Intraocular Pressure Variation by Pneumatic Tonometer Before and After Phacoemulsification

Cataracts represent the major cause of treatable blindness in developing countries. According to data , there are 45 million blind people in the world, of which 40% is due to cataract etiology. In Brazil, there are about 350,000 individuals blinded by cataracts.

One of the consequences observed after the cataract surgery is the variation of intraocular pressure (IOP). IOP is directly related to the volume of aqueous humor in the anterior chamber. Reports of oscillations after a cataract surgery range from +1.3 to -2.5 mmHg. The duration of this oscillation varies according to the literature studied. Some studies show that the oscillation seen in the first postoperative year was maintained for the 10-year period and was similar in patients of all ages. However, other authors have identified a non-permanent oscillation, which makes this topic controversial in ophthalmology.

There are a number of factors related to the degree of IOP reduction after a cataract surgery. Studies have shown that the preoperative IOP value, the depth of the anterior chamber, the volume of irrigation used during surgery and the age of the patients may interfere with the IOP variation in the postoperative period.

However, the gold standard tonometer for IOP measurement is Goldmann's. This measurement is closely related to important characteristics of the cornea, such as its thickness and curvature, and may underestimate or overestimate IOP values.

Another way to measure IOP is through a non-contact tonometer, blow or pneumatic. The blow tonometer has a pneumatic system that produces a jet of air, which leads to flattening of the cornea and on the surface of which a beam of parallel light rays is projected, in which only the reflected parallel and coaxial rays are picked up by the receiver of the device, obtaining a maximum peak of light reception when the cornea is flattened. Its main advantage is in its use in screening programs, the need for the use of eye drops and the lowest rates of contamination. The blow tonometer, as well as the flattening tonometer, is influenced by corneal factors, such as curvature and thickness, presenting the same parameters of under and overestimation of IOP.