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Surgical slit lamp helpful in corneal dissection, anterior segment surgery
The following surgical cases demonstrate the usefulness of this device in the changing field of ophthalmic surgery.
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 Thomas John |
The earliest evidence of image magnification utilizing a magnifying glass dates back to the Book of Optics that was published by Ibn al-Haytham (Alhazen) in 1021.
Starting in 1860, loupe magnification was used for surgical intervention. However, it was not until 1921, when Nylén of Sweden transformed an ordinary laboratory microscope into a monocular operating microscope for ear surgery, that the first operating microscope was introduced. In the same year, Holmgren first used the binocular operating microscope.
These technological advances led to the development of true microsurgery. Ophthalmologists were the second group of physicians to use microscopes in the operating theater during the 1940s. In 1953, highly professional operating microscopes were made available, and in the 1960s, developments in the areas of microsurgical techniques, microinstruments and suture materials took place.
Paradigm shift
The modern day operating microscope provides a wide range of magnifications and has the capability of zoom function, all of which are controlled by the foot pedals. This allows the surgeon’s hands to be free to perform surgery.
This change in the way eye surgery was done forced eye surgeons to use all four limbs during surgery. Thus, the introduction of the binocular operating microscope resulted in a paradigm shift in the way ophthalmic surgeons performed eye surgery.
The operating microscope has served us well over several decades. During this time, much of the surgical procedures in the anterior segment required only gross, full-field views with depth perception for corneal and cataract surgeries. This scene is currently in a process of continual change, as surgeons are slowly moving away from full-thickness penetrating keratoplasty to selective tissue corneal transplantation.
Selective tissue corneal transplantation replaces diseased parts of the cornea with similar donor tissue while retaining the healthy portions of the patient’s cornea. With the increasing use of lamellar keratoplasty techniques, corneal surgeons require the ability to visualize the corneal thickness and perceive the various corneal depths while doing surgery.
In the absence of a cross-sectional view of the cornea, surgeons in the past have injected air into the anterior chamber and viewed the dark band between the reflective surface of the air-bubble within the anterior chamber and the corneal surface blade edge as the estimate of the remaining corneal thickness. This technique is laborious and, at best, a rough estimate of the corneal thickness.
Currently, we need the ability to directly view the corneal thickness in real-time with the aid of a slit view, much like the way we examine the anterior segment in a clinical setting. In order to meet this surgical need, the surgeon may consider the use of an intraoperative surgical slit lamp. Over time, the use of an intraoperative surgical slit lamp would possibly become the gold standard for ophthalmic microsurgery.
Other areas of continued development in surgical viewing of the operative field include the ongoing experiments with video-assisted systems to further miniaturize the instruments for magnification and to gain a more comfortable working position for the surgeon.
In this article, I present various surgical cases with the use of an intraoperative surgical slit lamp, demonstrating the usefulness of such a device in our changing field of ophthalmic surgery, from PK to selective tissue corneal transplantation.
Case 1 (Figure 1)
In Descemet’s stripping automated endothelial keratoplasty (DSAEK), there is a surgical concern as to fluid being trapped within the donor-recipient interface that may contribute to postoperative donor disc detachment. Various techniques have been described to eliminate potential fluid within this interface. One technique is to create “venting” incisions on the recipient cornea up to and inclusive of the interface, without detaching the donor corneal disc. Four such incisions are usually made per eye.
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Images: John T |
These incisions are routinely made on all cases undergoing DSAEK because the interface is not visible with the conventional view provided by standard operating microscopes. With the use of a surgical slit lamp, the interface is clearly visible and there is no fluid seen in the donor-recipient interface. Hence, no venting incisions are required. Surgical slit lamp is beneficial in DSAEK surgery.
Case 2 (Figure 2)
A patient presents with a large Descemet’s membrane detachment that occurred as a complication of clear cornea phacoemulsification. This Descemet’s membrane detachment caused significant corneal edema and blurred vision after the cataract surgery. A large air bubble is used to attach the Descemet’s membrane to the inner stromal surface of the patient’s cornea. A Lindstrom roller was used to compress the corneal dome to facilitate a uniform attachment of the Descemet’s membrane to the inner corneal stroma.
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Unlike the conventional, full-field view that does not allow adequate visualization of the Descemet’s membrane-stromal interface, the slit view of the surgical slit lamp confirms good, uniform attachment of the Descemet’s membrane in this case and intraoperative clearance of the corneal stromal edema that is visible by the decreasing stromal thickness seen with the surgical slit beam.
Case 3 (Figure 3)
Two weeks after an uneventful clear cornea phacoemulsification, cortical lens remnants left behind in the superior,
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equatorial portion of the lens capsule migrated inferiorly and presented as cloudy lens material in the retro-IOL potential space between the IOL and the posterior lens capsule, causing blurred vision.
A bimanual surgical technique is used to clear the cortical lens remnants without damaging the posterior lens capsule. The surgical slit lamp view helps to assess this region during surgery.
Case 4 (Figure 4)
Figure 4 displays the surgical steps in managing pseudophakic bullous keratopathy caused by a closed-loop IOL. The procedure includes PK, removal of the closed-loop IOL, automated anterior vitrectomy and scleral-fixated posterior chamber IOL.
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The junction between the donor corneal graft and the rim of the recipient cornea is important because there may be a step in which the edge of the donor graft may be slightly higher as compared with the edge of the recipient cornea causing surface irregularities. Additionally, very tight sutures may also contribute to irregularities at this donor-recipient circular junction. The slit beam allows proper evaluation of this junction. In this case, a uniform, smooth junction is seen, confirming a good endpoint for this surgery.
Case 5 (Figure 5)
This is a case of advanced keratoconus with significant corneal thinning, apical cone scarring and contact lens failure (per history), and the patient was referred for surgical management. The surgical options include full-thickness PK, use of intrastromal Intacs (Addition Technology) and lamellar keratoplasty.
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Of these three surgical options, lamellar keratoplasty may be considered as the best option because the patient’s endothelium is retained and no prosthetic device is introduced into a very thin cornea. However, total lamellar keratoplasty is a challenging surgical procedure, in which the surgeon must dissect the cornea and remove all of the corneal stroma from a very thin cornea and not cause any tear or Descemet’s membrane perforation.
This challenging technique becomes even more difficult with the full-field view provided by the conventional operating microscopes. The surgical slit lamp provides direct visualization of the corneal thickness throughout the surgical procedure and helps prevent or decrease the chance of Descemet’s membrane perforation.
Case 6 (Figure 6)
DSAEK is becoming the preferred surgical procedure over PK in the surgical management of corneal endothelial decompensation. However, DSAEK can also result in endothelial graft rejection and graft failure. This is a case of DSAEK graft failure after graft rejection that did not fully resolve with standard medical management. Hence, a disc-exchange is required that is superior to a full-thickness PK.
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Figure 6 demonstrates the surgical steps in this case of DSAEK disc-exchange. The surgical slit lamp view aids in fully assessing the donor-recipient interface, and no venting incisions on the recipient cornea is required (see also Figure 1).
Case 7 (Figure 7)
This is an example of an intraoperative donor disc that “flipped” or unfolded in the wrong direction during a DSAEK procedure, resulting in the donor endothelium facing the host inner corneal stroma. Removal of the donor disc and reinsertion with the proper orientation are required. It may be difficult in such a case to clearly confirm the endothelial surface from the stromal surface using the full-field view afforded by conventional operating microscope.
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Here, the surgical slit beam clearly identified the endothelial surface from the stromal surface, and on evaluating the cut-edge of the donor disc, the cut margin of the Descemet’s membrane is clearly seen, which further confirms the endothelial side of the donor disc.
Case 8 (Figure 8)
This is an extremely rare case presentation for surgical management. This patient had undergone an uneventful artificial cornea, namely a keratoprosthesis. About 6 months after the surgery, the patient sees a cornea specialist with a history of redness and eye pain. The patient is then referred with a bandage soft contact lens.
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On clinical exam, the patient has no cornea and no keratoprosthesis. Removing the bandage contact lens provides direct visualization of the iris surface and the pupil with vitreous in the papillary space. The patient’s eye is immediately patched after antibiotic application, and he receives intravenous prophylactic antibiotics and underwent emergency eye surgery. The surgical slit beam aides the surgical procedure, especially during the iris membrane peeling and anterior segment reconstruction and a large diameter PK.
Surgical pearls and tips
Take advantage of the surgical slit lamp when available. Use both the broad-beam and narrow-beam as needed, along with the retro-illumination, by changing the angle of the beam to facilitate viewing various anterior segment tissues during surgery as demonstrated in the case examples provided.
Conclusion
The use of an intraoperative surgical slit lamp provides the visualization that is needed for the newer corneal dissection techniques and anterior segment surgery. Selective tissue corneal transplantation of the cornea requires meticulous lamellar dissections of the cornea without tearing or perforating the Descemet’s membrane during such procedures. The surgical slit lamp is helpful in these advanced corneal and anterior segment surgical procedures.
References:
- Haeseker B: [Microsurgery, a ‘small’ surgical revolution in the medical history of the 20th century]. Ned Tijdschr Geneeskd. 1999;143(16):858-864.
- John T. Surgical Techniques in Anterior and Posterior Lamellar Corneal Surgery. New Delhi, India: Jaypee Brothers Medical Publishers; 2006.
- John T. Step by Step Anterior and Posterior Lamellar Keratoplasty. New Delhi, India: Jaypee Brothers Medical Publishers; 2006.
- John T. Selective tissue corneal transplantation: A great step forward in global visual restoration. Expert Rev Ophthalmol. 2006;1:5-7.
- Tamai S. History of microsurgery – from the beginning until the end of the 1970s. Microsurgery. 1993;14(1):6-13.
Thomas John, MD, is a clinical associate professor at Loyola University at Chicago and is in private practice in Tinley Park and Oak Lawn, Ill. He can be reached at 708-429-2223; fax: 708-429-2226; e-mail: tjcornea@gmail.com. Dr. John has a small financial interest in some of the surgical instruments and is a speaker for ASICO.
