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

Glaucoma Beyond OHTS

European Glaucoma Prevention Study

Paralleling the landmark Ocular Hypertension Treatment Study (OHTS) in the US was the European Glaucoma Prevention Study (EGPS).

They enrolled 1,077 patients with above normal pressures, but no evidence of glaucoma. In the random, double-masked clinical trial treatment was Dorzolamide drops versus placebo. The end point was evidence of glaucoma damage seen as optic nerve damage or visual field defect.

They identified essentially the same risk factors as the OHTS:

  • older age,
  • larger cup-to-disc ratio (C/D), cup-to-disc asymmetry,
  • higher PSD (pattern standard deviation from visual field) and
  • less corneal thickness.

The following 3-D bar graphs show their results, looking very much like the OHTS results.

Ophthalmology 2007;114:3-9

Additional general health items were evaluated as possible risk factors.

Predictor

Hazard Ratio

P value

Diabetes

0.89

0.79

Cardiovascular Disease

1.84

0.01

High Blood Pressure

1.22

0.30

High Blood Pressure Medications

1.46

0.053

The possible effect of diabetes is difficult to evaluate because patients with any sign of retinopathy were excluded from the study.

Pooled Data to Create a Risk Predictive Model

These two study groups, OHTS from the US and EGPS from Europe, then pooled their results to develop a prediction model for developing glaucoma over five years.

The predictive model was structured using a point system for each of the risk factors identified in the combined study statistics. See Table 1 below. These are five measurements we would have after an initial glaucoma evaluation. The sum of the points then indicate the 5-year risk of developing glaucoma. See Table 2.

Points

Baseline Predictor

0

1

2

3

4

Age

<45

45-54

55-64

65-74

≥75

Mean IOP

<22

22-23

24-25

26-27

≥28

Mean CCT

≥600

576-600

551-575

526-550

≤525

Vertical C/D

<0.3

0.3-<0.4

0.4-<0.5

0.5-<0.6

≥0.6

Mean PSD

<1.8

1.8-<2.0

2.0-<2.4

2.4-<2.8

≥2.8

Table 1. Assigning point values to identified glaucoma risk factors.

IOP = Intraocular Pressure, CCT = Central Corneal Thickness, C/D = Cup to Disc Ratio, PSD = Pattern Standard Deviation from the visual field.

Sum of Points

0-6

7-8

9-10

11-12

>12

Est. of 5-yr. Risk

≤4.0%

10%

15%

20%

≥33%

Table 2. Using the point system to estimate the chance of developing glaucoma over five years.

As an estimate of risk Table 2 sometimes helps make decision as to whether or not to start treatment.

The authors of this study point out that several factors were not included in this study, myopia, diabetes, race, cardiovascular disease, family history of glaucoma, and exfoliation syndrome and pigment dispersion.

Ophthalmology 2007;114:10-19

CB-08