13.4 Stains, Instillation Technique, and Safety Traps

13.4 Stains, Instillation Technique, and Safety Traps

Vital stains

Fluorescein is an orange dye that fluoresces green under cobalt-blue light. It pools in epithelial defects, so it reveals corneal abrasions, dendritic ulcers, and the tear meniscus during applanation tonometry, and it is used in the Seidel test to detect aqueous leakage from a wound. Two exam facts matter: fluorescein permanently stains soft contact lenses (always remove lenses first), and the tear breakup time (TBUT) is measured after fluorescein instillation.

Lissamine green and rose bengal stain devitalized and dead epithelial cells, useful in evaluating dry eye and ocular surface disease.

Correct instillation technique

This is heavily tested because it is the COA's daily skill.

• Wash hands and verify the right patient, right drug, right concentration, right eye, right time.
• Tilt the head back; gently pull down the lower lid to form a pocket (the inferior fornix).
• Instill one drop into the fornix without touching the bottle tip to lashes or eye (prevents contamination).
• Have the patient close gently and apply punctal occlusion at the inner canthus for 1-2 minutes to limit drainage into the nose and systemic absorption.
• If giving two different drops, wait about 5 minutes between them so the first is not washed out.
• Document drug, concentration, eye, and time.

Medication safety checks

The COA confirms the label, expiration date, and color/clarity of the solution; uses one bottle per patient when possible; and never instills an unlabeled drop. Pink/red caps generally indicate mydriatics/cycloplegics, while different cap colors signal glaucoma classes (a useful at-a-glance check, never a substitute for reading the label).

Predictable exam traps

Worked scenario

After routine dilation a hyperopic patient with a known shallow anterior chamber develops a painful red eye, blurred vision, halos around lights, and nausea. This is acute angle-closure glaucoma precipitated by the dilating drop, an emergency. The COA does not wait or re-dose; the patient is moved to the physician immediately for IOP measurement and treatment. Knowing dilation can trigger angle closure in narrow-angle eyes is a frequently tested judgment point.

Contamination control

The bottle tip is the main contamination risk. Never let the dropper touch the lashes, lid, or ocular surface, because that transfers organisms and can seed an infection in a vulnerable eye. Multi-dose bottles used across patients are a documented source of cross-contamination, so single-patient use is preferred, especially for post-surgical or ulcer patients. Discard any bottle that is cloudy, discolored, or past its expiration date. Hand hygiene before and after every patient is non-negotiable.

The five rights, applied to the eye

Medication errors in ophthalmology often come down to the wrong eye or the wrong concentration. Adapt the classic five rights: right patient, right drug, right concentration, right eye, right time. Confirm laterality out loud against the order, because OD and OS errors are easy and consequential (imagine atropine in the wrong eye of an amblyopia patient). When an exam stem buries a detail like "patient is allergic to sulfa" or "has asthma," that detail is the cue that one tempting option is contraindicated.

Allergy and reaction recognition

The COA should recognize a developing reaction: a preservative or drug allergy presents as itching, lid swelling, conjunctival redness, and watering after instillation, most notoriously with brimonidine and some preservatives (benzalkonium chloride). A vasovagal response, by contrast, presents as pallor, sweating, and faintness from anxiety, not the drug itself. Distinguishing a true drug reaction from a benign sting or a vasovagal episode, and reporting it accurately to the physician, is the safe, defensible action.

Wrong-drug and wrong-strength traps in detail

The exam writers love near-miss distractors. A question may offer proparacaine and pilocarpine together (both end in similar sounds but one anesthetizes and one constricts), or phenylephrine 2.5% versus 10% (same drug, very different safety). It may pair tropicamide with atropine when the clinical goal calls for a short-acting agent, hoping you forget atropine lasts up to two weeks. Train yourself to read the concentration and the duration as carefully as the drug name. A drug that is "correct" but at an unsafe strength or with the wrong duration is still the wrong answer.

Storage, expiration, and look-alike bottles

Some agents have specific storage needs: certain prostaglandin bottles are refrigerated before opening, and reconstituted antibiotics have short shelf lives. Discard expired or cloudy solutions and never top off one bottle from another. Because many ophthalmic bottles look alike and U.S. cap-color conventions are only a guide, the COA reads the label every time. A scenario that mentions a chipped, unlabeled, or expired bottle is steering you toward "do not use it," not "use it quickly."

Putting traps together

When a stem feels like two answers are correct, the deciding cue is almost always a buried risk factor: asthma (avoid timolol), narrow angle (dilation danger), sulfa allergy (avoid acetazolamide and dorzolamide), pregnancy or pediatric age (dose adjustments), or an active herpetic dendrite (no steroids). Scan every stem for that one disqualifying detail before committing to an answer.