness in an eye exam
In order for an individual to see clearly, light from the environment must be shone into the eye and focused directly on the retina. People who are nearsighted (also known as myopia) either have an eye that bends light too much or an eye that is too long. People who are farsighted (also known as hypermetropia) are the opposite; they have eyes that either do not bend light enough or have an eye that is too short. Your optometrists typically uses a piece of equipment called a phoroptor to determine the nature of your refractive prescription
Eye exams and the use of lenses
The use of Concave vs Convex lenses in an eye exam
In order to correct for your nearsightedness or your farsightedness, lenses can be used to refract light so that it becomes in focus on the retina. People who have eyes that are nearsighted require the use of a lens that is concave in nature. People with eyes that are farsighted require the use of a lens that is convex in nature. The power of a lens is graded with a unit called a diopter, which is typically the number that is found on your glasses prescription.
How are prisms used in an eye exam?
Another way your optometrists can bend light to benefit your vision is through the use of prisms. Prisms are not put in your glasses to change to focal point of glasses; rather, they are used to bend light for the benefit of the muscles that control your eye movements. People who have subtle discrepancies between their eyes, people with some types of “lazy eyes”, and people with symptoms of double vision can all benefit from prisms.
Conclusion
You may be surprised to learn that your eye doctor needs to know a lot of physics in order to perform your eye exam. In fact, vision is so dependent on physics that many of the tests and procedures during an eye exam are based on principles of light and optics. If you want to learn more about how your eyes work and what happens during an exam, we encourage you to watch our video or come in for a visit. We would love to chat with you about all things vision-related during your eye exam!
Hopefully this post gave you an introduction to how much physics is used during an eye exam. Whether its the anatomy of the eye and it’s structures, or the tests and terms used during your eye exam, physics is essential. For more information, visit Prpic Eyecare Centre and see how their services can help you optimize you ocular health and preserve your vision, call 604-337-2575 or email us at info@prpiceyecare.com
