The basis of manual small incision cataract surgery is the tunnel construction for entry to the anterior chamber. The parameters important for the structural integrity of the tunnel are the self-sealing property of the tunnel, the location of the wound on the sclera with respect to the limbus, and the shape of the wound. Cataract surgery has gone beyond just being a means to get the lens out of the eye. Postoperative astigmatism plays an important role in the evaluation of final outcome of surgery. Astigmatic consideration, hence, forms an integral part of incisional considerations prior to surgery.

2. WOUND CONSTRUCTION IN MANUAL
SMALL INCISION CATARACT SURGERY
• basis of manual small incision cataract surgery is the tunnel construction
for entry to the anterior chamber.
• important for the structural integrity of the tunnel
• self-sealing property of the tunnel,
• the location of the wound on the sclera with respect to the limbus, and
• the shape of the wound.

3. HISTORY ….
• Self-sealing cataract incisions were mentioned by Kratz et al. in 1980 and by
Girard in 1984.
• Kratz thought of scleral tunnel as an astigmatic neutral way of entering the
anterior chamber.
• In 1984, it was shown by Thrasher et al. that a 9.0-mm posterior incision
induces less astigmatism than a 6.0-mm limbal incision.
• In 1990, Michael McFarland developed a sutureless incision
• Pallin described a Chevron shaped incision.
• During the same period, Singer popularized the frown incision.

4. SURGICAL LIMBUS
• Surgical limbus is a 2mm wide zone.
• For ease of description this zone can be divided into:
• Anterior limbal border is represented by insertion of conjunctiva into peripheral cornea, which overlies the
termination of Bowman’s membrane.
• Under microscope, anterior limbal border can be identified as a zone in clear cornea where fine conjunctival
vessels are terminating.
• Blue zone: Posterior to anterior limbal border, there is a blue zone which terminates in midlimbal line. This
zone extends for 1 mm superiorly and 0.8 mm inferiorly.
• Under microscope, blue limbal zone can be identified as bluish translucent area, after dissecting overlying
conjunctiva and tenon’s capsule from anterior limbal border
• Midlimbal line overlies the Schwalbe’s line which is termination of Descemet’s membrane. It is the junction
of blue and white zone of limbus.
• White zone: It starts at midlimbal line and extends for 1 mm and terminates in posterior limbal border.
This zone overlies the trabecular meshwork.
• Posterior limbal border: Posterior limbal border is situated 1mm posterior to the midlimbal line. It overlies
the scleral spur and iris root.
• The colour differences of the limbal region occurs because of interdigitation of the corneal fibers into scleral

5. SURGICAL LIMBUS

6. Surgical anatomy
External Incision
Scleral Tunnel
Scleral Pocket
Corneal Valve
Internal Incision
7.5 mm
6.5 mm
7.5 mm
1.5 mm
1.5 mm
The scleral tunnel has six aspects: size (i.e., the length of the tunnel), shape
(style), location, depth, width, and entry into the anterior chamber.

7. SQUARE INCISIONAL GEOMETRY
• Ernest et al. had proposed "square incisional geometry."
• This concept states that an ideal self-sealing wound has a length equal to its
width.
• means the length of the tunnel must be equal to or exceed the width of the tunnel,
it is a guideline and not a strict rule for surgical planning.
• In reality, however, the length (SIZE) is usually larger 6-7 mm than width (4mm )
because of the need to have expanded wound to allow the exiting nucleus.
a to e (length) and a to d (width) should be equal. This
demonstrates a square incisional geometry that
would ensure that the wound is self-sealing in nature

8. EXTERNAL INCISION
• The scleral groove external incision is initiated by the Bard-Parker knife with number 15
blade or razor blade on blade breaker handle .
• The anterior limit of the incision is 2-3 mm behind the limbus, and
• The width of the tunnel is the distance between the external scleral incision and the
internal corneal entry incision which should be at least 4 mm in size.
Dimensions of the scleral tunnel.
The width of the tunnel is the distance between the internal corneal
entry and the external scleral incision. In this diagram,
the width of the tunnel is c+L+S (should be about 4 mm)

9. CONCEPT OF ASTIGMATIC FUNNEL
• Paul Koch described the ‘Incisional Funnel’ indicating the astigmatic: neutral zone.
• corneal astigmatism is directly proportional to the cube of length of incision and inversely
proportional to the distance of the incision from the limbus.
• The incisional funnel is an imaginary pair of curved lines representing relationship between
astigmatism and incision lengths.
• The lines diverge from limbus, separating as the distance from the limbus increases.
• Incisions made within the funnel are free of astigmatism (astigmatically neutral)
Corneal astigmatism is directly proportional to the
length of scleral incision and inversely proportional to
the distance of the incision from the limbus.
Incisions made within incisional funnel are astigmatically
stable
The optimal length of scleral incision has been determined
to be 6-8 mm and a distance from limbus 2-3 mm.

10. Situation
If we shift the incision
Posteriorly
There is more tissue
trauma & Dissection
But it is less astigmatic
with Less tissue shag
But
The instruments tend to
go anteriorly
External Incision

11. External Incision
Shape
A frown incision
will open more
A straight
incision will open
less on posterior lip
depression
Chevron Incision is
Geometrically more stable
Back-cut Frown or the Chevron
Prevents tissue slip
Smile incision is a curvilinear incision which runs parallel to the limbus. With this incision, there is an
increased chance of corneal flattening after surgery in the vertical meridian with increased induced
astigmatism
Straight incision, as the name suggests, is a straight line incision about 2 mm away from the limbus. This
incision induces moderate flattening and consequently moderate astigmatism after surgery
Frown incision is difficult to make for a beginner. The blade that is used to make the initial groove has to
be made with one smooth movement of the hand. The base of the curve is about 2 mm from the limbus.
There is minimal induced astigmatism with this wound and is the preferred type for majority of the
surgeons
Chevron ‘v’ incision. This incision is quite difficult to make. The tunnel size in this incision is relatively
smaller. Hence, maneuvering a large nucleus through this would be difficult. However, this incision has
least/nil induced astigmatism
Blumenthal side cuts devised by Dr. Michael Blumenthal. This incision has a straight line and two
oblique cuts at its two ends. This increases the space in the tunnel for an easy delivery of the nucleus

12. Depending on Nuclear Size and Hardness
We decide the incisional length
Size
External Incision
The primary deciding factor in the length of the incision is always the grade of
cataract as well as size of nucleus and not the size of the intraocular lens (IOL) to be
implanted.
The length of the incision
(which is the distance
between the two ends, but
not along the curvature)
varies from
5 to 6 mm for cortical
cataract, and
7 to 8 mm for nuclear
sclerotic grade IV cataract.

13. Scleral Tunnel
The tunnel is dissected by
wriggling action forwards
one part must partly
overlap the next
Otherwise the tunnel will
be in multiple planes

14. Scleral Pocket
The scleral pocke dissection
Screwing motion action

15. Corneal Valve
If the internal incision is
more anterior the corneal
dissection will be more
For a bigger internal
incision it has to be anterior
A bigger internal incision with less corneal dissection
can be achieved if the incision is Curved.
The cornea is more curved
than the sclera so heel down
dissection with the splitter
prevents pre-mature entry

16. Internal incision
If the entry is not
parallel to the external
incision the internal
incision will run in the
wrong direction
If the internal incision
extends to the sclera
the corneal valve is lost
The initial entry should
be parallel to the
external incision and
limbus

17. The nucleus is usually
trapped in the tunnel. If
the scleral pockets are
inadequate
Scleral Pocket

18. 6.5 mm
7.5 mm
1.5 mm
1.5 mm
Scleral Pocket

19. The Cataract is not only wide
But also thick

20. The scleral pockets are like pleats
They accommodate not only
the breath of the nucleus
But also its thickness

21. Remember if we lift the upper lip we close the wound
If we press the posterior lip we open the wound

22. Our eye is curved like a Globe
Thecorneaismorecurvedthanthesclera
Since we start an incision
lightly initial external incision
is shallow
Due to the curvature of the
Globe the central incision
becomes deep
For the same reason
Peripheral incision
becomes shallow
So, we have a premature entry
in the centre
Or button hole in the corneal
periphery
The external incision guides
the sclerocorneal dissection

23. Scleral Spliting is started in the centre.
If premature entry
Occurs Visco
Reconstruction of the
AC.
The tunnel is dissected
In a separate plane

24. Button Holing
Occurs in the
Corneal periphery
The incision is shifted
To the other side
The scleral flap should neither be too thick nor be too thin.
A thin flap has a tendency to tear or give way to superior button-hole formation.
It is noteworthy that at every stage of tunneling, the tunneling blade should
remain "just visible" (0.25-0.3 mm deep) and no more.

25. SURGICAL VIDEOS

26. • The salient features of the tunnel construction are listed as follows:
• Scleral cauterization before tunnel construction reduces the risk of pre- and postoperative hyphema.
• Sharp tunnel instruments (such as the crescent knife and keratome) should be used to construct the tunnel. A
blunt keratome could cause stripping of Descemet's membrane.
• Only a correct sclerocorneal tunnel incision, at least 1-2 mm into the clear cornea, leads to a self-sealing wound.
• Stabilizing the sclera with toothed forceps makes tunnel construction easier. However, to avoid tunnel damage
and leakage, the forceps should not be used on the tunnel flap.
• With a half-thickness sclerocorneal tunnel incision, the direction of the crescent knife should always be parallel
to the sclerocorneal plane.
• Judge the depth of half-thickness sclerocorneal tunnel incisions by observing how clearly you can see the
crescent knife during the incision. If the crescent knife can be seen very clearly, this indicates that the scleral
layer is very thin and that the crescent knife might perforate to the outside (causing what is known as a button
hole).
• A button hole can be corrected by making a deeper frown incision and dissecting the tunnel in a deeper plane,
starting at the opposite side of the button hole.
• If the crescent knife is not visible during the incision, this indicates that you are working too deeply inside the
sclera; you may perforate towards the anterior chamber's angle (a "premature entry").
• A premature entry could lead to surgical complications, such as iris trauma or iridodialysis, iris prolapse, and a
tunnel that is not self-sealing.
• Manage a premature entry by starting a more shallow dissection at the other end of the tunnel. Suturing of the
wound is required at the end of surgery.

27. It is safe to have
A bigger incision and Stitches if required
Then to give a small one and cause tissue damage