In trying to use defocus curves, the horizontal (D) axis can be confusing. I propose to translate that axis to feet.
Defocus curves are normalized to label the maximum acuity as zero D.
When you have an IOL placed, there is an amount of lens diopters that would make the best focus be at far distances (such as infinity). People often "target" a max sharpness on an IOL to be nearsighted by some amount. This might be expressed as -0.75 D target. When I use the term target, that is accurate for planning. Once implanted, there is a focus reality, but for convenience, I will use the word target to also mean that. Maybe there is a better word to use for both, but for what you can control, you can control your target. You cannot control your reality.
So the D-scale conversion is very much a function of the target. I have made a spreadsheet, and will post some examples for various targets.
Initially, I will choose -targets from 0 D to 3 D as targets, and provide conversions from D to ft. Example, if your target is -1.5 D, then the 0 on the horizontal axis corresponds to 2.2 ft. The -1 on the axis corresponds to 1.3 ft.
Target: 0 Step size: 1
D on graph 2 1 0 -1 -2 -3 -4 -5 -6
Translate to ft far far far 3.3 1.6 1.1 0.8 0.7 0.5
Adjusted D #VALUE! #VALUE! #VALUE! 3.28084 1.64042 1.09361333333333 0.82021 0.656168 0.546806666666667
meters #VALUE! #VALUE! #VALUE! -0.3047999902464 -0.609599980492801 -0.914399970739201 -1.2191999609856 -1.523999951232 -1.8287999414784
ft #VALUE! #VALUE! #VALUE! far far far far far far
Target: -0.25 Step size: 1
D on graph 2 1 0 -1 -2 -3 -4 -5 -6
Translate to ft far far 13.1 2.6 1.5 1.0 0.8 0.6 0.5
Target: 0.5 Step size: 1
D on graph 2 1 0 -1 -2 -3 -4 -5 -6
Translate to ft far far far 6.6 2.2 1.3 0.9 0.7 0.6
Target: -1.5 Step size: 1
D on graph 2 1 0 -1 -2 -3 -4 -5 -6
Translate to ft far 6.6 2.2 1.3 0.9 0.7 0.6 0.5 0.4
Target: -2 Step size: 1
D on graph 2 1 0 -1 -2 -3 -4 -5 -6
Translate to ft far 3.3 1.6 1.1 0.8 0.7 0.5 0.5 0.4
Target: -2.5 Step size: 1
D on graph 2 1 0 -1 -2 -3 -4 -5 -6
Translate to ft 6.6 2.2 1.3 0.9 0.7 0.6 0.5 0.4 0.4
Target: -3 Step size: 1
D on graph 2 1 0 -1 -2 -3 -4 -5 -6
Translate to ft 3.3 1.6 1.1 0.8 0.7 0.5 0.5 0.4 0.4
The equation (1/D)/0.0254 gives you the results in inches.
I see I missed including target:1.0 in the table. I have already revised my spreadsheet, and will post an updated image. Let’s see if I want to incorporate other changes. For example, in addition to each “Translate to ft” line, I could add another line “Translate to cm” or “Translate to meters”.
Any questions on what this table is about or how you would use it?
Here’s how I do it (see my graph by clicking on image)
Here’s how I do it (see my graph by clicking on image)
Very nice useful presentation, Jimluck. I commend you.
Jimluck’s picture is best.
However I already expanded my spreadsheet, and it could be useful to somebody.
Translating Defocus Curves from D to feet
Target: 0 Step size: 0.5
D on graph 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3
Translate to ft far far far far far 6.6 3.3 2.2 1.6 1.3 1.1
Translate to m far far far far far 2.00 1.00 0.67 0.50 0.40 0.33
Target: -0.25 Step size: 0.5
D on graph 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3
Translate to ft far far far far 13.1 4.4 2.6 1.9 1.5 1.2 1.0
Translate to m far far far far 4.00 1.33 0.80 0.57 0.44 0.36 0.31
Target: -0.5 Step size: 0.5
D on graph 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3
Translate to ft far far far far 6.6 3.3 2.2 1.6 1.3 1.1 0.9
Translate to m far far far far 2.00 1.00 0.67 0.50 0.40 0.33 0.29
Target: -1 Step size: 0.5
D on graph 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3
Translate to ft far far far 6.6 3.3 2.2 1.6 1.3 1.1 0.9 0.8
Translate to m far far far 2.00 1.00 0.67 0.50 0.40 0.33 0.29 0.25
Target: -1.5 Step size: 0.5
D on graph 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3
Translate to ft far far 6.6 3.3 2.2 1.6 1.3 1.1 0.9 0.8 0.7
Translate to m far far 2.00 1.00 0.67 0.50 0.40 0.33 0.29 0.25 0.22
Target: -2 Step size: 0.5
D on graph 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3
Translate to ft far 6.6 3.3 2.2 1.6 1.3 1.1 0.9 0.8 0.7 0.7
Translate to m far 2.00 1.00 0.67 0.50 0.40 0.33 0.29 0.25 0.22 0.20
Target: -2.5 Step size: 0.5
D on graph 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3
Translate to ft 6.6 3.3 2.2 1.6 1.3 1.1 0.9 0.8 0.7 0.7 0.6
Translate to m 2.00 1.00 0.67 0.50 0.40 0.33 0.29 0.25 0.22 0.20 0.18
Target: -3 Step size: 0.5
D on graph 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3
Translate to ft 3.3 2.2 1.6 1.3 1.1 0.9 0.8 0.7 0.7 0.6 0.5
Translate to m 1.00 0.67 0.50 0.40 0.33 0.29 0.25 0.22 0.20 0.18 0.17
Target: -3.5 Step size: 0.5
D on graph 2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -2.5 -3
Translate to ft 2.2 1.6 1.3 1.1 0.9 0.8 0.7 0.7 0.6 0.5 0.5
Translate to m 0.67 0.50 0.40 0.33 0.29 0.25 0.22 0.20 0.18 0.17 0.15
I used a slightly different approach since I was planning to have a near eye and a far eye. I made up tables that showed the distance at various visual acuities, from where the curve went from 20/40 near to 20/40 visual acuity measurements. This allowed me to look at how different lens combinations would affect each other, and what predicted results would be if I went for more distance or near vision. I could check where the “near” lens would drop below 20/32 for distance and compare the “far” lens at that distance to predict possible holes in intermediate vision.
For example, here’s what I found for a -0.5D lens:
I used the distance at which vision crossed the line for 20/32 as a cutoff for “good” vision. A -0.5 lens gave me good near vision down to about 31", and my distance vision would be no worse than 20/25 from about 39" and beyond, assuming I had similar results.
For near I selected -1.75.
This predicted “good” near vision down to around 16", and the crossover between the lenses showed my intermediate vision never dropping below 20/32 with at least 20/25 vision out to around 32". (With both eyes I actually do a little better than this–I can read the J1 Jager line down to about 16", and can read the 20/20 line on the Snellen chart.)
I found making charts to see lens performance at different targets really useful for making a decision. Another thing that was VERY useful was measuring actual distances for different activities–how close is the kitchen counter for food prep, for example–to determine what visual distances you use most often–to factor into target decisions.
Note: I looked at as many defocus curves as possible and tried to include worst case results and tests with large sample sizes since near(er) vision was more important to me than distance.
Hi,
i dont quite understand how to read the curve. for example, at plano, visual acuity is 20/20 at 0D, but at -1 target, does the 20/20 visual acuity land at 39" and anything over 39" will have visual acuity about 20/25 to 20/40?
i dont quite understand how to read the curve. for example, at plano, visual acuity is 20/20 at 0D, but at -1 target, does the 20/20 visual acuity land at 39" and anything over 39" will have visual acuity about 20/25 to 20/40?
No. The real curve is smooth. So at 42 inches, the acuity might land at 20/21
This is two defocuse curves. It compares a standard Tecnic monofocal with the Eyhance monofocal. The visual acuity is on the Y axis. Defocus is on the X axis. For the regular monofocal the -1D (39") defocus acuity is 20/40. For the Eyhance it appears to be around 20/28 ish. If you want to use a defocus curve to predict acuity with different targets I would suggest that its easier to just shift the whole curve to the right.
hi Jim. not sure if you’re still in this forum but does this mean at plano, you can have good visibility from far up to 20 inches but only up to 39 inches for regular Technis? so Eyhance gives you 19 more inches of visibility? thank you!
hi Jim. not sure if you’re still in this forum but does this mean at plano, you can have good visibility from far up to 20 inches but only up to 39 inches for regular Technis? so Eyhance gives you 19 more inches of visibility? thank you!
I would suggest you not take that at face value. If you just go by that curve, it would seem that the Technis would perform as well as a regular monofocal at peak focus.
So you are reading the graphs correctly. I am saying to be skeptical of the graph.
thank you. i’m trying to find out how much more intermediate distance is eyhance really expected to provide, assuming average results.
It varies so much from person to person so take it all with a grain of salt. But I think it’s safe to say that most people can rely on getting decent vision down to 26" or so (outstretched arm / fingertips) with Eyhance. Don’t expect near. Do expect good dashboard vision in good light.
I would suggest that those defocus curves are suspect for the Eyhance lens. They show no loss of peak visual acuity due to the extended depth of focus features of the lens, and also show an unrealistically large gain in near vision at logMAR 0.2 and 0.3, with gains up to 1.0 D. Lenses that qualify as an EDOF require a minimum gain of 0.5 D, and Eyhance lens is not even marketed as an EDOF. The Eyhance has more like 0.25 D of a gain. These defocus curves comparing the Eyhance to the Tecnis 1 are much more realistic.
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The problem with a table of values is that distances at positive D defocus values are undefined (beyond infinity). To me it is much simpler to simply divide 1 meter by the negative defocus positions to get distance in meters. The value of defocus curves to the left of the peak vision point only have meaning and value when the lens is targeted to a negative value.
See this graph comparing the Tecnis 1 to the Eyhance. Also keep in mind that the Tecnis 1 has the least amount of depth of focus of all monofocals. Recent Alcon data showed that the difference between a Clareon and Eyhance was clinically insignificant.
The value of defocus curves to the left of the peak vision point only have meaning and value when the lens is targeted to a negative value.
True, but targeting (or ending up with) a negative value is pretty common, and those considering a form of monovision will be doing that.
Another thing that I think could be a revelation to some would be to have a linear distance scale on the horizontal axis. Revelation to some, but confusing to others. The use of diopters on the horizontal scale tends to devalue the part to the left. Suppose we target -1 D, I think that a graph with 10 meters on the left and 0 meters on the right could give people a different perspective.
Using a linear scale would not be practical. Keep in mind that 0 D is infinity for distance. If distances beyond about 12 feet were left out, then it may be of some value.
Yeah, 10 meters was more for shock value. Yet the story would be truth.
I agree that 12 feet is more practical, and would still tell the story.