Water Drinking Test and Its Reproducibility in Goldmann Applanation Tonometry and Pneumatic Tonometry

Glaucoma consists of a multifactorial disease caused by a deficiency in drainage of the aqueous humor, which may cause an increase in intraocular pressure (IOP), an impairment of the optic nerve and visual field changes. According to the most recent data , this disease is the second cause of blindness in the world (12.3%). An estimate indicates that, by 2020, there will be 79.6 million glaucomatous individuals in the world. The estimated prevalence of primary glaucoma in the Brazilian population was 3.4%, consisting of 2.4% open angle and 0.7% closed angle.

Glaucoma can be: open angle, angle-closure, congenital or secondary. Increased IOP is the major risk factor for glaucoma progression as well as its fluctuation (difference between the highest and lowest IOP measure) in primary open-angle glaucoma (POAG). In addition, age, family history, central corneal thickness, race, high myopia, hypermetropia, diabetes mellitus, hypertension and hypotension, gender, optic disc hemorrhages, suspected optic nerve excavation, and cardiovascular and cerebrovascular diseases.

The treatment depends on the classification of glaucoma, since in the POAG, the initial treatment is with topical monotherapy (ocular hypotensors). However, in some situations, drug treatment is not enough to stabilize the process of glaucomatous progression. In these cases, incisional surgery or laser treatment is necessary.

Trabeculectomy consists of an intervention to increase drainage of the aqueous humor, in order to control the IOP and prevent the progression of the disease. However, due to its complications, such as atalamia, hypotonia, the development of cataract and the risk of endophthalmitis, this procedure is indicated in the refractory cases to clinical and/or laser treatment. Thus, clinical treatment and trabeculoplasty are the treatments of choice. Trabeculoplasty is indicated in the cases of POAG, pseudoexfoliative, pigmented and in some cases of secondary and trabecular glaucoma visible to the gonioscopy.

The tonometer is the device used to detect IOP increase. Despite the existence of several models, Goldmann's applanation is considered the gold standard for this measurement, since it evaluates the force necessary to deform the surface of the cornea. This method is quite accurate, however, errors may occur in the result due to fluorescein patterns, very thick corneas, excessive pressure on the eyeball when holding the patient's eyelids or elevated corneal astigmatism without the adequate compensatory positioning of the planer.