Clinical Diagnosis of Microbial Keratitis and Contact Lens-Induced Peripheral Ulcer

Murali K Aasuri - MD

Murali K Aasuri, MD, completed his Junior Residency in Ophthalmology from the R P Centre, All India Institute of Medical Science, New Delhi, in 1992 and was also Senior Resident in Cornea Unit. He underwent fellowship training in Cornea & Anterior segment in 1994 and worked as a Research Ophthalmologist in 1995 at L V Prasad Eye Institute, Hyderabad, India. He is currently working as a Consultant in Cornea Service at L V Prasad Eye Institute.

He is also a Diplomate of National Board in Ophthalmology. His areas of interest include corneal diseases, contact lenses, cataract and refractive surgery. He is a recipient of Bausch & Lomb Young Investigator's Travel Fellowship Award at the CLAO meet, 1999 for a presentation on Silsoft contact lens fitting for pediatric aphakia. He has many publications in peer reviewed journals and was an invited speaker at International Symposia. He is teaching faculty for pediatric ophthalmology fellowship at L V Prasad Eye Institute. He was invited by ORBIS international as a Volunteer Faculty for teaching pediatric cataract at Chittagong, Bangladesh, 2002.

Microbial keratitis (MK), is a serious but rare complication associated with contact lens wear, which is considered to be the major predisposing factor for corneal infection in the United States and Western Europe.¹ When ulceration is severe, the diagnosis of microbial keratitis is primarily clinical and reasonably straight forward, and is substantiated largely by microbiological data. In contact lens practice the practitioner often sees microbial ulcers at a very early stage, where the diagnosis is entirely clinical. In these cases, ulceration is usually not severe and microbiological workup may not be informative. One condition that is often confused with early stage microbial keratitis is contact lens-induced peripheral ulcer (CLPU). This article discusses the various clinical clues that would be helpful in differentiating the two conditions.

Click to enlarge	Click to enlarge
Figure 1: Pseudomonas keratitis with contact lens wear.	Figure 2: Contact lens induced peripheral ulcer (CLPU).

Microbial keratitis (Fig 1) is an infection of the cornea characterized by excavation of the corneal epithelium, Bowman’s layer, and stroma with infiltration and necrosis of tissue.² CLPU (Fig 2) on the other hand is an inflammatory reaction of the cornea characterized in its active stage by focal excavation of the epithelium, infiltration, and necrosis of the anterior stroma. In CLPU, the Bowman’s layer remains intact.³

Clinical Presentation
Patients with MK typically present with significantly more symptoms than those with CLPU. Pain, redness, photophobia, and lacrimation are the usual symptoms, even at a very early stage in MK. On the other hand, patients with CLPU may present asymptomatically or with mild discomfort. Pain is unusual in a patient with CLPU and strongly points to MK. Except for lacrimation, discharge is very unusual in patients with CLPU. Loss of vision is unlikely in either of the conditions in the early stages of the disease. However, decrease of vision is almost never a feature of CLPU and strongly suggests an infectious etiology.

Click to enlarge	Click to enlarge
Figure 3: Sectoral congestion limited to the area of focal infiltrate.	Figure 4: Pseudoguttate changes on endothelium in MK.

Presence of lid edema is a strong pointer to MK and patients with CLPU usually show no evidence of lid swelling. However, the absence of lid edema does not rule out the possibility of MK. In CLPU, bulbar conjunctival injection is restricted typically to the quadrant where the focal infiltrate is located, whereas in MK injection is generalized (Fig 3).

Detailed biomicroscopic evaluation will reveal many distinguishing features between MK and CLPU. The cornea surrounding an infiltrate is typically clear in CLPU, while in MK some degree of stromal edema and folds is not uncommon. However, in the early stages of MK the surrounding cornea may remain clear. Diffuse infiltration in the anterior layers of the stroma, seen as fine granular collection of cells, is a typical feature of corneal inflammation. While infiltration is present in both MK and CLPU, it is localized to the affected quadrant of the cornea in the latter and is widespread in the former. Observation of the endothelial surface may reveal the presence of powdery debris or pseudoguttata in patients with MK, while it is very unusual to see such changes in CLPU (Fig 4).

Click to enlarge

Figure 5: Amoeboid shape of focal infiltrate in MK.

Focal infiltration should be evaluated closely for size, shape, location, density and overlying epithelial changes. In CLPU, focal infiltrates are not usually greater than 1.5 mm in diameter but can be bigger than this in MK. An increase in focal infiltrate size on follow-up examinations is a strong pointer to MK. In CLPU, focal infiltrate is round or sometimes slightly oval, whereas in MK the infiltrate can be of any shape. An irregular shape or gradual change in the shape of the focal infiltrate, particularly with an amoeboid extension, is strongly suggestive of MK (Fig 5). In CLPU, the infiltrate is generally located in the periphery or mid-periphery of the cornea, while in MK it could be closer to the central portion of the cornea. Often, the focal infiltrate in CLPU is located in the superior portion of the cornea, which is normally covered by the upper lid and could be missed on a cursory examination.

Click to enlarge	Click to enlarge
Figure 6a & b: Density of focal infiltrate: compare the opaque appearance in MK(6a) with the translucent appearance in CLPU (6b).	Figure 7

In MK, the infiltrate appears solid (opaque), and yellowish or grayish white, and can appear translucent and lighter in colour in CLPU (Fig 6a & 6b). In the active stage of both MK and CLPU, there is a full-thickness epithelial defect overlying the focal infiltrate. However, patients with MK can present with a patchy, granular looking infiltrate, without any epithelial defect and only stipple staining of the overlying epithelium (Fig 7). Sometimes, seemingly active CLPU may only have punctate epithelial staining pattern, which may be indicative of a resolving event.

Clinical Course
CLPU is a spontaneously resolving condition, where healing is facilitated by discontinuation of contact lens wear. Treatment does not require use of topical antibiotics or steroids. Patients may occasionally need lubricating eye drops or non-steroidal anti-inflammatory medication for symptomatic relief. The focal and diffuse infiltrates resolve over a period of one week, leaving behind a small, faint, circular scar. On the other hand, treatment of MK requires discontinuation of contact lens wear and the use of broad-spectrum antibiotics. It may take longer than a week for MK to resolve and after resolution there is usually a dense scar. Close follow-up care is critical in MK in order to resolve the condition at the earliest, while in CLPU it is necessary in order to avoid misdiagnosis.

Grading
On the basis of the clinical features described, we devised a scoring system as shown in Table 1. We applied this scoring system to our database of 44 CLPUs and 6 MKs. The mean scores are shown in Table 2. Based on these results, we suggest that a score of 7 or less indicates a typical CLPU, up to 10 indicates an atypical CLPU, and any score of 12 or more is definitive evidence of MK. Any score beyond 8 should raise a high index of suspicion of MK. In addition, diagnosis of MK is to be considered if the clinical picture continues to worsen on discontinuation of contact lens wear or if the infiltrate increases in size or develops an irregular shape during follow-up examinations.

Role of Microbiology
Although this article emphasizes the clinical aspects of differentiation between MK and CLPU, it is important to identify the role of microbiological investigations under some circumstances. We did not obtain any useful information from microbiological workup, if the focal infiltrate measured 1.0 mm or less. If the lesion is larger (>1.5 mm) or not responding to the conventional treatment, it is imperative that proper microbiological workup be done.

Conclusion
Differentiating MK and CLPU is important in contact lens practice in order to avoid unnecessary treatment and prevent possible complications. These two conditions can mimic each other causing a diagnostic dilemma. While it is possible to differentiate them clinically, a high index of suspicion needs to be exercised to avoid misdiagnosing MK. While practitioners with experience can have their own diagnostic criteria, those who have not seen many of these events can use the provided information and the scoring system to facilitate in the diagnosis. However, when in doubt it is better to seek a second opinion or treat the condition as MK.

Murali K Aasuri, M.D
Nagaraju Venkata, B.Optom
Vinod M Kumar, DOT

Prof. Brien Holden Eye Research Centre,
L V Prasad Eye Institute,
Hyderabad, India.

References

1. Liesegang TJ. Contact Lens_Related Microbial Keratitis:Part I:Epidemiology. Cornea 1997;16(2):125-131.

2. Cokington CD, Hyndiuk RA. Bacterial keratitis. In Infection of the Eye. Second Edition. Little, Brown & Co, USA, 1996.

3. Holden BA, Reddy MK, Sankaridurg PR, Rajeev B, Sharma S, et al. The histopathology of contact lens induced peripheral corneal ulcer. Invest Ophthalmol Vis Sci 1997;38, s201.