# Medical Physics - Eye

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#1
Hi. i have just started the medical physics topic and i'm stuck on a question set:

A) The combined power of the cornea and lens of a normal, unaccommodated eye is 59 dioptres. If the eye focuses on an object 250mm find the change in power, in dioptres of the eye.

B) A myopic eye has a far point o 1m and a near point of 150mm. State the type of spectacle (its diverging), needed for viewing an object at the normal far point and determine its power, in dioptres. Find the near point when wearing this lense.

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6 years ago
#2
(Original post by Hoggy789)
Hi. i have just started the medical physics topic and i'm stuck on a question set:

A) The combined power of the cornea and lens of a normal, unaccommodated eye is 59 dioptres. If the eye focuses on an object 250mm find the change in power, in dioptres of the eye.

B) A myopic eye has a far point o 1m and a near point of 150mm. State the type of spectacle (its diverging), needed for viewing an object at the normal far point and determine its power, in dioptres. Find the near point when wearing this lense.

Hi and welcome to TSR physics.

We don't do your questions for you, you need to tell us what theory you've done on this topic (optics) and how far you've got with this yourself. Where are you stuck?
We will take it from there.
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#3
(Original post by Stonebridge)
Hi and welcome to TSR physics.

We don't do your questions for you, you need to tell us what theory you've done on this topic (optics) and how far you've got with this yourself. Where are you stuck?
We will take it from there.
Ok sorry, have only done about 2 lessons on the topic so far, but the only equation been given is 1/u + 1/v = 1/f

i have done them but the answers i got didnt look right but ill put what i got anyway..
for the question asking what is the change power i got 4 dioptres which seams reasonable. The doubt is the next part asking for the power of the lens in which i got -0.17 dioptres
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6 years ago
#4
(Original post by Hoggy789)
Ok sorry, have only done about 2 lessons on the topic so far, but the only equation been given is 1/u + 1/v = 1/f

i have done them but the answers i got didnt look right but ill put what i got anyway..
for the question asking what is the change power i got 4 dioptres which seams reasonable. The doubt is the next part asking for the power of the lens in which i got -0.17 dioptres
I agree with the answer of 4 for the 1st one.

How did you get your answer for the 2nd one? The power of lens.
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#5
(Original post by Stonebridge)
I agree with the answer of 4 for the 1st one.

How did you get your answer for the 2nd one? The power of lens.
1/1 so 1 - 1/-0.12 ( minus as lens is diverging) and then doing 1/ answer
thats the answer i wasnt confident...got it by rearranging the equation i stated previously...forgot to mention also know equation P = 1/f.
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6 years ago
#6
(Original post by Hoggy789)
1/1 so 1 - 1/-0.12 ( minus as lens is diverging) and then doing 1/ answer
thats the answer i wasnt confident...got it by rearranging the equation i stated previously...forgot to mention also know equation P = 1/f.
Unless I'm missing something obvious here, where does the value 0.12 come from?
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#7
(Original post by Stonebridge)
Unless I'm missing something obvious here, where does the value 0.12 come from?
oh sorry again....was a typo meant to be 0.15.. :/
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6 years ago
#8
(Original post by Hoggy789)
oh sorry again....was a typo meant to be 0.15.. :/
I'm no expert on medical optics theory, unfortunately, but shouldn't you be considering the far point value (1m) to find the power of the myopic eye lens? Then the power of the lens that corrects that? The one that places the far point back to infinity? (I'm assuming the normal far point to be at infinity but correct me on that one if you've been told some other definition of far point. I understand there can be more than one.
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#9
(Original post by Stonebridge)
I'm no expert on medical optics theory, unfortunately, but shouldn't you be considering the far point value (1m) to find the power of the myopic eye lens? Then the power of the lens that corrects that? The one that places the far point back to infinity? (I'm assuming the normal far point to be at infinity but correct me on that one if you've been told some other definition of far point. I understand there can be more than one.
i believe you are correct in the fact it needs to be corrected back to infinity. I'll speak to my teacher tomorrow regarding the question. Many thanks for your help.
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