Cataracts are diagnosed through a comprehensive eye exam given by an ophthalmologist. This may include:

• Visual acuity test. An eye chart measures how well the patient sees at various distances with each eye.
  
  
• Slit-lamp exam. A microscope emitting bright light is used to examine the lens and other structures in the front of the eye. This device can also be used to check the back of the eye.
  
  
• Dilated pupil exam. Eyedrops widen the pupils so the examiner can see the back of the eye. After the exam, vision remains blurred for a short time.
  
  
• Tonometry. An instrument is used to measure the internal pressure of the eye. Two variations exist. During air puff tonometry, the eye is numbed with drops and a puff of air is blown at it to measure the amount of air deflected by the eye. During applanation tonometry, the eye is numbed and a slit lamp illuminates the eye so the physician can examine it. A small pressure-sensitive tip measures the pressure by touching the surface of the eye.

Various other tests may also be conducted to test for co-existing health conditions, such as diabetes or high blood pressure, which may accompany cataracts.