There are multiple reasons why vision may be blurry at night. Some of the major causes are cataracts, reflections off of glasses, night myopia, and higher-order aberrations. One of the simplest reasons is possibly due to cataracts. That a cataract is when the lens in your eye gets hazy and when it is hazy it doesn't allow as much light in or scatterers the light to other parts of the retina not helping with vision and can cause light sensitivity. That being said how many times I have heard from people without cataracts saying they have a hard time seeing at night is probably more than I have heard it from people with cataracts.
Let's move on to the next one which reflections off of the glasses. It doesn't take a genius to figure out that at night there is not a whole lot of light. So if any reflections are coming off the glasses then that light isn't getting to your eye and you can't see very well at night. The way we fix that is with Anti-Reflective (AR) coating/Anti-glare coating can help with this. You can clearly see what having an AR coating does to reflection off the glasses.
It also does one other thing with glasses and helps with night drive by making the light more focused. This helps with higher order aberrations also because makes the light more focused coming into the eye which can improve vision. That is why every lens in the phoropter (1 or 2 thing to determine glasses prescription) has an AR coating on every lens in it. The photo below this sentence really demonstrates how much of a change an AR coating can do at night.
You don't have cataracts and you have AR coating already and you still can't see very well at night. Well, then you might have night myopia. This affects 30% of the general population. Night myopia is a little more complex to explain. Let's start out by explaining accommodation also known as near vision. The lens inside your eye has to change shape for you to see things up close. How the lens determines how much it has to change shape varies on many different factors but one is light. That is why it is easier to read in brightly lit rooms compared to darkly lit rooms (menu at fancy restaurants). Now we are in a dark area and now accommodation (near vision) is freaking out and so it doesn't know if it supposes to relax or activate. This causes the glasses prescription to change sometimes very little sometimes a ton. When it changes a ton your vision is blurry at night and that is why sometimes people notice if they move the glasses closer or further away they see better (your glasses prescription changes determined by how close/far away your glasses are.
If you have AR coating, no cataracts and last doctor checked for night myopia (good on the doctor rarely do I see other eye doctors looking for it) then you might have some higher order abberations. This is even more complex to explain with words but very easy with image. The next image is going to show what small light does to the eye has pupil increases in size.
so the 1 mm pupil size is close to what the light source looks like but even at 1 mm you still see a halo you can imagine that is what the light suppose to look like just smaller. Every image at every pupil size should look like 1 mm but you can see all the distortion of the point light. We see a lot more than just one small point of light at night and all those lights being distorted can really blur up vision. The worst part is at night our pupils get larger to let more light in and then that light can become more distorted. This is where people get halos and lines of lights (that not just astigmatism) and other fun distortion with lights at night (some examples below). The way to help with this for minor cases is AR coating because it removes some of the distortion going into your eye but the best way to remove it is my specialty contact lens. Most of these distortions normally are caused by the cornea (front surface of your eye) so using a contact lens like a scleral contact lens normally removes these distortions and helps tremendously with vision! It works by acting like a new cornea that is free of distortion.
There are some other diseases like macular degeneration that can also decrease vision and dark adaptation does decrease with age and if you don't have a bunch of higher order aberration then the pupil does decrease in size throughout life which means less light going to the retina to be processed. I feel like I have talked enough about the most common reasons so I'm going to end it here.
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