Does the pin-hole normally under estimate the post cataract surgery vision ?

I know that a pin hole or PAM test will normally be performed before a cataract surgery to project what will be the vision after the surgery.

What is the behind theory of a pin hole test to simulate the lens without a cataract ?

In general, will a patient (with pre-operation vision around 20/50) have a post-cataract-operation vision better than the pin hole test ? Or hard to say.


Thanks

[Ray T Oyakawa, MD]

This has been answered.  Pinhole (at near), PAM, or RAM determines the retinal potential for vision.  The pinhole removes refractive errors including irrregular astigmatism.

The PAM test was developed by my Chief Resident, Dave Guyton (an optics and strabismus specialist) and John Minkowski at the Wilmer Institute of Johns Hopkins Hospital.  

Basically,  the PAM allows the patient to see the letters through small clear areas in the cataract.  The pinhole test does a similar thing.

These test results are variable and depend to the skill of the examiner and mental level of the patient.

Dr. O.

[Ray T Oyakawa, MD]

This has been answered.  Pinhole (at near), PAM, or RAM determines the retinal potential for vision.  The pinhole removes refractive errors including irrregular astigmatism.

The PAM test was developed by my Chief Resident, Dave Guyton (an optics and strabismus specialist) and John Minkowski at the Wilmer Institute of Johns Hopkins Hospital.  

Basically,  the PAM allows the patient to see the letters through small clear areas in the cataract.  The pinhole test does a similar thing.

These test results are variable and depend to the skill of the examiner and mental level of the patient.

Dr. O.

[taurus1203]

Thanks for your explanation.
Assuming there is no irregular astigmatism.
It seems the pinhole doesn't not necessary fully reflect the true potential as there may not much clear area in the cataract or the patient may not align the pin hole to the clearest point of the natural lens.
Base on your experience, does a patient normally have a better or worse than expected vision after the cataract surgery ?

Thanks

[Ray T Oyakawa, MD]

A 20/50 cataract would not fall in this category.  Some patients see better than pam and some worse.  It really depends as mentioned on the skill of the examiner and the patient.  Some patients really try hard and others do not.  As with any subjective test results depend on the patient's responses.

Dr. O.