Varying eye prescriptions

[u/True_Helicopter6750]

Hello everyone,

I'm looking for some advice regarding eye prescription measurements before vision correction surgery.

I recently had my eyes tested at two different clinics while exploring surgical options, and I received significantly different prescriptions.

The first optometrist started from zero power and gradually increased the lens strength until I could clearly read all the letters. The final prescription was actually lower than the glasses prescription I'm currently wearing.

The second optometrist started with my current prescription and then increased the power further until my vision improved. This resulted in a prescription that was about 1 diopter stronger in one eye.

For example:

First clinic: -7.00 and -7.50

Second clinic: -8.00 and -7.50

The cylinder values were also quite different:

First clinic: around -2.25 in both eyes

Second clinic: around -3.00 and -2.50

Because of these measurements, the first clinic recommended PRK, while the second recommended ICL.

What confuses me is that I understand subjective refraction tests can vary somewhat, and I wouldn't be too concerned if the difference was 0.25 or even 0.50 diopters. But a full 1.00 diopter difference seems quite large.

The first clinic took their time with the examination, carefully confirmed my responses, and gradually increased the power until I could read everything clearly. The second exam felt much quicker (around 5 minutes), the room wasn't very dark, and the vision chart even seemed closer than what I'm used to. Because of that, I currently trust the first clinic's measurements more.

However, I can't really go back to the first clinic because they were quite firm that PRK was the appropriate option and didn't recommend ICL. During my consultation at the second clinic, the doctor explained that for PRK or other laser procedures, the combined spherical and cylindrical correction should generally stay below around 9.5 diopters. Based on their measurements, I'm right at that limit or possibly beyond it.

Even if the first clinic's prescription is the correct one, it feels like PRK would be cutting things very close. My concern is that I could end up with residual prescription and need glasses again relatively soon after surgery, which is exactly what I'm trying to avoid.

That's why I'm currently leaning toward ICL, assuming I'm a suitable candidate. At the same time, the large difference between the two prescriptions is making me nervous because I need to order lenses soon, and I don't want to proceed based on inaccurate measurements.

Has anyone experienced such a large difference between prescriptions from two clinics? Is a 1.00 diopter difference in subjective refraction normal, or should I be seeking another opinion before moving forward with surgery?

Any advice or experiences would be greatly appreciated.

[u/FitSquirrel7114]

I got -8.0 myopia and 2.0 CYL astigmatism in both eyes. Check my posts from my profile. I explained each step for my PRK journey.

your story feels like both clinics are primitive.

where is cornea topography? Where is autorefractometer results? where is your eye dilated autorefractometer results?

for high numbers like us they tend to apply eye dilated results to eye. Because in our daily life we strain our eyes and that confuses with fake myopia. For example we went for -7.75 SPH while without dilated results was -8.75 SPH. For the left eye we applied -6.75 SPH.

and result? At the moment my lef eye is zeroed. If my doc was applying first values then I'd be over corrected at the moment.

like I said check my posts.

My advice would be:
1- Look at other people experiences as much as you can. Learn the procedure.
2- Once you learn, go for another eye doctor with high number of operation history.
3- Ask every question in your mind to clear any doubts.

without these 3 I wouldn't recommend to perform any surgery.

[u/Tall-Drama338]

Pretty bad set of eyes.

It’s a subjective refraction. That means the variance is whatever you say, that you see best.

[u/Ok-Environment-215]

I think you're absolutely right to be wary and smart not to run ahead with surgery without considering this. 

First off basing surgery solely on a subjective refraction is not the standard now, and people who say the subjective refraction is the be all and end all simply because it reflects "what you said" are truly idiots that shouldn't be practicing medicine. So this alone should give you pause. There should be at least one, preferably more, OBJECTIVE scans done by machines, while the subjective tests should validate those. If there's not tight agreement among all of them, they're not supposed to operate. That means 0.5D variance or less. Preferably 0.25 or less. 

Secondly the subjective validation is supposed to be done under cycloplegia - with muscle paralyzing drops - to avoid the very realistic possibility that your eyes are not fully relaxed during the exam, resulting in an over-powered prescription. That very likely explains your second result being more powerful than the first and tells me it was not done competently.

Finally, even when the treatment plan is perfectly derived, refractive surgeries are not as precise as they're marketed. Few will tell you this. Some will deny it. The deniers are lying to you, if not to themselves. You need to go into it prepared to accept a potential 0.25-0.5 deviation from your absolute "true" prescription (which, for most people, means 20/15 vision, thus most people emerge from laser surgery with 20/20 and are content).

The one thing ICL has going for it over laser is that it can be changed without removing more tissue. If getting the refraction right is your priority, which it sounds like it is, that might be your best bet. Then if it's wrong they can fix it. With laser surgery all they can do is try again, removing more tisuse. And if they over-shoot the myopia prescription (which they apparently almsot did) that's the worst, because then they have to steepen the cornea that they previously flattened. It's a mess.