Introduction

Ocular surface dysfunction is the final common pathway that occurs as a result of an imbalance of ocular surface protective mechanisms. Each protective mechanism has its specific role, be it mechanical and/or physiological. Externally, the eyelids act as a physical barrier for protection of the ocular surface, and with each blink it distributes the tear film. Meanwhile, the corneal and conjunctival epithelia provide the biodefense system against microorganisms and proteolytic enzymes. The tear film is crucial, since it lubricates, protects and nourishes, as well as provides a smooth optical refractive surface. As in an orchestra, each component must function in concert to create a harmonious (and healthy) whole. For example, poor epithelial adherence to the basement membrane can lead to recurrent corneal erosion; lagophthalmos can lead to exposure keratopathy; these can all be exacerbated by the loss of corneal sensation and dry eyes.

When conventional medical therapy fails and/or secondary complications (such as persistent epithelial defect, scarring) occur, surgical intervention needs to be considered. The primary goals are to increase lubrication, to assist healing and epithelial adherence, to remove visually significant opacities and to restore sight with minimal side effects. This chapter reviews the current knowledge on various surgical procedures that assist in the protection and stabilization of the ocular surface in a variety of diseases.

History

In 1986, McLean and MacRae observed that recurrent corneal erosion (RCE) often followed superficial corneal trauma but was not seen after deep stromal laceration.¹ In light of this, they described the technique of anterior stromal puncture (ASP) for the treatment of RCE, which employed a 20G needle at the slit lamp to make multiple punctures through loose epithelium and Bowman’s layer into the anterior stroma. This created a more secure bonding of the epithelium to the underlying basement membrane (BM), Bowman’s layer, and stroma. This treatment has been shown to be effective, particularly in post-traumatic corneal erosions.

Indication

The therapeutic aim of ASP is to enhance epithelial adhesion to the BM by microscopic, superficial scar formation. In RCE, the cause is thought to be failure of the wounded epithelial cells to adhere to the underlying stroma. This could be secondary to weak hemidesmosomal attachment, reduplication of the BM, the action of metalloproteinases,² and/or disruption of type VII collagen fibrils.³

ASP is a well-accepted treatment for RCE.1,4,5 ASP induces reactive subepithelial fibrosis or production of extracellular matrix proteins, both of which may be responsible for increased adhesion of the epithelium.⁶ Success rates of up to 80% have been reported in recalcitrant RCE.^1,4,5

While phototherapeutic keratectomy (PTK) has also been shown to be effective, there are advantages of ASP over PTK. ASP can be easily performed in the office or outpatient setting with simple, inexpensive equipment and causes minimal discomfort. Moreover, there is a low risk of inducing visually significant scarring and changes in refraction.

Recently, ASP was reported to be used for RCE after laser in situ keratomileusis (LASIK), which helped in resolving secondary diffuse lamellar keratitis.⁴ However, performing ASP immediately after LASIK may cause flap displacement and must be used judiciously.

Procedure

Anterior stromal puncture (ASP) is performed under topical anesthesia. Multiple superficial punctures are placed less than 0.5 mm apart in the affected area with a bent 25G needle attached to a 1- or 3-mL syringe. The needle can be bent at the tip with a needle holder to allow only superficial penetration into the cornea. Fluorescein can be instilled to define the affected area. Treatment is extended at least 1 mm into the normal epithelium bordering the lesion. Following the procedure, a bandage contact lens (BCL) is placed, and antibiotics drops are given until complete re-epithelialization. Usually, when ASP is begun, a much larger area of poorly adherent epithelium becomes visible.

ASP can also be performed with a short-pulsed Nd:YAG laser.⁷ The Nd:YAG laser (1.8–2.2 mJ) is focused at the BM zone after epithelial debridement. Spots are placed in rows approximately 0.20–0.25 mm apart. The advantage of laser over needle puncture is that the laser puncture is more uniform, shallow and translucent. There may also be less corneal scarring, so the procedure can be repeated and can be used closer to the visual axis.⁷

Contraindications

Anterior stromal puncture may result in subepithelial scars, and its use is not advisable if the erosion encroaches on the visual axis since the resulting scar may result in glare and a reduction in vision. In addition, if performed over the pupil, ASP may induce multifocal scars and irregular topographic changes. In general, however, the scarring is minimal and has little effect on vision.

Key Surgical Points

Complications

One of the major concerns with regard to the safety of ASP is corneal perforation. To address this concern, Rubinfeld and Laibson designed a specially bent needle for use on a disposable handle.⁵ An insertion depth of 0.1 mm was found to be sufficient to cause a therapeutic, fibrocytic reaction.⁶

Another concern is scarring, due to deep stromal penetration, which may affect vision, especially if the visual axis is involved. Smaller-gauge needles have been used to minimize scarring but deeper incisions were reported with 27G or 30G needles.

ASP can be a safe and effective therapy if performed under a magnified view at the slit lamp.

History

Occlusion of the nasolacrimal outflow tract was first described by Beetham in 1935.⁸ He reported resolution of dry eye in eight eyes with filamentary keratitis with electrocautery or diathermy to occlude the puncta. In 1975, Freeman⁹ proposed the use of punctal plugs to provide a reversible blockade of the nasolacrimal tract at the punctum. Semi-permanent and permanent punctal plugs are now widely used and are available in a range of sizes to ensure a good fit.

Indication

The principle behind punctal occlusion is the increase of the aqueous component of the tear film by blocking tear outflow and retention of both natural and artificial tears on the ocular surface. It has been shown to improve symptoms of lacrimal insufficiency. Tamponade is the most popular method, because surgery is not required and it is reversible.

Patients with severe keratoconjunctivitis sicca with or without underlying systemic collagen vascular disease often require permanent punctal occlusion. Punctal occlusion also plays a beneficial role in aqueous tear deficiencies secondary to ocular surface conditions, such as ocular cicatricial pemphigoid, Stevens–Johnson syndrome, and Sjögren syndrome.10,11 Dry eye secondary to reduced reflex tearing found in neurotrophic keratitis can also be effectively managed with this procedure. Finally, punctal occlusion may be beneficial in patients with dry eyes, due to increased evaporation from an exposed ocular surface. This may occur with lagophthalmos, exophthalmos seen with thyroid conditions, and following blepharoplasties. Other than dry eye syndromes, punctal occlusion has been shown to improve contact lens comfort and also may be helpful in the management of superior limbic keratoconjunctivitis.¹²

Punctal occlusion can dramatically improve the quality of life in many patients with moderate cases of dry eyes and can prevent visual loss in patients with severe cases of dry eyes.

Procedure

Contraindication/Cautions

Punctal occlusion is not indicated for all patients who have symptoms of dry eye. Many mild to moderate cases can be managed with the use of topical lubricating drops. Dry eye symptoms may manifest as a result of improperly fitted contact lenses; in these cases, a proper fitting will usually resolve the symptoms. Many commonly used oral medications with antihistaminic or anticholinergic properties can cause reversible ocular dryness. As such, punctal occlusion is not indicated when ocular dryness is a temporary condition.

Key Surgical Points

Complications

Punctal plugs can cause ocular discomfort and complications,15,16 such as punctum enlargement, loss or migration or extrusion of the implant, epiphora, pyogenic granuloma, local inflammatory reaction to silicone, dacryocystitis, and canaliculitis.^16,17

Granuloma formation is thought to be caused by local stimulation by the plug. Intracanalicular plugs are associated with higher rate of granulation tissue formation in the lacrimal tract when, compared with other forms of punctal plugs. Cases have been reported in which plug migration inside the lacrimal passage resulted in peripheral inflammations and infections, requiring surgical removal.¹⁸

Epithelial irritation caused by the exposed portion of the plug coming into contact with the cornea and conjunctiva may occur. Removing the plug or placing the plug with one of a different configuration may help.

History

The laser–tissue phenomenon of photoablation was first demonstrated in 1983 by Trokel and Srinivasan,¹⁹ who were working on the ultraviolet 193-nm excimer laser. Its potential role in refractive and therapeutic corneal surgery was quickly recognized. The excimer laser underwent extensive preclinical trials before it was applied to human eyes, and it is now being used for photorefractive keratectomy (PRK), LASIK and PTK.

Excimer laser PTK utilizes 193-nm wavelength ultraviolet light to break the molecular bonds in corneal tissue, in turn ablating the anterior stroma in a highly predictable fashion. It was approved by the FDA in 1995 for the treatment of visually significant anterior corneal pathologies, namely superficial corneal dystrophies, epithelial basement membrane dystrophy (EBMD) with irregular corneal surfaces, corneal scars and opacities.²⁰

Advantages

The main advantages of PTK over mechanical superficial keratectomy (SK) include precise tissue ablation with minimal damage to the surrounding tissues, a smooth residual bed for corneal re-epithelialization, and repeatability of the treatment. Compared to lamellar or penetrating keratoplasty (PKP), it is also less invasive, with more rapid visual recovery. PTK can be performed before or after PKP and does not impair the prognosis of PKP.²¹

Disadvantages

Phototherapeutic keratectomy may ablate normal tissue at a different rate from scar tissue, which may result in an irregular surface. Hence, masking agents are often used to fill in any irregular troughs to achieve a smoother surface. In contrast, a surgical plane between normal and abnormal tissue is more readily identified during mechanical SK, which provides a better surgical dissection.

Indications

Phototherapeutic keratectomy is best utilized for corneal pathologies affecting the epithelium or anterior 10–20% of the corneal stroma. For safety reasons, the residual corneal bed thickness must be greater than 300 µm at the end of the procedure. The indications for PTK can be separated into four broad categories,²⁰ although they often overlap:

Contraindications

It is important to identify patients who have conditions that predispose them to delayed epithelial healing and who would not be suitable candidates for PTK. They include immunocompromised individuals and patients with anesthetic corneas, severe dry eyes or uncontrolled uveitis.²⁰ Others may require additional procedures prior to PTK, e.g. a patient with lagophthalmos secondary to paralytic ectropion may require ectropion repair first. Any deep corneal pathology requiring removal of more than 20–30% of corneal thickness may be more suitable for anterior lamellar keratoplasty rather than PTK. If there is significant thinning in the treatment zone, PTK may predispose them to ectasia and hence should be avoided.

Preoperative Assessment

All patients should be assessed carefully to determine suitability for PTK. There are four main areas that the surgeon should consider: (1) whether the corneal pathology is amenable to PTK treatment anatomically, (2) the patient’s healing ability after surgery, (3) whether the goal of the PTK treatment is achievable, and (4) tailoring a surgical approach to the pathology. As with all surgeries, it is important to establish realistic expectations with the patient. For example, for a patient with granular dystrophy, the goal of PTK is often not a crystal-clear cornea, but rather improvement in vision so that one could delay or even avoid keratoplasty.

Procedure

For PTK, the surgical technique varies depending on the characteristics of the pathology. This includes the size, shape, location, density and depth of the lesions.

The general principles are: