IC-34: Update in penetrating and lamellar keratoplasty techniques
(Part 1)
Practical Pearls in Penetrating Keratoplasty
INSTRUCTION COURSE
ESCRS CONGRESS
SEPTEMBER, 2012
Dr. Rishi Mohan
MD, DNB, MAMS, FRCSEd
The MM Eyetech Institute, New Delhi, INDIA
Significant advances in microsurgical techniques in penetrating keratoplasty have been made and longterm chances for clear grafts are 75%-85%. Astigmatism after PKP still remains a perplexing problem
and almost 10% of patients with clear grafts may not obtain useful vision because of high postoperative
astigmatism.
Many studies have been conducted to elucidate the factors responsible for the creation of excessive post
operative astigmatism. Average postoperative astigmatism after PKP is approx. 4-5 dioptres, regardless
of the differences in surgical and suturing techniques amongst the experienced graft surgeons and
despite the advances in microsurgical methods.
Factors which SIGNIFICANTLY influence post-operative refraction
1. Aphakics (prior to PKP) show increased astigmatism.
2. Regrafts show less than average astigmatism.
3. Suture removal (continuous) induces a reduction in hyperopia & results in generally steeper corneas
but changes in astigmatism are unpredictable.
4. 0.25 mm over sized grafts show decreased hyperopia but do not change post operative astigmatism.
Factors found to have minimal or no bearing on the astigmatism
1. Type or nature of host disease.
2. Whether lens extraction is combined with PKP or not.
3.
No relationship with vitreous loss during surgery in aphakic PKP or in combined procedures.
4. Recipient factors, such as age, sex, past medical history or similarities of astigmatism in bilateral
grafts.
5. Donor variables such as age, sex, right eye versus left eye, time till enucleation, duration of storage
and surgeon variables on different days have no correlation with postoperative astigmatism.
The major factor contributing to post operative graft astigmatism is the creation of an overly large and
oval recipient hole due to unequal pressures being applied to the cornea during trephination. The donor
button is punched from the endothelial side and is generally quite circular. Therefore, the problem is of
fitting a round button into an oval opening.
Oval Opening
Round Button
With an average ovality of 0.31 mm, an estimated 3.1 Dioptres of astigmatism would be generated by
this factor alone. It is thought that in aphakes, a less stable corneal ring may produce more ballooning
and distortion during trephination, so as to give an increased ovality to the recipient bed resulting in the
higher degree of astigmatism associated with aphakic keratoplasties. Obliquity in the trephination and the
mismatch in the cut profile of the donor (endothelial side punch) and the recipient (epithelial side
trephination), also generates astigmatism due to the tight suturing required to bring about posterior lip
apposition.
Methods suggested to overcome / prevent high post operative astigmatism
1. Use an oversized graft.
2. Use a trephine where the entire host cornea is visible so as to observe the central ballooning and
apply even pressure.
3. Use trephines which reduce the need for downward pressure when trephining the host cornea, thereby
reducing distortion eg. vacuum trephines, motorized trephines.
Various reports are available regarding the role of the suturing technique comparing continuous with
interrupted sutures and combinations thereof and the effect of subsequent suture removal.
Some
common findings summarized from these reports are as follows:-
1. Intraoperative keratometry, keratoscopy and suture adjustments make for significantly lesser post
operative astigmatism in the short-term. Long-term results may, however, be unpredictable.
2. Average keratometries show a steepening of approx. 1.0 D in 3-12 months after surgery which
can be only partly attributable to suture removal.
3. Techniques of combining interrupted with running sutures probably offer a better method for
astigmatism control as the changes can be monitored and suture removal done selectively.
4. Corneal topography as a guide to selective suture removal is better than keratometric control and
works best when the keratographic patterns are focal indentation, D-shaped and oval. If the mires
are disrupted or incomplete, topography is less informative .
In the developing world, corneas often have significant vascularisation at the limbus due to chronic
trachoma, conjunctivitis, pollution effects, dry eye, allergic conjunctivitis, meibomian gland disease and
a host of other lid and adnexal conditions. This effectively reduces the truly circular clear portion of the
cornea and makes for the production of excessive vascularisation, scarring and fibrosis in the region of
the suture knots. It, therefore makes good common sense to keep the number of suture knots to the
minimum which is a factor favouring the use of running sutures.
With regards to the donor material, the quality of tissue available, the lack of lustre and large pre-existing
epithelial defects on the donor button, often make it difficult to perform good intraoperative keratoscopy
and so suture adjustment during surgery can be difficult.
Practical pearls
1. Use a vacuum based Barron von Hessburg trephine for the recipient cut. This may increase cost
slightly but substantially reduces slippage (and, therefore, decentration), oblique cuts and precipitous
entry into the anterior chamber.
2. Use oversized grafts ~ 0.25-0.5 mm, (except in Keratoconus) where, preferably use a similar size
donor button till 7.0mm dia, 0.25mm oversize till 8.25mm dia and 0.5mm oversize donor for larger
grafts.
3. Use a
corneal punch (Cottingham) or the Barron punch with disposable trephine blades for
endothelial side punching with a Teflon block (again preferably vacuumised for better hold and
centration).
4. Generally, a combined continuous and interrupted suturing technique is preferred; usually 12
interrupted + 12 bite continuous 10-0, or 8 interrupted 10-0 + a torque and an antitorque 11-0
continuous suture ( 8 bites each). Keep the knots buried on the donor aspect as far as possible.
5. Attempt to perform suture adjustment on table, where possible, using a keratoscopic mires device /
safety pin / surgical keratometer.
6. Begin to do topography based selective suture removals (if interrupted sutures are placed) after 8-12
weeks and suture adjustments of the running suture beginning 6-8 weeks post op.
7. If 12 months after complete suture removal, there is still significant astigmatism (>4D), then one
may consider relaxing keratotomies / arcuate incisions (earliest 1 year post suture removal) or other
form of refractive surgery (LASIK etc).
Finally, any sweeping comment on postoperative astigmatism in PKP cannot really be made because
factors such as the trephining technique, tension, placement, length and depth of sutures, timing of the
post-PKP suture removal, variability and inequality in wound healing and other surgeon factors, vary
considerably. It is necessary for corneal surgeons to refine their techniques based on their individual
experiences and critically assess the outcome of their surgical approaches.
Tips on tissue handling in PKP
1. Protect the corneal endothelium at all times.
2.
Avoid stretching the donor while suturing (thus reducing Descemet’s folds and straite
keratopathy).
3.
Always hold the anterior edge of the cornea upto 2/3rd thickness, never full thickness.
4.
Grip the tissue edge perpendicularly to prevent torque while passing the needle.
5.
Use the side of the forceps with 2 teeth in the cut stromal area and the single tooth on the
epithelial surface, where possible.
Tips on suturing
1.
Hold needle at the junction of the anterior 2/3rd and posterior 1/3rd, close to the meeting of the
spatulated and rounded zones.
2.
Keep the flat of the needle parallel to the corneal lamellae with no tilt or angulation.
3.
The needle tip enters vertically, centripetal to the point of grasp of the forceps, and exits at 75%
depth posterior to the forceps. One can appreciate the ‘elastic’ resistance of the Descemet’s
membrane as the needle exits at the correct depth.
4.
Do not grasp the protruding needle end to prevent blunting; push it from behind till at least 1/3 rd
its length is jutting out. Take care the needle tip does not get touched.
5.
Don’t grasp or pull the nylon thread too tightly to avoid weak spots developing in the thread.
6.
The width of the bite on the donor side should be 0.8-1.0 mm and slightly more on the host side,
1.0-1.5 mm.
7.
Approximate the posterior edges of the tissues as closely as possible to minimize lambda effect.
Dr. Rishi Mohan,
MD DNB MAMS FRCSEd