Intraocular pressure is one of the most important
modifiable risk factors in the management of glaucoma.
Though different tonometers are available, their
measurement is not always interchangeable &
reproducible. Central corneal thickness is known to
affect the accurate IOP measurements & it has different
effects on different tonometers.
To compare measurements of IOP using GAT and
NCT in different IOP ranges (<11, 11-25, >25 mm Hg)
and evaluate the influence of CCT on IOP measurements
by these techniques.
Materials and Methods:-
IOP was measured by NCT followed by GAT in
218 eyes of 112 patients (both eyes of 106 patients and
single eye of 6 patients due to various reasons; eg – one
eyed patient, corneal scar in one eye) attending the eye
OPD of a tertiary hospital of West Bengal by a single
observer. Mean of three consecutive readings were taken
for analysis by both techniques. IOP values were
compared in the three IOP ranges (<11, 11-25, >25 mm
Hg) between the two techniques. CCT values were
obtained from them using ultrasonic pachymeter.
Statistical analysis was done to know whether the two
methods were interchangeable across the three IOP
Though good agreement was seen between GAT
and NCT, the later showed a tendency to overestimate
IOP in the lower IOP range and underestimate in the
normal and high IOP range. Mean values of GAT and
NCT showed a statistically significant difference in the
normal IOP range (11 - 25 mm Hg, significance level )
and high IOP range (>25 mm Hg). However in the lower
range, the difference did not reach the level of
significance. NCT is more influenced by CCT. To
conclude, though NCT has good accuracy and
predictability to be used as a screening tool, but GAT is
accurate in all IOP ranges.
Keywords : Tonometers , Intraocular Pressure, Central Corneal Thickness, Goldmann Applanation Tometry , Non Contact Tonometry.