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Three Part Question

In [adult patients with simple corneal abrasions], is the [short term use of topical anaesthesia] [safe and effective in providing pain relief]?

Clinical Scenario

A 35 year old gentleman presents to the Emergency department complaining of painful left eye with foreign body sensation. Slit lamp examination demonstrates a corneal abrasion. You apply topical anaesthesia and he feels instantly better. He then requests to take the drops home. Your consultant tells you that it is dangerous to give topical anaesthetics because patients will go on to develop corneal ulceration and impaired healing. You wonder if there is any evidence to support this.

Search Strategy

MEDLINE 1966 to March 2015 using the OVID interface
EMBASE 1974 to March 2015 using the OVID interface
[(*CORNEAL INJURIES/) OR (corneal AND abrasion* OR corneal AND injur*).ti.ab] AND [(*ANESTHESIA, LOCAL/ OR *LIDOCAINE/ OR *ANESTHETICS, LOCAL/) OR (topical AND anaesthesia OR topical AND anesthesia).ti.ab] LIMIT to human AND English Language

Search Outcome

44 papers were found from the literature search and 3 papers were found relevant to the three-part-question.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Ting et al Jan 2009 Australia	Forty-seven subjects with uncomplicated corneal injury recruited over 12 months in ED and given either placebo (saline) or 0.4% amethocaine	Pilot randomized double blinded trial	1.Primary outcome: Healing of corneal defect (absence of fluorescein stain uptake)	1.Persisting corneal defect slightly more likely at 36–48 h in the amethocaine group than in the saline group, although the numbers were small (A:2/7 vs. S:1/9) P = 0.55.	Trial included patients with keratitis with wielding flash exposure. Some lost to follow up
			2.Secondary outcomes: Use of oral analgesia, unscheduled medical review, visual problems, and satisfaction with treatment received, patient pain perception (three hourly visual analogue scale)	2.Oral analgesia used (A:0/17 vs. S:0/21) P = N/A, ongoing visual problems (A:3/17 vs. S:1/21) P = 0.307, need for unscheduled medical review (A:2/17 vs. S:2/21) P = 1, and patient satisfaction (A:17/17 vs. S:21/21) P = N/A —did not differ between the two groups. Mean cumulative eye pain scores lower for the amethocaine group (A:404±75mm vs. S:629±172mm), no statistical testing completed.
Waldman et al 2014 New Zealand	One hundred and eleven patients recruited with simple corneal abrasions in ED of tertiary teaching hospital were given either tetracaine (amethocaine) or saline.	Double blind randomized control trial	1.Primary outcome: Safety of topical anesthesia and impact upon corneal healing. (Persistence of fluorescein uptake at 48h and occurrence rates of complications)	1.No significant difference in corneal healing - percentage of patients with persistent fluorescein uptake at 48 hours between the two groups (T:23.9% vs. S:21.3%, difference=2.6%, 95% CI=-14% to 20%, p=0.761) or persistent symptoms at 48 hours (T:21.7% vs. S:21.3%, difference=0.4%, 95% CI=-16% to 17%, p=0.957).	Underpowered – insufficient sample size. Compliance with administering eye drops not recorded. Some patients reported burning with tetracaine – does this unblind the trial? Mixed-model statistical analysis used, thus patients may not follow normal distribution as many reported no pain. Therefore statistical analysis may not be accurate.
			2.Secondary outcome: Pain reduction and patient perception for effectiveness of treatment (100mm VAS and patients asked to rate overall effectiveness)	2.No clinical difference in VAS pain scores between the groups. Average difference in pain was 0.53 on a 100mm scale, CI = -0.19 to 1.24, p = 0.149, deemed clinically insignificant. Patients in the tetracaine group rated the study drugs' overall effectiveness significantly higher (7.7) compared to patients in the saline group (3.8) (difference=3.9, 95% CI=2.4 to 5.3, p<0.0005)
Ball et al 2010 Canada	Thirty three patients recruited from tertiary ED with simple corneal injury and given either 0.05% proparacaine or placebo	Prospective randomized control trial	1.Primary outcome: Pain reduction (visual analogue pain scale)	1.Pain reduction significantly better in the proparacaine group than in the placebo group, (median improvement of 3.9cm on the visual analog scale vs. 0.6cm (p = 0.007).	Single centre with very small number of patients. Does not take into account patient compliance.
			2.Secondary outcome: Patient satisfaction	2.The proparacaine group was more satisfied (median level of satisfaction 8.0cm on a 10-cm visual analog scale v. 2cm, p = 0.027)

Comment(s)

Corneal abrasions are common presentations to the Emergency Department. They are very painful and oral analgesia is relatively ineffective. Topical anaesthetics often bring about immediate pain relief, but many clinicians are reluctant to use them for fear of causing corneal damage. Traditional arguments against the use of topical anaesthetics refer to their inhibitory action on the ability of corneal epithelium to oxidise glucose and pyruvate, leading to delayed healing. Topical anaesthetics also reduce the corneal sensation, rendering the patient more vulnerable to further injury due to the loss of this important protective mechanism. Most of the evidence against the use of topical anaesthetics comes from studies involving enucleated rabbit eyes with prolonged exposure. Such animal research may not be applicable to living human subjects for obvious reasons. The best available literature in the ED appears to support the safety and efficacy of the short term use of topical anaesthetics in corneal abrasions. However, we need larger randomized controlled studies before the safety of the short term use of topical anaesthetics can be fully elucidated.

Clinical Bottom Line

There is emerging evidence in the Emergency Medicine literature that the short term use of topical anaesthetics can be considered safe and effective for pain relief for corneal abrasions.

References

1. Ting JY, Barns KJ, Holmes JL Management of Ocular Trauma in Emergency (MOTE) Trial: A pilot randomized double-blinded trial comparing topical amethocaine with saline in the outpatient management of corneal trauma
2. Waldman N, Densie IK, Herbison P Topical tetracaine used for 24 hours is safe and rated highly effective by patients for the treatment of pain caused by corneal abrasions: a double-blind, randomized clinical trial
3. Ball IM, Seabrook J, Desai N, Allen L, Anderson S Dilute proparacaine for the management of acute corneal injuries in the emergency department