The optic nerves of identical twins are genetically identical.

Question

The optic nerves of identical twins are genetically identical. When only one of a set of identical twins is visually impaired, certain areas of the affected twin’s optic nerve are atrophied whereas the corresponding areas of the other twin’s optic nerve is unaffected. No such differences are found when neither twin is visually impaired. Therefore, this discovery proves definitively that blindness is caused by damage to the structure of the optic nerve.

The argument above depends upon which one of the following?

A.The optic nerve of a blind person is smaller than that of anyone not suffering from visual impairment.

B.The relative size of the optic nerve of visually impaired individuals is not the result of corrective treatments or medications used to treat visual impairment.

C.The optic nerve of a person with an identical twin is no larger, on average, than the optic nerve of a person who is not an identical twin.

D.When a set of identical twins are both visually impaired, their optic nerves are in the same relative condition.

E.Individuals who have an identical twin are no more likely to suffer from visual impairment than are those who do not.

Siva2021 · Accepted Answer

Conclusion :- Therefore, this discovery proves definitively that blindness is caused by damage to the structure of the optic nerve.
Option B :-The relative size of the optic nerve of visually impaired individuals is not the result of corrective treatments or medications used to treat visual impairment.
This option shows that the shrinkage of the optic nerve of impaired persons is not due to an alternate cause i.e Corrective treatments or medications used to treat visual Treatment. The alternate cause is ruled out. This premise strengthens the conclusion that blindness is caused by damage to the optic nerve,not any other reason. Please give me kudos . I need them badly

prerakgoel03 · Answer

Conclusion :- Therefore, this discovery proves definitively that blindness is caused by damage to the structure of the optic nerve. 
If there is any alternative cause,this would not hold.

Check option B
 The relative size of the optic nerve of visually impaired individuals is not the result of corrective treatments or medications used to treat visual impairment.   
 Negate this and you will get an alternate cause which destroys the argument. 
 Therefore B is correct.

gmat_India · Answer

A. Irrelevant 
B. Correctly assumes that gap between premises and the conclusion. 
C. Irrelevant
D. This is not assumed but implied from the argument given. 
E. Irrelevant

By assuming that the treatment of the visual impairment did not affect the optic nerve, it is clear that optic nerve plays a part in the visual impairment.

gmatexam439 · Answer

The optic nerves of identical twins are genetically identical. When only one of a set of identical twins is visually impaired, certain areas of the affected twin’s optic nerve are atrophied whereas the corresponding areas of the other twin’s optic nerve is unaffected. No such differences are found when neither twin is visually impaired. Therefore, this discovery proves definitively that blindness is caused by damage to the structure of the optic nerve.

The argument above depends upon which one of the following?

A.The optic nerve of a blind person is smaller than that of anyone not suffering from visual impairment. - This is a fact set. Irrelevant

B.The relative size of the optic nerve of visually impaired individuals is not the result of corrective treatments or medications used to treat visual impairment. - Correct. This option removes the possibility of any alternate cause.

C.The optic nerve of a person with an identical twin is no larger, on average, than the optic nerve of a person who is not an identical twin. - This is a fact set. Irrelevant

D.When a set of identical twins are both visually impaired, their optic nerves are in the same relative condition. - This information is given in the premise. Even if this were to be correct, it doesn't give any information about the cause of blindness.

E.Individuals who have an identical twin are no more likely to suffer from visual impairment than are those who do not. - This is a fact set. Irrelevant

kill3rlook5 · Answer

This is a causal argument. Since the optic nerve in the blind twin is smaller than that in the twin with normal vision, the argument concludes that damage to the optic nerve is the cause of blindness. To weaken this argument, we need to assert either that there is some other cause, or that the causality is reversed. Answer B asserts that the causality could be reversed: the small size of the optic nerve might be the result of the treatments given to the blind child. Therefore, the correct answer is B.

Subject Area: Critical Reasoning

Categories: Weaken

Subject Area: Critical Reasoning

Categories: Weaken

dragonz91 · Answer

This Q doesn't look like a proper assumption Q. The Conclusion states 'damage to optic structure' causes blindness. The argument doesn't require anything about the SOURCE (whatever be it!) of the optic nerve damage.

I can see other options are even worse, but OA is also not a correct assumption answer. VeritasKarishma please suggest/comment.

I can see other options are even worse, but OA is also not a correct assumption answer.  VeritasKarishma  please suggest/comment.

Jupiter3 · Answer

Assumption question. 
logic chain: premise: factor A and factor B happen at the same time. conclusion: a is b's cause. this conclusion is based on 
an assumption that B is not A's cause. Namely, optic impairments are caused by nerve atrophies but not cause nerve atrophies.

KarishmaB · Answer

The optic nerves of identical twins are genetically identical. 
When one is visually impaired, the optic nerve atrophies whereas the corresponding areas of the other twin’s optic nerve is unaffected. 
No such differences are found when neither twin is visually impaired.

Conclusion: It proves definitively that blindness is caused by damage to the structure of the optic nerve.

Now here is a gap in the logic. We know that optic nerve of blind people is atrophied while it is unaffected in people with no visual impairment. So from this we are concluding that blindness is caused by damage to th optic nerve.

But what if damage to optic nerve is an effect of visual impairment? What if impairment is caused by something else and because of impairment the optic nerve shrinks? But if we conclude that optic nerve atrophy is the reason for impairment, we are assuming that optic nerve atrophy is not the direct or indirect effect of impairment. It is the cause.

(B) The relative size of the optic nerve of visually impaired individuals is not the result of corrective treatments or medications used to treat visual impairment.

Correct. We are assuming that the atrophy of the optic nerve is not the result of visual impairment i.e. we are assuming that atrophy of optic nerve doesn't happen after impairment because of treatment. We are instead concluding that it is the cause of visual impairment so impairment happens after the optic nerve atrophies.

So (B) is correct.

VerbalBot · Answer

Automated notice from GMAT Club VerbalBot: 

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

 This post was generated automatically.

The optic nerves of identical twins are genetically identical.

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Critical Reasoning (CR) Questions

The optic nerves of identical twins are genetically identical.

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards