Introduction

Trichiasis is a condition that affects the eyes and leads to eyelashes growing towards the front of the eye, which is known as the ocular surface. This can lead to layers within the eye, such as the cornea, getting scratched by the eyelashes, which can result in visual impairment and discomfort.¹ Trichiasis can be caused by many factors, such as infections, including Chlamydia trachomatis, which is the leading global cause of blindness. This infection leads to the eyelid being scarred, therefore, the eyelashes are misdirected.² There are many other causes of this condition; however, the main cause is the aforementioned infection, which leads to vision issues alongside sleep difficulties.³ This disease is very prevalent in countries within South America, Central America, Asia, Africa, and the Middle East, with a lower prevalence in Europe. Studies have also demonstrated that females are more susceptible to Trichiasis than men due to Chlamydia trachomatis being more prevalent in women than in men.⁴ In 2016, this condition affected 2.8 million people, with over half of those affected living in sub-Saharan Africa. Most of the blindness cases are also in this geographical area, which is likely to be due to lower healthcare accessibility.⁵ It is important to understand the pathophysiology of this condition, due to this disease being more prevalent in certain groups of people and due to many of the causes not being understood in great detail. This article is going to explore the pathophysiology of Trichiasis and investigate the different causes of this condition. Treatment methods will also be explored.

Anatomy and Normal Eyelash Growth

The eyelashes and eyelids have a very specific structure. The eyelid is composed of many layers, including the skin, the orbital septum, which separates the eyelid from structures located in the eye, orbital fat, as well as the conjunctiva, which lines the inside of the eyelids. As well as these structures, there are tarsal plates which contain eyelash follicles alongside Meibomian glands. The upper lid contains 100 eyelashes, which is higher than their lower eyelid, which contains approximately half of this number. This is why the upper eyelid is more noticeable regarding the eyelashes than the lower eyelid, which contains fewer eyelashes.⁶ Eyelashes are meant to have an angled orientation, which is referred to as an oblique orientation., The angles between follicle roots and the skin, as well as other eyelash angles, vary between people and differ significantly between ethnic groups.⁷ The function of eyelashes is to ensure proper health of the eyelid margin, which is the area between the skin and the conjunctiva.⁸ Eyelashes are integral in maintaining ocular health as they protect the true ocular surface from dust and facilitate blinking. Many recent studies have investigated the role of eyelashes in protecting against Ultraviolet light and radiation that is emitted by the sun.⁹

Pathophysiology of Trichiasis

Many different causes and mechanisms result in the presentation of Trichiasis. Trichiasis occurs due to eyelashes not growing properly, as well as eyelid margins not being optimally positioned. The follicles may have a shape or orientation that differs from the norm, which results in eyelashes growing towards the ocular surface. This causes damage to the cornea and results in Trichiasis.¹⁰ Entropion of the eyelid margin can also occur, in which the eyelid margin rolls inward, which can be due to inflammation. Due to this, the eyelashes misalign, and this results in the aforementioned phenomenon of eyelashes growing abnormally regarding their orientation.¹¹

There are many different causes of Trichiasis, alongside the Chlamydia trachomatis infection that has been mentioned previously. This infection is the most common cause of this condition and is a sexually transmitted disease in most cases. This infection leads to discharge from the penis and other symptoms in men, but many women are asymptomatic which allows this to be neglected.¹² This is one possible reason why Trichiasis caused by the trachomatis infection is more prevalent in women than in men.⁴ 

Another condition that causes cicatricial changes within the eye (scarring of the eye tissues) is Stevens-Johnson syndrome (SJS). This is an inflammatory condition that typically causes a rash on the skin and can spread to areas of the eye and cause inflammation. SJS leads to blindness in some cases, and the ocular surface is damaged in severe instances when the eyelid tissue is damaged, leading to eyelashes growing in the wrong direction.¹³

Another disease which results in Trichiasis is ocular cicatricial pemphigoid (OCP). OCP is an autoimmune condition that leads to scarring on the skin and results in the conjunctiva shrinking. Scarring of the eyelid tissue results in many complications, such as cicatricial entropion, therefore leads to eyelashes misaligning as previously mentioned.¹⁴ The ocular surface and the eye in general are susceptible to burning, which can be due to chemical or thermal factors. Burns can result in cicatricial entropion, thus, trichiasis is not uncommon.¹⁵ Blepharitis is another inflammatory eye condition that is commonly referred to as eye dandruff. This causes similar symptoms to SJS due to the eye margin being damaged.¹⁶

Changes to the structure of the eye also cause Trichiasis. As people age, eyelid laxity occurs, which is when eyelids and eyelid muscles, such as the orbicularis oculi muscles, weaken. This results in eyelid entropion in the upper and lower eyelids, therefore leading to trichiasis.¹⁷ Surgeries to treat the eyelid margin and other operations which involve the eyelid or other parts of the eye increase the likelihood of Trichiasis. Surgeries increase the chance of trauma to these regions; therefore, this must be considered before a surgery takes place.¹⁸ 

Removing and treating eyelid tumours is important as eyelid tumours can potentially contribute to Trichiasis; however, as aforementioned, surgical interventions also increase the risk of this condition, whether excision is done or cryotherapy is utilised.¹⁰

Trichiasis can also have unknown as well as congenital causes. Some individuals have a family history of this condition; therefore, in some instances, if a cause is not established, it is assumed that this disease is linked to genes. Individuals who have this disease from birth have congenital Trichiasis, where eyelid and eyelash positions are abnormal; these instances should be further investigated.¹⁹

Pathological Effects on the Eye

Many effects on the eye result from Trichiasis. Firstly, the cornea gets damaged due to the eyelashes rubbing against the cornea, leading to a high prevalence of corneal ulcers in Trichiasis instances.²⁰ The cornea may also become opaque due to damage to the epithelium of the cornea, which decreases vision for those affected.²¹ Inflammation is also very common; the conjunctiva is very commonly targeted due to this disease, and this leads to conjunctivitis.³ Secondary infection is a common phenomenon which occurs as a result of a prolonged period of irritation; therefore, monitoring for these infections is necessary for Trichiasis patients.² As aforementioned, corneal ulcers are a risk alongside epithelial issues.²⁰ Neovascularisation in the cornea, in which new blood vessels form in the cornea, greatly impairs vision, and scarring further exacerbates this issue.²²

Clinical Implications and Management Considerations

When treating and managing Trichiasis, many different factors and possibilities must be considered. Firstly, it is important to recognise the symptoms of this condition so that it can be appropriately diagnosed and treated. Symptoms include foreign bodies appearing on the eye surfaces, alongside the eyes becoming red. Patients are also very sensitive to light, leading to a condition known as photophobia.²³ To elucidate the extent of the damage to the eye and diagnose this disease, lash number and symptoms can be assessed, as well as a slit-lamp examination, which examines the different structures within the eye.²⁴ To treat Trichiasis, there are a few different approaches that are utilised. Surgical interventions are typically the best form of treatment; however, epilation, in which eyelashes in contact with the eye are removed, is a good alternative procedure. This is especially effective when surgery is not always available.²⁵ Cryotherapy is an alternative approach that involves destroying the eyelash follicles that lead to misdirected lashes using very cold temperatures. This technique is very effective with lid margin splitting. This is a surgical intervention in which the lid margin is separated to ensure that trichiasis lashes are properly exposed to the cold temperatures without normal lashes being affected.²⁶

Summary

In summary, Trichiasis results from eyelashes growing towards the ocular surface, and this can be due to many different inflammatory conditions; however, Chlamydia trachomatis is the main cause of this condition. This condition affects the eyes in many ways, such as impaired vision, damage to the cornea, and those affected are also susceptible to secondary infections. Diagnosing those with this disease early is very important, as this condition is indeed the leading cause of blindness, and the damage is very difficult to treat. Diagnosing symptoms is becoming more efficient over time, with the aforementioned methods developing over recent years.

Treatments such as surgical intervention are effective, and a more combinatorial approach using different treatments is becoming increasingly common in Trichiasis instances. In the future, the outcomes of those who have received treatments need to be monitored over time, and research regarding why women are more susceptible to Chlamydia trachomatis should also be carried out.¹⁷ Surgery needs to be more accessible to those who need it, particularly in lower-income countries which are affected by this disease. With improved diagnostics, treatments, and an understanding of this condition, Trichiasis will be less prevalent in the future, and patient outcomes will greatly improve.