A patient is a -10 Diopter myope. An examiner holds a direct ophthalmoscope 2 cm from the patient's eye. W hat lens power should be dialed into the direct ophthalmoscope to allow inspection of the retina for an emmetropic examiner?
Ametropia
No
U
A
For a myopic patient, light rays leaving the patient's eye are convergent. These convergent light rays form a real image that is 1/10 = 0.10 m (10 cm) in front of the patient's eye. The vergence of the light rays entering the ophthalmoscope in this example is: = 1 / (0.10-0.02) = 1 / 0.08 = +12.5 diopters
To create zero vergence light that can be viewed by the emmetropic examiner, the lens in the direct ophthalmoscope must have a power of -12.5 diopters.
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