What is glaucoma and is there more than one type?  

‘It is a disease in which the optic nerve is damaged by high intraocular pressure, leading to irreversible loss of vision,’ Francisco J. Muñoz Negrete, president of the Spanish Glaucoma Society (SEG) and head of the Ophthalmology Department at the Ramón y Cajal Hospital, explains to SMC España.

There are several types of glaucoma, although the main and most frequent, as Muñoz Negrete points out, is primary open-angle glaucoma. ‘It represents 95% of cases,’ says the specialist, who is also Professor of Ophthalmology at the University of Alcalá de Henares (UAH).

María Isabel Canut Jornada, vice-president of the Spanish Glaucoma Society (SEG) and president of the Catalan Ophthalmology Society (SCOFT), explains that the different types of glaucoma depend on different criteria. These include the age of onset, within which congenital, juvenile and adult glaucomas are differentiated, or the angular width - referring to the relationship between the iris and the cornea in the aqueous drainage area -, which can be open or closed angle.

Primary or secondary glaucomas can also be classified, ‘depending on whether it is a primary dysfunction or secondary to other ocular or systemic pathologies’, explains the vice-president of the SEG to SMC Spain.

What is the incidence of glaucoma in Spain and worldwide, and what are the estimates for the future?  

Glaucoma is the leading cause of blindness and irreversible visual impairment in the world. According to the Spanish Glaucoma Society, it affects more than 3 % of the population in Spain. However, as the professor from the University of Alcalá points out, ‘it depends on age, as the incidence increases with age’.

Worldwide, as reported in a study published in the Journal of Global Health in 2022, the global incidence rate of primary open-angle glaucoma, the most common type, was 23.46 per 10,000 people per year aged between 40 and 79.

In terms of the total population, a study published in 2020 in Nature reported a worldwide prevalence of 2.4% for this type of glaucoma during the first twenty years of the 21st century.

In terms of forecasts, a study published in Ophthalmology estimated that by 2040, the number of people aged between 40 and 80 affected by glaucoma worldwide will approach 112 million.

‘The prevalence increases with age. Given the progressive ageing of the European population, prevalence is expected to increase in the next decade,’ says SCOFT's president.

What are the first signs of the disease? 

This is one of the main problems with this condition: ‘Open-angle glaucoma has no symptoms,’ says the president of the SEG. ‘When the patient notices vision loss, the disease is very advanced and has caused irreversible and profound damage to the visual field,’ he adds. This lack of early signs makes it known as ‘silent blindness’. In addition, vision loss affects the peripheral part of the visual field and progressively moves towards the central part, which also makes early diagnosis difficult.

‘Only when the intraocular pressure (IOP) greatly exceeds the figures considered normal, between 10-21 millimetres of mercury (mmHg), it can give some non-specific symptoms. Also in cases of extreme pain, when IOP exceeds 40 mmHg,’ says Canut.

An article published in Ophthalmology highlights that more than half of glaucoma cases globally are not detected before the disease manifests its symptoms. The same study estimates that, in 2020, about 44 million cases of posterior open-angle glaucoma went undetected.

Furthermore, the authors point out that the regions where glaucoma is most underdiagnosed are Africa and Asia: almost 77% of these non-diagnoses occurred in these continents.

How is it diagnosed? 

‘The determination of ocular pressure usually acts as a screening, as it is the most important risk factor,’ explains the SCOFT president. In addition, examination of the optic nerve by the ophthalmologist usually alerts to possible changes, according to the specialist.

‘For diagnosis, a series of tests are needed that must be interpreted by an ophthalmologist,’ says the UAH professor. Muñoz Negrete points out three of them: tonometry, in which ocular pressure is measured, the anatomical study of the retina by means of a retinography - in which a fundus photograph is taken - and an optical coherence tomography, and, finally, a functional study by means of the visual field. ‘All these tests together give us the diagnosis and the severity of the disease,’ concludes the SEG president.

Can glaucoma be treated and what are the main developments in treatment? 

‘It can and should be treated, above all to prevent and avoid progression once it is already established,’ Canut stresses. ‘There are therapeutic algorithms depending on the type of glaucoma, age of onset and evolutionary stage, focusing on the different therapeutic modalities: medical, laser and surgical treatment,’ says the vice-president of the SEG.

Muñoz Negrete gives an example: ‘An initial glaucoma can be treated with selective laser trabeculoplasty (SLT) or eye drops that reduce ocular tension. If this is not enough, surgery is needed.

As for new developments, Canut differentiates between diagnostic and therapeutic. In the first group, and related to prevention, he mentions the inclusion of technology with a high capacity for detecting lesions in early stages, emphasising its availability for the entire population receiving ophthalmological care in Spain. The vice-president of the SEG is particularly interested in genetic research: ‘It will provide us with lines of early diagnosis and gene therapy in a broad way’.

With regard to therapeutics, Canut points to the appearance of new pharmacological lines and lasers that complement the therapeutic objective ‘without compromising the visual changes after their application’. Muñoz Negrete also comments on these innovations: ‘The novelties in medical treatment are going to be prolonged drug release devices, which are injected inside the eye and avoid having to use drops’.

The SCOFT president also mentions the main surgical innovations: ‘New techniques have been implemented, such as MIGS - minimally invasive surgery - and, above all, their degree of safety. As a whole, ‘they have allowed a better approach to glaucoma, improving patients’ quality of life,’ Canut points out.

How does it affect patients? 

‘If diagnosed late, it causes severe visual impairment that limits the patient's life and makes him or her dependent for everyday tasks,’ says the SEG president. Canut agrees with him and adds: ‘As soon as there is a visual limitation, the quality of life and social interaction is more than compromised’.

Both specialists emphasise the psychological impact. ‘The moment of diagnosis is usually experienced with a reasonable degree of anguish,’ says the SCOFT president. Muñoz Negrete says that depression is often present, associated with the patients' dependence.

What are the main risk factors for glaucoma? 

They can be demographic, ocular and non-ocular. Among the ocular ones is the main known risk factor: elevated eye pressure (IOP). ‘It is estimated that the risk of glaucoma with IOP higher than 26 millimetres of mercury (mmHg) can be up to 12 times higher than in individuals with normal IOP,’ stresses the SEG vice-president.

However, Canut insists on not using a specific IOP limit as a measure for detecting or diagnosing glaucoma: ‘It requires a comprehensive study in which a change in IOP is accompanied by morphological, structural and functional alterations of the optic nerve’.

Another related but independent risk factor is a central corneal thickness (CCT) that is thinner than the normal range. ‘The measurement of the CCT serves as an aid in the interpretation of the IOP reading and determines the risk of developing glaucoma,’ explains the SEG vice-president. This would also include having high myopia.

In terms of demographic variables, advanced age is another important risk factor. ‘The prevalence of glaucoma increases exponentially with age,’ says the SCOFT vice-president. On the other hand, racial-ethnic characteristics are also an important risk factor: ‘A prevalence up to three times higher has been found in African-Americans compared to whites,’ Canut explains.

Finally, among the non-ocular factors, Canut pays special attention to family history of glaucoma. ‘There are studies that show how the probability of having primary open-angle glaucoma (POAG) was 9.2 times higher for people who have a first-degree relative with confirmed POAG,’ he says.

This group also includes type 2 diabetes as a risk factor. ‘In the absence of conclusive data, there are population-based studies that support the evidence that this is an important risk factor, linking it to microvascular changes in the optic nerve head and finding an increased likelihood of retinal nerve fibre layer damage in people with type 2 diabetes,’ Canut explains.

What is the relationship between myopia and glaucoma?

‘Myopic patients are at greater risk of suffering from glaucoma, and the more dioptres, the greater the risk,’ says the SEG president. The data support this. According to this study published in Ophthalmology, each additional dioptre of myopia is associated with a 20 % increased risk of open-angle glaucoma. The authors of this other study, published in the American Journal of Ophthalmology, focus on people with high myopia: ‘The risk increases sharply in cases of high-grade myopia’.

In addition to being a risk factor for the development of glaucoma, myopia is also an added difficulty for its diagnosis, as pointed out in this study published in Biomolecules. ‘Myopic patients have established visual field defects that can mimic glaucoma,’ say the authors. In addition, ‘high myopia may be associated with clinical features that resemble glaucomatous damage, making it difficult to accurately diagnose glaucoma,’ they explain.

For all these reasons, and taking into account ‘other retinal alterations associated with magna myopia’ -which occurs when myopia exceeds six dioptres-, Muñoz Negrete calls for special attention to be paid to the population with high myopia.

Can the disease be prevented? 

‘It can only be prevented with early diagnosis, with regular ophthalmological check-ups, especially in at-risk populations,’ says Muñoz Negrete. Canut agrees: ‘It is necessary to visit the ophthalmologist regularly, in order to establish a diagnosis in the earliest stages that can condition a good visual future’.