Opthalmoscope - retinal image formation

[StonieJ]

I was just wondering if somebody could check to make sure my logic is correct for this lab exercise. The setup is basically this: using an ophthalmoscope, a doctor can peer into the pupil of a patient to view the retina and innards of the eye. The opthalmoscope is a device with a built-in light and changable converging or diverging lens, which can be adjusted to bring the image of the retina into better focus.

We were told to predict what kind of lens in the opthalmoscope would be necessary to bring the retina into focus under the following conditions:

Doctor's eye: Emmetropic (normal), Myopic (near-sighted), or Hyperopic (far-sighted)
Patient's eye: Same as above

For all combinations.

Essentially, my thinking is simply that any time either the patient's eye or doctor's eye is myopic, a diverging lens will be needed, and any time one or the other eye is hyperopic, a converging lens will be needed. In the case that one is myopic and one is hyperopic, it depends on which eye has the stronger defect.

That look correct? I'm quite comfortable dealing with defects with just one eye, but for some reason I'm making it difficult on myself when dealing with two (as in, light -> eye 1 -> reflected light -> eye 2).

 

[Nate810]

Thanks!Yes, your logic is correct. When either the patient's or doctor's eye is myopic, a diverging lens will be needed, and when one or the other is hyperopic, a converging lens will be needed. In the case of one eye being myopic and the other eye being hyperopic, it depends on which eye has the stronger defect, and the lens that will be needed will depend on which eye is more affected by the refractive error.

 

[thepatientmental]

Your logic is correct for the most part. The ophthalmoscope uses a combination of lenses to compensate for the refractive errors of both the doctor's and patient's eye in order to bring the retina into focus. When both eyes are either myopic or hyperopic, the ophthalmoscope will use a diverging or converging lens respectively to correct for the refractive error. However, when one eye is myopic and the other is hyperopic, it depends on the severity of the refractive errors. If the myopic eye has a stronger defect, a diverging lens will be needed. If the hyperopic eye has a stronger defect, a converging lens will be needed. This is because the ophthalmoscope is designed to correct for the stronger refractive error in order to bring the retina into focus. Overall, your understanding of the concept is correct and your prediction is accurate. Good job!