Cornea plana 2 (CNA2) is a
congenital disorder that causes the
cornea to flatten and the angle between the
sclera
The sclera, also known as the white of the eye or, in older literature, as the tunica albuginea oculi, is the opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some crucial elastic fiber. In humans, and som ...
and
cornea to shrink.
This could result in the early development of
arcus lipoides, hazy
corneal limbus, and
hyperopia.
There is evidence that cornea plana 2 is caused by mutations in
KERA gene encoding ''
keratocan
Keratocan (KTN) also known as keratan sulfate proteoglycan keratocan, is a protein that in humans is encoded by the ''KERA'' gene.
Keratan sulfate proteoglycans (KSPGs) are members of the small leucine-rich proteoglycan (SLRP) family. KSPGs, par ...
''.
Cornea plana 2 is an
autosomal recessive
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
disorder.
Signs and symptoms
Cornea plana commonly presents as a flat
cornea, early-onset
arcus lipoides, low
anterior chamber depth, and an indistinct border between the
sclera
The sclera, also known as the white of the eye or, in older literature, as the tunica albuginea oculi, is the opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some crucial elastic fiber. In humans, and som ...
and
cornea due to a decreased angle between the two.
Although a small corneal diameter is anticipated, measuring it can be challenging because the scleral tissue overlaps the
cornea by a few millimeters. In the patients who have cornea plana, the
anterior chamber depth has been found to vary from 0.8 to 2.1 mm.
Moreover, high
hyperopia,
strabismus, microcornea, posterior embryotoxon, iridocorneal adhesions, iris lumps, iris wasting, and pupillary abnormalities can all be present.
Instead of
hyperopia,
myopia
Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include ...
has been identified in a few cases.
As many as 90 percent of cases have a bilateral presentation, which is linked to
sclerocornea
Sclerocornea is a congenital anomaly of the eye in which the cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts ligh ...
.
Finally, congenital
ptosis
Ptosis (from the Greek: πτῶσις 'falling', 'a fall', 'dropped') refers to droopiness or abnormal downward displacement of a body part or organ. Particular cases include:
* Ptosis (eyelid)
* Ptosis (chin)
* Ptosis (breasts)
* Visceroptosis, ...
has also been reported, and the absence of corneal protrusion is most likely the cause.
Diagnosis
Clinical presentation,
keratometry
A keratometer, also known as an ophthalmometer, is a diagnostic instrument for measuring the curvature of the anterior surface of the cornea, particularly for assessing the extent and axis of astigmatism. It was invented by the German physiologi ...
,
pachymetry
Corneal pachymetry is the process of measuring the thickness of the cornea. A pachymeter is a medical device used to measure the thickness of the eye's cornea. It is used to perform corneal pachymetry prior to refractive surgery, for Keratoconu ...
, and endothelial imaging are used to make the diagnosis.
Since the decreased refraction in the autosomal recessive form is more severe than in the autosomal dominant form, corneal refraction measurements can be used to differentiate between CNA1 and CNA2.
Histology is distinguished by
acanthosis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...
,
keratinization of the corneal
epithelium
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
,
Bowman's membrane
The Bowman layer (Bowman's membrane, anterior limiting lamina, anterior elastic lamina) is a smooth, acellular, nonregenerating layer, located between the superficial epithelium and the stroma in the cornea of the eye. It is composed of strong, ...
defects, and
stromal
Stromal cells, or mesenchymal stromal cells, are differentiating cells found in abundance within bone marrow but can also be seen all around the body. Stromal cells can become connective tissue cells of any organ, for example in the uterine mucosa ...
vascularization and scar formation.
See also
*
Cornea plana 1
Cornea plana 1 (CNA1) is a congenital disorder that causes the cornea to flatten and the angle between the sclera and cornea to shrink. This could result in the early development of arcus lipoides, hazy corneal limbus, and hyperopia. Cornea ...
*
Keratoglobus
Keratoglobus (from Greek: ''kerato-'' horn, cornea; and Latin: ''globus'' round) is a degenerative non- inflammatory disorder of the eye in which structural changes within the cornea cause it to become extremely thin and change to a more globular ...
References
Further reading
*
*
External links
The University of ArizonaEyeWiki
{{Congenital malformations and deformations of eye
Eye diseases
Congenital disorders of eyes
Autosomal recessive disorders