Search that question and you get five pages about which bottle to buy. Lipid or aqueous. Preserved or preservative-free. Gel at bedtime, something thinner for the desk, something with a lipid layer for the office air-con that runs at nineteen degrees from March onwards. None of those pages tell you what that fifth year buying the bottle looks like and the two that purport to discuss time horizons give up at twelve weeks.
Here is the version with the timeline left in.
The least flattering answer goes first
Artificial tears are symptom management.
They add water, and in some formulations oil, to a tear film deficient in one or the other. The relief they provide is tangible and repeatable, and lasts until the drop has drained through the puncta and evaporated with the rest of your tear film. What they do not do is act on the tissues beneath the meniscus of the drop. A blocked meibomian gland in the margin of your lid does not reopen by virtue of a drop landing on the surface of your eye, and a lacrimal gland that has stopped producing aqueous fluid is not inclined to resume function by virtue of the drop replacing the fluid it failed to make.
This is not a criticism, it is a description; one that becomes important because it describes what is going to be needed in addition.
What the longest trial actually found
In terms of trials, the best answer to the phrase 'long run' is 6 months.
A 2021 multicentre, double masked, randomised trial published in The Ocular Surface investigated treatment response in 99 participants either with lipid based nanoemulsion or non lipid aqueous drops taken at least 4 times daily. The clinic visits were on days 0, 30, 60, 90, 120, 150 and 180 (PubMed). The symptoms were reduced from day 30, and remained reduced throughout the trial in both treatment arms. The signs followed later, with lid wiper epitheliopathy improving from day 60, tear break up time and staining from day 120 and lipid layer grade only improving from day 90 in the lipid arm.
By day 180, 19% of participants no longer met diagnostic criteria for dry eye disease.
Turning that statistic on its head, it means that 81% still did, and that the drops were taken 4 times per day, in a trial administered by people who expected them to help.
The limitations of the trial are instructive. As both treatment arms involved active drops, there was no control group of people taking no treatment, and the benefit seen cannot be definitely ascribed to either formulation. The authors only attribute efficacy to 'most mild-to-moderate aqueous-deficient and evaporative dry eye'. They advise that the study is the first step towards stratifying management according to subtypes and severity, rather than making definitive recommendations. Finally, the follow up ended at day 180; about year two, or year five, which this trial says nothing about, and neither does much else I can find.
This is an answer to the question posed in the headline. The long term evidence is not weak, it is mostly absent.
The base under all of it is graded low quality
A cochrane review published in 2016, analysing 43 randomised controlled trials and pooling their 3,497 participants reached a conclusion most product pages would find dissatisfying. There is insufficient evidence to determine whether different over the counter artificial tears show any difference in efficacy in signs and symptoms compared to each other or to placebo (PubMed).
They note that there was one comparison across two trials, 175 participants, where 0.2% polyacrylic acid showed benefit over 1.4% polyvinyl alcohol. Other than that, it was all contradictory or ineffective. Their summary conclusion is that over the counter artificial tears may be safe and effective for signs and symptoms, and that there may be little difference between products.
And that is the key word. May.
Their assessment of the evidence was low grade due to high risk of bias across the included studies, and outcome reporting that was inconsistent or unclear, preventing quantitative synthesis. Across the included studies, diagnostic criteria, interventions and outcome measures were so inconsistent that between study analysis was challenging, and they explicitly state that their findings could be impacted significantly by those inconsistencies. Finally, they note that there are 18 additional eligible trials, involving 2,079 patients, listed in trial registries that have not published findings yet. There is plenty of scope for further evidence in this space, and as yet, no consensus.
If you have ever been shopping around trying to find the magic drop, this is a useful finding. Nothing in those trial results means the bottle you haven't tried is going to be substantively better than the one you have.
Read together, that systematic review and the trial mentioned earlier suggest a reasonable level of certainty about short term relief. After that it's all inference.
Drops are the first rung, not the ladder
TFOS DEWS II Management and Therapy Report, published in 2017 in The Ocular Surface, is where the staged view of this comes from (PubMed). An international subcommittee assessed the therapeutics literature and constructed a severity graded algorithm, considering tear replacement as first line with additional therapeutics added as the disease progressed. Its most clinically relevant finding is that distinguishing between aqueous deficiency and evaporative disease is crucial because it informs management. Due to the differing pathophysiology of these subtypes, treatment is aimed specifically at the mechanism present.
Which is why "are these drops any good" is not as useful of a question as "are drops alone sufficient management for my presentation?"
This report is also realistic about the strength of evidence. It acknowledges that many of the treatments it recommends lack Level 1 support due to "inadequate masking," randomisation, controls, "selection bias," or sample sizes too small to draw conclusions from. It states openly that predicting treatment response for individual subtypes remains a challenge, and that further evidence is required to both justify the use of many treatments and to determine where in the management algorithm to place them.
When the answer is a clinician rather than another bottle
There is a cultural expectation in this category that frequent use of eyedrops is a failure on the patient's part, and that the patient is somehow doing it wrong.
This is incorrect. If you find yourself needing lubricating eyedrops frequently, consistently over a period of time, that is information.
That is a reason to seek clinical assessment, rather than a reason to feel inadequate. If you have been using your drops regularly for a month and the symptoms remain the same, the frequency of use is not the issue. The cause of the symptoms is. Whether you are blinking effectively over long hours, whether your environment is excessively drying, whether you actually have an evaporative component that your drops do not address, whether you are experiencing pain as opposed to discomfort, whether you have crusts or swelling on your eyelids in the mornings, or whether your symptoms are laterally asymmetric; these are the things that require investigation. An optometrist or ophthalmologist is able to assess you for aqueous deficiency versus evaporative disease and stratify your management appropriately. The stepped management described in the DEWS II report is only a guideline until you have had that assessment, and can determine whether further therapeutic options are available besides drops.
One clarification that needs to be made is that there is an important difference between lubricating artificial tears, and the vasoconstrictive decongestants sold as redness relievers that cause rebound hyperaemia. The claim that eyedrops cause dependence is often conflated with the entirely separate topic of vasoconstrictors.
The household version, and what it honestly is
Instilled eye drops are not new in the pharmacopeia of Indian medicine. Ashchyotana, the instillation of medicinal drops directly into the eye, is one of the netra kriyakalpa treatments described in the Sushruta Samhita and the Ashtanga Hridaya, alongside seka, the poultice, tarpana, the ghee pooling treatment, and anjana, the collyrium. Ashchyotana is classically described for tired, heated, watering, or red eyes that require repeated treatment, to cool, soothe, and relieve discomfort.
In practical modern terms, this is your grandmother recommending haldi in warm milk, gulab jal kept in the fridge door for hot eyes after a day in traffic, a triphala water rinse in the morning, a cold compress over the eyes for ten minutes. Nobody in your family would consider any of them to be a secret, and none of them should be sold as a panacea for dry eye disease.
Here is the caveat. This is cultural usage, and it is anecdotal, and neither supports the other.
The ayurvedic netra drops prepared at Darakhtveda are soothing, refreshing, and provide relief from dryness, which is actually the totality of what we claim them to do. Nothing more, nothing less, and the traditional framing of those drops in terms of cooling, comfort and relief is the same size as that claim: comfort and daily upkeep, not the restoration of a gland.
What sustainable use actually looks like
Nothing in this post suggests that you stop using drops. In the above-mentioned 6 month trial, the symptoms were reduced from day 30 in both treatment arms and remained reduced throughout the trial.
For most people, that is an acceptable cost-benefit ratio for the price of a bottle.
The error is believing that the contents of the bottle are the entire treatment.
If your eyes are dry because you blink less effectively over 8 hours gazing at a screen, or because the air in the room is consistently drier than your tear film, or because the meibomian glands in your lid are not secreting oil onto the film, the drop is substituting for what is still occurring every day. Reasonable use of artificial tears is as a measure for comfort, while the underlying condition is investigated or treated; frequent breaks from the screen, warm compresses if there is gland involvement confirmed by an eye care practitioner, and a clinical examination of the lid margin rather than another eight week trial on a new formulation.
