Target IOP, what is it?

Presented by Dr Ravin N Das as an introduction in the session "Peer to Peer Review on Glaucoma".

(Cross-references:

  1. Introduction and Target Intra-ocular pressure - Dr. Ravin Das
  2. The role of intra-ocular pressure in glaucoma (Landmark studies in Glaucoma) - Dr. Shabbir Hussain (Slide 1-28)
  3. Implementing what we have learnt - Dr. Major Avinash Mishra (Slide 29-50)
  4. Achieving the targets set by the studies & reaching difficult target pressures - Dr. Rahul Shukla (Slide 51-85)
  5. Lumigan™ the Indian experience (L.E.E.D) - Dr. Shabbir Hussain. (Slide 86-100)


Definition

The American Academy of Ophthalmology defines TARGET IOP as - "Upper limit of IOP that prevents further glaucomatous damage".

Also called the "Ideal Pressure", "Safe Level of IOP"

Neuropathy progresses very slowly as long as the pressure for the individual remains below this value.

It is not an ABSOLUTE value, but needs to be re-assessed with time.

Target IOP may be classified under 3 heads -

Ideal Target Pressure - Least risk of progression
Acceptable Target Pressure - Low risk of progression
Borderline Target Pressure - High risk of progression.


Examples

A. Healthy ONH, no field changes, presenting IOP = 28 mm Hg

Ideal Pressure --- 20-22 mm Hg
Acceptable Pressure --- 23-24 mm Hg
Borderline Pressure --- 25-26 mm Hg

B. Near total cupping, corresponding visual field changes, IOP = 18 mm Hg

Ideal Pressure --- 8-10 mm Hg
Acceptable Pressure --- 11-13 mm Hg
Borderline Pressure --- 14-15 mm Hg


Methods to determine the Target IOP

1. Numerical Methods

  • Always aim for an IOP < 21mm Hg
  • Lower the IOP by 30%
  • Lower the IOP by 1/3 of the baseline
  • Lower the IOP as much as possible
  • Calculate the T.IOP = ((1-RP+VFS)/100) x RP (RP = reference pressure (is the pressure on presentation), VFS = visual field score)

2. Theoretical Methods include -

  • Highest IOP recorded
  • Age of the patient (greater the age, lower the IOP)
  • Extent of ONH damage
  • Pace of the disease
  • Systemic disorders (DM, HT, etc.)

Methods to the determine Target IOP - Theoretical (ONH changes)

ONH Changes
%age IOP reduction required
up to 0.3 CDR
20%
0.4 to 0.5 CDR
30%
0.6 to 0.7 CDR
40%
0.8 to total cupping
60%


Methods to determine the target IOP - Theoretical (VF changes)

Referene IOP
Target IOP (mm Hg)
Mild VFL
Moderate VFL
Severe VFL
20
16
14
10
30
23
20
15
40
25
25
20
50
30
25
20

Classifying VFL (AAO classification)

Mild VFL -

  • Optic nerve abnormalities consistent with glaucoma, but VF are normal

Moderate -

  • VF abnormalities restricted to either hemifield but do not extend within 5° from fixation

Severe -

  • VF abnormalities in both hemifields or within 5° from fixation


Summary

Set higher Target IOP levels for -

Higher IOP at initial presentation
Shorter life expectancy
Early ONH damage

Set lower Target IOP levels for -

Lower IOP at initial presentation
Longer life expectancy
Advanced ONH damage