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Central Corneal Thickness and Glaucoma

Central Corneal Thickness and Glaucoma. Prof. Shlomo Melamed The Sam Rothberg Glaucoma Center Shiba M. C. How REALLY important is it for Glaucoma An Attempt to make some “Seder” in this issue, based on Evidence Based Medicine. What do we practically know about CCT ?.

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Central Corneal Thickness and Glaucoma

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  1. Central Corneal Thickness and Glaucoma Prof. Shlomo Melamed The Sam Rothberg Glaucoma Center Shiba M. C. How REALLY important is it for Glaucoma An Attempt to make some “Seder” in this issue, based on Evidence Based Medicine

  2. What do we practically know about CCT ? * The Thicker the Cornea, the Higher IOP measurement by Goldman Tonometry, and vice versa * Thin Cornea is an independent risk factor for conversion of OHT to POAG, among others..(OHTS)

  3. And what about other claims… * CCT correlates with Lamina Cribrosa Structure and means much more than just altered IOP measurements… * Thin cornea is associated with Glaucoma Progression… * How important is CCT in other types of Glaucoma… * What is the role of other corneal parameters like shape, structure, elasticity, harmony , Hysteresis..

  4. CCT is a new Modewith a Herd-like Echo..Everybody talks about CCT However, we should all stick ONLY with the important conclusions of Evidence Base Medicine !! Now, Let’s see what we have…

  5. Claim 1 :CCT is an independent risk factor for Conversion of OHT to POAG Proof: Strong! * OHTS has shown that the thinner corneas are associated with more conversion * Blacks have higher risk and they have thinner corneas

  6. However, CCT is not the only important risk factor… * OHTS has its limitations, especially regarding its design to find other risk factors such as Family Hx, Myopia and Diabetes * There is no data regarding the RELATIVE importance of CCT among the other factors…

  7. The European Glaucoma Prevention Study –”European OHTS” – Miglior et al. * RR for CCT was only 1.3 vs. 1.7 in OHTS!! * Apparently black population in USA (25%) contributes to role of CCT

  8. Also, In OHTS, Old Age is a risk factor… But, the good practice is to be more aggressive with the YOUNG patient, with longer life span …

  9. A Clinical Example:A 55 yo with IOP=26 mm Hg, his father and brother have glaucoma, he is –5.0 myopic but his CCT is 620 microns. Would you treat??.. I certainly would, despite the normal CCT and “no case” per OHTS…

  10. Claim 2:Thick Corneas will give Higher IOP measurements Proof: Generally Accepted Several studies indicate direct correlation between CCT and IOP measurements

  11. However, in the only study correlating IOP, CCT and Direct Intracameral IOP readings – No such correlation was found Feltgen, Leifert and Funk , BJO, 2000 * 73 patients studied in OR * No systematic error of Applanation Tonometry with increasing CCT

  12. So, are there other physical parameters of the cornea which may affect IOP measurement? The obvious, based on clinical practice: * Irregular Astigmatism (Corn. Graft) * Lens behind Cornea in Flat AC * Very Steep and Bulging Cornea * Irregular Epithelium (H. Simplex)

  13. Corneal Biomechanical Properties are more important to IOP measurement than just Thickness * Corneal Resistance * Corneal Structure * Corneal Elasticity * Corneal Harmony (String-Like Response) **Corneal Hysteresis

  14. What is Corneal Hysteresis? If Cornea is pushed by air impulse, an advanced electro-optical system can record 2 applanation pressure measurements: one while the cornea is moving inward and the other as the cornea returns. The difference between these 2 measurements is Corneal Hysteresis (CH) Corneal Resistance Factor (CRF)- Overall “Resistance” of the Cornea

  15. Corneal Hysteresis

  16. Comparison of Corneal Hysteresis distribution of normal, keratoconic, and Fuchs’ subjects

  17. Corneal Hysteresis of 15 eyes pre- and post-LASIK

  18. So, Claim 3 will be:Are factors other than CCT like Corneal Biomechanics and Hysteresis important in IOP measurement? Absolutely Yes!!. The new Dynamic Contour Tonography provides accurate IOP measurements les influenced by corneal properties

  19. Claim 4:CCT is directly related to Lamina Cribrosaand susceptability to Glaucoma Very Intuitive, but absolutely no proof!!. In fact, a study by Jonas&Holbach (IOVS , 2005) disproves this concept

  20. The Jonas&Holbach Study * Histomorphometric study of 111 enucleated eyes * CCT and Central Lamina Cribrosa Thickness were statistically independent of each other * Lamina Cribrosa Thickness at the Optic Nerve border and CCT were also independent of each other ** Conclusion: No Anatomic Correspondence between CCT and ONH

  21. Cornea may reflect on Lamina Cribrosa * It is not necessarily the Corneal Thickness which is important * Corneal Hysteresis may correlate better with Glaucoma susceptability

  22. Claim 5:CCT is important in Glaucoma Progression We don’t know!! 2 conflicting studies reach opposite conclusions * Herndon,Weizer & Stinnett, Arch. Ophthalmol., 2004 * Jonas et al. , IOVS, 2005

  23. Herndon et al. Study * Objective: Is CCT related to level of glaucoma severity at the Initial Examination * Retrospective analysis of 350 eyes CCT lower in Blacks VS. Whites * Lower CCT was associated with worsened AGIS score, worsened MD of VF, increased Horizontal C/D

  24. Jonas et al. Study * Objective: At presentation of patient, is ONH damage and rate of VF progression related to CCT ? * A Prospective study of 861 eyes (Normal, OHT and POAG), F/U of 5 years * CCT correlated positively with area of neuroretinal rim, but negatively with VF loss.Progression of VF defects in 119 eyes (21%) was independent of CCT in Univariate and Multivariate analysis

  25. Claim 6:Is CCT lower in other types of Glaucoma? * PXFG – Conflicting Reports. Some show association with thin cornea and some do not * NTG – More studies show correlation with thin cornea, some do not. Corneal Hysteresis is apparently more important..

  26. Corneal Hysteresis in NTG IOPcc = Compensated IOP for Corneal Resistance Factor IOPg = Goldman IOP

  27. So, in SummaryIt is not that simplistic * CCT is an independent risk facor for OHT conversion, but not the only/most important one * You should not disregard other factors: Age, ON asymetry, Myopia, Family Hx of Glaucoma , PXF etc.

  28. Overall Biomechanical Properties of the Cornea, manifested by Corneal Hysteresis , are more important * CCT is only one factor in Corneal Hysteresis * Cornea can be Thin, but Rigid, and vice versa * Thick Cornea does not necessarily mean High Corneal Hysteresis

  29. Although intuitively it is tempting to correlate CCT with Lamina Cribrosa susceptability.. * Anatomical Studies Disprove this correlation * Only Conflicting, partial reports on significance in Glaucoma Progression

  30. So, we should definitely add Pachymetry and Dynamic Contour Tonography to our Armamentarium But… Use CCT in the appropriate clinical setting Know its limitations Apply Common Sense..

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