Glaucoma

2. Describe tests and ways to diagnose glaucoma, with reference to pneumotonometry and the spot light test.

3. Research the pathophysiology of glaucoma.

4. Evaluate current treatments for glaucoma, with reference to the eye drops mentioned in the case.

1. Elderly people are more at risk of developing glaucoma, especially after 60 years of age. Ethnicity is also a big factor with African Americans most likely to develop glaucoma, with risk increasing from 40 years onwards as opposed to 60 in the general population.[1] Asians are more at risk of angle closure glaucoma in particular. A particular injury to the eye is a risk factor since it can immediately increase the intraocular pressure. The lens can also become dislocated which reduces the drainage angle and increases pressure. Family history has been linked to an increased likelihood of developing certain types of glaucoma suggesting that there is a genetic component increasing susceptibility. [2] The use of frequent corticosteroids has also been implicated in developing glaucoma [3] as it interferes with the trabecular meshwork and increases glycosaminoglycan levels.[4,5] Recently people with diabetes mellitus have been associated with glaucoma as diabetes causes retinal ischaemia with an insufficient blood supply. [6] 2. Tonometry is a common test used for detecting glaucoma. The eye is numbed and then magnified using a lamp, after which the tonometer is placed next to the cornea so it is just touching. It then measures intraocular pressure. A pachymeter is another device that can be used. This involves measuring the central corneal thickness with a probe placed perpendicular to the cornea. This test can be used in conjunction with tonometry since a thin corneal thickness in people with high intraocular pressure is a strong indicator of glaucoma development. [7] A visual field test can be performed which involves indicating whenever a flash of light is seen on a screen (light spot). This is useful as peripheral vision is often lost first. [8] Gonioscopy is a test which uses a lens with a mirror in it which is placed into the dilated eye and measures the angle between cornea and iris. [9] 3. The increase of intraocular pressure in the eye is the focal point of different glaucoma types which can lead to blindness if untreated. The lens in the eye is surrounded by a fluid called the aqueous humour. This provides nutrients but also needs to be replaced as it can become toxic. [10,11] It is drained through the trabecular meshwork whilst it is replenished by the ciliary body where it is also made. The raised intraocular pressure is either due to the trabecular meshwork being blocked or the drainage angle is reduced which both result in excess aqueous humour. [12] There is a change in the shape of the optic disc with it becoming circular due to the loss of ganglionic axons at the lamina cribrosa. This is a structure in the optic nerve head which acts as a pressure barrier and allows the axons to leave the eye. It can become malformed by excess pressure which leads to the death of retinal ganglion cells by apoptosis and causes the vision loss. [13] 4. Eye drops are a common treatment for people who are likely to develop glaucoma. They either work by reducing production of the aqueous humour, increasing drainage of fluid in order to reduce intraocular pressure or both in the case of adrenergic agonists which mimic adrenaline however there is a risk of an allergic reaction occurring in the eye. Beta adrenergic agonists reduce fluid production but can have side effects however like bradycardia, hypotension and impotence to name a few. [14] There are laser treatments like a laser iridotomy which involves making a hole so fluid can drain out or a trabeculoplasty, however the prognosis for the latter is poor. Surgical options for severe glaucoma such as a trabeculectomy are available which involves making a new collecting bag for fluid to drain although there is a risk of infection and a need for recovery time.

1. A case control study is used here to determine if diabetes is linked with glaucoma. To achieve a representative sample without bias, three specific sites were chosen across Nepal with people from various ethnic backgrounds included. The study was carried out for 15 months and this could have been carried out for longer since this is a relatively new link and more evidence is needed to definitely prove the hypothesis. A power calculation was performed, resulting in 90% at the 95% confidence interval showing a high probability of diabetes and glaucoma being linked with someone with diabetes being 3.5 times more likely to develop glaucoma. The exclusion criteria were those under 15 years of age, people with secondary glaucoma and those with other ocular pathologies. Patients were selected using a non-random consecutive sampling technique at each site in order to get an accurate representation from each area. There were 173 patients with glaucoma used and an additional 510 in the control group. Obviously a higher number in the group with glaucoma is desirable however it is not always feasible when there are strict criteria to meet. McNemar's test was used in order to give statistical significance to the results. The study is from 2013 only so is also recent and likely to be factually correct. 2. This article looks at the link between central corneal thickness (CCT) and glaucoma. The study was for 2 years which is a suitably long time especially since glaucoma presents itself slowly so this study was chosen. However only 121 patients met the inclusion criteria so the results are less likely to be reliable as this is not a large sample size. People were included if intraocular pressure was above 22mm Hg with hypertension, there was no other ophthalmological damage and had a diagnosis of open angle glaucoma. Conversely the exclusion criteria were those people who had surgical treatments or secondary glaucoma which is appropriate since the study only looks at primary glaucoma and hypertension. A control group was also used so the results obtained could be compared with those people with normal ophthalmological data. The three groups were therefore those people with glaucoma, those with hypertension and a normal group. The results showed that those with hypertension had the largest central corneal thickness followed by those with glaucoma and lastly the control group. This same order stood when intraocular pressure was determined. This shows that CCT is of importance in glaucoma and confirms the original hypothesis which aimed to determine a correlation. The article is from February 2014 so it is very recent and up to date. 3. This study focusses on the outcomes for people with glaucoma following laser iridotomy. In total there were 52 patients with just 79 eyes meeting the criteria for selection. This reduces the reliability as this is not a large sample size. There were 34 women used when perhaps the numbers should have been more equal to be representative. The mean age is 64.6 which is understandable since the risk of glaucoma increases greatly after 60 years of age. There were a wide variety of ethnic groups included however like Black, White, Asian and Hispanic. 40 of these eyes were right eyes so there is an equal distribution here. The excellent breadth in ethnicity is representative and as such was chosen. 51 of the 79 eyes required additional treatment following iridotomy showing it is not a permanent solution in the majority of cases. It directly names another study, suggesting it is an improvement as the previous study had not factored in a particular treatment. The statistical analysis included the two sample t-test, the paired t-test and regression analysis all at the 5% significance level indicating a high level of certainty. The study was published in 2013 so it is recent and therefore more likely to have correct information about glaucoma and iridotomy.