IOP, CCT, and Hysteresis (M) Flashcards
Why is the IOP correction factor no longer done?
relationship was not linear
What is the normal range of IOP?
10 to 21mmHg
What are the problem cells in the trabecular meshwork when there is trouble with outflow?
juxtacanilicular
What is the device that has the tip match the contour of the cornea so that the IOP is independent of the CCT or corneal irregularity?
Dynamic Contour Tonometry (DCT) or Pascal DCT
What is the difference between the “systolic IOP” and the “diastolic IOP” called? 1. What does this indicate? 2
- ocular pulse amplitude (OPA)
2. higher for glaucoma patients
What are the contributions to variable IOP?
- peaks and troughs with circadian rhythm
2. supine position
What were the risk factors that were most likely to develop glaucoma found in the OHTS?
- above 25.75mmHg IOP
2. less than 555um corneal thickness
What are the three measurements that the ocular response analyzer (ORA) provides?
- difference between measurements (corneal hysteresis)
- IOPcc = corneal compensated IOP
- IOPg = Goldmann correlated IOP
What is the non-contact tonometer that takes a measurement as the cornea is flattened and as it recovers? 1. What does this measure? 2
- ocular response analyzer (ORA)
2. corneal hysteresis (tensile strength of cornea)
What is taking multiple IOP readings on the same patient with the same tonometer in a given day called?
serial tonometry
What errors lead to an underestimate of IOP for Goldmann readings?
- mires too thin
- repeat measurements
- over 3D with the rule cyl
- thin cornea
When is the IOP the highest?
during sleep
What did the OHTS study show?
- only 10% of people with IOP 24 to 32 ended up getting glaucoma with no Tx
- Tx did help to reduce the risk of developing glaucoma
- thinner corneas lead to artificially lower IOP and vice versa
What errors lead to an overestimate of IOP for Goldmann readings?
- mires too thick
- pressure on globe from examiner or blepharospasm
- valsalve
- superior gaze of over 15deg
- over 3D against the rule cyl
- thick cornea
What is the equation for the IOP?
IOP = AHP - TMOut - UvScOut + EVP AHP = aqueous humor production TMOut = trabecular meshwork outflow UvScOut = uveoscleral outflow EVP = episcleral venous pressure
What was the most significant risk factor for an ocular hypertensive patient to convert to glaucoma?
reduced CCT
What are the three categories of central corneal thickness amounts?
- normal
- thin CCT (less than 530) is significant
- thick CCT (more than 590) may be protective
What techniques should be used in order to obtain the patients peak IOP?
- alternate morning and afternoon appointments
2. obtain at least one IOP within 1 to 2 hours of awakening
What is the disadvantage of a tonopen?
less accurate
What has proven to be the key factor resulting in progression of glaucoma?
mean IOP
How much of a decrease in the rate of progression does each 1mmHg lowering of IOP cause?
10% decrease
What is the normal central corneal thickness (CCT)?
544
What are the factors that decrease the hysteresis of an ORA?
- Age
- Fuch’s dystrophy
- eye rubbing prior to measure
- POAG
- ocular pulse amplitude
- PSD on VF
What are the factors that increase the hysteresis of an ORA?
CCT
What is the silicone hydrogel lens that contains sensors detecting IOP over 24hrs called?
Triggerfish IOP monitoring CL
What is the normal CH value for patients while doing the ORA? 1. High CH value? 2
- 7 or lower
2. 12 or higher
What is the baseline physiological IOP that is the lowest it can possibly be (name and number)?
episcleral venous pressure (9 to 11mmHg)
