34th Annual Scientific Meeting proceedings

Microsurgery has essential differences compared with general surgery, from the use of specific instruments, the need for magnification, tissue tactics as well as suturing technique, and knot construction.^1,2  Ophthalmic tissue tactics study how the forces are applied during dissection, cut, and suture of the ocular tissues as well as the interaction between instruments and ocular tissues.³

The purpose of this presentation is to discuss the fundamentals of surgical manipulations applicable to the cornea and conjunctiva and provide an overview of ocular microsurgical instruments and their optimum utilization.

INSTRUMENTS
Tissue-instrument interaction and dealing with frustration
When performing microsurgery we deal with the frustration and fatigue of the surgeon. One of the basic concepts to prevent the situation is understanding how the force is applied.^1,3 In ocular surgery, instruments are held in pencil grip compared to general surgery where palm grip is a common feature. While palm grip is designed to allow movement of wrists and elbows providing power, it sacrifices control and it should be avoided in delicate ophthalmic procedures. In pencil grip, instruments are held between your first and second fingers, and fingertips are used to control and rotate the instrument. However, the instrument is less stable in our hand, therefore it is crucial to avoid the tendency to grasp the instruments with excessive pressure because this will block our movements and lead to fatigue with tension in the hand and forearm (Fig 1). On the other hand, this excessive finger pressure will affect to instrument efficiency itself causing splaying on the tips and resulting in loss of control and stability (Fig 2).²

OCULAR TISSUES
Every tissue has its own mechanical characteristics (elasticity, sectility, cohesion) which determine how the surgical instruments are specifically applied.⁴

INCISION and DISSECTION
The term sectility refers to the ability of the tissue to be separated by the microsurgical instruments. The higher the sectility the more easily it can be divided which helps with incision construction.⁵  

CORNEA. The cornea has a lamellar structure which influences incision and dissection. When sectioning, its lamellar disposition induces lamellar deflection of incision (tends to deviate to become more parallel to the lamellae). Even if the cornea has high sectility, it can be increased by immobilizing the tissue. While incising it is important to stabilize the globe near the limbus with the fixation forceps and the blade is positioned perpendicular to the plane of the cornea while pushing it in the direction of the point of stabilization.^2,5 Corneal knives and microsurgical blades (eg. 64,69 Beaver blades) are commonly used for corneal incisions.²

Corneal dissection (keratectomy) is performed using specific instruments which allow a precise intralamellar dissection. Corneal dissectors instruments include Martinez corneal dissector and crescent corneal knife. They are designed to allow the blade to be oriented parallel to the corneal lamellae during dissection. In lamellar dissection modulation of tissue sectility becomes crucial. To increase the sectility of the fibers between two corneal lamellae we should increase the tissue tension focally which depends on how the corneal flap is held while the interlamellar fibers are divided.^2,3,5 

CONJUNCTIVA. From a surgical perspective, it is composed of three layers:  The epithelial layer, the sub-epithelial fibrous layer called Tenon´s capsule (TC), and the episcleral space (surgical landmark for gonioimplant or eviscerations).³

When the conjunctiva is incised while grasped with a forceps, the tissue will deform and be displaced which will affect the shape and position of the incision when released.³  

Conjunctival dissection can be performed on a superficial or deep plane. Superficial dissection separates the conjunctival epithelium from the TC using a combination of blunt and sharp dissection. TC is a very resilient tissue and its presence in a conjunctival graft is responsible for contraction and surgical failure. TC visualization and dissection are important in this procedure. Application of irrigation solution to the conjunctival cut margin makes this distinction easier because TC will appear white when hydrated.¹ Conjunctival local sectility can be enhanced either by making the fibers tense with forceps (stretching the fibers) or with scissors itself.³ Tenotomy scissors: ring handled (Stevens) or spring handle (Wescott) are essential for dissecting the conjunctiva from TC, they have blunt tips and may be straight or curved. ^2,3,5 

SUTURE
CORNEA. The cornea should be stabilized with a 0.12 corneal fixation forceps at the exact position the needle pass and not adjacent to this position. The two teeth side of the forceps are used on the stroma and the single tooth side on the epithelial side.⁶ The needle should be inserted perpendicular to the cornea surface and sutures placed  90% deep in the stroma keeping symmetry. Shallow sutures result in internal wound gape.⁶ There are different options for knot creation including a 3-1-1 closure or Surgeon’s knot (probably the most commonly used in equine ophthalmology) and the slipknot technique (1-1-1). The conjunctiva has an inherent tendency to curl which is important to take into consideration while suturing because can lead to epithelial inclusion cyst formation using counterpressure will help to prevent it.¹

SUTURE MATERIAL CHOICE
Spatulated needles are crucial in corneal surgery as permit the needle to pass through the lamellar structure of the cornea, which allows for accurate placement with minimal disruption. Needles are available in different curvatures, for corneal surgery,  small needles with 3/8 to 1/2 curve are predominantly used.⁵ To improve directional control and avoid bending delicate ophthalmic needles, the needle should be held at approximately mid-shaft, and the needle shaft and be oriented perpendicular to the jaws of the needle holder. The use of suturing forceps is extremely helpful in suture material handling and knot creation.^1,3,4,6 Nonabsorbable suture has the advantage of causing less tissue reaction, but it requires suture removal. Absorbable material includes polyglycolic acid, and polyglactin while the most common nonabsorbable suture is monofilament nylon.²

Figure 1

Figure 2

References

1. Macsai MS, Fontes BM. Trauma suturing techniques. In: Ophthalmic Microsurgical Suturing Techniques. 1st Edition. (M. S. Macsai (Ed.), Springer-Verlag Berlin Heidelberg, pp. 61 - 70, 2007.
2. Herring IP. Corneal Surgery: Instrumentation, Patient Considerations, and Surgical Principles. Clinical Techniques in Small Animal Practice 18:3; 152-167,2003;.
3. Eisner G. An Introduction to Operative Technique: Tissue Tactics In: Springer Berlin, Heidelbergin (editor) Springer-Verlag Berlin Heidelberg  p: 38-118,1980.
4. Larry Benjamin. The Physics of Wound Closure, Including Tissue Tactics. In: Ophthalmic Microsurgical Suturing Techniques. 1st Edition. (M. S. Macsai (Ed.), Springer-Verlag Berlin Heidelberg, pp. 1 -8, 2007.
5. Nasisse MP. Principles of Microsurgery. Veterinary Clinics of North America: Small Animal Practice Volume 27, Issue 5, September p: 987-1010, 1997.
6. Pagano, L.; Shah, H.; Al Ibrahim, O.; Gadhvi, K.A.; Coco, G.; Lee, J.W.; Kaye, S.B.; Levis, H.J.; Hamill, K.J.; Semeraro, F.; Romano, V. Update on Suture Techniques in Corneal Transplantation: A Systematic Review. J. Clin. Med. 2022, 11, 1078. https://doi.org/10.3390/jcm11041078 

Figure 2  Reference 1

Macsai MS, Fontes BM. Trauma suturing techniques. In: Ophthalmic Microsurgical Suturing Techniques. 1st Edition. (M. S. Macsai (Ed.), Springer-Verlag Berlin Heidelberg, pp. 61 - 70, 2007.