A Study on Microbial Keratitis.

Saradha, D (2012) A Study on Microbial Keratitis. Masters thesis, Madurai Medical College, Madurai.


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INTRODUCTION: Keratitis is an inflammation of the cornea caused by infectious Organisms or non infectious agents. Microbial keratitis is potentially a Vision threatening condition that can be caused by bacteria, viruses, fungi or Parasites. Infectious keratitis is a significant public health problem. The Reported incidence range from 11 per 1,00,000 person years in the United States to 799 per 1,00,000 person years in the developing nations like Nepal. In India the annual incidence is reported to be 11.3 per 10,000. Infectious Keratitis requires prompt diagnosis and treatment to prevent blindness or Even enucleation. Few clinical signs distinguish infectious keratitis from corneal Inflammation associated with trauma, hypersensitivity and immune Mediated conditions. Diagnosis is assisted by the patient’s history and Ocular examination, focusing on the presence or absence of an epithelial Defect and stromal inflammation. Microbiological tests are needed to Establish aetiological agents and antimicrobial susceptibility.Presumptive Treatment of the keratitis is often begun immediately after specimens are Obtained for isolation.The regimen may be changed based on reports of Culture and antimicrobial susceptibility test. Given the rapid progression and virulent nature of many infectious Agents, any corneal inflammation should be considered a threat to vision, Requiring prompt evaluation and treatment. Subsequent endophthalmitis (inflammatory process involving the Ocular cavity and adjacent structures), leading to loss of vision or even loss Of the eye is an ever present danger in such settings. Cornea is a transparent avascular structure which consists of 5 layers. 1. Corneal epithelium with its basement membrane 2. Bowman’s membrane 3. Substantia propria (stroma) 4. Descemet’s membrane 5. Endothelium Normal mechanisms which prevent corneal ulcerations include Eyelid – is a physical barrier providing protection against Mechanical injuries. Smooth corneal surface with intact epithelium Tear film containing enzymes combined with the mechanical Action of blinking eyelids, reduces the likelihood of microbial attachment And survival on the corneal surface. Generally microbial agents do not cause keratitis in immuno competent Hosts or hosts without prior epithelial injury. There are exceptions however In which organisms such as Neisseria gonorrhoea, Listeria monocytogens, Shigella and corynebacterium spp, may invade an intact epithelial surface. Corneal Ulcer : Is an inflammatory or more seriously infective condition of the cornea Involving disruption of its epithelial layer with involvement of corneal Stroma. Predisposing risk factors associated with microbial keratitis usually Involve disruption of the corneal epithelium such as wearing of contact Lenses, trauma (Iatrogenic and traumatic), contaminated ocular medications, And altered structure of the corneal surface. Contributing risk factors include diabetes mellitus, immunodeficiency, Exposure keratoplasty (eg. Grave’s exophthalmopathy, Bell’s palsy). Surface alterations from or with dysfunctional tear states (eg. Sjogren’s Syndrome, neurotrophic cornea, chemical burn, Steven Johnson syndrome, Medication related) and anatomical abnormalities (eg. Neoplasia, cicatrical Pemphigoid and traumatic lid scarring) Ocular trauma other than corneal surgery repeatedly account for 48% to 65% of all corneal ulcers in some developing countries. But such trauma Was responsible for only 27% of corneal ulcer in U.S., whereas in India Trauma accounts for 60% of the corneal ulceration. Contact lenses are the most common risk factor for microbial keratitis Diagnosed in the US. The annual incidence of contact lens associated Keratitis is estimated at 0.04% for individual with daily wear soft lenses and 0.21% for individuals with extended wear lenses. Several studies have reported that bacterial pathogens are responsible For most of the cases of microbial keratitis. Most of the bacterial keratitis are caused by 5 major groups. Staphylococcus spp, streptococcus spp, (streptococcus pneumoniae, Group A through G. Streptococci) other Gram positive organisms (Bacillus and Propionobacterium spp) Gram negative organisms (eg Pseudomonas, Hemophilus and Moroxella) and the Enterobacteriacae, (Proteus, Klebsiella, Enterobacter and Citrobacter) With the advent of refractive surgery, especially Laser Assisted Insitu Kerato Mileusis (LASIK), more unusual organisms such as Nocardia and Mycobacterium spp are also causing keratitis. The apparent change in the causal organisms could be the result of Numerous factors such as improved isolation techniques, increased use of Topical corticosteroid (ie. Refractive and cataract surgery) increased Population of immuno deficient patients and an expansion in the use of soft Contact lenses, especially extended wear and cosmetic lenses. Fungi are generally responsible for less than 10% of corneal infections In most clinical cases reported in the United States whereas in India,fungal Keratitis accounts for more than 60% of the cases. Keratitis due to moulds Occur more commonly in areas with a warmer and more humid environment. The fungi are usually inoculated into the cornea by trauma involving Plant or vegetable matter. Topical cortico steroids for medical or surgical ocular conditions (LASIK) and the use of soft contact lenses as a bandage for post operative or Damaged corneas may increase the likelihood of fungal keratitis. The incidence of fungal keratitis varies according to geographic Location and ranges from 2% in newyork to 35% in Florida. Fusarium spp Are the most common cause of fungal corneal infection in the Southern US Whereas candida and Aspergillus spp are more common in the Northern States.In India Fusarium species are the most common organisms followed By Aspergillus species. Patients with fungal keratitis generally have fewer inflammatory signs And symptoms than patients with bacterial keratitis. In 2006, the CDC began to receive reports of an increased incidence of Contact lens associated Keratitis. Major predisposing risk factors for keratitis resulting from Candida spp Are prolonged epithelial ulceration, topical cortico steroid use, recent Keratoplasty and current use of a bandage soft contact lens (ie. Recurrent Erosion, persistent epithelial defect). Fungal keratitis remains a diagnostic and therapeutic challenge. Difficulties are related to establishing a clinical diagnosis, isolating the Causative agent in the laboratory and treating the keratitis effectively with Topical antifungal agents. Even if the diagnosis is made accurately, management remains a Challenge because of the poor corneal penetration and limited commercial Availability of antifungal agents The small area of active infection and the need to avoid excessive Corneal thinning by unnecessary scraping needs ocular akinesia and patient Cooperation. This may be accomplished through use of topical anaesthetics in Patients old enough to cooperate, with general anaesthesia potentially Needed in children. Specimens are collected by using sterile surgical blades, blunt platinum Spatulas or calcium alginate swab (often dipped in trypticase soybroth). Materials from the scraping is transferred directly to glass slides and Appropriate culture media. The slides should be clean to avoid artifacts and Sterile to avoid contaminating the instrument. Multiple slides are desirable To permit Gram stain, calcoflour and KOH wet mount and acid fast stain. If the patient had been treated before evaluation, and there is Uncertainty regarding the diagnosis, it may be wise to consider stopping the Medication for 12 to 24 hrs and then proceeding with culture. Antimicrobials should not be stopped in cases of severe or rapidly Progressive destruction. As a clinical routine for microbiologic evaluation of the patient with Suspected keratitis, direct inoculation of material from corneal scrapings into Blood, chocolate and Sabouraud’s agar plates with ‘C’ Streaks provide the Support for growth of majority of bacterial and fungal pathogens. Liquid thioglycollate broth is then inoculated by transferring the Material from corneal scrapings from the spatula or surgical blade to a cotton Tipped applicator or calcium alginate swab. The swab is then inserted into The bottom of the tube to enhance the growth of possible anaerobic Pathogens. Aerobic and anaerobic cultures of the corneal scraping should be Incubated for 7 days before being reported as no growth. Mycobacterial And fungal cultures should be incubated for 4 to 6 weeks before being Reported as no growth. The results of corneal cultures should be interpreted with regard to the Clinical situation, the adequacy of sampling and the possibility of Contamination by organisms present on the skin, eyelids and conjunctiva. Supportive evidence for a pathogenic role of species are growth on Two or more media, heavy growth of the organism and a Gram stain directly Smeared from the lesion containing organisms compatible with those Isolated from culture. Antibiotic sensitivity testing was performed by Kirby- Bauer disc Diffusion technique, using 0.5 Mac Farland’s turbidity as the standard Inoculum’s density on Mueller Hinton agar plates. The recent increased incidence of fungal infections and the growing Number of newer antifungal agents have multiplied the demand and interest For invitro antifungal susceptibility testing. WHO Treatment Guidelines for the treatment of corneal ulcers: No fungal hyphae seen on smear Fungal hyphae seen on smear Cefazolin 5% and Gentamycin 1.4% drops hourly Natamycin 5% drops hourly alone (no antibiotics) Ciprofloxacin may be used instead Of gentamycin. If hourly drops is not possible Then a sub-conjunctival inj. Can Be considered. Or Amphotericin B 0.15% drops Hourly Treatment frequency, duration and followup: Daily examination until the ulcer Starts improving Examination every 2 days until The ulcer starts improving Then gradually reduce the Frequency of drops and follow up Over 2 weeks Then continue drops at least 3 Hourly for at least 2 weeks after Healing of the ulcer. Refer to tertiary ophthalmic centre if: Not improving after 3 days Treatment Not improving after 7 days Treatment Adjunctive therapy: Includes cycloplegics; analgesics; anti-glaucoma medication if indicated. Do not use any preparation containing steroids. Investigate for diabetes mellitus as a possible risk factor for corneal Ulceration

Item Type: Thesis (Masters)
Uncontrolled Keywords: Microbial Keratitis.
Subjects: MEDICAL > Microbiology
Depositing User: Subramani R
Date Deposited: 19 Aug 2017 02:17
Last Modified: 19 Aug 2017 02:17
URI: http://repository-tnmgrmu.ac.in/id/eprint/1467

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