Aspects of the diagnosis and treatment of glaucoma

Abstract

Glaucoma is one of the most common causes of blindness in the world, and it is important that screening tests as well as treatment possibilities are improved continuously. A reliable but more rapid screening test than those already available would be of great interest. In addition, new and more effective treatment options would be most valuable. The aims of the present thesis were to evaluate the reliability of a new and rapid peripheral colour contrast sensitivity test as a tool for glaucoma screening and to gain more information on latanoprost, a recently developed prostaglandin analogue, in glaucoma treatment Colour contrast sensitivity was analysed with a system described by Arden and co-workers, using a computer controlled colour monitor. The test objects for the central test were letters of standard optotype subtending a visual angle of 3°. For the peripheral test, the test object was a colour contrasting annulus concentric with a fixation spot. The annulus had a radius of 12.5° in the extramacular field and a width of 1°. The colour contrast of the letter or the annulus in relation to the background could be changed, and a colour contrast threshold value could be obtained in the protan, deutan and tritan colour axes. In a study of glaucoma patients, ocular hypertensive patients and normals, the peripheral colour contrast sensitivity test was found to distinguish the glaucoma patients from the normals. However, it was difficult to find a reliable cut-off point if the test is to be used as a screening test. In a five-year prospective study of ocular hypertensive patients, the peripheral colour contrast sensitivity test could not clearly predict which patients would develop glaucoma and which would not, given that the Glaucoma Hemifield Test is used as the golden standard. A change over time in the protan axis may, however, indicate glaucoma development. For a test to be used in glaucoma screening, it is necessary to know whether other common eye diseases such as diabetes and cataract affect the outcome. Therefore, the influence of diabetes and cataract on peripheral and central colour contrast sensitivity was also studied. Diabetes type II was found to affect both peripheral and central colour contrast sensitivity, the tritan axis being the most affected one. For the tritan axis, the central colour contrast sensitivity seemed to correlate well with the degree of diabetic retinopathy, indicating the possibility of a new functional test of diabetic retinopathy. Cataract, even moderately developed, affected both peripheral and central colour contrast sensitivity. Central colour contrast sensitivity seemed to be poorer in pseudophakic eyes than in normal eyes. Thus, both diabetes type II and moderate to severe cataract must be considered if the colour contrast sensitivity test is to be used for glaucoma screening. The choice of material for the IOL may also be of importance for postoperative central colour contrast sensitivity. The prostaglandin analogue latanoprost effectively reduces the IOP at the original concentration of 0.005%. However, several patients need additional treatment. Therefore, the effect of pilocarpine in combination with latanoprost was studied. When pilocarpine was added to latanoprost, there was an additional reduction in the intraocular pressure (IOP) (7.4%), and when latanoprost was added to pilocarpine the reduction was even more pronounced (14.2%). Therefore, it seems that latanoprost and pilocarpine can be combined in glaucoma treatment. In certain eyes, an increased iris pigmentation was seen as a side-effect of latanoprost. This side-effect may be dose-dependent. Therefore, the original concentration of 0.005% was compared to a lower concentration, 0.001%. Latanoprost 0.005% was more effective than latanoprost 0.001% in reducing the IOP. However, the lower concentration was sufficiently effective to have a potential for clinical use in many patients. Latanoprost 0.005% gave an IOP reduction of 35% after four weeks of treatment, which was in agreement with earlier results. The lower concentration was, however, surprisingly effective and gave an IOP reduction of 27.7%. This thesis is based on the following papers: