By Maynard Pohl, OD
PCLI—Bellevue, WA

Imagine that your first exam of the day is a 1-day post-op cataract patient with moderate pain, terrible vision, marked corneal edema and unusual inflammation with hypopyon. What would you think? Would you say to yourself:

• This is toxic anterior segment syndrome.
• or Whadaya kiddin’ me… this is endophthalmitis!

Marked anterior segment inflammation with hypopyon formation is evident.

Toxic anterior segment syndrome (TASS) represents a toxic reaction in the intraocular anterior segment, whereas endophthalmitis is an actual infection inside of the eye. Although the treatment for TASS and endophthalmitis is different, clinically they can look quite similar.

Optometric physicians involved in post-op cataract care play a key role in distinguishing between these two conditions and directing the appropriate management of the patient to achieve the best possible outcome. While a definitive diagnosis of endopthalmitis must be made as soon as possible in order to achieve a good result from treatment, TASS can improve over time with no special treatment other than frequent topical steroids.

Although signs and symptoms can help determine the best course of treatment, comanaging optometric physicians need to immediately communicate the status of the patient with the surgeon or surgery center.

Several clinical signs and symptoms can help differentiate between TASS and endophthalmitis

Onset of Signs and Symptoms

• Because TASS is caused by toxicity, it almost always manifests as an atypical inflammation on the day following surgery.
• The Endophthalmitis Vitrectomy Study indicates that, while some cases of endophthalmitis can be detected one day post-op, most cases do not show up until later.

Signs

• Unlike classic endophthalmitis, lid swelling is uncommon with TASS and conjunctival/episcleral/scleral injection is often minimal.
• With TASS and endophthalmitis, all the corneal endothelium becomes insulted and functions poorly and limbus-to-limbus corneal edema is present. This is unlike the patchy corneal edema sometimes seen after uncomplicated cataract extraction.
  
  The eye exhibits diffuse, limbus-to-limbus corneal edema.
• With the vast majority of TASS cases, such diffuse edema, extending from limbus to limbus, is present by day one and is an important differentiating sign from endophthalmitis.

• Iris findings in TASS may include areas of iris atrophy and more often a dilated and minimally reactive pupil, particularly when the IOP is severely elevated.
• Because residual pharmacologic pupillary mydriasis commonly manifests at the 1-day post-op exam, pupil findings are not a reliable diagnostic finding.
• With TASS, trabeculitis and/or impeded outflow of aqueous through the trabecular meshwork often increases IOP to severe levels (50 to 60 mm Hg), a finding which is unusual in endophthalmitis during the early post-op period.
• However, occasionally, ciliary body shutdown with subsequent ocular hypotony is reported in eyes diagnosed with TASS.

Symptoms

• Although pain tends to have a stronger association with endophthalmitis, both TASS and endophthalmitis may result in either significant or no pain.
• Unless IOP is severely elevated (above 40 mm Hg), patients with TASS typically experiences some discomfort but minimal pain. While not definitive, this is a differentiating finding.

Summary

1. an unusual amount of inflammation and
2. limbus-to-limbus corneal edema
3. in a patient with minimal pain on the first day following cataract surgery.

Frequent (q ½ hour) topical corticosteroid drops with careful in-office monitoring is the management plan along with prompt referral to the surgical center for continued care. The patient’s therapeutic response to frequent topical steroids is the definitive, yet often nerve-racking, test. If the condition shows some improvement by day’s end, TASS can be assumed. Should the condition worsen despite treatment, then endophthalmitis of infectious etiology is the likely diagnosis and immediate additional measures to enable definitive diagnosis must be implemented.

I highly recommend a conservative approach to differential diagnosis with the assumption that patients of this type are experiencing endophthalmitis until proven otherwise. Endophthalmitis remains a possibility until a therapeutic response to topical steroids is clearly evident for several days.

An ad hoc task force currently investigating TASS recently reported that it has found no single cause for the outbreak. However, they have identified a number of potential etiologic factors pertaining to both cataract surgery products and instrument procedures. These include:

• Preoperative use of non-steroidal anti-inflammatory drugs (NSAIDs)
• Use of intracameral anesthetics
• Addition of preserved epinephrine to balanced salt solution
• Improper dosing, mixing, or injection of intracameral antibiotics
• Residue accumulation on reusable cannulas
• Certain IOLs

Surgical instrument cleaning and the flushing of reusable hand pieces and tips between cases appears to be critically important, and rapid turnover over of operating suites between patients poses a risk factor for incomplete flushing of such devices.

At the time of this writing, I am happy to report that we have not experienced any known cases of TASS in any of our surgical centers.