This document discusses the corneal endothelium and techniques for assessing its health and function. The corneal endothelium is a single layer of hexagonal cells that maintains corneal clarity by pumping fluid out of the stroma. Assessment techniques described include specular microscopy, which examines cell density, morphology, and patterns at high magnification; confocal microscopy and anterior segment OCT for in vivo imaging; and ultrasound pachymetry to measure corneal thickness as an indicator of endothelial function. Common endothelial diseases like Fuchs' dystrophy and conditions affecting assessment are also reviewed.

1. Assessment of
corneal endothelium
R. SENTHIL PRASAD

2. What ?
• Monolayer of hexagonal cells – simple squamous type.
• Keeps the cornea in a relatively dehydrated state by
endothelial pump action.
• Also acts as a barrier to the
aqueous humor
• Endothelial cell density is highest at
birth - 6000 cells/mm2 & constantly
decreases with age
• Normal endothelial cell density is
between 2000 and 3000 cells/mm2
• The central endothelial cell density
decreases at an average rate of
0.6% per year in normal corneas.

3. • Lacks regenerative capacity.
• Endothelial cell loss results in enlargement- polymegathism;
and spread of neighbouring cells to cover any defective area
which alters the shape of endothelial cells – pleomorphism
• Endothelial decompensation occurs when cell density falls
below 500 cells/mm2

4. Why ?
• To study the normal endothelial morphology
• To learn about pathological changes that occur in corneal
endothelial diseases
• Pre-operative endothelial health
• High risk surgeries
• Comparing different techniques
• Effect of refractive surgeries on endothelium
• Assessment of donor corneal status before
transplantation.

5. How ?
• Specularreflectionusing slit lamp biomicroscopy
• Specular reflections are normal light reflexes bouncing off a
surface.
• The fundamental basis of specular reflection of light, dictates
that, on a convex reflecting surface (such as the cornea), there is,
for a given position of light source and observer, only a single
point will produce a specular reflection.
• Corneal epithelium – high reflectence
Corneal endothelium – low reflectence
• The light source should be placed 30˚
to one side & the microscope 30˚ to
the other side.

6. • Area of illumination should be kept as small as possible to
reduce extraneous reflected light.
• Highest possible magnification should be used.
• Best viewed monocularly.
• Guttae and keratic precipitates appear as non-reflective dark
areas.

7. Specular microscope
• Specular microscopy is the study of corneal layers under very
high magnification.
• Endothelial cellular shape, size, density & distribution can be
analysed.
• Light beam of specular
photomicroscope passes
through the cornea & it
encounters series of
interfaces between optically
distinct regions. Some light
is specularly reflected back
to the photomicroscope &
forms a image which is
captured.

8. • Types of Specular Microscopes
• 1. Clinical specular microscope
• Contact wide field : higher magnification & resolution
• Non-contact wide field : lower magnification & resolution
• 2. Eye bank specular microscope
• 3. Slit lamp attached
• Parameters analysed
• Cell density (CD)
• Co-efficient of variation of cell area (CV)
• Percentage of hexagonal cells (6A)

9. • Celldensity(CD)
• Number of cells present in a unit area
• Cell density alone cannot determine the stability of the
cornea.
• Insult to endothelium – decrease in cell density
• Cellshapevariations
• Cells with scalloped boundaries
• Round cells
• Square cells
• Triangular cells
• Pentagonal cells
• Alteration in cell shape has not been directly correlated with
changes in physiologic function of the affected cells.

10. • Co-efficientof variation(CV)
• Coefficient of variation of the cell area =
SD in cell area/average cell area
• Large CV – wide variety in cell sizes – higher polymegathism
• lower CV - more stable cornea
• Causes of polymegathism
long-term contact lens wear, diabetes, post cataract surgery, post
penetrating keratoplasty, keratoconus, inflammation & ageing.
• Diabetic patients show an
increase in endothelial cell
damage and polymegathism
with increasing duration of
diabetes

11. • Percentageofhexagonality(6A)
• Percentage of hexagonal cells is calculated as number of
hexagonal cells divided by the number of cells counted.
• The cornea with a low coefficient of variation and higher
percentage of hexagonality is implied to have a stable
endothelial monolayer - can withstand the trauma of surgical
procedure.
• Any cornea with more than 50% hexagonality and less than
30% coefficient of variation might be viable for
transplantation.

13. Eye bankspecularmicroscope
• Konan’s Eye bank specular microscope - high quality images of
the donor cornea.
• Rapid and accurate cell count, as well as other parameters
such as polymegathism and pleomorphism.
• Built in pachymeter to measure corneal thickness.
• Donor corneas must be warmed to room temperature for at
least 1 to 2 hours before evaluation to eliminate artifacts that
appear in the endothelium at low temperatures.
• Examination can be done even with the corneas being kept
inside storage media, thus minimising chances of
contamination.
• Warming the preserved corneas will not affect the endothelial
viability.
• Donor endothelial cell density should be greater than at least
1500 cell/mm2 to ensure sufficient density for corneal
deturgescence.

15. Confocal microscope
• Confocal literally means ‘having a common focus’.
• Confocal microscope’s imaging system collects light only from
a small spot on the specimen, thus giving very high resolution.
• Single point of tissue is
illuminated by a point light source
& simultaneously imaged by a
camera in the same plane.
• Instantaneous illumination of
small areas of tissue with
numerous tiny spots of light
which are reconstructed to form a
full field of image with high
resolution & magnification.

16. • In vivo confocal microscopy (IVCM) is an noninvasive imaging
and diagnostic tool, which enables morphological and
quantitative analysis of ocular surface microstructure.
• On IVCM, corneal endothelium is identified as a layer of
bright cell bodies with dark cell borders. The nuclei are rarely
recognizable.
• Advantages:
- Can be used in patients with corneal
oedema. (whereas specular microscopy
cant be used)
- Can scan the entire cornea (so does
contact specular microscope)
• Disadvantages
-Needs trained skilled person to use
(Specular microscope is easier to use and
does not require a learning curve)

17. Types of confocal microscope
• Tandem scanning confocal microscope (TSCM)
• Scanning-slit confocal microscope (SSCM)
• Laser scanning confocal microscope (LSCM)
OS
OD

18. Anterior segment OCT
• Corneal thickness is a indirect qualitative measure of
endothelial well being as pathology of endothelium leads to
increase in corneal thickness.
• AS-OCT can detect corneal thickness which is comparable to
ultrasound pachymetry.
• Also useful in pre-operative & post operative evaluation of
cornea in corneal refractive surgeries.
• Ultra High Resolution(UHR)-OCT showed that DM in patients
with Fuchs’ dystrophy appeared as a thickened band of 2
opaque lines: smooth anterior line and wavy and irregular
posterior line with areas of localized thickening
• To assess the graft tissue in post operative endothelial
keratoplasty patients.

20. Ultrasound pachymetry
• Indirect way of assessing endothelial pump mechanism.
• Ultrasonic waves are emitted which bounce back from the
posterior surface of cornea.
• Mean central corneal thickness – 540±30 µm
• CCT > 700 µm is indicative of endothelial decompensation.

21. Fuchsendothelialcornealdystrophy
• Bilateral accelerated endothelial cell loss.
• Corneal guttata
• Endothelial decompensation -> Stromal oedema -> epithelial
oedema (advanced cases) -> Microcysts & bullae formation
• Treatment:
- Topical hypertonic saline, IOP reduction, Hair dryer
- Bandage contact lens, lubrication & anterior stromal puncture
- DSAEK or DMEK
Corneal endothelial disorders

22. • Metaplasia of endothelial cells.
• Associated with iris
abnormalities, glaucoma &
alport syndrome
• Three forms – PPCD1-3
• Often asymptomatic
• Subtle vesicular, band like or
diffuse endothelial lesions
• Treatment not required
Posteriorpolymorphouscorneal
dystrophy

23. • Focal or diffuse thickening of DM with endothelial degeneration
• Two types : CHED1 & CHED2
• Symptoms : Photophobia & watering
• Signs : corneal clouding & thickening; variable visual impairment
• Treatment : Lamellar or penetrating keratoplasty
Congenitalhereditaryendothelialdystrophy

24. • Use of sharp instruments.
• Avoiding contact of instruments with corneal endothelium
using meticulous technique.
• Adequate maintenance of AC throughout procedure
• Soft shell technique during nucleus delivery
• Low phaco energy
• IOL implantation with proper technique (reverse soft shell)
• Thorough AC wash with no residual nuclear fragments
• TASS prevention
• Post operative wound leak, choroidal detachment, pupillary
block, ciliary block, and suprachoroidal hemorrhage can cause
flat AC.
Techniquestominimiseendothelialdamageintra-operatively