Vision is Subjective

A few things that I frequently talk to my own patients about that might be of some use to you out there is internetland:

1) Vision is subjective. What do I mean by that? Mostly what I am referring to is that the perception & description of "blur" varies greatly between patients. It is anything but standard. We're talking about "how blue is the sky" and "on a scale of 1-10 how much does it hurt to have your foot smashed when someone steps on it" kind of thing. What is & is not "blurry" and how to describe to another person exactly what you see is virtually impossible to ACCURATELY PINPOINT. And even if we could exactly pinpoint to the Nth degree how blurry your vision eye doctors we really can only do TWO things: a) eliminate refractive error and b) treat existing eye disease. If you have no eye disease and you're wearing the correct Rx...that's all we can do. Most people are happy with that, but some 20/20 patients will still tell us "it's so blurry". Ok, we believe you! But...we're limited by what we can do about it. There are other things besides disease & refractive error that cause blur, mostly optical aberrations: spherical aberration, coma, pincushion/barrel distortion, chromatic aberration, field curvature, etc, also macular cone spacing...but we can't really DO anything about any of those here in the real world. Just measuring them in a human eye takes special expensive lab equipment, and we cannot (yet) make a pair of glasses that would eliminate any of those other optical aberrations. Sometimes we have to tell healthy patients with good Rx's that we're at the limit of how "clear" we can make their vision.

2) Subjective testing is what it is: subjective. Ok so we just got finished reading a diatribe on how vision is subjective...but don't we optometrists base our glasses Rx's off of "subjective refraction"? Well yes & no. By the time we have you in the chair & behind the phoropter we've already taken multiple OBJECTIVE measurements on your eyes & refractive status. So we know basically what we're going to Rx you...possibly exactly what it's going to be. So we let you "fine tune" your Rx by offering you a little more or a little less, a little to the left & a little to the right, etc. But there are no "wrong" answers here. If you "choose" something way off, we're not giving it to you. Plus a lot of the time we're "bracketing" anyway...showing you just to the left & just to the right of your Rx but NOT RIGHT ON. So there REALLY isn't a wrong answer there...they're BOTH BLURRY choices. This is one reason why so many people get frustrated by the process of subjective refraction: they assume (incorrectly) that the lenses are "supposed" to be getting subjectively clearer with each successive choice. But they're not. That's not how it works. You're really relying a lot more on the skill & experience of the doctor than you are on your own choices behind the phoropter. That's why it's important to find an optometrist that you connect well & communicate well with.

3) If you hear hoofbeats, think "horses", not "zebras". This is a derivation of Occam's Razor: the simplest solution is probably the correct one. If you're a contact lens wearer & your eye is red, it's probably from contact lens wear. It is probably not "pink eye", etc. It *could be* contagious viral or bacterial conjuntivitis, but that's not the MOST LIKELY cause. If your head hurts it's probably a tension headache, not a tumor. Ok it *could* be a tumor...but statistically it's probably not. Especially in the age of the internet, often patients Google their own eye symptoms/conditions & come up with some very IMPROBABLE scenarios ("zebras"). Even some docs do this. I had a patient with known, longstanding neurological deficits and known, longstanding ataxia (can't walk w/o falling down), and his neurologist referred him for another eye exam saying it "could be" his glasses. Well ok yes it "could be"...but the patient had been here annually for eye exams and his refractive status was virtually unchanged in 20 years. His ataxia is PROBABLY NOT the result of an incorrect glasses Rx. That's a "zebra" for sure.

4) A lot of eye conditions have the same symptoms: The human eye can only respond in a limited number of ways - pain, redness, foreign-body sensation, vision loss, light sensitivity. That's pretty much it. Consequently many patients will call me asking me to please refill their eye drop Rx from 2.5 years ago b/c "it's the same thing again." Well, how do you know it's the same thing? You don't. There's no way for you to know it's the same, or even for ME to know it's the same unless I *LOOK* at your eye. Listing the symptoms again (foreign body sensation, redness, blur, etc) over the phone does not help much, b/c most symptoms are the SAME for most eye conditions. Someone has to LOOK at your eye anyway.


  1. Can you address what is normal and abnormal when it comes to the blood vessels in the whites of your eyes. I often feel like mine are too red or there are too many. However I don't have any pain or vision problems. They are not growing into my cornea or the colored part of my eyes. While I do wear contacts, I only wear them about 50% of the time. And I often wear my glasses 4 or 5 days in a row, so I don't think that is the problem.

  2. well, that's is tough b/c I can't see your eyes. some amount of surface vasculature is normal, however assessing whether YOU have an abnormal amount or size of vasculature...I would need to see you.

    1. I notice that my eyes change daily. My eye doctor says a lot of the bluriness can be caused by my dry eyes.

      I have been using Restasis for 6+ months (with some improvement), consume ~2,000 mg of fish oil daily, drink many glasses of water daily, and get 7 hrs of sleep without a fan on. I have read online that many older women might have dry eyes, or people who live in really hot/dry areas...but I am a 21 year old male living in the Midwest. I have been allergy tested a couple of times recently and have found that I have no seasonal allergies. My eye doctor agreed with the allergist and said my entire issue is the dryness.

      No matter what I do, my eyes are so dry that it makes my eyes quite blurry even though my glasses are up-to-date, which goes along with your above post of being "perfect" but blurry. I wear my TruEyes contacts about 5 hours every 2 weeks and use unexpired BioTrue solution. (I have gone through all soft contact lenses and the Acuvue Moist and TrueEye were the only two daily disposables that fit....which isn't really an issue because I rarely wear contacts).

      Do you have any suggestions for what I can do to make my eyes wet enough to see clearer? My eye doctor suggested those plugs in my lower eyelids, but I know that there is some argument on whether or not those minimize Restasis' effect. If I understand correctly, the argument now stands with the plugs not having an effect on that is my next plan.

      Thanks for your time and awesome blog!

  3. Ok thanks. I am actually going to my eye doctor on Wednesday. Can you give me an idea of what might cause an abnormal amount or size of these blood vessels?

  4. plenty of things: inflammatory conditions, contact-lens fitting issues (specifically "too tight"), or even many, many years of contact lens wear...

  5. Thanks for taking the time to make this post. I feel reassured that when anyone is sitting in that chair, the optometrist has already taken objective measurements and whatever me might say is blurry or not is really just a fine tuning for subjective comfort.

    It would be scary to think that an Rx is completely up to how your good your sight is on a given day when you go into the docs!

  6. Thanks for taking the time to post this! It is reassuring to know that when you sit down in that chair, the optometrist has already made objective measurements and the "fine tuning" is really just for subjective comfort.

    It would be scary if your Rx is dependent on how good your sight holds up on a given day at the docs!

  7. Thanks for taking the time to post this! It is reassuring to know that when you sit down in that chair, the optometrist has already made objective measurements and the "fine tuning" is really just for subjective comfort.

    It would be scary if your Rx is dependent on how good your sight holds up on a given day at the docs!

    March 7, 2012 6:49 PM

  8. unfortunately I don't have much new info for you. sounds like you're doing all the right things. I'm not a big fan of plugs, but that's just me. I'll do them if I think they'll help, but not very often. have you tried "lid scrubs"? maybe some of your dryness is meibomian gland dysfunction. that would be an OTC thing you could try:


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