Craig Blackwell, MD
Ophthalmology

Santa Cruz, CA
Diplomate: American Board of Ophthalmology
Fellow: American Academy of Ophthalmology

Welcome to the Website of Craig Blackwell, MD

An Ophthalmology Practice in Santa Cruz, CA

Pressure and Glaucoma

June 29th, 2008

Can lowering eye pressure help prevent the development of glaucoma?

Ocular Hypertension is the term we use when the eye pressure is above the normal range, but has not caused any damage. When damage occurs due to pressure then we use the term glaucoma.

Ocular Hypertension Treatment Study

In 1994 recruitment began for a large nationwide study of people who had elevated intraocular pressures to answer that very big question.

Criteria for enrollment in the study was pressure of 24 or above in at least one eye, and no evidence of glaucoma damage at baseline. (Average pressure is 16, with the normal range extending up to 20.)

1,636 people were enrolled and followed for a minimum of five years.
Participants were divided into two groups:

  • Half were assigned to receive pressure lowering drops
  • Half were observed without treatment.

Overall Result

Arch Ophthalmol. 2002;120:701-713

POAG is Primary Open Angle Glaucoma.

This chart, scanned from one of the OHTS articles, shows the comparison of rates of developing glaucoma between the untreated group and the group that got pressure lowering drops. It clearly shows that lowering pressure reduces the chance of developing glaucoma. Note it does not reduce it to zero.

Pressure Level and Glaucoma Risk

Arch Ophthalmol. 2002;120:714-720

This table is enlarged from the size in the original article, but it contains such useful information that it is worth a bigger look. The X-axis is corneal thickness. The Y-axis is pressure. The height of the bars represents percent chance of developing glaucoma.
Clearly, if you have thinner corneas and higher pressures you have an increased chance of developing glaucoma.

Optic Nerve and Glaucoma Risk

Arch Ophthalmol. 2002;120:714-720

This table accompanies the above table 1. This time the Y-axis is the vertical cup-to-disc ratio, which is a measure of the thickness of the rim of the optic nerve. A higher VCD means a thinner rim of nerve tissue
Clearly people who have thinner rims, higher VCD, have an increased risk of developing glaucoma.

Estimating Risk

During an eye exam we perform the following tests:

  • measure pressure, on everyone
  • measure corneal thickness (if pressure or nerve is suspect)
  • examine the nerve to estimate VCD, on everyone
  • visual fields (if other finding suspicious)

So, at your exam, we can get a pretty good starting estimate of glaucoma risk. If nerve and field show no damage then we can refer to the above charts and discuss your risk of developing glaucoma and whether or not you want to start pressure-lowering drops. For the person who consistently takes their medication and follows-up with regular monitoring it is rare to lose vision to glaucoma.