2. Abnormalities of Shape of Cornea
ECTATIC CONDITIONS OF CORNEA
- Keratoconus
- Keratoglobus
- Pellucid Marginal Degeneration
- Keratoconus posterior
3. KERATOCONUS
Keratoconus (conical cornea) is a progressive non-
inflammatory bilateral (85%) ectatic condition of cornea in
its axial part.It usually starts at puberty and progresses
slowly.
4. Etiopathiogenesis
lt is still not clear. Various theories proposed so far label it
as developmental condition, degenerative condition,
hereditary dystrophy and endocrine anomaly.
Essential pathological changes are progressive thinning and
ectasia which occur as a result of defective synthesis of
mucopolysaccharide and collagen tissue.
5. Clinical features
Symptoms. Patient presents with a defective vision
primarily due to progressive myopia and irregular
astigmatism, which does not improve fully despite full
correction with glasses.
• Vision becomes progressively more blurred and distorted
with associated glare, halos around lights, light sensitivity
and ocular irritation.
• Visual loss occurs primarily from irregular astigmatism and
myopia, and secondarily from corneal scarring.
6. Signs
The hallmark of keratoconus is central or paracentral stromal
thinning, apical protrusion of anterior cornea and irregular
astigmatism. The cornea thins near the centre and
progressively bulges forwards, with the apex of cone always
being slightly below the centre of the cornea. Following signs
may be elicited on examination:
1 Window reflex on cornea is distorted.
2. Placido disc examination shows irregularity of the circles
7. 3. Slit lamp examination may show thinning and ectasia
of central cornea, opacity at the apex, Fleischer’s ring at
the base of cone seen under cobalt blue filter, and folds in
Descemet and Bowman’s membranes. Very fine, vertical,
deep stromal striae (Vogt lines) which disappear with
external pressure on the globe are peculiar feature.
8. 4. On retinoscopy a yawning reflex (scissor reflex) and high
oblique or irregular astigmatism is obtained.
5. On distant direct ophthalmoscopy an annular dark
shadow ( due to total internal reflection of light) is seen
which separates the central and peripheral areas of cornea
(oil droplet reflex).
6. Munson’s sign, i.e. localised bulging of lower lid when
patient looks down is positive in late stages.
9. 7. Keratometry. Normal average keratometric values are 45D. In
keratoconus, kerarometric values are increased and based on it
the severity of keratoconus is graded as:
Mild ( <48 D),
Moderate (48-54 D),
Severe (>54 D).
8. Corneal topography, i.e. study of shape of corneal surface, is
the most sensitive method for detecting early keratoconus, Forme
Fruste refers to the earliest subclinical form of keratoconus
detected on topography.
10. Morphological classification
Depending upon the size and shape of the cone, the keratoconus is of three
types:
- Nipple cone has a small size ( <5 mm) and steep curvature.
- Oval cone is larger (5-6 mm) and ellipsoid in shape.
- Globus cone is very large (>6 mm) and globe like.
Complications
Keratoconus may be complicated by development of acute hydrops due
to rupture of Descemet’s membrane. The condition is characterized by
sudden development of corneal oedema associated with marked
defective vision, pain, photophobia and lacrimation.
11. Associations
Keratoconus may be associated with:
Ocular conditions, e.g. ectopia lentis, congenital
cataract, aniridia, retinitis pigmentosa, vernal
keratoconjunctivitis (VKC), atopic keratoconjunctivitis,
Leber’s congenital amaurosis, floppy eyelid syndrome and
corneal endothelial dystrophy.
Systemic conditions, e.g. Marfan’s syndrome, atopy,
asthma, eczema, hay fever. Down’s syndrome,Ehlers-
Danlos syndrome, osteogenesis imperfecta and mitral
valve prolapse.
12. Treatment
Treatment modalitie include:
Spectacle correction may improve vision in early cases. However,
later in the course of disease the falling vision may not be
corrected by glasses due to irregular astigmatism.
Contact lenses (rigid gas permeable) usually improve the vision in
early cases. In early to moderate cases, a especially designed
scleral contact lens {Rose-K) may be useful.
lntacs, the intracorneal ring segments, are reported to be useful in
early to moderate cases by the flattening affect.
Corneal collagen cross linking with riboflavin (CXL or C3R) and UV-
A rays may slow the progression of disease.
Keratoplasty may be required in later stages. Deep anterior
lamellar keratoplasty (DALK) or penetrating keratoplasty (PK) may
be performed.
13.
14. KERATOGLOBUS It is a familial and hereditary bilateral
congenital disorder characterised by thinning and
hemispherical protrusion of the entire cornea. It is
nonprogressive and inherited as an autosomal recessive
trait. It must be differentiated from congenital
buphthalmos, where increased corneal size is associated
with raised intraocular pressure, angle anomaly and/or
cupping of optic disc.
15. Pellucid Marginal Degeneration This is a painless
bilateral corneal thinning affecting the inferior cornea,
usually from 4 to 8 o’clock positions with no
conjunctival injection, lipid deposition or corneal
vascularization. The epithelium is intact and there is
no anterior chamber reaction. The cornea above the
area of thinning becomes ectatic, with myopic
‘against-the-rule’ astigmatism. The thinning may
slowly progress and rarely be associated with acute
hydrops.Pellucid marginal degeneration may
occasionally occur in conjunction with keratoconus.
16. KERATOCONUS POSTERIOR In this extremely rare condition, there
is slight cone like bulging of the posterior surface of the cornea. It
is non-progressive.
CORNEA PLANA, i.e. flat curvature or cornea which may occur in
patients with severe hypotony and phthisis bulbi and rarely as a
congenital anomaly.
MEGALOCORNEA – Megalocornea is when the horizontal diameter
of cornea of adult size at birth or 13mm or greater after the age
of 2 years
MICROCORNEA – The horizontal diameter is less than 10mm since
birth
17. Corneal Opacity
The word ‘corneal opacification’ literally means loss of
normal transparency of cornea, which can occur in many
conditions. Therefore, the term ‘corneal opacity’ is used
particularly for the loss of transparency of cornea due to
scarring.
Corneal Transparency maintained by
- Tear film
- Avascularity of Cornea
- Collagen fibres of stroma
- Corneal dehydration maintained by endothelium
- Normal IOP
18. Causes
1 Congenital opacities causes can be remembered by pnemonic (STUMPED):
• S Sclerocomea
• T Tear in Descemet’s membrane, Congenital glaucoma, birth trauma.
• U Ulcer: HSV, bacterial.
• M Mucopolysaccharidosis, Mucolipidosis.
• P Posterior corneal defect: Peter’s anomaly, posterior keratoconus.
• E Endothelial dystrophy: Congenital hereditary posterior polymorphous.
• D Dermoid
2. Healed corneal wounds.
3. Healed corneal ulcers.
19. Clinical features
Corneal opacity may produce loss of vision (when dense opacity covers
the pupillary area) or blurred vision (due to astigmatic effect).
Types of Corneal Opacity
Depending on lhe density, corneal opacity is graded as,
NEBULA
MACULA
LEUCOMA
20. 1 Nebular corneal opacity
It is a faint opacity which results due to superficial scars
involving Bowman’s layer and superficial stroma
A thin, diffuse nebula covering the pupillary area
interferes more with vision than the localised leucoma
away from pupillary area.
Further, the nebula produces more discomfort to patient
due to blurred image owing to irregular astigmatism than
the leucoma which completely cuts off the light rays.
21. 2. Macular corneal opacity
It is a semi-dense opacity produced when scarring involves
about half the corneal stroma
22. 3. Leucomatous corneal opacity
leucoma simplex. It is a dense white opacity which results
due to scarring of more than half of the stroma
23. 4. Adherent leucoma
It results when healing occurs after perforation of cornea
with incarceration of iris
24. 5. Corneal facet - Sometimes, the corneal surface is
depressed at the site of healing (due to less fibrous tissue);
such a scar is called facet.
6. Kerectasia - this condition, corneal curvature is
increased at the site of opacity (bulge due to weak scar).
25. Anterior staphyloma
An ectasia of pseudocornea (The scar formed from organised
exudates and fibrous tissue covered with epithelium) which
results after total sloughing of cornea, with iris plastered
behind it is called anterior staphyloma
26. Secondary changes in corneal opacity which may be
seen in long-standing cases including
Hyaline degeneration,
Calcareous degeneration,
Pigmentation and
Atheromatous ulceration.
27. Treatment
1 Optical iridectomy. It may be performed in cases with central
macular or leucomatous corneal opacities, provided vision
improves with pupillary dilatation.
2 Phototherapeutic keratectomy (PTK) performed with excimer
laser is useful in superficial (nebular) corneal opacities
3 Cosmetic-coloured contact lens gives very good cosmetic
appearance in an eye with ugly scar having no potential for vision. Presently,
this is considered the best option, even over and above the tattooing for
cosmetic purpose.
4 Keratoplasty provides good visual results in uncomplicated
cases with corneal opacities, where optical iridectomy is not of
much use.
28. 5. Tattooing of scar.
It was performed for cosmetic purposes in the past. It is suitable only
for firm scars in a quiet eye without useful vision.
For tattooing Indian black ink, gold or platinum may be used.
To perform tattooing, first of all, the epithelium covering the opacity is
removed under topical anaesthesia (2% or 4% xylocaine).
Then a piece of blotting paper of same size and shape, soaked in 4%
gold chloride (for brown colour) or 2% platinum chloride (for dark
colour) is applied over it.
After 2-3 minutes, the piece of filter paper is removed and a few drops
of freshly prepared 2% hydrazine hydrate solution are poured over it.
Lastly, eye is irrigated with normal saline and patched after instilling
antibiotic and atropine eye ointment. Epithelium grows over the
pigmented area.
33. Keratoplasty also called corneal grafting or corneal transplantation,
is an operation in which the patient’s diseased cornea is replaced by
the healthy clear cornea.
Indications:
Corneal scars or opacity
Ectatic corneal diseases not amenable to refractive correction by
spectacles or contact lenses
Corneal oedema not responding to medical treatment
Corneal ulcer
Anterior staphyloma
34. Donor tissue:
Donor corneas are harvested from cadaveric donors within 6–8
hours after death, sometimes up to 12 hours after death in
countries with cold climates or if the donor is refrigerated.
Types of Keratoplasty
Autokeratoplasty
Rotational
Contralateral
Allokeratoplasty
Penetrating Keratoplasty
Lamellar Keratoplasty (Anterior and Posterior Keratoplasty)
Small patch graft
35. Surgical technique of penetrating
keratoplasty
A- Excision of donor corneal
button
B and C- Excision of recipient
corneal button
D- Suturing of donor button into
recipient’s bed
E- Showing pattern of continuous
sutures in keratoplasty
F- Image of a patient eye with
interrupted sutures in
keratoplasty
36. Complications
1 Early complications.
Flat anterior chamber
Iris prolapse
Infection
Secondary glaucoma
Epithelial defects and
Primary graft failure.
2. Late complications.
Graft rejection
Recurrence of disease and
Astigmatism.
