Anterior Scleral Staphyloma
Being essentially avascular and acellular tissue, the sclera’s main role is tectonic, encasing the contents of the eye in a strong collagenous coat. Disease of the sclera that leads to a weakening of the structure are relatively rare. Inflammation is the most frequent underlying pathology (scleromalacia). Common other etiologies include high myopia, trauma and surgery [long cataract wounds previously, scleral buckling or repeat vitrectomies using a 20 g system nowadays]. Rarely, it is associated with therapy such as an intravitreal injection or trans-scleral laser application; finally, the condition may be congenital.
Discrepancy between the resistance of the sclera and the intra-ocular pressure (IOP) may lead to thinning and eventual bulging of the tissue. If this process involves the sclera alone, it is referred to as ectasia. If the underlying uvea is also affected, lining the bulging sclera, the condition is called staphyloma.
Smaller staphylomas usually do not require treatment, but a large anterior staphyloma should be treated to prevent eyewall rupture. This surgical approach is focused on anterior staphylomas induced by trauma, but the same basic treatment principles apply to staphylomas of other etiologies and will refer to certain differences as appropriate. Posterior staphylomas are not addressed such as that caused by high myopia, which is typically treated with removal of the internal limiting membrane and gas tamponade (hopefully prior to the development of a consequent macular hole) or, occasionally, by macular buckling.
Classification
Staphylomas are classified by their location or etiology. Anterior staphylomas are located in the anterior sclera and are primarily due to inflammatory or traumatic etiologies. Those over the ciliary body are called ciliary staphylomas; those between the ciliary body and the limbus are referred to as intercalary staphylomas (Fig. 1).
A ring staphyloma is an intercalary staphyloma that extends circumferentially to surround the cornea. Anterior staphylomas of inflammatory origin are typically secondary to rheumatoid arthritis, zoster, tuberculoma, etc.
Equatorial staphylomas result primarily from developmental or degenerative factors. They are frequently associated with chronic open-angle glaucoma and/or retinal detachment; they are often first discovered during retinal detachment surgery. Equatorial staphylomas rarely require scleral grafting; however, they can cause difficulties during scleral buckling.
Posterior staphylomas, in most instances, are also of developmental or degenerative causes. They are commonly located at the optic nerve head, and are accompanied by areas of pronounced choroidal atrophy. Posterior staphylomas are usually found in patients with high degrees of myopia; in one study, they were demonstrated in 37.7% of eyes with pathologic myopia.
Traumatic scleral staphylomas occur following severe ruptures or, more rarely, penetrating injuries (Fig. 2). While these may involve the equatorial region or posterior sclera, it is much more common for an anterior scleral trauma to cause a staphyloma clinically significant enough to require surgical repair. Most often these staphylomas occur in the setting of significantly and persistently elevated IOP. The tissue bulging tends to become a progressive process, particularly if accompanied by prolonged elevation of the IOP.
Preoperative Considerations
General Considerations and Management Principles
As a locus minoris resistentiae, staphylomas represent a weak structural part of the eyewall, susceptible to rupture with possibly devastating consequences. Additionally, anterior staphylomas may exacerbate existing glaucoma which, in turn, may initiate a vicious circle. The elevated IOP leads to progressive bulging of the sclera and further destruction of the angle structures. The aqueous outflow is further compromised, resulting in additional elevation of the IOP.
Surgical correction is aimed at restoring the structural integrity of the eyewall and reconstituting the normal curvature of the globe. Normalizing IOP should also be part of the overall management.
In most cases scleral grafting is the preferred method of treatment. Large staphylomas should almost always be treated in this fashion due to the risk of progressive anterior segment disorganization. In most patients, filtering surgery is recommended for treatment of concomitant glaucoma.
In most cases scleral grafting is the preferred method of treatment. Large staphylomas should almost always be treated in this fashion due to the risk of progressive anterior segment disorganization. In most patients, filtering surgery is recommended for treatment of concomitant glaucoma.
Preoperative Evaluation
Posterior staphylomas are detected by ophthalmoscopic examination or ultrasonographically. Equatorial staphylomas are usually not diagnosed before surgery is performed for a condition such as a retinal detachment or strabismus. Occasionally, however, equatorial staphylomas are visible through the conjunctiva when the eye is in extreme rotation.
Conversely, anterior staphylomas are readily discovered by their striking appearance. The sclera’s curvature is enhanced, which is best visualized when viewed from the plane of the staphyloma’s base. The most remarkable feature of the lesion is its bluish discoloration, resulting from colored bulge is noticed in the anterior sclera several weeks to months after injury as the sclera becomes increasingly thinner and the choroid becomes visible.
Patients without an obvious, local or general etiology explaining the presence of the staphyloma should undergo a thorough medical evaluation to identify any possible systemic inflammatory disease. Confirmation or exclusion of glaucoma by measuring the IOP and examining of the optic disk are also critical.
Indications and contraindications
Surgical intervention is an absolute indication if the staphyloma has ruptured or if rupture is imminent. Anterior staphylomas with elevated IOP should be treated in a timely fashion to prevent progressive anterior segment deterioration. Surgical repair may also be indicated for adequate cosmesis.
Equatorial staphylomas, discovered during surgery for other indications, require individual consideration. The decision whether treatment is necessary also depends on how the staphyloma affects management of the condition for which the surgery is performed. Often no specific treatment is indicated, but extra care must be taken to avoid scleral perforation during retinal detachment surgery (in any case but specially) in the presence of an equatorial staphyloma. If the history is suggestive or the surgeon is aware that the eye to be operated on for a retinal detachment has a staphyloma, vitrectomy and not scleral buckling should be performed; preferably, the vitrectomy is done using a transconjunctival approach with the smallest possible gauge at the greatest angle upon cannula insertion.
If perforation of a staphyloma is imminent in a blind but otherwise comfortable eye, scleral grafting should still be offered as an alternative to enucleation.
Surgical Techniques
Anesthesia
General anesthesia is performed to avoid the risk of applying significant pressure on the globe from retrobulbar or peribulbar block. External pressure may result in rupture of a thin staphyloma. Additionally, the procedure may be lengthy and other regions of the body may also be needed to be operated on to obtain donor material.
Graft materials
Although other materials are also available (periosteum, autologous periosteum, dura mater, etc), homologous sclera is the most commonly used one (Fig. 3). The material is stored in glycerin or alcohol or frozen in antibiotic solution for up to 3 months from the date of preservation until needed. If frozen sclera is used, it is first slowly thawed at room temperature or in a warm (37o C) water bath with gentle shaking; once thawed, the material should be refrigerated at 2-6oC and then used within 24 hours. Glycerin-dehydrated sclera may be used for up to 1 year from the date of preservation. It should be rinsed and soaked as described above for glycerin-preserved sclera.
Surface Preparation and Grafting
The procedure begins with complete removal of the conjunctiva overlying the staphyloma. Usually a limbal incision is chosen, allowing for the best closure after the graft has been placed. Wide margins of normal sclera should be exposed on all sides of the staphyloma. Throughout the entire surgery, great care must be taken when working in the area of the staphyloma to avoid puncturing the thin sclera and the underlying uvea.
It is very helpful to introduce bridle sutures in the adjacent muscles, making subsequent rotation of the globe more atraumatic. It has to be remembered that not only direct pressure (over the staphyloma), but by indirect pressure (exerted anywhere on the globe) can also lead to rupture by elevating the IOP. Once the conjunctiva has been adequately opened and the bridle sutures placed, light bipolar cautery may be applied to the area of the staphyloma, shrinking it to more closely approximate the normal contour of the eye. This maneuver is not without risks, so the surgeon has to be very cautious to avoid penetrating the sclera.
The defect is then measured and a donor graft is fashioned. The graft should be larger than the staphyloma by at least 2 mm on all sides of the defect. The donor scleral shell is then thoroughly inspected for defects. The area of grafting is chosen so as to match as much as possible the normal thickness and color of the patient’s sclera adjacent to the staphyloma. Pigment and any loose material are scraped from the donor using a sclalpel blade. At this time the sclera is also thinned where necessary to provide for a graft of uniform thickness. A neatly shaped and well-matched graft provides the best cosmetic result while maintaining good structural integrity.
The graft is then sutured into place with multiple interrupted sutures (Fig. 1). Over the sclera, we prefer 7-0 vicryl sutures because nylon sutures tend to protrude through the conjunctiva with time, causing irritation. The technique of suturing is critical; stretching the graft must be avoided. The graft becomes secure before the vicryl absorbs.
The sutures should enter the donor graft first, about 1 mm from the free edge and then enter the recipient sclera directly beneath its exit from the donor tissue. The sutures should exit the recipient sclera just outside the edge of the graft. The sutures are tied firmly yet not too tight so as to prevent stretching or distorting the graft. Multiple interrupted sutures are placed on all sides of the graft in order to provide a watertight seal over the recipient bed. In cases where the graft abuts the limbus, the graft is trimmed to follow the normal curvature of the limbus. 9-10 or 10-0 nylon sutures are used to attach the graft to the limbus/cornea. It is best to thin the graft further where it is to join the limbus to create a smooth junction between the graft and the cornea. Burying the knots is mandatory to prevent postoperative discomfort for the patient (Fig. 4A and B).
It is preferable to cover the graft, once sutured into place, with vascularized episcleral tissue. Meticulous closure of the conjunctiva follows (Fig. 5). If the graft joins the limbus, the conjunctiva is allowed to overlap the cornea by approximately 1 mm. This helps to prevent later exposure of the graft’s edge at the limbus. If the graft is well covered by vascularized tissue, there is a little chance of graft failure.
If medically uncontrollable glaucoma is also present, this should be treated at the time of scleral grafting. Depending on the individual case, trabeculectomy may be performed or a shunt (e.g. Ahmed valve) implanted. The site of the glaucoma procedure is dependent on the location of the staphyloma, and should be as distant as possible.
Dressing and Immediate Postoperative Care
Topical cycloplegic, antibiotic and corticosteroid therapy is usually sufficient to prevent infection and suppress an excessive inflammatory reaction. The IOP must be monitored and kept in the normal range. The eye does not have to be shielded after the first few days following surgery, but it has to remain protected from significant external pressure. Over a period of months, the graft becomes incorporated into the normal surrounding sclera, providing a tectonically sound and cosmetically pleasing result.
TECHNICAL ALTERNATIVES AND PITFALLS
Alternative Techniques
Depending on the size of the lesion and the degree of thinning, globe’s integrity can be restored by means other than grafting. Suturing with or without scleral resection, is the most commonly used option. The sutures approximate the opposite edges of normal sclera over the staphyloma. If not resected, the staphyloma bulges inward. Suturing is recommended if only a very small area of the sclera is involved in the staphyloma.
Other, previously used methods (surface diathermy, buckling) are much less commonly utilized today. With the increasing success rate of grafting, enucleation has also become less frequent, being performed usually for cosmetic reasons in blind eyes.
If sclera as a donor material cannot be used or for those who prefer alternative donor materials, a variety of homografts and autografts (fascia lata, aortic tissue, periosteum, etc.) are available. If the sclera is involved in a systemic disease (e.g. rheumatoid arthritis) or rejection of the donor sclera is expected, autogenous periosteum is recommended. Though it involves an additional surgical procedure on the patient, periosteum is not rejected, is less likely to melt away, and provides permanent strengthening of the weakened sclera.
Potential Problems
Common potential problems include pre-or intraoperative rupture of the staphyloma; suturing rather than grafting too large a staphyloma; improper choice of donor material; over-trimming of the donor tissue; improper suturing and failure to treat coexisting glaucoma.
Outcomes
With proper surgical technique and postoperative care, the tectonic success approaches 80% - although the etiology also plays an important role in determining the long-term outcome.
Complications and Their Management
Rupture of the staphylomas is the most dangerous complication. If possible, such a rupture should be treated by a surgeon experienced in posterior segment techniques. Tissue prolapse should be handled as required by the nature and extent of the prolapsed tissue. Accompanying retinal lesions have to be properly treated.
Postoperative complications include graft exposure and failure, and infection.
Prognosis and Results
In addition to the quality of the surgery, the ultimate anatomical success of surgical intervention for staphyloma is determined by the underlying disease. Localized staphylomas, regardless of etiology, have a good prognosis if treated properly. Staphylomas caused by certain severe local (e.g. high myopia) or systemic (advanced and progressive connective tissue disease) conditions are more difficult to treat and may have a much poorer prognosis.
The visual success is primarily determined by other factors such as macular pathologies (scar following open globe injury, etc.) or glaucomatous damage.
REHABILITATION/LONG-TERM FOLLOW-UP
If the staphyloma is localized, due to self-limiting nature, the patients do not require special follow-up once the donor tissue has healed. Patients with chronic inflammatory disease, however, have to undergo regular examinations to timely detect donor failure or development of new staphyloma.
Dr. Faisal Osmani
MD, PGD, Ophthalmologist
Eye Health Clinic
RETINA IMPLANT Alpha AMS
Like a camera in your eyes
The RETINA IMPLANT Alpha AMS is a subretinal implant. It contains a microchip, similar to a digital camera, which is implanted under the retina. In adult patients whose vision has been affected by retinal degeneration, the chip can help to partially restore functional eye sight.
One implan t, three components
The implantThe RETINA IMPLANT Alpha AMS is placed under the retina so that the function of the degenerated photoreceptors (rods and cones) can be replaced. The chip is only 3.2 x 4 mm in size with a height of 70 µm. It is equipped with 1600 photodiodes, which convert the incident light into an electrical signal. This signal is amplified and relayed via electrodes to the
retinal signal processing layers which are still functional. Following the natural optical path, the signal is then transmitted to the brain via the optic nerve.
There are a number of indications that causes the loss of retinal photoreceptors (rods and cones). The inner retina and optic nerve, however, still form an intact connection with the brain and do not lose their functionality. This is also the case in retinitis pigmentosa. Due to this lack of photoreceptors, the retina can no longer convert light into electric signals [via the photoreceptors], and thus no visual information can be sent to the optic nerve. The subretinal implant RETINA IMPLANT Alpha AMS is able to replace the functionality of the degenerated photoreceptors to a limited degree by way of electrical stimulation of the outer retinal tissue. As a result, information can be transmitted to the visual cortex of the brain through the optic nerve, thus generating visual images. The chip is only 3.2 x 4 mm in size with a height of 70 µm. It is equipped with 1600 photodiodes, which convert the incident light into an electrical signal. This signal is amplified and relayed via electrodes to the retinal signal processing layers which are still functional. From there, the signal follows the natural optical path through the optic nerve into the area of the brain (visual cortex), where the incoming information is interpreted and visual images are produced. By placing the implant under the retina, the patient is able to make use of their natural eye movements to see. A special camera for taking pictures outside the eye is not required.
The receiver and the control unit The components of the RETINA IMPLANT Alpha AMS implanted in the eye rely on an external power supply. The compact handheld device (15 cm x 9.2 cm x 2.8 cm) contains batteries and an electronic circuit that generates a magnetic alternating field in the transmitting coil (transponder D). It can easily be carried in a pocket. Consequently, energy is transmitted via induction through the skin to the receptor implanted behind the ear in the cranial bone, as long as the transmitting coil is magnetically coupled to the receiver coil. The current generated in the receiver coil is fed to the eyeball via a cable running under the skin to the temple. The current is passed through a thin conductor strip through the eye wall (sclera) to the microchip under the retina. The microchip can then be switched on and operated.
Visual acuity and visual fieldDue to the technical characteristics of the RETINA IMPLANT Alpha AMS, a theoretical maximum visual acuity of 0.07 (20/280) with a horizontal visual field of 13° is possible. The best visual acuity achieved so far by a patient with the RETINA IMPLANT Alpha AMS is 0.037 (20/546). The implant does not allow for colour-vision. However, some shades of grey are distinguishable.
EyesightPrevious patients used their eyesight mainly for orientation: sources of light from windows or lamps in rooms, street lanterns and road markings as well as the outlines of buildings in the outdoors are used.
Experiences we value.Since 2005, the current chip and the predecessor model have been implanted in 60 patients mostly in Europe (as of November 2016), 20 of those received the current version of the RETINA IMPLANT Alpha AMS.
The experience and feedback we receive from our patients inspire us to continue researching and developing this product.
However, we must also note that the users benefit to varying degrees from the RETINA IMPLANT Alpha AMS and that it is not possible to predict at this point how well a specific patient will see with the implant.
