Benjamin Lin MD, Emily Neag BS
Introduction
Tapping the anterior chamber is a key skill to have in your back pocket when managing high IOP. The #1 rule of AC taps is to avoid hitting the lens if they are phakic! This can result in a traumatic cataract. You can perform an AC tap at either the slit lamp or in an exam chair, and you should practice both to have multiple options:
Option 1: Laying back in an exam chair:
- Pros:
- Easier for beginners because you have both hands easily available without having to worry about slit lamp positioning
- This requires less cooperation from the patient (no need to position at the slit lamp)
- It is easier to visualize aqueous flowing into the syringe
- Cons:
- You lose precision because you are not at the microscope performing the procedure – not ideal if there is a difficult view into the AC or if the AC is shallow.
Option 2: At the slit lamp
- Pros:
- Much safer if there is a shallow AC or a difficult view such as if there is lots of heme/fibrin or corneal edema from a recent IOP spike.
- Cons:
- The patient must be more cooperative with positioning. If the patient inadvertently drifts back and subsequently moves forwards to correct themselves while you are still in the eye, you may inadvertently damage the lens or iris.
- If you need to use a cue tip to fixate the eye, it can be difficult for beginners to also maintain focus with the slit lamp, especially if the patient moves
- In order to see aqueous flowing into the syringe, you have to take your eyes off the oculars to look at the syringe. This can also be challenging for beginners.
- Tips: If doing at the slit lamp, it may be useful to have a second person hold the person’s head in position to avoid inadvertent movement.
Supplies
- Eye pad or 4×4 gauze
- 1 cue tip
- Lidocaine gtts
- Betadine gtts
- Betadine swaps
- 32 gauge needle on a 1cc syringe
- Lid speculum
The procedure
- 1) Patient prep
- Tape eye pad to patients ear to catch extra drops
- Give the patient a drop of proparacaine
- Remove plunger from the syringe
- Alternate giving lidocaine and betadine drops, 4 rounds total
- Swab the upper and lower eyelids to clean off eyelashes
- Place lid speculum
- 2) The tap
- Stand or sit at head of patients bed
- Use cue tip to press down on sclera opposite of your planned tap site – this well help anchor the eye in place
- The insertion path of your needle should be:
- Roughly parallel to the iris and just anterior to the limbus
- Following a track that avoids crossing the pupil
- Option 1 (somewhat safer): Entering horizontally straight into the anterior chamber near the superior or inferior limbus
- Option 2: Entering at the lateral clock hour (9 o’clock for OD and 3 o’clock for OS) and travelling in either the 12 o’clock or 6 o’clock directions.
- Regardless of which option you pick, the tip of the needle should never travel over the pupil to avoid any inadvertent lens trauma
- Brace your hand on the patient’s forehead/cheek
- Insert the needle gently until you feel a slight pop as it goes through the cornea
- Watch the cornea as the AC fluid drains.
- After about 10-15 seconds, the eye generally equilibrates to around an IOP of 10-15. Starting from an IOP of 40s to 50s, this generally means taking out roughly ~0.03 to 0.05 cc.
- Recheck IOP. If it remains too high, repeat the procedure
