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12/14/09
Limbal Stem Cells: The New Future
A life of blindness is a struggle many face because of failed attempts to treat
disorders damaging the eye surface.-I feel it doesn’t read the best, but it is not terrible.
Transition into this sentence. Ocular burns and Steven-Johnson syndrome, a disease in
which the upper layer of skin, the epidermis, separates from the dermis, the lower layer
of skin, are two of the many diseases that can cause blindness.-This reads poorly
because of the way the first problem, ocular burns, is not defined while Steven- is. I feel
you will need to define ocular burns also and break the sentence in half. In the past,
such disorders that damage cells on the eye surface-this is repeated, corneal cells, posed
a challenge to treat because scarring and epithelial defects often remained after
treatment. What you have written thus far is fine, but I feel it could be condensed and
written more efficiently. The cornea, clear section on the surface of the eye that helps
bend light, was often transplanted from a healthy donor to treat these disorders (Tsai et
al., 2000). In order to tell the story, you need to start with the general info. You mention
the cornea here and corneal cells above. Therefore, you should discuss the general
structure of the eye in the beginning and you will not have to define these things later.
This can then transition into damaging the cornea, treating the damage, and so on…
Unfortunately, corneal transplants have a rejection rate of up to 30 percent, require a
long recovery time and fail to improve vision or alleviate symptoms 66% of the time
(Pfister, 1994;Burman & Sangwan, 2008). Transition into this sentence Symptoms such
as ocular surface scarring-didn’t you say this already? and the formation of vessels can
persist following a transplant. Due to these side effects, one hope for the future may be
the use of stem cell transplants. Stem cells are essential for cell regeneration and repair
and help maintain homeostasis-you need a better description of what stem cells are. It
is critical that the reader understand this. (Dua & Azuara-Blanco). Transition Limbal stem
cells maintain the integrity of the corneal epithelium.-What does that mean? Bring it
down to the reader. They can become any other type of cell including corneal cells.Limbal stem cells can become any cell type? Are you sure about this…. There are
different kinds of stem cells. You should look this up. Therefore, they can be used to
replace the damaged ones.-Basics first. Where do you get them? Scientists have
experimented with limbal cells-you are repeating limbal cells too often in ocular surface
reconstruction. Pelligrini, an ocular surgeon,-does this matter? first used limbal stem
cells in sheet form-sheet form? to treat patients with corneal damage in 1997 (Sullivan
& Clynes, 2007).-say it was successful in the sentence. How successful what it? Since
that first successful operation, limbal stem cells have been transplanted and yielded
promising results. Limbal stem cell transplants are the new future of ocular surface
reconstruction.
Limbal stem cells reside in a supportive environment in the eye called the stem
cell niche.-This is basic info and should be in the intro. Research by Charukamnoetkanok
(2006) supports that the stem cell niche, named the Palisades of Vogt, protects limbal
cells and helps maintain their amazing properties. Their ability to differentiate into
different cell types gives them the ability to replace whatever cell type needs them the
most (Li et al. 2007).-you said this already Limbal cells can also differentiate into
different cell types more rapidly than corneal epithelial cells-these are stem cells too?
can, making them more effective in corneal transplants (Pfister, 1994). Since many
ocular disorders damage the epithelial surface of the cornea, limbal stem cells will
replace damaged cells with new corneal cells, thus improving visual acuity.-Almost this
entire paragraph is a repeat of what you already said in the first paragraph. I am going
to stop here. Make this as efficient as possible without losing meaning. Also, tell a story.
Avoid just listing facts in order. Transition, describe, think like the reader.
Scientists have begun exploring the potential of limbal stem cells in corneal
surface reconstruction. Use of autograft, the transplantation of tissue from one part of
the body to another; and allograft, the transplantation of tissue from one person to
another, transplantations of limbal stem cells as an alternative to corneal transplants
have become popular. Autograft transplantations are used in patients with unilateral
ocular damage, damage in only one eye. Limbal cells are taken from the healthy
opposite eye and transplanted into the damaged eye. Limbal stem cells can be
expanded on an amniotic membrane, a protective organ that surrounds and protects
the fetus, and then transplanted but this is usually done only when the donor eye
doesn’t have enough limbal stem cells for the transplant. Amniotic membrane use to
expand limbal stem cells in combination with this procedure allows for more rapid cell
growth of the epithelium and may help prevent infection, but scientists are unsure of
why (Meller et al., 2002). Allograft transplantations are used in patients with bilateral
ocular damage, damage in both eyes. Limbal cells are taken from relatives and
transplanted into both eyes. Even though tissue is matched and living donors are
preferred, immunosuppressants are still required following the surgery. Both allograft
and autograft surgeries have been widely accepted by the medical community in
treating ocular surface disorders (Ozdemir et al., 2004).
Research has shown that autograft transplants tend to yield better outcomes
than allograft transplants. In an experiement by Ozdemir et al. (2004), limbal allograft
transplant patients had a follow up period that was 4 months longer than the autograft
patients and only 11% of transplants resulted in functional vision whereas with limbal
autografts it was 80%. The authors also explained how it is more difficult to reduce
formation of capillaries with allograft transplants. Capillary and vessel formation
regressed in all patients with autograft transplants but only in 4/9 patients who
underwent allograft transplantations. The authors believe the failure of many allograft
transplantations was due to the advanced stage of ocular surface destruction that the
patients in the allograft group of the experiment had. Many people do not have a choice
between autograft and allograft surgery. Autograft surgery is only available to those
with unilateral ocular disorders since the limbal cells must be derived from the healthy
opposite eye. Allograft surgeries are probably less effective because the limbal cells are
derived from another person. The authors speculate that perhaps the role of allograft
transplantations, instead of to completely treat, should be to stabilize the ocular surface
for future surgeries.
There have been significant advancements in the field of corneal surface
reconstruction since limbal stem cells have been investigated. This has led to the
introduction of many effective types of surgery being made available across the globe.
Promising research and studies have shown limbal allograft and limbal autograft
surgeries to be some of the most efficient types to treat ocular surface disorders. So far,
limbal stem cells have restored vision to many blinded by ocular surface disorders and
given them the opportunity to live a better life. The worker in a factory that received an
ocular burn, the child from a third world nation with vitamin A deficiency, and the beach
lover that didn’t wear sunglasses and damaged her corneal surface all faced a bleak
future before the introduction of limbal stem cell transplantations. By continuing to
explore the vast potential of these limbal stem cells, further uses and applications can
be discovered. The full potential of limbal stem cells and their astonishing healing
properties has yet to be unearthed.
References
Burman, S., & Sangwan, V. (2008). Cultivated Limbal Stem Cell Transplantation for
Ocular Surface Reconstruction. Clinical Ophthalmology, 2(3), 489-502.
Charukamnoetkanok, P. (2006). Corneal Stem Cells: Bridging the Knowledge Gap.
Seminars in Ophthalmology, 21, 1-7.
Dua, H.S., & Azura-Blanco, A. (2000). Limbal Stem Cells of the Corneal Epithelium.
Survey of Opthalmology, 44, 415-425.
Meller, D., Pires, R.T.F., & Tseng, S.C.G. (2002). Ex Vivo Preservation and Expansion of
Human Limbal Epithelial Stem Cells on Amniotic Membrane Cultures. Br J
Ophthalmol, 86, 463-471.
O’ Sullivan, F., & Clynes, M. (2007). Limbal Stem Cells, a Review of their Identification
and Culture for Clinical Use. Cytotechnology, 53(1-3), 101-106.
Ozdemir, O., Tekeli, O., Ornek, K., Arslanpence, A., & Yalcindag, N.F. (2004). Limbal
Autograft and Allograft Transplantations in Patients with Corneal Burns. Eye, 18,
241-248.
Pfister, R.R., (1994). Corneal Stem Cell Disease: Concepts, Categorization, and
Treatment by Auto-and Homotransplantation of Limbal Stem Cells. The Contact
Lens Association of Opthalmologists, 20, 64-72
Tsai, J., Li, L.,& Chen, J. (2000). Reconstruction of Damaged Corneas by
Transplantation of Autologous Limbal Epithelial Cells. The New England Journal
of Medicine, 343, 86-93.
Li,W., Hayashida, Y., Chen, Y., Tseng S. (2007). Niche regulation of corneal epithelial
stem cells at the limbus. Cell Research, 17, 26-36.
The number below will change with each revision. These numbers are simply indicative
of the amount of improvement required at this point. When you receive a 9 or greater,
the review is ready. DrT
6/10