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  • Eye Health & Wellness

How Far Can The Human Eye See

  • Last updated December 1, 2022

4 min read

Courtney Dryer, OD
Written byCourtney Dryer, OD
Jovi Boparai, MD
Reviewed by Jovi Boparai, MD
Courtney Dryer, OD
Courtney Dryer, ODOptometristCharlotte, NC

Bio

Dr. Courtney Dryer earned her doctorate from Southern College of Optometry, Memphis, Tennessee in 2011. She opened her own practice Autarchic Spec Shop in 2013 in Charlotte, NC. She has had the privilege of writing for numerous optometric publications and serving in various industry capacities. In 2015, Vision Monday named her a rising star and one of the most influential women in optometry. Her optometric passions include practice management, specialty contact lenses, and dry eye management.

Jovi Boparai, MD
Jovi Boparai, MDCo-founder & CEO of CorneaCarePhiladelphia, PA

Bio

Dry eye disease is tough! I get it. I have struggled with dry eyes for several years from contact lens use, and from spending countless hours looking at computer screens. In college, my dry eyes got so bad that I couldn’t wear contact lenses, because of a constant “foreign body sensation” when I had them in. I had to stop reading every 30 minutes because my eyes would start to burn and my vision would get blurry. I tried a plethora of treatments and nothing seemed to work. Dry eye disease was not only impacting my eyes, but also my emotional wellbeing. It was preventing me from enjoying life, and getting in the way of my professional training. I felt overwhelmed, frustrated and hopeless.

It was only when I realized that my dry eyes were linked to my lifestyle, environment and overall health did things start to make sense. I noticed that on days when I spent less time on the computer, my eyes felt better. My symptoms would flare when it was windy, or when there was low humidity. I knew that if I wanted to get ahead of my dry eyes, I needed to not only treat my eyes, but to also address my lifestyle. I started a consistent regimen of artificial tears and eyelid hygiene. I switched from monthly contact lenses to daily contact lenses. I started taking scheduled breaks from looking at a computer. I ate a healthier diet focused on anti-inflammatory/antioxidants foods, and I bought a humidifier for my room. In the beginning doing all this seemed impossible, but over time it became part of my usual routine. Not only did my eyes feel better, but I was overall healthier and happier! Turns out what is good for my eyes, was also good for my mind and body. I carried this lesson with me as I started my career to become an ophthalmologist and ophthalmic surgeon.

Because of my personal journey and professional training, I believe dry eye treatment starts by listening to and empowering the patient. I listen for the struggles and cue in on their strengths, while picking up on their lifestyle. Only then do we together start building a treatment plan that incorporates good eye hygiene with small, but impactful lifestyle changes. Our sight is our most important sense, and it is intimately linked to our very being. I want dry eye patients to not only get their dry eyes under control, but to also enjoy good mental and physical health, and live a fulfilling life. What is good for the eyes should also strengthen the mind and fortify the body!

Get to know me a little better!

Hobby: vintage watches
Food: peanut butter
Superhero: Superman
Guilty pleasure: desserts
Secret power: has never had a headache

Training:

Undergraduate: University of Pittsburgh Honors College
Medical school: Weill Cornell Medicine
Ophthalmology residency: Wills Eye Hospital.

How far can the human eye see?

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Table of Contents

Overview

The naked eye has the capability of seeing a distance object light-years away under the right conditions. The eye’s line of sight, the brightness of light from the object, and eye health are factors that determine how far the human eye sees. The eye’s clarity and sharpness are measured during an eye exam and can be affected by any ocular pathology that affects eye health or uncorrected refractive error.

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Key Points

  • The object’s brightness and an unobstructed view determines the distance from which the human eye is able to see the object.
  • Visual acuity is the clarity measure of one’s vision.
  • Eye health, refractive error, and ocular aberrations and components affect vision.

How Far Can The Human Eye See?

Viewing the night sky, a full moon or a planet like Saturn through a telescope is different than viewing with the naked eye. Exactly how far can the human eye see? Several factors affect the distance you can see including the capability of the human eye, the brightness of the object and an unobstructed view.

Brightness Factor

M33 is a spiral galaxy located within the Triangulum galaxy. It has a brightness magnitude of 5.7, which makes it one of the most distant objects that can be viewed by the unaided eye (under exceptionally clear and dark skies). M33 is slightly further away from us than the Andromeda galaxy which is located 2.6 million light-years from earth.1,2

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Earth’s Curvature

Due to the curvature of the earth, the farthest object one can see is about 3 miles, but if the earth was flat or one was at a higher vantage point like on top of a mountain, it would be possible to see bright lights in the distance hundreds of miles away, according to livescience.1

Despite 70 years of investigations, the limits of human vision still remained unclear. Rod cells respond to individual photons, yet it remains unknown whether a single-photon incident on the eye can be perceived by a human.3 Research has demonstrated the number of photons at the cornea that reach the retina is somewhere between 10-30%.4

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    Visual Acuity and The Human Eye

    When your vision is checked by an eye doctor or optician, 20/20 is considered normal vision. Visual acuity is a measure of the clarity or sharpness of one’s vision. Visual acuity is a measurement of your ability to see a distance object or a near object and taken using a Snellen chart. The measurement of vision is based on what a “normal” person can see at a distance of 20 feet. For example, 20/20 vision means the patient can see the same as what a normal person sees at 20 feet. Visual acuity is the smallest retinal image appreciated by the eye.5

    Your eye health, refractive error, spatial distance between the photoreceptors, optical aberrations, and pupil size can affect your visual acuity.

    Eye Health

    Eye health can affect your visual acuity. Any ocular pathology or disease process that affects an ocular structure can limit human vision. Conditions of the cornea like keratoconus cause aberrations in vision and even distort the patient’s view. Similarly, cataracts can cause obstructions in your central line of sight and distort colors. Diabetic retinopathy and age-related macular degeneration are eye conditions that make it difficult to see.

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    Refractive Error

    If one cannot view a distance object than they are considered myopic (near-sighted). Individuals with myopia have eyes with a slightly longer length than normal. However, if it is difficult to see near objects, patients are hyperopic (far-sighted) with shorter eyes than normal.7

    Lastly, astigmatism is one of the most common refractive errors and occurs when parallel rays of light entering the eye are brought to a focus at two distinct focal lines perpendicular to each other, rather than to a single focal point resulting in halos and glare.8

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    The Human Eye: How It Works

    The cornea, iris, and lens compose the front of the eye. The retina and optic nerve, equally important structures are located in the back of the eye.

    Front of the Eyeball

    The cornea is the clear dome over the surface of the eye. Its purpose is to protect the eye and refract rays of light. The structure of the eye called the iris allows the appropriate amount of light to enter the retina. The iris is like the shutter of a camera. It allows enough light to enter the eye to activate the retina. The iris dilates in the dark and constricts in the light allowing more bright light through the pupil under scotopic (dark) conditions than under photopic conditions (light). For this reason, when driving, it may be more difficult to see a distant object on a dark night compared to a clear day. Made of tissue, the crystalline lens can change its shape to adjust the power of the eye and to focus the image on the retina called accommodation.9

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    Back of the Eyeball

    The retina is a layer of photoreceptors and glial cells that captures incoming photons and transmits them along neuronal pathways as both electrical and chemical signals to the brain in order to see a picture.10

    It is composed of two different types of cells: rod cells and cone cells. The activation of rod cells and cone cells, also called photoreceptors, initiates our vision. One type of rod cell exists for dim light vision and three types of cone cells enable one to see colors.10 Finally, the signals from the eyeball are sent to the brain through the optic nerve.

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    Putting It All Together

    The capability of human vision remains unknown though a bright object and an unobstructed view are important to see a distance object like the Andromeda galaxy. Additionally, the visual acuity of the human eye is affected by eye health and refractive error. Types of ocular pathology like age-related macular degeneration of astigmatism can have an affect on how the eye sees. Furthermore, visiting an eye doctor to have your vision checked, and your glasses prescription updated is vital to optimizing the capabilities of the eye.

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    What’s Next

    Learn to love your eyes! Read more eye health and wellness tips on our blog.

    Bibliography

    1. Wolchover, N. How far can the human eye see? LiveScience. Published May 7, 2012. Retrieved November 4, 2022.
    2. Messier33 (The Triangulum Galaxy). NASA. Published February 20, 2019. Retrieved November 4, 2022 from https://www.nasa.gov/feature/goddard/2019/messier-33-the-triangulum-galaxy
    3. Tinsley, J., Molodtsov, M., Prevedel, R. et al. Direct detection of a single photon by humans. Nat Commun 7, 12172 (2016). https://doi.org/10.1038/ncomms12172
    4. Field GD, Sampath AP. Behavioural and physiological limits to vision in mammals. Philos Trans R Soc Lond B Biol Sci. 2017;372(1717):20160072. doi:10.1098/rstb.2016.0072
    5. Caltrider D, Gupta A, Tripathy K. Evaluation Of Visual Acuity. 2022 Aug 22. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 33231977.
    6. Van der Sande E, Haarman AEG, Quint WH, Tadema KCD, Meester-Smoor MA, Kamermans M, De Zeeuw CI, Klaver CCW, Winkelman BHJ, Iglesias AI. The Role of GJD2(Cx36) in Refractive Error Development. Invest Ophthalmol Vis Sci. 2022 Mar 2;63(3):5. doi: 10.1167/iovs.63.3.5. PMID: 35262731; PMCID: PMC8934558.
    7. Artal P, Benito A, Tabernero J. The human eye is an example of robust optical design. J Vis. 2006 Jan 10;6(1):1-7. doi: 10.1167/6.1.1. PMID: 16489854.
    8. Read SA, Vincent SJ, Collins MJ. The visual and functional impacts of astigmatism and its clinical management. Ophthalmic Physiol Opt. 2014 May;34(3):267-94. doi: 10.1111/opo.12128. Epub 2014 Mar 18. PMID: 24635572.
    9. Bailey, S. T. M. D. Twa, J. C. Gump, M. Venkiteshwar, M. A. Bullimore and R. Sooryakumar, “Light-Scattering Study of the Normal Human Eye Lens: Elastic Properties and Age Dependence,” in IEEE Transactions on Biomedical Engineering, vol. 57, no. 12, pp. 2910-2917, Dec. 2010, doi: 10.1109/TBME.2010.2052393.
    10. Nguyen KH, Patel BC, Tadi P. Anatomy, Head and Neck, Eye Retina. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.

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