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

Overview

The purpose of this study is to evaluate the reproducibility of tonometry in the Goldmann applanation apparatus and pneumatic in the water drinking test.

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. The measurement of IOP can also be performed through another type of tonometer: non-contact, pneumatic or blow. It was first used in 1973 by Forbes and its advantages are: 1) no need for the use of eye drops, 2) it can be performed by people who are not doctors, 3) it has a low risk of contamination and 4) it can be used for screening programs. However, a study by Britt et al. showed the presence of lachrymal film dehiscence and the existence of microaerosol with the air blow, which would make this method not so aseptic. According to the study, where the pneumatic tonometer was compared with that of Goldmann, the results obtained were: 50% of the evaluated eyes showed no differences between the two devices and in 85% they were between approximately 2 mmHg. In another study which compared the IOP values measured by the mentioned tonometers, it was verified that the pneumatic tonometer underestimates the IOP values, compared to Goldmann, in thin corneas; however, there is no significant difference between the measurements of the two tonometers in thick corneas. The Water Drinking Test (WDT) is a propaedeutic widely used to evaluate the maximum intraocular pressure (IOP) and its fluctuation. These data are extremely important for the expected result in relation to the reproducibility of the exams, since in the study , showed that the WDT can be used to estimate the peak and diurnal fluctuation of supine IOP in the simplified daily stress curve (another method for the same purpose of the WDT) in patients under treatment for glaucoma. Glaucoma is a serious eye health problem, as it has a high incidence and prevalence worldwide and is the leading cause of irreversible blindness in the world. Therefore, it is extremely important to perform tests that will detect altered IOP values. The IOP values obtained over a 24 hour period are important data, since they are required to control and conduct the treatment of glaucoma. In the past, the WDT has often been used to diagnose patients with this pathology. Due to a series of studies,it was found that the WDT can not be used as a diagnostic test, but as a tool to evaluate changes in IOP peaks. In addition, a comparison of reproducibility between devices will facilitate a better evaluation, speed, safety and efficacy in the treatment, contributing to increase the quality of life of the patient and also to guide other studies in this area.

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