Introduction

This post is fairly long. Please consider using the navigation links below:

What is Glaucoma – In a Nutshell
The Risk Factors – Age – Family History – Ethnicity – Increased IOP / OHT –
Refractive Error – Hypertension – Diabetes – Heart Disease – Raynaud’s Phenomenon –
Migraine – Sleep Apnoea – Nocturnal Hypotension – Steroid Use –
Ocular Trauma – Uveitis – Central Corneal Thickness – Smoking –
Pigment Dispersion and Psuedoexfoliation
Summary
Skill Activity
References

Please note, this is educational advice geared at eye care professionals and NOT a source for personal medical management. For registered practitioners, please keep in mind that this article does not replace your professional judgement when examining patients and no responsibility will be assumed by the author or website for misdiagnosis of patients that you see.

If you ever had to name an eye disease that causes even the most experienced optometrists and ophthalmologists a headache trying to diagnose, it’s glaucoma. It can be silent and stealthy, slowly damaging the retina and eating away at both the patient’s vision and optic nerve. Sometimes the eye looks healthy, but glaucoma is causing irreparable damage and in other cases the eye may look like it has glaucoma, but is in fact perfectly healthy.

So, what else can we consider to help us assess the chance that our patient might be at risk of getting this tricky disease? We can examine the risk factors that need careful consideration, of which there are many!

Before we dive into the numerous risk factors of glaucoma, it is worth just briefly touching upon what glaucoma is.

What is Glaucoma – In a Nutshell

Glaucoma isn’t a single entity; rather, it encompasses a group of eye conditions that share a common thread: progressive damage to the optic nerve¹. This vital nerve connects the retina—the light-sensitive tissue at the back of the eye—to the brain. When the optic nerve suffers injury it can often cause irreversible loss of vision.

So why do we worry about this progressive disease? Besides the progressive loss of vision that it causes, it is one that we can intervene with and slow the progression of – especially if it is caught early enough. The disease affects over 76 million people worldwide² and thus is a common ocular pathology. It is also predicted to affect approximately 112 million by 2040², so if we do not try to identify the disease early, many people will suffer through preventable sight loss. As optometrists, we are in a key position to identify those at risk and direct them to the appropriate professionals to manage and treat those with the risk of sight loss in their lifetime.

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The Risk Factors

The following sections will cover the risk factors for glaucoma and aim to cover why they pose a risk factor for the disease. Whilst they are called “risk factors”, it does not necessarily mean that patients falling within one or many of the listed categories will have glaucoma but you should have glaucoma at the front of your mind when a patient is identified to be within them. Similarly, a patient that does not fall in any risk factor category should not be assumed to be immune from it. ALWAYS use your professional judgement and the results of the numerous tests when managing your patient and act in their best interests.

Age

Drainage. The aqueous humour, a fluid that nourishes the anterior part of the eye, is in continual balance between its production in the ciliary body and its drainage through the trabecular meshwork of the angle and uveoscleral routes³. Over time, these drainage channels may become clogged with a lifetime of impurities within the aqueous humour³ (such as pigments or immune-response cells), causing a gradual increase in the intraocular pressure. As such this increase in IOP may result in damage to the nerve fibre and subsequent damage to the optic nerve head.

Narrowing of Anterior Chamber Angles. Over time, the crystalline lens within the eye becomes thicker⁴. This lens sits directly behind the iris^3,4, which forms part of the posterior surface of the drainage angle. As the lens gets bigger, it presses the iris forward, causing the drainage angle to get narrower⁴, which can affect the delicate balance between aqueous humour production and drainage, causing an increase in IOP over time and subsequent damage to the retinal nerve fibres¹.

General Aging/Cellular Senescence. Senescence is the stable exit of cells from the cell cycle caused by oxidative stress and cellular damage⁵. This causes cells to cease dividing and entering a state of permanent growth arrest. This can cause issues in the trabecular meshwork and affect the ability to drain aqueous as effectively causing a rise in IOP⁵. Senescent retinal ganglion cells cease to work over time and this causes their associated retinal nerve fibre axons to die off, again providing a chance for vision loss⁵. This would also account for the gradual increase in the cup-to-disc ratio with increasing age. Furthermore senescence in vascular endothelial cells⁵ may affect blood flow and further cause issues with the balanced ocular dynamic within the eye and lead to glaucomatous damage.

In summary, as we get older, our bodies do not work as well as they used to and as such this leads to the risk of ocular diseases, such as glaucoma, to increase.

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Family History

A family history of glaucoma is one of the main risk factors for developing the disease^1,6 and it is thought that 50% of all people diagnosed with glaucoma have a predisposed genetic risk^6,7. This is because glaucoma development is likely to be due to multiple issues regarding the anatomy and physiology of the eye, which is coded for by our genes⁷. We inherit our genes from our parents and, as such, if a parent with glaucoma passes on a gene that was influential in them developing glaucoma, then the risk of glaucoma developing in their children increases.

It is worth mentioning that a patient with a first-degree family history of glaucoma is thought to have nine times the risk⁷ of developing glaucoma compared to someone without a family history of glaucoma, with the risk being greater when it is a sibling (up to ten times the risk⁶) or if multiple first-degree relatives have a glaucoma diagnosis.

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Ethnicity

The ethnicity of the patient can also prove to be a significant risk factor in glaucoma development^2,7. It has long been established that those of a Black, Afro-Caribbean ethnicity have five⁸ to six⁷ times the risk of developing open angle glaucoma than non-Hispanic white individuals and East Asian ethnicity being more at risk of angle-closure glaucoma than Caucasians^2,7.

Additionally, there may also be both cultural and socio-economic factors^2,7,8 that contribute to the likelihood of developing glaucoma and the stage it presents at. These factors may include, but are not limited to, perceived need for frequent eye examinations, lifestyle and ease of access to healthcare.

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Ocular Hypertension (OHT)

Glaucoma has a long association with the intraocular pressure (IOP) of the eye and many patients that you will see will associate the “puff of air test” of tonometry with a check for glaucoma. As stated earlier, high IOP is not diagnostic of glaucoma but a risk factor for developing it.

Whilst having an IOP over 21 mmHg does increase the risk of developing primary open angle glaucoma, it has been found that on 17.5%¹⁰ of patients (or approximately 1 in 6) with ocular hypertension will go on to develop visual field loss within 5 years. If this is coupled with approximately half¹⁰ of patients with glaucoma having an IOP of less than 21 mmHg (a condition known as normotensive glaucoma) it is important to remember that high IOP only serves as a risk factor as opposed to a definite component to diagnose the condition.

That said, the risk of developing glaucoma does increase the higher the IOP rises, so do be mindful that further investigation, management and often treatment is required for IOPs measuring 30 mmHg or above. As always, use your professional judgement when dealing with your patients.

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Refractive Errors

A patient’s refractive error is also deemed a risk factor and both hyperopia and myopia are so for their own reasons.

Myopia. Myopic patients are often myopic due to the axial length of their eye rather than excessive refracting power of the eye. With this increased size, the eye is susceptible to mechanical and structural stresses which can lead to increased susceptibility to the optic nerve head to IOP and progressive degeneration of the retinal ganglion cells¹¹.

Many large scale studies have looked into the relationship between myopia and glaucoma risk, with the Blue Mountains Eye Study¹² suggesting myopia of less than -3.00 dioptres increased the risk of open angle glaucoma by 2.3 times compared to emmetropes and 3.3 times when myopia was over -3.00 dioptres. The Beaver Dam Eye Study¹³ found that myopes were 60% more likely to develop open angle glaucoma than emmetropes.

Hyperopia. Hyperopic eyes tend to have shorted axial lengths and are smaller. This means less room for the working components of the eye and as such, this causes the anterior chamber to be anatomically shallower and the anterior chamber angles to be narrower¹⁴. This shallowing increases as the hyperopia increases as the higher the hyperopia, the shorter the axial length. With the chambers shallow and the angles narrow, the drainage of the anterior chamber is impeded and can be susceptible to becoming blocked by the iris, thus increasing the risk factor for angle closure glaucomas¹⁴.

In general, the risk factors associated with refractive error tend to increase significantly when the refractive error is in excess of 3 dioptres^12,13,14 and as such, any patient with a refractive error in excess of this should cause you to consider their risk of glaucoma.

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Systemic Health Issues

It should be apparent that the eye is not the only organ within the body and with it being a peripheral organ, it is susceptible to systemic health complaints. Each health complaint can pose its own risks, so the following section will look briefly at each of them. Of course, the article will look at the most common and most significant systemic health conditions as there are many others that may increase glaucoma risk, but are outside of the scope of this article.

Hypertension (High Blood Pressure)

Hypertension, more commonly known as high blood pressure, is where the pressure of the blood moving through the cardiovascular system is higher than ideal, which can lead to cardiovascular diseases such as strokes and heart failure¹⁵. It was estimated that over 26% of the adult population had hypertension in 2017¹⁶ and as such, it is a common finding during a patient’s history and symptoms. It is thought that hypertension increases the risk of open angle glaucoma by 1.7 times¹⁷.

Both of these result in an increase in IOP which could go on to damage the optic nerve head. However, several studies have commented that the strong correlation between hypertension and open angle glaucoma could purely be that of increased risk of hypertension occurs with increasing age, rather than a risk factor alone⁷.

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Diabetes

Diabetes also poses several risks of developing glaucoma. Those with diabetes are more prone to retinal diseases caused by the effect of the diabetes on their retinal vasculature. Diabetic retinopathy and occlusive retinal diseases can cause hypoxia to occur within the retina, causing growth of new, leaky vessels (neovascularisation). These vessels can grow into the anterior chamber angles and occlude outflow of aqueous and subsequently increase IOP dramatically¹⁸.

Additionally, diabetes itself causes dysregulation of cells throughout the body.¹⁸ This is also thought to occur in the retinal cells^7,18 and as such may offer another reason as to why diabetes increases the risk of glaucoma development.

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Heart Disease and Heart Surgery

The heart is responsible for circulating the blood around the body. Any disease that affects the heart, not limited to heart failure, atrial fibrillation and myocardial infarction (also known as a heart attack) can affect blood flow around the body and lead to damage of organs. The eye is no exception and as such there is a strong correlation between heart disease and glaucoma²⁰.

Poor Circulation and Raynaud’s Phenomenon

Following on from above, poor circulation within the body can lead to disruptive changes and damage to peripheral organs such as the eyes. Raynaud’s Phenomenon is an example of abnormal vasoregulation and is characterised by a whitening or bluing of fingers and toes as an over-reaction to cold or stress²¹.

A patient with Raynaud’s Phenomenon is at a higher risk of normal tension glaucoma^21,22. This is due to a reduced blood supply to the optic nerve head and the differences of pressure (both IOP and blood pressure) across the optic nerve head can lead to the nerve being more susceptible to optic nerve head damage at lower levels of IOP^21,22.

When encountering a patient with suspect optic nerve heads or visual field plots but with IOPs within the normal range, do ask about Raynaud’s. For me, it is a staple question in my case history but it is definitely worth enquiring about if glaucoma is suspected.

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Migraine

Patients attending for routine eye care often describe seeing an aura associated with migraine, or complaining of classic migraine headaches. It can be all too easy to dismiss this as a normal finding of little ocular concern, but it is in fact another risk factor for glaucoma^21,22 – especially normal tension glaucoma.

Obstructive Sleep Apnoea

Obstructive sleep apnoea is a where the muscles of a patient’s throat relax during sleep, causing a narrowing or blockage of their airway²⁴. As the body is not breathing during these episodes²⁴, there is a reduction of oxygen reaching the eye and optic nerve, potentially causing hypoxic damage and reducing the the integrity of the retinal ganglion cells²⁵, which can lead to glaucoma.

There is evidence to suggest that episodes of sleep apnoea cause the IOP to drop²⁴, with this fluctuation of IOP throughout the night likely causing mechanical stress to the retina and contributing towards the pathogenesis of glaucoma.

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Nocturnal Hypotension

It can be worth discussing blood pressure control with your patient, ensuring they are taking their antihypertensive medication as prescribed and relaying any concerns to the ophthalmologists managing their glaucoma, where appropriate.

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Long-Term Steroid Use / Steroid Responders

Corticosteroids belong to a group of anti-inflammatory medications frequently used to treat and manage different ocular and systemic conditions. However, their use can result in notable side effects related to the eyes. One well-documented effect is an increase in IOP after steroid administration, which can lead to ocular hypertension²⁷. Steroids generally have this impact whether applied topically, periocularly, but in some cases when taken systemically or inhaled²⁷.

The steroids tend to create mechanical obstruction of aqueous outflow through changes to the cells within the trabecular meshwork of the angle^27,28, hence raising the IOP. However, these changes do not occur in everyone – in fact 65% of people have negligible increase in IOP²⁸ upon steroid use, 30% have a moderate rise of 5-15 mmHg in IOP²⁸ and about 5% have a marked increase of over 15 mmHg²⁸ when exposed to steroid medication. Whilst it may only represent a small proportion of the population, it is critical to ask about medication use during the case history and factor in if steroid use is behind any findings of increased intraocular pressure.

With most cases, a mild increase in IOP over a short course of time is unlikely to cause significant damage, but in those that have IOPs that respond markedly to steroid use and those that are on longer term steroid treatment, it is important to refer back to the prescriber (patient’s general practitioner, rheumatologist etc.) to see if steroids can be switched to an alternative anti-inflammatory^27,28. Referral to an ophthalmologist to consider treating the steroid-induced intraocular hypertension to prevent it becoming a steroid-induced glaucoma would also be advised²⁸. It is noted that IOPs tend to return to baseline level following cessation of steroid treatment^27,28.

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Ocular Trauma

Ocular trauma refers to any form of injury that occurs to the eye, eyelid or surrounding ocular tissues. It can include blunt trauma²⁹ (such as being hit in the eye by a ball), or penetrating injury²⁹ (such as that occurred from a stray BB gun pellet).

Milder and Davis’²⁹ paper “Ocular Trauma and Glaucoma” covers this in more detail with the various ways that ocular trauma can lead to increased glaucoma risk. It should be noted that the subtle signs of damage to the eye following blunt trauma may be missed or deemed insignificant at the time, but the slight change within the ocular dynamics may pose an issue over time²⁹. From my experience within glaucoma clinics, quite often when there is a difference in cup-to-disc ratio between eyes or IOP asymmetry, patients tend to report a historical traumatic injury and as such, this question should be asked and response documented on their records and any referrals, if warranted.

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Uveitis

Uveitis, a condition where the uvea of the eye becomes inflamed, affects over 2 million people worldwide³¹. The condition can cause significant damage to the retina and the structures within the eye³¹, which in turn can lead to raised intraocular pressures, damage to retinal ganglion cells and damage to the nerve fibres, ultimately leading to glaucoma.

It should be noted that there is often the presence of cells and flare within the anterior chamber when uveitis is active^31,32, so this thickened and debris-filled aqueous has a tendency to clog the trabecular meshwork³¹ and thus increase intraocular pressure, providing yet another mechanism for glaucoma to develop.

Management of uveitis can pose difficulties for ophthalmologists and optometrists as the inflammation is often managed with steroids and, as stated above, can lead to increased IOP^27,28,31 and increased risk of glaucomatous damage. A thorough case history should be obtained from every patient and when they mention a history of uveitis be sure to explore their treatment and management as this could aid your understanding of their glaucoma risk.

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Central Corneal Thickness (CCT)

A large scale study, called the Ocular Hypertension Treatment Study (OHTS), found that the central corneal thickness (or CCT) provided a significant predictor of which patients with ocular hypertension would go on to develop glaucoma^33,34. It found that eyes with a CCT of less than 555 µm were three times more likely to develop glaucoma compared to those eyes with a CCT of 588 µm or more^33,34.

There are two arguments currently in play with these findings and debate still rages as to whether this is truly an independent risk factor.

Essentially, thinner corneas are generally more flexible and will tend to under-estimate the IOP upon measurement. A thinner cornea and a borderline OHT measurement is likely to indicate the eye is of a normal or well-controlled pressure, when in reality it isn’t³⁴. This could lead to misdiagnosis or wrongful assumption that the IOP is under control, leading to a higher chance of developing glaucoma³⁴.

The other side of this argument is that it truly is an independent risk factor. There could be structural differences within the collagen within the eye that results in a thinner cornea and as such there may be other collagen-related weaknesses in the eye that make it more susceptible to glaucoma³⁵.

Both sides of the argument indicate that those with thinner CCTs are at risk of developing glaucoma, so when you do have a patient that has a CCT of less than 555 µm – do consider the results you obtain via tonometry carefully and holistically look at the overall picture before signing them off with normal IOPs.

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Smoking

Smoking is a recreational activity that has long been associated with negative health effects. The act of inhaling smoke reduces the intake of oxygen and increases the intake of other harmful gasses including carbon monoxide. This, in turn, causes reduction in the available oxygen required by the highly metabolic retinal cells³⁶ as well as provides additional stress on the retina, leading to increased risk of retinal cell death³⁶ and resulting in glaucomatous damage.

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Pigment Dispersion Syndrome and Pseudoexfoliation Syndrome

Both of these conditions are major risk factors in glaucoma development and are not likely to be referred to by your patient in a case history – unless they have already been diagnosed with either condition. Their inclusion in detail is out of the scope of this article, but both conditions have cellular debris that enters the aqueous and as such clogs the trabecular meshwork, leading to an increase in IOP. Future articles will cover this in more detail, but have been mentioned here for completeness.

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Summary

As an optometrist, ophthalmologist or another eye care professional, it is important to consider your patients’ case histories and risk profile. This article, despite its length, briefly touches upon factors that increases the glaucoma risk for patients. Whilst not every patient presenting with a risk factor will develop glaucoma, it is vital that you recognise the significance of that factor and investigate them fully.

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Skill Activity

Please take the time to try these multiple choice questions based on the text above.

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References

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2. Tham YC, Xiang L, Wong TY, Quigley HA, Aung T, and Cheng CY (2014). global prevalence of glaucoma and projections of glaucoma burden through 2040: A systematic review and meta-analysis. Ophthalmology 121(11): P2081-2090.
3. Wadhwa A, Jadhav C, and Yadav KS (2022). Bimatoprost: promising novel drug delivery systems in treatment of glaucoma. Journal of Drug Delivery Science and Technology 69: 103156.
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5. Zhang Y, Huang S, Xie B, and Zhong Y (2024). Aging, cellular senescence and glaucoma. Aging and Disease 15(2): 546-564.
6. Okeke C (2017). Glaucoma risk increases in families: spread the word. Glaucoma Research Foundation [online]. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10917531/. [Accessed: 28th April 2024].
7. McMonnies CW (2017). Glaucoma history and risk factors. Journal of Optometry 10(2): 71-78.
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9. NICE guideline [NG81] (2017 – amended 2022). Glaucoma: diagnosis and management. National Institute for Health and Care Excellence [online]. Available at: https://www.nice.org.uk/guidance/ng81/chapter/recommendations#treatment [Accessed: 28th April 2024].
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15. Carretero OA, and Oparil S (2000). Essential hypertension. Part 1 – definition and etiology. Circulation 101(3): 329-335.
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17. Nislawati R, Zainal ATF, Ismail A, Waspodo N, Kasim F, Gunawan AMAK (2021). Role of hypertension as a risk factor for open-angle glaucoma: a systematic review and meta-analysis. BMJ Open Ophthalmology 6(1):  e000798.
18. Song BJ, Aiello LP, and Pasquale LR (2016). Presence and risk factors for glaucoma in patients with diabetes. Current Diabetes Report 16(12): 124.
19. Fong DS, Gottlieb J, and Ferris III FL (2001). Understanding the value of diabetic retinal screening. Archives of Ophthalmology 119(5): 758-760.
20. Marshall H, Mullany S, Qassim A, Landers J, Casson RJ, Craig JE, Ridge B, et al. (2021). Cardiovascular disease predicts structural and functional progression in early glaucoma. Ophthalmology 128(1): 58-69.
21. Mallick J, Devi L, Malik PK, and Mallick J (2016). An update on normal tension glaucoma. Journal of Ophthalmic and Vision Research 11(2): 204-208.
22. Barsegian A (2022). Normal-tension glaucoma: pathogenesis. Glaucoma Today November/December 2022: 24-29.
23. Drance S, Anderson DR, Schulzer M (2001). Collaborative normal-tension glaucoma study group. Risk factors for progression of visual field abnormalities in normal-tension glaucoma. American Journal of Ophthalmology. 131(6): 699-708.
24. Thomas K (2024). Breathing uneasily: sleep apnoea and glaucoma. Acuity Winter 2024. [Online.] Available at: https://www.college-optometrists.org/professional-development/college-journals/acuity/all-issues/winter-2024/breathing-uneasily-sleep-apnoea-and-glaucoma [Accessed: 29th April 2024].
25. Ucak T, and Unver E (2020). Alterations in parafoveal and optic disc vessel densities in patients with obstructive sleep apnea syndrome. Journal of Ophthalmology [Online.] Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7056990/ [Accessed: 29th April 2024]
26. Addis VM (2024). Systemic factors in glaucoma. Review of Ophthalmology. [Online.] Available at: https://www.reviewofophthalmology.com/article/systemic-factors-in-glaucoma#:~:text=Exaggerated%20nocturnal%20hypotension%20or%20dips,of%20well%2Dcontrolled%20intraocular%20pressure. [Accessed: 29th April 2024].
27. Phulke S, Kaushik S, Kaur S, and Pandav SS (2017). Steroid-induced glaucoma: an avoidable irreversible blindness. Journal of Current Glaucoma Practice 11(2): 67-72.
28. College of Optometrists (2022). Clinical management guidelines: steroid-related ocular hypertension and glaucoma. College of Optometrists [Online]. Available at: https://www.college-optometrists.org/clinical-guidance/clinical-management-guidelines/glaucoma_steroid [Accessed: 29th April 2024].
29. Milder E, and Davis K. (2008). Ocular trauma and glaucoma. International Ophthalmology Clinics 48(4): 47-64.
30. College of Optometrists (2023). Clinical management guidelines: trauma (blunt). College of Optometrists [Online]. Available at: https://www.college-optometrists.org/clinical-guidance/clinical-management-guidelines/trauma_blunt [Accessed: 29th April 2024].
31. Kalogeropoulos D, and Sung VCT (2018). Pathogenesis of uveitic glaucoma. Journal of Current Glaucoma Practice 12(3): 125-138.
32. College of Optometrists (2023). Clinical management guidelines: uveitis (anterior). College of Optometrists [Online]. Available at: https://www.college-optometrists.org/clinical-guidance/clinical-management-guidelines/uveitis_anterior [Accessed: 29th April 2024].
33. Gordon MO, Beiser JA, Brandt JD, et al. The ocular hypertension treatment study: baseline factors that predict the onset of primary open-angle glaucoma. Archives of Ophthalmology 120:714–720. discussion 829-30.
34. Medeiros FA, and Weinreb RN (2012). Is corneal thickness an independent risk factor for glaucoma? Ophthalmology 119(3): PMC3811124.
35. Vithana EN, Aung T, Khor CC et al. (2011). Collagen-related genes influence the glaucoma risk factor, central corneal thickness. Human Molecular Genetics 20(4): 649-658.
36. Mahmoudinezhad M, Nishida T, and Weinreb RN et al. (2022). Impact of smoking on visual field progression in a long term clinical follow up. Ophthalmology 129(11): 12351244.
37. Lee CS, Owen JP, Yanagihara RT et al. (2020). Smoking is associated with higher intraocular pressure regardless of glaucoma: a retrospective study of 12.5 million patients using the Intelligent Research in Sight (IRIS) registry. Ophthalmology Glaucoma 3(4): 253-261.