J Cataract Refract Surg. Nov;27(11) Relation between corneal thickness and intraocular pressure measurement by noncontact and applanation . Despite numerous studies and publications, ophthalmologists frequently do not make an association between IOP and corneal thickness. A wide choice of. Central corneal thickness (CCT) is known to affect the accuracy of intraocular Association between measured intraocular pressure and central corneal.
The Importance of Corneal Thickness | Glaucoma Research Foundation
If you have high IOP, careful management of your eye pressure with medications can help prevent vision loss. Studies about the cornea, the clear part of the eye's protective covering, show that corneal thickness is an important factor in accurately diagnosing eye pressure.
The study's goal was to determine if early intervention with pressure lowering medications could reduce the number of ocular hypertensive OHT patients that develop glaucoma.
During the study, a critical discovery was made regarding corneal thickness and its role in intraocular eye pressure and glaucoma development. Why is Corneal Thickness Important? Corneal thickness is important because it can mask an accurate reading of eye pressure, causing doctors to treat you for a condition that may not really exist or to treat you unnecessarily when are normal.
This may be important to your diagnosis; some people originally diagnosed with normal tension glaucoma may in fact be more accurately treated as having regular glaucoma; others diagnosed with ocular hypertension may be better treated as normal based on accurate CCT measurement.
In light of this discovery, it is important to have your eyes checked regularly and to make sure your doctor takes your CCT into account for diagnosis.
This is dangerous because if your actual IOP is higher than your reading shows, you may be at risk for developing glaucoma and your doctor may not know it. Left untreated, high IOP can lead to glaucoma and vision loss.
- The Importance of Corneal Thickness
The probe was kept applied to the cornea until five pulses of equal amplitude were recorded. All statistical analyses were performed by computer on right eyes only, to reduce bias SPSS for Windows, ver.
Although it may appear that there is a large variation around the mean for all instruments, this is in fact because there was a wide range of IOPs in the subject group.
Corneal Thickness and Intraocular Pressure in the Barbados Eye Studies
Linear regression analysis shows that the Tono-Pen was least affected by differences in CCT, followed by the Goldmann tonometer. The OBF pneumotonometer was most affected by these differences Table 1.
The Tono-Pen appeared to be least affected by the various thicknesses of different corneas, whereas the OBF pneumotonometer appeared to be most affected. Discussion Despite numerous studies and publications, ophthalmologists frequently do not make an association between IOP and corneal thickness.
A wide choice of instruments is now available to measure IOP. Goldmann applanation tonometry is widely accepted as the international gold standard for measurement of IOP and is the most commonly used method. Its accuracy depends on many factors.
Obviously, this has important implications in diagnosis and management. It is thus especially important that we know how much different tonometers are affected by different corneal thicknesses, so that we can make appropriate allowances. Furthermore, with the potential risk of transmission of prion proteins, there is a move toward using disposable tonometer heads or protective coverings.
In many clinics in Europe, ophthalmologists are switching to the Tono-Pen because of the protection offered by the disposable sheaths. Similarly, the OBF comes with a disposable head and offers the same advantage. If pressures recorded by different instruments in the same patient are to be considered, it is important that we compare these instruments and ascertain the extent to which each may be affected by variables such as corneal thickness.
Although it was comparatively steeper with the Goldmann tonometer, the difference was not statistically significant. It therefore implies that the two applanation instruments are affected less than the contact pneumotonometer.
The Tono-Pen is a small, computerized, handheld instrument that operates on the MacKay Marg principle. It is thought to be relatively unaffected by corneal surface abnormalities, 16 unless these are gross e. This is a modified version of that first described by Langham 21 and allows measurement of IOP, pulse rate, pulse amplitude, and pulsatile ocular blood flow.
The principle of action and the calculation of IOP are complex and are described in detail elsewhere. The resistance to the airflow through the center of the tonometer is then measured. Theoretically, it has been claimed that the calculation of IOP by pneumotonometers is not affected by CCT, because flexural rigidity of the cornea can be ignored.
Although in theory the OBF pneumotonometer should not be affected by CCT, the results of this study suggest otherwise. This probably reflects the mechanism by which it measures IOP. During measurment, the tip of the pneumotonometer is applanated to the cornea.
Gas at constant pressure flows down a central hollow tube, pushing against a terminal membrane, deforming the cornea.