NZ Optics March 2024
The damage that drops can do!
By Dr Alex Ioannidis
OCULAR SURFACE DISEASE (OSD) is a multifactorial disorder of the conjunctival epithelium, cornea, lacrimal and meibomian glands resulting in either deficient or inappropriate tear production. This can decrease visual activity (VA) and result in significant ocular discomfort^1. OSD can occur in conjunction with many other ocular conditions and often co-exists with glaucoma.
At present, 11% of the five million Americans over 50 who have dry eye disease (DED) also have glaucoma^2. Topical medical therapy is the most common initial treatment for glaucoma and 49-59% of glaucoma patients on such medications have some form of OSD^3. OSD in these patients can be a pre-existing condition that is exacerbated by topical therapy or a novel disease that manifests after initiation of topical glaucoma therapy. Topical glaucoma medications can cause significant morbidity, with patients complaining of a burning sensation, irritation, itching, tearing, skin pigmentation and decreases in VA, often within three months of medication initiation^4.
Furthermore, untreated primary open angle glaucoma (POAG) patients have a higher risk of OSD, in part due to a 22% lower basal tear turnover rate in comparison to patients without glaucoma^5. The resulting OSD symptoms in patients with glaucoma can lead to poor medication compliance. Cessation of therapy by the patient without informing the physician can result in elevated IOP and disease progression.
OSD is also linked to a higher rate of failure in filtration glaucoma surgery, Thus, management of OSD in glaucomatous patients is important when trying to reduce further ocular morbidity and to improve the success of glaucoma therapy.
Examining cases
A 69-year-old female patient with unilateral POAG presented complaining of chronic conjunctival injection and irritation. Her condition was stable, based on serial visual field testing and OCT analysis of the optic nerves. Her IOP was 18mmHg with Goldmann applanation tonometry (GAT). Her glaucoma was being treated with latanoprost nocte in the left eye. On this last review she was found to have developed a cataract and was keen to explore ger options for reducing or eliminating the drop burden on her ocular surface. Clinical examination revealed significant skin pigmentation and conjunctival injection of the left eye (Figs 1 and 2).
Cataract surgery was performed in combination with implantation of the iStent injection system in the trabecular meshwork. Her postoperative IOP was 14mmHg and the lantanoprost drops were ceased in the left eye. Within a month there was a marked improvement in the appearance of her conjunctiva with resolution of the symptoms of irritation. Her forniceal conjunctiva ceased to be injected (Fig 3).
The chronic use of IOP-lowering medications can have other unintended consequences on ocular surface management. The use of prostaglandin analogues has also been associated with local tissue atrophy in the orbit (a type of orbitopathy) reported to occur with several prostaglandin analogues^6. This can result in deepening of the orbital sulcus due to the loss of adipose and connective tissue on that area (Fig 4 and 5).
Preservative-induced inflammation
Corneal toxicity secondary to chronic medication use is another area where interventions, such as iStent injection system, can make a significant difference in eliminating the gritty and stinging sensation associated with drop instillation.
The main culprit in these cases is the preservative benzalkonium chloride (BAK). BAK has been shown to strongly induce the expression of inflammatory mediators in the lens epithelial cells, compared with lantanoprost or timolol. The Blue Mountains Eyes Study and Ocular Hypertension Treatment Study both suggested higher rates of cataract formation in those receiving anti-glaucoma therapy. Miyake conducted studies that suggested use of BAK-preserved drops prior to cataract surgery increased the risk of cystoid macular oedema^7. Chronic BAK exposure has been associated with significant ocular surface toxicity, often manifesting as a diffuse punctate keratopathy (Fig 6). With BAK eliminated from the ocular surface following minimally invasive glaucoma surgery (MIGS), significant improvement of the overall corneal health can be seen, with resolution of the signs (Fig 7).
In conclusion, the use of microtrabecular shunts, such as the iStent injection system, has been revolutionary in the management of mild to moderate stable glaucoma. The chronic use of drops has a detrimental effect on the ocular surface of these patients, resulting in secondary morbidity which can be significant but can also result in poor adherence to management protocols. It is therefore advantageous to offer this cohort of patients access to MIGS options to reduce or eliminate the drop burden and achieve better outcomes and disease management.
Disclosure: This article was sponsored by Glaukos, though independently written by Dr Alex Ioannidis.
You can see this article in full, including Figures and References, within the March 2024 issue of NZ Optics – The Magazine for New Zealand’s Ophthalmic community.