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Infectious keratitis

Differential diagnosis of keratitis following refractive surgery is essential for ensuring early and appropriate treatment

Roibeard O’hEineachain

Posted: Tuesday, April 3, 2018

Although infectious keratitis is very rare following LASIK, differential diagnosis between infectious and non-infectious inflammation should be made as soon as possible, because the earlier the treatment the better the outcome, said Vikentia Katsanevaki MD, PhD, at the 22nd ESCRS Winter Meeting in Belgrade, Serbia.

The true incidence of infectious keratitis following refractive surgery is unknown and estimates have varied widely from zero to 1.5% of treated eyes. A survey of ASCRS members conducted in 2001 suggested an incidence of about one infection per 3,000 procedures, while the 2008 ASCRS survey suggested an incidence of one infection in every 1,102 procedures.

Of the 19 cases reported in the 2008 survey, eight (42%) were LASIK performed with a microkeratome, two were LASIK with femtosecond laser flap creation (10.5%), and eight cases had surface ablation procedures (42%). The time of presentation ranged from one week to more than one month postoperatively.

 

In most cases described in the literature it is not possible to determine the origin of the infection. However, there are predisposing factors, including breaks in the epithelial barrier and excessive surgical manipulation. In surface procedures delayed postoperative re-epithelialisation of the cornea may play a role, although it may also be the infection that causes the poor re-epithelialisation in such cases.

Sterile lamellar keratitis following LASIK in its usual diffuse lamellar keratitis (DLK) manifestation occurs much more commonly than infectious keratitis, with reported incidences of 2%-4%. Its characteristics include central circular opacity and stromal thinning. Its cause is not understood, but it seems to occur in clusters of patients treated on the same day, Dr Katsanevaki noted.

DIFFERENTIAL DIAGNOSIS
There are a few signs and symptoms on first examination that can help differentiate between infectious and sterile lamellar keratitis. In terms of symptoms, infectious keratitis will be marked by pain and decreased vision, whereas non-infectious keratitis is more typically characterised by soreness rather than pain, grittiness in the eye and decreased vision. In addition, there is ciliary injection in eyes with infectious keratitis whereas this is not seen in non-infectious keratitis.

 

Furthermore, in eyes with infectious keratitis the opacity is focal or multifocal but rarely diffuse and extends into to the flap. In eyes with non-infectious keratitis the opacity is diffuse, rarely focal and it is confined to the interface. Furthermore, in infectious keratitis there is an anterior chamber reaction and hypopyon, whereas in non-infectious keratitis the eye is quiet.

The course of treatment in the two conditions is also very different. In sterile keratitis, the first line of action is to increase steroids. For eyes with grade I DLK, she recommended hourly dexamethasone and for grade II or grade III washing out the interface, and hourly dexamethasone.

Infectious keratitis cases require a more rigorous workup and treatment. Lifting the flap and obtaining samples for staining and cell culture to identify the pathogens responsible is always recommended and can be particularly helpful in cases where first-line treatments are ineffective, she advised.

In cases where the onset of keratitis occurs within the first two postoperative weeks staphylococcal and streptococcal species are the most commonly isolated pathogens. Therefore, treatment should start with three loading doses at five-minute intervals with a topical fourth-generation fluoroquinolone, such as gatifloxacin 0.5% or moxifloxacin 0.5%, followed by three doses every 30 minutes. That should be alternated with a 50mg/mL dose every 30 minutes with a rapidly bactericidal antimicrobial agent with increased activity against gram-positive organisms, such as vancomycin, Dr Katsanevaki said.

Late onset infectious keratitis can occur from two weeks to three months following surgery and is usually caused by opportunist organisms such as fungi, nocardia and atypical mycobacteria, she noted. When it occurs, she recommended the same fourth-generation fluoroquinolone regimen alternated with amikacin 50mg/mL every 30 minutes. Additional measures can include the use of oral doxycycline, 100mg twice daily, to inhibit collagenase production, and discontinuation of corticosteroids.

Vikentia Katsanevaki: vikentia2015@gmail.com


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