Deng_edit_Deng 21/01/2010 10:31 Page 83
Corneal Epithelial Stem Cell and Disease – Past, Present and Future
When the disease is sectoral, there is a distinct contrast between the
Figure 1: Slit-lamp Photograph of a Cornea with
normal corneal and conjunctival epithelia because the latter is more Partial Limbal Stem Cell Deficiency (A) and Stippling
permeable to fluorescein. At the more advanced stage, vision
Fluorescein Staining in a Vortex Pattern (B)
deteriorates further because of the irregularity of the epithelial surface
and invasion of fibrovascular tissue onto the cornea. Recurrent epithelial
AB
breakdown may be more frequent and is often persistent. The corneal
surface is more irregular and the light reflex is dull. In total LSCD, the
corneal surface is completely covered by a fibrovascular pannus.
Keratinisation can occur if there is an associated deficiency of aqueous
and mucin tears (see Figure 2). The patients are functionally blind.
Diagnosis of Limbal Stem Cell Deficiency
Diagnosis of LSCD can be made based on clinical findings during
Figure 2: Slit-lamp Photograph of a Cornea with
careful slit-lamp examination. If LSCD is partial and mild, the clinical Total Limbal Stem Cell Deficiency (A) and the
signs tend to be subtle and could be missed or attributed to other
Irregular Corneal Surface (B)
conditions, such as dry eyes, infectious keratitis or recurrent erosion
syndrome. On the other hand, the presence of a superficial
AB
neovascularisation may be due to previous infectious keratitis and not
LSCD. A correct diagnosis of LSCD is therefore imperative to provide
appropriate treatment and avoid unnecessary surgery because
patients with severe LSCD are poor candidates for penetrating or
lamellar keratoplasty. Confirmation of LSCD can be achieved by
impression cytology
12
or immunocytology.
13,14
Impression cytology is a well-established and non-invasive test to Figure 3: In Vivo Laser Scanning Confocal Images of
diagnose ocular surface diseases.
15,16
It is performed by using a
the Basal Epithelial Cells – Normal (A) and Moderate
cellulose acetate filter paper or a biopore membrane device to collect
Limbal Stem Cell Deficiency (B)
the very superficial layers of the corneal epithelial cells after
AB
instillation of topical anesthestic medication. Periodic acid Schiff,
Gills’s haematoxylin or Papanicolaou stain are commonly used to
identify goblet cells on the impression cytology specimens.
The presence of goblet cells on the cornea indicates the invasion of
conjunctival cells. Goblet cells are not always detected in LSCD,
especially in advanced mucous membrane pemphygoid and Stevens-
Johnson syndrome. The sensitivity of impression cytology is
calculated to be only 72% based on the study by Sacchetti et al.
14
More importantly, 18% of patients with LSCD diagnosed on the basis of
clinical findings alone do not have LSCD, as shown by the absence of
conjunctival epithelial-specific cytokeratin 19. This finding highlights the cornea may not be affected and patients may be asymptomatic or
necessity for more sensitive tests to avoid misdiagnosis of LSCD.
13,14
have only mild symptoms. No surgical intervention is necessary. In
cases in which the inciting cause – such as contact lens, topical
In vivo laser scanning confocal microscopy is a relatively new and medications, chronic ocular surface inflammation or autoimmune
non-invasive diagnostic imaging technique that visualises the cornea causes – is known, removal of the inciting agent and treatments to
at the single-cell level.
17–20
It has been used to aid in the diagnosis of control inflammation may have potential benefit by preventing further
fungal and Acanthamoeba keratitis. It has also been used to study the insult to the residual stem cell populations.
cellular structure in a wide range of corneal conditions including dry
eye,
21,22
corneal dystrophies
23,24
and corneal innervations
25,26
in normal If the central cornea is affected in partial LSCD, removing the
and pathological conditions.
27
Laser scanning confocal microscopy conjunctival epithelial cells could allow the normal corneal epithelium
can detect early subtle cellular changes in LSCD. The corneal basal to heal and cover the central visual region.
28
To avoid epithelial
epithelial cells are larger and the nucleus becomes hyper-reflective breakdown, care must be taken not to remove a large area of
(see Figure 3). The use of in vivo confocal microscopy in the diagnosis conjunctival epithelium if the remaining normal limbus is small.
of early LSCD is under investigation.
Amniotic membrane transplantation has been shown to successfully
Management restore the ocular surface in patients with partial LSCD.
29
The amniotic
Partial Limbal Stem Cell Deficiency membrane has anti-inflammatory properties and possibly provides an
Treatment of LSCD is based on the extent and severity of the disease. improved microenvironment for LSCs. If the Bowman’s layer is
In partial LSCD or at the early stage of the disease, corneal and damaged, as it often is in advanced LSCD, the amniotic membrane
conjunctival epithelial cells can co-exist for a long period of time and can also serve as a new basement membrane to facilitate
the peripheral fibrovascular pannus may be stationary. The central re-epithelialisation of the ocular surface.
EUROPEAN OPHTHALMIC REVIEW 83
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