Does the classification vary from doctor to doctor
I cannot say for sure, but it would not surprise me. Maybe someone else can answer that part of your question better.
So, for instance mine are 539 um OD 529 um OS. I assume that is thin.
Yes, that is thinner than average.
However, corneal biomechanical properties are essential to understanding this properly. The strength and flexibility (elasticity) of your cornea are as important as the CCT -- possibly more important, in my opinion. (I'm not a doctor.)
From the Ocular Hypertension Treatment Study:
Patients with a corneal thickness of 555 microns or less had a 3-fold greater risk of developing glaucoma when compared to patients with corneal thickness greater than 588 microns.
However, I think we need to understand that in context. Part of that context is that the study looked at people with elevated IOP. We have also learned more about corneal biomechanics since the Ocular Hypertension Treatment Study was conducted.
It is possible to have thick but soft and weak corneas, and that does not convey the expected advantages of a thick cornea.
It is also possible to have thin but strong and flexible corneas. Those would not be associated with all the expected disadvantages of thin corneas.
We also know that you cannot use a CCT correction factor (for IOP) for any individual patient because those factors only work across a population (on average).
For these reasons, I prefer to take advantage of modern technology like the Reichert Ocular Response Analyzer (ORA) and the Reichert 7CR tonometer. The 7CR provides a corneal compensated IOP value (IOPcc). The difference between that and your normal IOP (IOPg on this tonometer), you get an idea of your personal corneal biomechanics -- and you can do this at home if you have that tonometer.
For a more complete and proper assessment, the Reichert Ocular Response Analyzer (ORA) provides detailed diagnostics of your corneal biomechanics, including corneal hysteresis (CH) and corneal resistance factor (CRF) and other metrics. An example of an ORA waveform is shown in this study:
Corneal Hysteresis as a Biomarker of Glaucoma: Current Insights
Corneal hysteresis (CH) is an independent factor that predicts the risk of glaucoma progression. It is important to know both CH and CCT.
So my suggestion is to obtain your corneal biomechanical metrics via an exam with the Reichert Ocular Response Analyzer at your ophthalmologists' office. Only after you have those values (you'll get a nice printout), consider what risk your CCT values may or may not represent.
I guess I should add that your IOP provides an important context as well. It appears that elevated IOP can cause remodeling of the cornea, possibly changing the thickness.
I will link another study on CCT: A 10-year follow up of ocular hypertensive patients within the Bolton Corneal Thickness Study. Can measured factors predict prognostic outcomes?. it offers another reference point for CCT. These studies are very useful for clinicians. But please keep in mind my above advice about the importance of your individual corneal biomechanics. These studies look at populations; what is important to you are your own corneas. I don't know of a way to properly access your individual risk in regard to corneal thickness without knowing your corneal biomechanics -- the CCT thresholds are population wide metrics that did not account for individual corneal biomechanical properties.
Patients with a CCT of 579microm or more, a presenting intraocular pressure of 26mmHg or less and age 75 years or less had a lower risk of developing POAG within this cohort of patients.
Bottom line: consider both your CH and CCT (at least).
