Is microsporidial keratitis an emerging cause of stromal keratitis? A case series study.

Abstract

Microsporidial keratitis is a rare cause of stromal keratitis. We present a series of five cases of microsporidial keratitis from a single centre in southern India with microbiologic and histopathologic features.
Patient charts of five cases of microsporidial stromal keratitis diagnosed between January 2002 and June 2004 were reviewed retrospectively for clinical data, microbiologic and histopathologic data. The presence of microsporidia was confirmed by special stains on corneal scrapings and/or corneal tissues, and electron microscopy. All patients were immunocompetent with a preceding history of trauma in three. Four patients presented with unilateral, small, persisting deep stromal infiltrates, of uncertain etiology, in the cornea, which were not responding to conventional antimicrobial treatment and required penetrating keratoplasty in three. Fifth case was unsuspected and underwent keratoplasty for post-traumatic scar. Three of five cases were diagnosed on corneal scrapings, prior to keratoplasty, while two were diagnosed only on histology. The microsporidia appeared as oval well defined bodies with dense staining at one pole. None of the patients showed recurrence following keratoplasty.
Microsporidia, though rare, should be suspected in chronic culture-negative stromal keratitis. Organisms could lie dormant without associated inflammation.

Full text

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BioMed Central
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BMC Ophthalmology
Open Access
Case report
Is Microsporidial keratitis an emerging cause of stromal keratitis? –
a case series study
Geeta K Vemuganti*1, Prashant Garg2, Savitri Sharma3, Joveeta Joseph3,
Usha Gopinathan3 and Shashi Singh4
Address: 1Ophthalmic Pathology Service, L.V. Prasad Eye Institute, Hyderabad, India, 2Cornea Service, L.V. Prasad Eye Institute, Hyderabad, India,
3Jhaveri Microbiology Centre, L.V. Prasad Eye Institute, Hyderabad, India and 4Centre for Cellular and Molecular Biology, Hyderabad, India
Email: Geeta K Vemuganti* - geeta@lvpei.org; Prashant Garg - prashant@lvpei.org; Savitri Sharma - savitri@lvpei.org;
Joveeta Joseph - joveeta@yahoo.com; Usha Gopinathan - usha@lvpei.org; Shashi Singh - shashis_99@yahoo.com
* Corresponding author
Abstract
Background: Microsporidial keratitis is a rare cause of stromal keratitis. We present a series of
five cases of microsporidial keratitis from a single centre in southern India with microbiologic and
histopathologic features.
Case presentation: Patient charts of five cases of microsporidial stromal keratitis diagnosed
between January 2002 and June 2004 were reviewed retrospectively for clinical data, microbiologic
and histopathologic data. The presence of microsporidia was confirmed by special stains on corneal
scrapings and/or corneal tissues, and electron microscopy. All patients were immunocompetent
with a preceding history of trauma in three. Four patients presented with unilateral, small,
persisting deep stromal infiltrates, of uncertain etiology, in the cornea, which were not responding
to conventional antimicrobial treatment and required penetrating keratoplasty in three. Fifth case
was unsuspected and underwent keratoplasty for post-traumatic scar. Three of five cases were
diagnosed on corneal scrapings, prior to keratoplasty, while two were diagnosed only on histology.
The microsporidia appeared as oval well defined bodies with dense staining at one pole. None of
the patients showed recurrence following keratoplasty.
Conclusion: Microsporidia, though rare, should be suspected in chronic culture-negative stromal
keratitis. Organisms could lie dormant without associated inflammation.
Background
Microsporidia are small, oval, obligate intracellular
eukaryotic protozoan parasites, widely distributed in ver-
tebrates and invertebrates, but mostly cause infections in
immunocompromised individuals [1-3]. The ocular man-
ifestations include superficial punctate keratoconjunctivi-
tis [4-6], and corneal stromal keratitis [7-14] and these
two manifestations are directed by the genus involved as
well as the immune status of the patient. Keratoconjuncti-
vitis is usually seen in immunocompromised individuals
or in contact lens wearers; mostly by genus Encephalitozoon
while the stromal keratitis is caused by Nosema and Micro-
sporidium. However, recent reports suggest that keratocon-
junctivitis can also occur in immunocompetent
individuals [15,16]. A review of the literature in English
using PubMed revealed eight cases of corneal stromal
Published: 17 August 2005
BMC Ophthalmology 2005, 5:19doi:10.1186/1471-2415-5-19
Received: 15 April 2005
Accepted: 17 August 2005
This article is available from: http://www.biomedcentral.com/1471-2415/5/19
© 2005 Vemuganti et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Table 1: Summary of clinical features in Microsporidial keratitis
Age/ Dur of
Sym
Med. TxtraumavisionInfiltrate VascClin diag MicroTreat FU
40/F
2/F
23/M
70/F
37/F
7 mon
1.5 mon
2 yrs
1 mon
4 mon
AV, AF
AB
AV
?
-
-
-
-
-
+
6/8+Crys K
HSV
HSV
IK
Desce
Neg
Micros
Micros
Micros
Neg
-
Itracon
Itracon
Cefaz
Nil
PK
PK
Scar
PK
PK
cfcf
cfcf
+
AB = antibacterial
AV = antiviral
AF = antifungal
Cfc = counting fingers close to face
HSV = herpes simplex keratitis
Crys K = crystalline keratopathy
PK = Penetrating Keratoplasty
Micros = Microsporidia
Slit lamp biomicroscopy of cornea of case 1 in diffuse illumination with central mid to deep stromal infiltrate and surrounding stromal edema
Figure 1
Slit lamp biomicroscopy of cornea of case 1 in diffuse illumination with central mid to deep stromal infiltrate and surrounding
stromal edema.

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involvement, all of which were diagnosed based on iden-
tification of the organisms in the tissue sections and/or by
ultrastructural studies [7-13]. We present a series of five
cases of corneal stromal keratitis from a single tertiary eye
care centre, caused by Microsporidium, two of which were
diagnosed based on the clinical and microbiologic find-
ings. These cases highlight the importance of identifying
the clinical presentations, microbiology, and histopathol-
ogy including electron microscopic findings for proper
management of these cases.
Methods
In a retrospective study, all cases of microsporidial kerati-
tis, diagnosed and managed at L V Prasad Eye Institute,
Hyderabad, India between January 2002 and July 2002
were included. The medical records of the patients were
specifically reviewed for past and personal history, clinical
findings. The microbiologic work-up of the corneal lesion
included 1) corneal scrapings stained by Gram, Giemsa
stain and potassium hydroxide- calcofluor white prepara-
tion, 1% acid fast stain, 2) culture of the scrapings in cul-
ture media to facilitate growth of bacteria, fungi and
parasites. In cases that underwent therapeutic penetrating
keratoplasty, the corneal button was bisected and submit-
ted to microbiology and histopathology. Routine histol-
ogy stains and special stains like 1% acid fast stain,
modified trichrome stain, Gram and Gomori's methen-
amine silver stain were performed on the permanent sec-
tions. In three cases, part of the tissue was submitted in
2% glutaraldehyde for electron microscopy. The patients
underwent systemic evaluation to rule out any evidence of
immunosuppression, HIV testing of the serum by ELISA
(after obtaining informed consent) was done in all cases.
Case presentation
In this study period, five cases of microsporidial keratitis
were diagnosed at L V Prasad Eye Institute, Hyderabad,
India. The mean age of patients was 34 (range 2–70 years)
years with three male patients. Four cases presented as
keratitis, two of which were diagnosed by microbiological
Slit lamp biomicroscopy of cornea of case 3 in diffuse illumination shows a large stromal infiltrate
Figure 2
Slit lamp biomicroscopy of cornea of case 3 in diffuse illumination shows a large stromal infiltrate.

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processing of the corneal scrapings and two by tissue diag-
nosis, while one presented with a corneal scar with a post
traumatic descemetocele with unsuspected infection. Brief
clinical history of all cases (Table ) is given below.
Case 1
A 40-year-old lady presented to our institute with recur-
rent pain, redness, watering and blurred vision of seven
months duration. During this time she had received topi-
cal steroids, antiviral and antifungal medications. How-
ever, there was no resolution in the signs or symptoms.
The treating surgeon felt she was worsening and referred
her as a case of crystalline keratopathy due to the nature
of the stromal infiltrate. At presentation, she had a BCVA
of perception of light and accurate projection of rays.
There was 1+ lid edema and conjunctival congestion.
There was a central mid to deep stromal infiltrate measur-
ing 1.5 × 1.5 mm with surrounding stromal edema (figure
1). The overlying epithelium was intact with epithelial
edema. Endothelium showed exudates arranged as a sheet
over an area of 5.0 × 5.0 mm. There was 360° of superfi-
cial vascularisation. Since the infiltrate had not shown any
signs of resolution and there was no definitive diagnosis
in hand, all the medications were discontinued and she
underwent a penetrating keratoplasty for that eye on 25/
03/02. The post-operative period was uneventful and at
last follow up she was doing well with a BCVA of 6/18.
She was treated with topical Chloramphenicol, Pred-
nisolone acetate1%, and Lacrigel. She was later prescribed
Tablet Itraconazole 100 mg BD for one month. Her
immune status was found to be normal.
Slit lamp biomicroscopy of cornea of case 4 in diffuse illumination shows two discreet stromal infiltrates
Figure 3
Slit lamp biomicroscopy of cornea of case 4 in diffuse illumination shows two discreet stromal infiltrates.

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Case 2
Parents of a 2-year-old male child brought him with com-
plaints of white spot on the black of the left eye and swell-
ing of the lids since one and half months. The child had
red eye three months back which subsided with eyedrops
(Ofloxacin and Tobramycin) but the opacity persisted.
Vision could not be assessed as he was photophobic.
Examination under anaesthesia revealed flat lids and a
quiet conjunctiva. The cornea showed the presence of a
mid to deep stromal infiltrate 1.0 × 1.0 mm with sur-
rounding cellular reaction. There was surrounding stro-
mal edema extending about 2 mm from the infiltrate
edges. AC was deep and quiet. The IOP was within normal
limits. A diagnosis of resolving infectious keratitis or a
HSV stromal immune keratitis was kept in mind and he
was started on Cefazolin eye drops 2 hourly with close fol-
low up. He showed improvement and 15 days later four
hourly Betamet e/d was added. The child was comforta-
ble. He returned two months later with a recurrence of the
stromal infiltration in the same location. Deep corneal
scrapings were done under anaesthesia which revealed
spores suggestive of Microsporidium. He was started on oral
Itraconazole 50 mg BD. After 15 days of therapy there was
no response and considering the risk of amblyopia a pen-
etrating keratoplasty was done on 8/04/02. The post oper-
ative period was uneventful and the child is doing well
and is relieved of his symptoms as noticed by his parents.
Case 3
A 23 years male patient presented with a history of pulling
sensation in the left eye off and on since 2 years. This was
associated with pain, redness and watering. He had been
diagnosed and treated as HSV keratitis for the same. He
was presently on treatment with Acyclovir ointment 3
times a day and Tears plus eye drops 3 times a day. His vis-
ual acuity was counting fingers close to face. The lids were
edematous with a diffuse papillary reaction of the con-
junctiva. Cornea showed the presence of a central,
irregular epithelial defect 2.5 × 3.0 mm with surrounding
stromal edema. There was scarring at the edges and the
Gram stain of corneal scraping showing gram positive oval microsporidial spores (×500, 4a)
Figure 4
Gram stain of corneal scraping showing gram positive oval microsporidial spores (×500, 4a).

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corneal sensations were decreased. Rest of the findings
was within normal limits. Viral scrapings were taken and
he was started on Acyclovir eye ointment 5 times a day
with cycloplegics. The scrapings were inconclusive for
viral etiology, there was a clinical resolution and as the
epithelial defect reduced in size, he was started on Beta-
met eye drops drop to drop with the antiviral. The lesion
completely resolved and he was continued on topical
lubricants.
He returned with a recurrence 15 days later and was again
started on topical corticosteroid under antiviral cover.
Oral Acyclovir was also started in a dosage of 400 mg 5
times day. The lesion again resolved and the antivirals
were discontinued. However, the lubricant eye drops were
continued and the corticosteroid was tapered. He was on
regular follow-up and seven months later a recurrence was
seen with a stromal infiltrate and the presence of endothe-
lial exudates (figure 2). There were deep vessels seen in the
inferior half of the cornea. The central area showed
marked thinning and a tissue adhesive with bandage con-
tact lens was applied. The corneal scrapings in Gram stain
revealed oval bodies suggestive of microsporidial spores.
He was started on oral Itraconazole 100 mg BD with top-
ical ciprofloxacin and cycloplegics. Despite treatment he
showed a shallowing of the AC suggestive of leak under
the glue and the procedure was repeated. He developed
360° deep and superficial vascularisation. He was
continued on the same treatment and is on regular follow-
up. On the last follow-up visit the glue and BCL had come
off and revealed a scar with thinning of the corneas in that
1% acid fast stain of corneal scraping showing acid fast positive oval microsporidial spores (×500, 4b)
Figure 5
1% acid fast stain of corneal scraping showing acid fast positive oval microsporidial spores (×500, 4b).

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region. He was advised to continue oral therapy for 2
weeks, and come for review.
Case 4
A 70-year old female presented with complaints of pain,
redness, watering and diminution of vision in the left eye
of one month duration. She gave history of injury with
grass six months ago. Visual acuity in right eye was 6/12
and hand movements with counting finger in the left eye.
Right eye on examination was within normal limits. Left
eye lids were edematous, conjunctiva was congested, cor-
nea showed the presence of an anterior mid stromal infil-
trate in nasal paracentral area with overlying epithelial
defect of 1.5 × 1.5 mm (figure 3). In the temporal paracen-
tral area, there was an area of deep stromal infiltrate with
underlying endothelial exudate. Smears revealed gram-
negative oval bodies. Cultures were positive for gram-pos-
itive cocci and gram-positive bacilli. Patient was started on
Cefazolin eye drops half hourly. The clinical picture was
the same at one and half months, therefore a decision was
taken to penetrating keratoplasty in the left eye. Post-oper-
ative period was uneventful.
Case 5
A 37-year-old male presented with history of injury in left
eye during a fight 4 years ago. His vision decreased but he
did not use any medications. On examination, vision in
right eye was 6/6 and in the left eye it was PL positive, PR
accurate. Right eye examination was within normal limits.
Left eye showed trace conjunctival congestion, there was
diffuse corneal scarring with central descemetocoele.
Anterior chamber view was hazy and there was total cata-
ract. He underwent optical penetrating keratoplasty with
extracapsular cataract extraction with intraocular lens
implantation under local anesthesia in left eye. The post-
operative period was uneventful and at last follow-up his
vision in the left eye was 20/400.
Section showing intact epithelium, with deep stromal infiltrates (arrow) (Hematoxylin and Eosin stain, ×20)
Figure 6
Section showing intact epithelium, with deep stromal infiltrates (arrow) (Hematoxylin and Eosin stain, ×20).

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Microbiology
Four patients in this series had presented as ulcerative
keratitis and one as post-traumatic corneal ectasia. Two of
the four patients, diagnosed as stromal keratitis, under-
went deep stromal scrapings, which demonstrated micro-
sporidial spores. The diagnosis was made on observing
oval refractile bodies in the corneal scrapings, both within
cells as well as in extracellular location. The Gram (figure
4) and Giemsa stained smears revealed variable staining
of the parasites. The oval body had a dark polar nucleus.
The parasite was acid fast and appeared as red oval struc-
ture on smears stained with 1% acid fast stain (figure 5).
Corneal scrapings stained with calcofluor white showed
oval fluorescent bodies in clumps. Bacterial and fungal
cultures from these cases did not reveal any organisms
except in one case (case 4) that showed a significant
growth of Staphylococcus epidermidis.
Treatment
Three cases were initially treated medically based on the
findings of smear examination. In case 1 the treatment
was started with fortified cefazolin and fortified gen-
tamicin even though oval bodies were seen in the smear
examination. In other two cases where scraping was per-
formed the treatment was started with oral itraconazole
100 mg twice daily and topical ciprofloxacin 0.3%. The
infiltrate resolved with medical therapy in one case. Even
this case developed progressive thinning for which tissue
Section of corneal button which shows oval bluish purple spores of microsporidia with a dark band (modified grams chromo-trope stain, ×1000)
Figure 7
Section of corneal button which shows oval bluish purple spores of microsporidia with a dark band (modified grams chromo-
trope stain, ×1000).

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adhesive and bandage contact lens was applied. Penetrat-
ing keratoplasty was performed in four cases. The
indications were non-responding keratitis in three cases
and thinning with ectasia in one case. Postoperatively all
cases were managed with corticosteroids (Prednisolone
acetate 1%). The graft was clear in all cases with no evi-
dence of recurrence of infection.
Histopathology
Out of four corneal buttons included in the study three
were from patients diagnosed as stromal keratitis and one
was from a corneal scar with descemetocele, undergoing
optical PK. The epithelium was intact in two, showed
edema in one and was ulcerated in one case. Bowmans
layer was destroyed in 3 out of 4 cases. There was moder-
ate to severe stromal inflammation, at places forming
micro abscess (fig 6). The stromal inflammation consisted
of polymorphonuclear cells, mostly seen in the pre-
Descemet region and extending to the superficial layers. A
few macrophages were also seen. Inflammation was
absent in the corneal scar tissue. Routine staining showed
Microsporidial spores as oval bodies, 2 – 3 µ wide and 3 – 5
µ in length involving mostly the deep stroma, with exten-
sion into anterior layers in 2 cases. The spores showed a
thick band like nucleus at one pole and stained positively
with modified Gram Trichrome stain (figure 7), 1% acid
fast stain (figure 8) and variably with GMS. The unstained
and faintly stained spores showed thick walled capsule
that was birefringent on polarized light. The case with
corneal scar and a descematocele showed a corneal scar
with marked thinning in the central stroma (figure 9).
There was no inflammatory infiltrate, but the stroma
showed oval, spores of microsporidia in all section (figure
10). These were seen mostly in the deeper stroma, at
places extending to mid and superifical stroma. The semi-
thin sections of these tissues showed many viable, mature,
immature, and degenerated spores, many of them being
intracellular. The electron microscopic examination
revealed an electron lucent thick capsule with a single
nucleus and 11 – 13 tubules in the cytoplasm (figure 11
Section of corneal button in which the spores appear red with darkly stained band at the tip (1% acid-fast stain, ×1000)
Figure 8
Section of corneal button in which the spores appear red with darkly stained band at the tip (1% acid-fast stain, ×1000).

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with inset as figure 12). Some of the sporoblasts were uni-
formly dark and osmophilic.
Discussion
Microsporidia are eukaryotic, spore forming, obligate
intracellular, protozoan parasites with two developmental
phases – schizogenic and sporogenic. The size of the
spores varies from 1 to 20 µm and they are spherical, oval
or elongate. They can infect a broad range of vertebrates
and invertebrates and are considered ubiquitous [17].
They are becoming increasingly recognized as opportunis-
tic infectious pathogens in immuncompromised patients,
causing intestinal, ocular, sinus, pulmonary, muscular
and renal diseases [1-3]. Like in all other organs, ocular
microsporidial infection was rare before the era of AIDS,
the first case being reported by Ashton et al in 1973 [7], in
a vascularized corneal scar, unsuspected of infectious eti-
ology. Since 1991, cases of microsporidial keratoconjunc-
tivitis have been reported from immunocompromised
patients and of late even in immunocompetent individu-
als [4-15], one of which was from this centre [16].
Diagnosis of microsporidiosis currently depends on mor-
phological demonstration of the organisms in one or
more readily obtainable specimens such as stool, duode-
nal aspirates, urine, sputum,
bronchoalveolar lavage fluid, conjunctival smears [18].
Definitive species identification is made by using the
specific fluorescein-tagged antibody (immunofluores-
cence) technique, electron microscopy and also by PCR
[18-21].
nasal discharge,
Ocular microsporidia could be isolated or part of systemic
microsporidiosis in immunocompromised patients and
can manifest as either stromal keratitis or keratoconjunci-
tivitis. A careful review of previously published cases and
the cases reported in this series suggests that
microsporidial stromal keratitis is a slowly progressive
keratitis-affecting individual of any age. No definitive pre-
Section of corneal button of case 4 showing marked thinning in the central stroma (descematocele, arrow)
Figure 9
Section of corneal button of case 4 showing marked thinning in the central stroma (descematocele, arrow).

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disposing factors could be identified in this series. The his-
tory of trauma was elicited in only 2 of 5 cases from our
series and 1 of 7 previously published reports [7].
Clinically, microsporidial stromal keratitis could mimic
suppurative or non suppurative inflammation and
vascularization of the cornea and includes a differential
diagnosis of herpes simplex virus keratitis, fungal or bac-
terial keratitis. The diagnosis can be made either by cor-
neal biopsy or deep corneal scrapings as was done in two
of our cases. One of the non-invasive emerging technique
of diagnosing microsporidial keratitis is with the help of a
confocal microscopy [21] using a 24× contact objective
lens and a Nipkow disc in imaging. The spores appear as
high contrast intraepithelial or intrastromal opacities.
The duration of symptoms in this series ranged from one
month to 2 years suggesting a slow indolent nature in the
initial phase. Except one case, none of them gave any
history of preceding trauma, illness, immunosupression
or any local predisposing factors. The youngest patient in
this series was 2 years, which is very unusual. Four of the
cases in this series were diagnosed as infectious keratitis;
two were diagnosed and treated as viral keratitis to which
they showed response but after few months showed recur-
rence of infiltrates. The subsequent corneal scrapings in
three cases were diagnosed as microsporidial keraitits.
This is in contrast to the other reports where the diagnosis
was made only on corneal sections.
Section of corneal button of case 4 showing the presence of oval, spores of microsporidia in the stroma, unaccompanied by inflammatory infiltrates (PAS stain, ×500)
Figure 10
Section of corneal button of case 4 showing the presence of oval, spores of microsporidia in the stroma, unaccompanied by
inflammatory infiltrates (PAS stain, ×500).

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On microbiologic examination of the corneal scraping,
the differential diagnosis of microsporidia includes bacte-
ria or yeast, but can be confirmed by special stains like
Grams trichrome stain, 1% acid fast stain [19,22-24].
These oval or round structures are non-budding which
differentiates them from yeast. Histologically, the organ-
isms are seen within the stromal keratocytes, histocytes as
well as between the stromal lamellae. They are seen as
oval gram positive structures with a thick wall. They stain
red with modified trichrome stain and acid fast stain best
demonstrates the organisms. However, it should be noted
that all species may not be acid fast. The inflammatory
cells in the corneal
polymophonuclear cells as well as few histiocytes, with
varying degrees of stromal necrosis, thus explains the cor-
neal thinning in these cases.
stroma consisted of
Under electron microscope the spores of microsporidia
show sporoplasm and a tubular polar filament with vary-
ing number of coils depending on the species. Therefore,
ultrastructurally, it is possible to identify the species. The
organisms of Nosema species, as seen in our series,
measure 3 – 5 microns in length and 2 – 3 micron in
width. The organisms are not surrounded by parasitopo-
rous vacuole within the host cells and the number of coils
in the cytoplasm varies between 10 – 14.
Therapeutically, there is no definitive medical therapy for
this entity. Font et al treated their case with fumagillin
0.3% and oral Albendazole but there was no response.
After making a diagnosis of microsporidial keratitis in our
series, two received itraconazole for few weeks, while one
case received cefazolin. Only one case responded to itra-
conazole treatment while the other two cases showed per-
sistence of infiltrates with corneal thinning, and
necessitated surgical intervention. Even in the case that
responded to medical treatment there was progressive
thinning that required application of tissue adhesive.
The electron microscopic examination of the corneal button revealing macrophage with three spores
Figure 11
The electron microscopic examination of the corneal button revealing macrophage with three spores.

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Though this is a small case series, but reviewing the litera-
ture and in the light of these findings, it is possible for us
to suggest that in the absence of effective medical therapy
it is reasonable to manage these cases surgically. Penetrat-
ing keratoplasty helped eradicating infection in 4 cases of
our series and 6 cases from previously published reports.
It is important to note that the infection is mostly
restricted to stroma and has not been demonstrated in
deeper ocular tissues. The other favorable feature in these
cases is that none of them had recurrence of infection
postoperatively.
It is not clear how the microsproidia enter into the eye- it
could be either due to trauma or contact with
contaminated water, food. The normal lifecycle of micro-
sporidia includes: once invasion of the spore into the
human host cell occurs, the contents are discharged into
the cytoplasm. Within the cell the sporoplast divides by
binary fission to form schizont with 2–6 nuclei, which
split into unicellular meronts. The meronts then secrete a
rigid capsule and the fully formed spore measures about
2.5 × 1.5 microns. The cell eventually ruptures to continue
the cycle and further destruction of the host tissue.
Conclusion
This is the largest series of ocular infection by Microsporidia
in immunocompetent individuals manifesting as stromal
keratitis. This series suggests the need for a high index of
suspicion in diagnosing microsporidial infection in cul-
ture negative stromal keratitis. Use of special stains, tissue
biopsy and electron microscopy aids in confirming the
diagnosis of this infection. Due to lack of effective medical
therapy, surgical treatment appears to be a reasonable
option in the management of these cases.
Competing interests
The author(s) declare that they have no competing
interests.
Inset shows an electron lucent thick capsule with a single nucleus and 11 – 13 tubules in the cytoplasm
Figure 12
Inset shows an electron lucent thick capsule with a single nucleus and 11 – 13 tubules in the cytoplasm.

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Authors' contributions
GKV was involved in collecting data, carrying out the anal-
ysis and drafting the manuscript. PG provided the clinical
information and edited the manuscript. SS participated in
its design, carried out the microbiological work up and
edited the manuscript. JJ collected data, participated in its
design and helped to draft the manuscript. UG partici-
pated in its design and carried out the microbiological
work up. Ssingh carried out the electron microscopic anal-
ysis. All authors read and approved the final manuscript.
Acknowledgements
We are grateful to Dr. Govind Visvesvara, CDC, Atlanta for reviewing our
slides. Financial support: Hyderabad Eye Research Foundation, Hyderabad
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