Prantik Aditya, Bachelor in Clinical Optometry

Fellow Optom, Dr. Shroff Charity Eye Hospital, Delhi, India


The cornea is the clear front surface of the optical system of the eye, which allows light to enter the eye for vision. It provides approximately 65 to 75 percent of the focusing power of the eye. The Central thickness of the cornea can be measured indirectly by Pachymetry (1). The normal central corneal thickness (CCT) is around 510–520 microns (µ) (2). It is measured using optical or ultrasound methods. Thicker corneas are associated with higher intraocular pressures (IOPs) (3) due to increase in resistance to indentation and vice versa in thin corneas. Myopic patient have thinner CCT then hypermetropia and emmetropes patient it may be because of longer axial length following corneo-scleral stretch thus making sclera thinner, and so the corneal stroma will also become thinner in similar way during myopic progression (4).

Other factors such as race, age, sex, obesity, systemic diseases such as Diabetic mellitus, Hypertension, Thyroid also affects CCT (5).

CCT & Race: CCT was assumed to be a constant but subsequently found that it varies (6). In an unpublished study done in our hospital, we found out that the mean CCT of the North Indian Population (sample size: 1635) is 525.27µ. While in Central India it is seen that mean CCT is 514 ± 33µ and in South India is found to be 511 ± 33µ. Among the central Asian the mean CCT was found to be comparable: 552 ± 33µ in Chinese, 540 ± 33µ in Malays, and 540±33µ in Indians was seen in a study (7, 8).

CCT & Gender: Females have shorter axial length and thus steeper cornea than males and so lower CCT than males (9).

CCT & IOP: Increase in CCT leads to increase in IOP also. Previous analyse suggest that every 10 µ change in CCT leads to 0.28unit increase in IOP in Goldmann Applanation Tonometry (10). Glaucoma, the silent killer of eye increased IOP is one of the major cause for it. However increased in IOP cannot always leads to diagnosis of glaucoma.

An increase in collagen fibres and a consequent increase in the thickness of the cornea (11, 12). Corneal endothelial deturgescense mechanism secondarily causing corneal thickening (oedema) can also cause higher IOP (11, 12).

Figure 1:  Performing Ultrasound Pachymetry

CCT & Age: Further CCT also changes with age (13). CCT decreases with age (14) as suggested in earlier studies. According to a study done, a 10-year increase in age would lead to approximately a 7.0 µdecrease in CCT (15). It is because keratocytes, the major cellular components of the cornea stroma decreases with age and that the collagen fibers are broken down as part of the normal aging process and thus resulting in lower CCT with age (16).With aging there is reduced production of aqueous humour which leads to reduction of IOP (17) and structural changes in trabecular meshwork which increases the resistance to aqueous outflow, increasing IOP (18).

CCT & Medication: Patient taking anti-glaucoma medication and topical prostaglandin can also reduce CCT thus making the cornea thin and giving over or under estimated IOP readings (19).

Take Home Message:

Measuring CCT can be an important factor in diagnosing of many corneal related complication as well as glaucoma.


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