0.25-0.5 Difference in eyes. Ocular Dominance? When to reduce?

Hi All,

I have a 0.25 difference between in my prescriptions atm (R-7.75 / L-8.0)

I know that this has been covered a bit in other threads. So yes. I have used the search function!

Would still love for people to chip in with their view if they have time.

Not Not mentioned in another thread that a 0.25-0.5 difference in eyes is within the realm of ocular dominance.

A post from Tat and a response from David talking about just dropping 0.25 diopter difference on the next pair of glasses. Because I guess. 0.25 difference is essentially useless.


So I have a few questions.

  • Do people agree that essentially a 0.25 difference should be ditched on the next reduction?

  • When to reduce? If one of my eyes is reading 20/20 on the Snellen and the other is reading 20/25 or 20/30 is that fine to reduce? or;

  • Do I wait until both eyes are 20/20? or;

  • Is that impossible for both eyes to be 2020? Because of ocular dominance?

Answers and help would be greatly appreciated!

Thanks LeMeow Crew!

1 Like

What a rabbit hole you have sent me down!


My thoughts are to let sleeping dogs lie, especially ones as little as 0.25D. :dog:

I can’t give a useful answer on any of your questions. My sleeping dog is a very big one, and I am still letting it lie. :smile:

1 Like

I’m curious about this as well since I have a 1.63 (spherical equivalent) or 1.75 diopter gap to deal with. I will need to start equalizing within the next couple of years (assuming 4 cycles per year and ~0.125D to 0.25D drop per cycle) if I’m going to have any chance of getting my eyes equalized before reaching 20/20.

If the goal is just to hit a 0.5 diopter gap between the eyes to support ocular dominance, I can plan to wait a bit longer to start equalizing. I have seen others on here aiming for full equalization between both eyes though, so that had been my plan until I started reading more.

1 Like

Thanks Ursa,

I will use that metaphor.
I really want to give this sleeping dog a kick up the ass and get him to reduce!!
But yes, stick to the metaphor.

Yes, I’ve heard both and mixed advice before. Either wait, or just reduce. But wanted to raise it again because it hasn’t been discussed in a while.

1 Like

You might get bitten - that is the point of the metaphor. :wink:

1 Like

bumping this one up again coz would love to get some answers on this.


Well, I have a diiference of 0.25 or 0.50 (R -8 cyl -2(.5) L -8.(2)5 cyl -1.5 - SE is equal) and I just use equal prescription (contacts without cylinder even!). Yet still see some progress.

1 Like

@Markiyan oh thats good to know!
And do you reduce bifocally, when you can see the 20/20 when using both eyes.
Or do you reduce monofocally, when each individual eye can see 20/20?

1 Like

Well, things were a bit tricky now.

With my fall-back normalized (-9.00 CYL -1.50), left eye has lower visual acuity (some of 20/40 at night) despite being less undercorrected (-9.50 CYL -1.75 is full correction), so 0.63 undercorrection. Right eye’s full at -9.00 CYL -3.25, so 0.87 undercorrection. Yet it sees a row better (some of 20/30 at night). Remember there’s a need to compensate cylinder for vertex distance as well - I have full glasses cylinder R -3.25 L -1.75 and full contacts cylinder R -2.25 L -1.25.

But I am more a contact lens user now, so I use -7.00 contacts for both eyes, no cylinder correction. They allow me to see my computer from 55-70 cm distance. Left eye is favored as it sees significantly better without cylinder correction. I am still undercorrected for distance, but these days I will choose some glasses to wear over contacts for distance (-1.50 sphere and maybe a bit of cylinder, e.g. -1.0 or -1.5 - full contacts cylinder is R -2.25 L -1.25). Therefore, I can’t judge yet how quick on each eye I will reduce. The fact is I have improved by 1/4 diopter in 2 months, because I measure centimeters with contacts in and resulting cm measurements in -1~-3 (33-100 cm) range are very accurate, up to 1/8 diopter. Even if some mistake has dropped into my calculations, I am a rational optimist and won’t re-measure it hundred times to make sure it’s really the case.

My arguments why I should get rid of astigmatism first:

  • I did not have it 2 years ago
  • It’s easier to track my vision when there’s only “spherical” variable
  • Easier to use contacts: I did not find toric contacts I could wear comfortably
  • I have a tendency to strabismus: I do eye exercises to eliminate that so it could fix astigmatism as well
1 Like

In reply to your first post:
my take on equalising

1 Like

Thanks Bianca!

Ive re read your post.
Thats really helpful.
Thanks so much.

I had another question.
So do you reduce when say one eye is seeing 20/20 and the other is seeing 20/25?
Do you acknowledge this as the ocular dominance and not worry too much?

Jake mentioned the other day in relation to ocular dominance and reducing… “when the higher diopter eye has caught up to previous relative levels”

I interpret this as if you know what your own ocular dominance is, just watch out for that and make sure you reach that before you reduce. i.e. your eyes are at the same relative level
as they were at the previous higher diopter…Thoughts?

All diopters are ranges and lenses are scaled arbitrarily by quarter diopters, so obviously it matters which end of the range you are at.
Dominant eye confident with 20/20 and non-dominant one is still just getting 20/25 on better days but is closer to 20/30 or 20/40 on other days => not OK for next reduction.
Dominant eye confident with 20/20 and non-dominant one is confident with 20/25 most of the time => OK for next reduction.

Having said that I had the general weekly pattern of 4-5 days with the current normalised, 1 day with 0.25D higher correction (to enjoy clarity + remind myself of clarity) favouring the non-dominant eye, 1-2 days with zero diopter reset or next normalised. If the higher correction feels like a nice relief then the current normalised glasses are challenging enough. If it is too much of a relief, maybe I reduced too quickly and then I would step back for a while and then reduce back again. If the next normalised starts to feel OK for the non-dominant eye, too, I’d shift over to them.

You are reducing 0.25D only, but if the 0.25D reduction means a drop of 4 or more lines on the Snellen for the non-dominant eye, then it is too early.
I agree with Jake of course, best to avoid increasing the gap. Maintaining the relative levels is fine.


Thanks so much for the detailed response.
I think @halmadavid had similar queries. David you may like to read some of these posts Bianca has here.