Contact lens associated microbial keratitis: practical considerations for the optometrist

Figures & data

Table 1 Types of microbial keratitis and the primary risk factors for acquiring these infections in Westernized countries

% MK due to:	Bacterial	Fungal	Acanthamoeba
Contact lens	33.7^Citation7–50.3^Citation5	25^Citation124–29.2^Citation33	85^Citation84–93^Citation86
Trauma	15^Citation5–36.4^Citation7	8.3^Citation33–26^Citation124	7^Citation86–15^Citation84
Ocular surface disease	6.9^Citation7–21.3^Citation5	29^Citation124–41.7^Citation33	NR
Othera	13.4^Citation5–23^Citation7	16.7^Citation33–20^Citation124	NR

Note:

a Other refers to history of ocular surgery, steroids, systemic disease, and unknown risk factors.

Abbreviation: MK, microbial keratitis; NR, not reported.

Table 2 Annual incidence of contact lens-related bacterial, fungal, and protozoan keratitis

Lens type	Bacterial	Fungal	Acanthamoeba
Overall incidence	4^9/10,000	∼1/50,000^Citation119,a	1–33/million^Citation35
Soft lenses (daily wear)	1.9^Citation9–4.1^8/10,000	NR	NR
Soft lenses (extended wear)	19.5^9/10,000	NR	NR
Hydrogel	9.3^Citation10–20.9^8/10,000	NR	NR
Silicone hydrogel	20.9^Citation14–25.4^9/10,000	NR	NR
Gas-permeable (daily wear)	0.8^Citation10–4.0^8/10,000	NR	NR
Orthokeratology	7.7^18/10,000	NR	NR

Note:

a Estimation calculated from Konda et al¹¹⁹ which stated 5% of all contact lens microbial keratitis is fungal.

Abbreviation: NR, not reported.

Table 3 Clinical characteristics of the different forms of microbial keratitis

Clinical characteristics	Bacterial keratitis	Fungal keratitis	Acanthamoeba keratitis
Onset of symptoms	Rapid	Several days^Citation62	Rapid
History	Contact lens wear, trauma, and ocular surface disease	Vegetative trauma, contact lens wear, and ocular surface disease	Water exposure and contact lens wear; may have been treated prior as herpes simplex
Key differentiating slit lamp findingsa	Round or oval shaped lesion, and anterior chamber flare^Citation81	Feathery borders, satellite lesion, and necrotic slough^Citation81 *Yeast infection mirrors bacterial ulcers^Citation62	Early:^Citation85 epithelial disruption without stromal disease and perineural infiltrates Late:^Citation85,Citation86,Citation103 ring infiltrate
Treatments	Fluoroquinolones, chloro-fluoroquinolones, and fortified antibiotics	Natamycin, voriconazole, and amphotericin	Polyhexamethylene biguanide, chlorhexidine, propamidine, neomycin, and oral voriconazole
Healing time (days)	3.5–6.8^Citation98,b	31–40^Citation102	140–547^Citation103,Citation127,Citation129 Steroid:^Citation103 163±50c No steroid:^Citation103 94±45c
Percentage with visual acuity worse than 20/30	13.9^Citation9	30^Citation129	0 (early diagnosis)^Citation85 44.4 (late diagnosis)^Citation85 Prior steroid use equaled worse outcome^Citation86,Citation103
Percentage requiring penetrating keratoplasty	0^Citation9–13^Citation131	16.8^Citation124	20–32^Citation87
Cost^Citation7 (US$)	1,200–1,800	4,648	5,697

Notes:

a All conditions will likely have redness, photophobia, discharge, and significant pain.

b For ulcers ranging from >1 mm² to <4 mm².

c Data presented as mean ± standard deviation.

Figure 1 Copan E-swab.

Table 4 Culture yields obtained from the cornea and contact lens paraphernalia

Type of microbe	Positive cultures from cornea (%)	Positive cultures from lens case (%)	Positive cultures from lenses (%)	Preferred culture media
Bacteria	37^Citation123–63^Citation120	80^Citation119–83^Citation5	67^Citation118–92^Citation119	Chocolate agar Blood agar Thioglycollate broth Brain–heart infusion broth
Fungal	76^Citation93–94^Citation8	70^Citation124–84^Citation59	57^Citation124	Sabouraud’s dextrose agar
Protozoan	23^Citation93–88^Citation87	23^Citation30	23^Citation30	Nonnutrient agar with Escherichia coli

Table 5 Common microorganisms responsible for contact lens-related microbial keratitis

Common microorganisms associated with contact lens microbial keratitis
Bacteria (71%–88%)^Citation8,Citation119
Gram-positive
Staphylococcus spp.^Citation11	20%
Coagulase-negative Staphylococci^Citation5,Citation112,Citation123	16.8%–49%
Staphylococcus aureus^Citation112	5.9%
Staphylococcus epidermidis^Citation119	4.8%
Gram-negative
Pseudomonas^Citation5,Citation10,Citation11,Citation112,Citation119,Citation122,Citation123	19%–73.5%
Serratia^Citation5,Citation11,Citation119,Citation122	4.8%–23%
Fungal (2.6%–5%)^Citation6,Citation8,Citation10,Citation119
Filamentous
Fusarium^Citation124	51%a–68%b
Aspergillus^Citation124	9.2%a–11%b
Yeast
Candida^Citation124	2%b–12%a
Acanthamoeba (0.9%–4%)^Citation8,Citation119
Acanthamoeba castellanii^Citation125,Citation126	38%–66%
Acanthamoeba polyphaga^Citation126	30%

Notes: The specific microbes that are in bold text indicate the most common species. Percentages do not add up to 100 as sterile keratitis cases can also be found.

a non-Fusarium outbreak¹²⁴ (January 2001–September 2004 and October 2006–December 2007);

b Fusarium outbreak¹¹¹ (October 2004–September 2006).

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