Pachymetry measures corneal thickness, important for understanding corneal health and associated with glaucoma evaluation, as it affects intraocular pressure (IOP) readings. Central corneal thickness (CCT) varies with factors like age, sex, and ethnicity, and its measurement is crucial for glaucoma risk assessment and treatment planning. Routine CCT measurement is recommended for glaucoma patients due to its prognostic value in predicting disease progression and the need for further research into its role in other types of glaucoma.

1. PACHYMETRY IN GLAUCOMA
EVALUATION

2. INTRODUCTION
• Pachymetry (Greek words: Pachos = thick + metry = to measure) is
term used for the measurement of corneal thickness
• It is an important indicator of health status of the cornea especially
of corneal endothelial pump function
• The thickness of the cornea was first reported in ancient textbooks
on physiological optics (Helmholtz and Gullstrand)

3. TYPES OF PACHYMETRY
Contact methods
• Ultrasound(mean CCT 544 μm)
• optical such as confocal
microscopy (CONFOSCAN)(mean
CCT 530 μm)

4. TYPES OF PACHYMETRY
Non-contact methods
• Optical biometry with a
single Scheimpflug camera
(SIRIUS or PENTACAM)
• Dual Scheimpflug camera
(GALILEI)
• Optical Coherence
Tomography (Visante)
• Optical Coherence
Pachymetry (ORBSCAN)

5. CORNEAL THICKNESS IN NORMAL EYE
• It ranges from 0.7 to 0.9 mm at the limbus and varies between 0.49
mm and 0.56 mm at the centre
• The Central corneal thickness (CCT) reading of 0.7 mm or more is
indicative of endothelial decompensation
• Peripheral corneal thickness is asymmetric so that temporal cornea is
thinnest followed by the inferior cornea

6. CORNEAL THICKNESS IN NEWBORN AND
CHILDREN
• Corneal configuration in newborns is similar to that of the adult
cornea
• It has been found that cornea on day one is significantly thicker and
decreases in thickness as the child grows older
• The average corneal thickness in infants is 585 ± 52 microns
• The superior peripheral cornea is thinnest in newborn

7. FACTORS AFFECTING CORNEAL THICKNESS
• Higher in younger patients, male patients and diabetic patients
• The mean CCT of black children is thinner than that of white children
• The PITX2/Pitx2 mutation seen in Axenfeld-Rieger malformations
results in reduced corneal thickness
• Central corneal thickness does not correlate with refraction or
systemic hypertension

8. ROLE IN CLINICAL PRACTICE
• Glaucoma: for applying correction factor in actual IOP determination
Congenital Glaucoma: to assess the amount of corneal edema
• Refractive surgeries: preoperative screening and treatment plan of
keratorefractive procedures like LASIK, astigmatic keratotomy,even prior to
radial keratotomy
 Post operative follow up of keratoplasty patients to determine endothelial
cell function and its recovery and to become alert to early graft
decompensation

9. ROLE IN CLINICAL PRACTICE
• Contact lens: To assess corneal edema
Assessing cornea thinness as in corneal disorders like Terrien ’s and
Pellucid marginal degenerations, keratoconus, keratoglobus, post
LASIK ectasia.
 Other cases of corneal decompensation as in herpetic endothelitis

10. FACTS ABOUT CCT IN GLAUCOMA
Bechmann in 2000 found following association of CCT with different
forms of glaucoma
1)Increased CCT measurements are found in patients with ocular hypertension,
which can lead to falsely elevated IOP readings
2) Decreased CCT is found in patients with low tension glaucoma, resulting in
falsely reduced IOP measurements

11. FACTS ABOUT CCT IN GLAUCOMA
3) CCT was found to be lower in patients with Pseudoexfoliation
syndrome (PXS) and in Primary open angle Glaucoma (POAG)
4) There is no difference in corneal thickness in individuals with
Pigmentary Glaucoma(PG) and Primary angle Closure Glaucoma (PACG)

12. EVIDENCE BASED GUIDELINE FOR CORNEAL
PACHYMETRY IN GLAUCOMA
• Patients who have risk factors for developing Primary Open Angle
Glaucoma
• Elevated intraocular pressure repeatedly measured >24 mm Hg
• African descent
• Advancing age (>65 years old)
• Family history of glaucoma

13. ROLE IN GLAUCOMA
• Applanation tonometry is based on Imbert Fick’s law, which assumes that cornea
is a perfect flexible, dry, sphere which is infinitely thin
• Therefore increase in the tissue in thicker cornea makes it less compliant and
subsequently leading to overestimation of IOP and Viceversa
• Ocular Hypertension Treatment Study (OHTS) group published that central
corneal thickness (CCT) was an important independent risk factor for progression
from ocular hypertension to early glaucoma

14. OCULAR HYPERTENSION TREATMENT STUDY
• The Ocular Hypertension Treatment Study (OHTS) highlighted the
prognostic significance of CCT in identifying patients with ocular
hypertension (OHT) who would progress to glaucoma
• A multivariate model which included the baseline characteristics of
1618 OHT individuals showed that thinner CCT was the most
important predictive factor for the development of POAG

15. OCULAR HYPERTENSION TREATMENT STUDY
• The routine measurement of CCT should be included in the initial
assessment of all glaucoma patients
• The prognostic value of CCT is well recognized in OHT patients, but its
predictive value in other glaucoma suspects and patients with
established glaucoma is less certain

16. Tonometry artefact
• IOP is the principal modifiable risk factor for the progression of established
glaucoma and for the development of glaucoma from OHT
• A 1mmHg decrease in IOP was associated with a 10% decreased risk of
both perimetric progression in the EMGTS and the development of
glaucoma in the OHTS
• It was found that found that the most accurate GAT reading was obtained
in eyes with CCT of approximately 520 μm

17. Tonometry artefact
• Every 100 μm deviation from this value would result in an error in
IOP measurement of 7 mmHg
• A positive correlation between CCT and IOP has been verified
Thick cornea would result in an artefactually increased IOP reading,
whereas a thin cornea would result in an artefactually reduced IOP
reading

18. CORRECTION FACTOR
• In chronic eye diseases like glaucoma and glaucoma suspects for
every increase in central corneal thickness of 50 microns, the
correction done is to decrease the recorded IOP by 2.5mmHg
• For acute onset diseases it was recommended to correct by 10 mmHg
for every 50 microns

19. BIOLOGICAL RISK FACTORS
• Extent of lamina movement was increased in individuals with thin corneas
compared with those with thick corneas(Lesk et al)
• After IOP reduction, the improvement in neuroretinal rim blood flow was also
smaller compared with patients with thicker corneas
• This supports the hypothesis that eyes with thinner CCT may have an increased
risk of developing glaucomatous damage due to laminas that are more
susceptible to being displaced in response to IOP changes

20. BIOLOGICAL RISK FACTOR
• Physical structures of the optic disc, including depth of cup and disc
area, have been reported by some studies to be correlated with CCT
• Another less likely hypothesis is that a thin cornea increases
trabecular exposure to oxidative damage

21. GENETIC ASSOCIATION
• CCT is one of the most heritable human traits and may explain some
aspects of the genetic predisposition to glaucoma
• Genome-wide association studies and candidate gene analyses have
uncovered associations between CCT and novel loci. These may
provide candidate genes for the interrogation of POAG

22. GENETIC ASSOCIATION
• Studies that confirmed a genetic link between CCT and open angle
glaucoma may enable us to determine the mechanisms underlying
this association
• Two missense mutations in a subtype of collagen-8, which if
inactivated results in thinning of the corneal stroma, were detected in
a group of White patients with very thin CCT and advanced POAG

23. GLAUCOMA TREATMENT
• Ocular hypotensive medications have been shown to alter corneal
thickness
• latanoprost and tafluprost and a significant decrease in CCT possibly
by modifying the corneal extracellular matrix

24. GLAUCOMA TREATMENT
• Topical b blockers have been associated with a reversible increase in CCT
• Topical carbonic anhydrase inhibitors can cause irreversible corneal
decompensation and increased corneal thickness in eyes with underlying
cornea diseases but they do not significantly alter CCT in healthy corneas
• Thicker CCT was associated with a less significant decrease in IOP after
starting ocular hypotensive medications in the OHTS

25. GLAUCOMA TREATMENT
• The percentage reduction in IOP after laser trabeculoplasty was
significantly greater in eyes with thinner corneas (CCT<555 μm )

26. VARIABILITY IN CENTRAL CORNEAL
THICKNESS
• CCT measurements vary with race, sex, age and other environmental
factors, which may confound the relationship between glaucoma and
corneal thickness
• Most epidemiological studies have found that men have thicker corneas
compared with women
• CCT also varies with age, with a small but significant inverse relationship
between CCT and age (range 2–10mm per decade) being reported in the
majority of cross-sectional studies

27. VARIABILITY IN CENTRAL CORNEAL
THICKNESS
• Hence, it may take up to 20 years for the change in CCT to be clinically
significant and to warrant remeasuring
• CCT is also influenced by environmental factors. Dry eyes and long-
term contact lens wear are associated with a decrease in CCT
• An indoor occupation and sleep are associated with an increase in
CCT

28. CORNEAL BIOMECHANICS
• CCT is regarded as a correlate of corneal rigidity, but this is only applicable to
structurally normal corneas
• An edematous cornea, though thicker, may result in lower GAT readings because
of reduced corneal rigidity .Conversely,scarred cornea, though thinner, may have
increased corneal rigidity leading to artefactually higher IOP readings

29. CORNEAL BIOMECHANICS
• Corneal cross-linking results in a significant increase in IOP 12 months after the
procedure despite CCT remaining unchanged. This is presumably because of
increased corneal rigidity

30. CONCLUSION
• The prognostic value of CCT is well recognized in OHT patients, but its
predictive value in other glaucoma suspects and patients with
established glaucoma is less certain
• Nevertheless, the routine measurement of CCT should be included in
the initial assessment of all glaucoma patients, as it aids in the
interpretation of IOP measurements, risk stratification and the setting
of a target IOP

31. CONCLUSION
• An adequately validated correction algorithm for GAT measurements
does not exist and better methods of tonometry which are less
influenced by corneal properties, should be developed and adopted
into clinical practice
• Most studies investigating the significance of CCT have included
patients with POAG, and the role of CCT in PACG and secondary
glaucoma is still poorly understood and warrants further investigation

32. THANK YOU