Fig. 10.1
Split fixation. Humphrey visual field (10-2) from a patient demonstrating inferior split fixation and inferior paracentral defect in the left eye. Reproduced with permission from Practicing Ophthalmologists Learning System. American Academy of Ophthalmology, Copyright© 2014–2016
10.2.1 Topical and Medication Therapy
Topical medical therapy is usually is the first line of treatment in NTG patients, especially in the pre-perimetric and early stages of NTG. If there are no contraindications to a specific topical drug class (allergic reactions, bronchospasm, cardiac disease, etc.), topical therapy is initiated with single or combination drugs. Typical maximum therapy is a combination medication (beta-blocker and alpha-agonist (timolol/brimonidine) or beta-blocker), combined with a third-line agent carbonic anhydrase inhibitor (CAI) (dorzolamide) and a prostaglandin analog at bedtime (latanoprost). Topical beta-blockers have been debated as a less efficacious first line of treatment in patients. A study conducted out of the Early Manifest Glaucoma Trial showed that betaxolol combined with selective laser trabeculoplasty (SLT) had little reduction in IOP in patients with a baseline IOP of 15 mmHg or less [13]. In addition, oral beta-blockers may mask elevated IOP in true POAG patients. With the postulated vascular factors that may contribute to NTG, carbonic anhydrase inhibitors or alpha-agonists may be of increased benefit, especially with the postulated neuroprotective role of the latter [14, 15]. Miotic agents can be used as a last line of therapy; however, polypharmacy should be monitored in these patients as it may cause difficulty with compliance and surface irritation. Oral CAIs are rarely given to NTG patients, as IOP is relatively low even prior to surgical intervention. Oral medications can be reserved for further lowering of IOP prior to surgical intervention if necessary.
If topical or systemic IOP-lowering medications do not adequately control the IOP and risk of progressive visual field loss is imminent with advancing glaucomatous optic neuropathy, or difficulty with compliance of the medical regimen is documented, surgical intervention is pursued.
10.2.2 Intraocular Pressure Targeting
The acceptable and appropriate level of IOP varies from patient to patient. In most instances, target IOP is determined from the Collaborative Normal Tension Glaucoma Study Group finding that a reduction of visual field progression from 35 to 12 % was correlated with a decrease in IOP at least 30 % from baseline. Consideration of other risk factors such as thin central corneas and the presence of disc hemorrhages may lead the surgeon to consider earlier surgical intervention if progression is observed [16, 17]. In addition, women, older age, and history of migraine headaches showed increased progression, with two-thirds of all patients showing signs of progression after 7 years [2].
10.2.3 Preoperative Patient Considerations
As with any intraocular surgery, preoperative assessment of the well-being and life expectancy of the patient should be accounted for in the decision to proceed with surgery. Since NTG patients often have vascular comorbidities, length of the surgery and anesthesia consideration should be discussed with the anesthesiologist and the patient prior to the intervention. Prior to proceeding with surgery, it is important to discuss with the patient goals, expectations of the surgery, complications, and importance of follow-up visits, as postoperative management of the surgical site is imperative and is not without failure.
10.3 Surgical Technique
10.3.1 Anesthesia
Topical anesthesia is a safe and effective alternative to retrobulbar anesthesia for glaucoma surgery and allows the surgeon to monitor a patient’s pain response to rare but devastating complications, such as suprachoroidal hemorrhage [18–20]. Topical anesthesia is becoming more commonplace in anterior segment surgery, and the procedures discussed below can be routinely performed without retrobulbar injections, peribulbar injections or general anesthesia, which all carry significant potential risk (intra-arterial injection, intrathecal injection, globe perforation, extra-ocular muscle paralysis, atrophy, and retrobulbar hemorrhage).
Depending on surgeon preference and individual surgical efficiency, topical anesthesia can range from 15 to 60 min (Table 10.1) with additional re-administration to obtain an adequate desired effect. With the use of these analgesics, blitz anesthesia (topical plus intracameral and anterior subTenon locally administered anesthesia) has been proven to be safe and effective in anterior segment surgery [21].
Table 10.1
Topical anesthesia for anterior segment surgery
Agent (trade name) | Concentration (%) | Onset of action | Duration (min) |
|---|---|---|---|
Lidocaine (xylocaine) | 1, 2, 4 | 4–6 min | 30–60 |
Proparacaine | 0.5 | 30 s | 15 |
Tetracaine | 1 | 30 s | 25 |
10.3.2 Trabeculectomy with Mitomycin-C for Normal Tension Glaucoma
The treatment of choice in NTG patients is trabeculectomy with adjunct mitomycin-C (MMC). Trabeculectomy alone has been shown to control IOP in primary open-angle glaucoma patients with ocular tensions only below 22 mmHg. In the same study, less than (1/5th) 17 % of patients with NTG treated with trabeculectomy and no adjunct antimetabolite therapy achieved a target IOP less than 30 % of baseline [22]. Patients with NTG require lower target IOPs and are at greater risk for failure; therefore, the use of intraoperative MMC should be considered for use in all cases for better long-term success [23].
10.3.3 Surgical Steps for Trabeculectomy with Adjunctive Mitomycin-C
1.
Obtain informed consent.
2.
Administer adequate anesthesia as appropriate for patient.
3.
Preparation of the eye with 5 % betadine directly into the fornices.
4.
Place eyelid speculum (preference to a temporal hinged-speculum, wire, or turn-knob).
5.
Place and secure clear corneal traction suture 1 mm from limbus at the superior aspect of the cornea. (7-0 vicryl or 6-0 silk on a spatulated needle.)
6.
Create a small opening in the conjunctiva and Tenon capsule at the limbus (in the presence of conjunctival scarring) or 1 mm posterior to the limbus.
7.
Inject 1.5 cm3 of 2 % lidocaine with epinephrine beneath the conjunctiva and Tenon capsule to create a bleb of moderate size. (Preservative-free lidocaine can be used if there is concern for exposure to intraocular contents. Epinephrine provides a longer duration of action.)
8.
Massage the subconjunctival anesthetic in a posterior direction, gently rolling a cotton swab from limbal edge toward the optic nerve posterior to disperse the agent of choice. (This also in creates a dissection plane for aqueous flow once the sclerostomy has been made and after conjunctival closure.)
9.
Create a 5.5 mm superior (superotemporal or superonasal) fornix-based conjunctival peritomy. (In the absence of preexisting conjunctival scarring, create with a 1-mm conjunctival skirt of tissue remaining at the limbus; in the presence of preexisting conjunctival scarring, create the peritomy directly at the conjunctival/limbal junction.)
10.
Gently dissect into sub-Tenon space toward the optic nerve, using a gentle spreading technique with blunt tip ophthalmic surgical scissors. Care should be taken when handling the conjunctiva to avoid fraying or button holes.
11.
Obtain hemostasis with cautery if necessary.
12.
Mark the eye for flap creation remove strikethrough with a caliper.
13.
With a super sharp blade, create a 3 × 2.5 mm partial thickness rectangular scleral flap. The flap should be approximately 1/2 to 2/3 the thickness of the entirety of the sclera in that location.
14.
Gently dissect anteriorly into clear cornea with a 57-blade (or flap/crescent blade of choice). Do NOT enter the anterior chamber at this point. Application of MMC may be compromised if this occurs.
15.
Apply desired concentration of MMC directly to bare sclera. Take precaution to avoid medication exposure to epithelium.
16.
Remove sponge(s) and copiously irrigate with balance salt solution.
17.
Create a paracentesis.
18.
Enter the anterior chamber within the previously made plane of the scleral flap.
19.
Create a sclerostomy with a corneoscleral punch within the anterior base of the sclerostomy.
20.
Perform a superior surgical peripheral iridectomy. (Cautery through the sclerostomy to the iris may be necessary.)
21.
Ensure flow through the sclerostomy with irrigation of BSS from the temporal paracentesis.
22.
Close the flap with 10-0 nylon suture to the desired flow rate. Recommended closure: single interrupted 10-0 nylon in an anatomical clockwise position of flap; releasable 10-0 nylon in an anatomical clockwise position of flap (see instructional Video 10.1).
23.
In an alternating locking, non-locking fashion, create a water-tight conjunctival closure with a recommended 9–0 vicryl suture on a blood vascular needle.
24.
Deepen the anterior chamber with BSS to create elevation of the bleb and to ensure that it is water-tight.
25.
(Optional) Inject viscoelastic material into the anterior chamber to prevent postoperative hypotony. Step 25 is recommended in cases with previous longterm use of ocular hypotensive agents.
Table 10.2 outlines key surgical steps in the procedure. Modifications to the surgical procedure are adjusted based on patient-specific factors (Table 10.3).
Table 10.2
Key points for trabeculectomy surgery with mitomycin-C in normal tension glaucoma patients
• Use of topical/subconjunctival anesthesia |
• Fornix-based conjunctival flap with 1 mm skirt at base (in the absence of previous conjunctival scarring) |
• Adjunctive use of MMC: 0.4 mg/mL for 2 min |
• Releasable flap suture (10-0 nylon) |
• Running, interlocking closure of wound (9-0 vicryl on blood vascular (BV) needle) |
Table 10.3
Preoperative and intraoperative special considerations
Preoperative | Intraoperative |
|---|---|
• Avoid uncontrolled IOP elevation | • Adjust scleral flap resistance precisely |
• Avoid uncontrolled hypertension | • Avoid hypotony with viscoelastics |
• Minimize blood pressure dips | • Consider placing a releasable suture |
• Check IOP in first few hours |
10.3.4 Antimetabolites in Glaucoma Surgery
Antifibrotic agents have been used as adjunctive therapy for three decades to prevent fibrosis and scarring associated with glaucoma surgical failure. In a meta-analysis of five studies comparing intraoperative use of MMC and 5-fluorouracil (5-FU), MMC adjunctive therapy reached target IOP of less than 30 % of baseline and sustained the IOP-lowering effect better than those treated with 5-FU [24].
Use of MMC and 5-FU in NTG patients can improve success of target IOP and delay visual field progression in NTG patients [25–27]. In most cases of NTG, the use of MMC is during surgical intervention with trabeculectomy, as these patients typically have endured multiple medications and are at risk of failure due to episcleral fibrosis, and require lower IOPs for control of progression [28].
5-Fluorouracil (5-FU) is reserved for postoperative subconjunctival injection and increases the success of trabeculectomy in patients who are at higher risk for fibrosis, as well as those requiring extremely low IOPs. Please see Table 10.4 for a comparison between 5-FU and MMC.
Antifibrotic agent | Mechanism of action | Delivery route | Dosage | Frequency | Side effects |
|---|---|---|---|---|---|
MMC | Antineoplastic antibiotic (from Streptomyces caespitosus) | Intraoperative SubTenon’s sponge | 0.2–0.4 mg/mL | Varies based on patient; usually between 1 and 4 min | Hypotony maculopathy |
5-FU | Pyrimidine analog; blocks DNA synthesis via inhibition of thymidylate synthesis in fibroblasts | Subconjunctival injection | 5 mg in 0.1 mL | As needed, daily if necessary to prevent scarring | Corneal toxicity, bleb leak |
However, adjunct therapy to increase success of surgery is not without risk. Postoperative hypotony and infection can ensue with the use of MMC, and 5-FU injections can induce corneal epithelial toxicity and wound leaks [29–31].
Topical nonsteroidal anti-inflammatory drops have shown an inhibitory effect on wound healing can be considered in patients intolerant to other anti-scarring postoperative therapies [32].
A newer alternative to antimetabolite treatment during surgery is placement of collagen material to promote structured fibroblast growth along a biodegradable matrix. Used in place of antimetabolites, the implant material has not yet been proven to be as effective in maintaining and achieving target IOP as previously discussed adjunctive agents with traditional trabeculectomy surgery [33].
10.4 Postoperative Management
Optimal postoperative care is key in helping to achieve success in filtering surgery. Achieving target IOP, preventing postoperative complications, and maintaining a viable filtering bleb requires frequent visits in the weeks after surgery. All topical tension-lowering medications should be discontinued after the filtering surgery to promote aqueous production. The eye should be treated with anti-inflammatory and antibiotic eye drops. Topical ointment can aid in patient comfort with suture irritation.
Steroid management (Table 10.5) should be based on clinical signs of inflammation. An anterior chamber reaction is generally present after surgery and typically resolves faster than injection of the conjunctiva at the surgical site. Steroid taper should be tailored to resolution of the conjunctional injection at the operative site to favor surgical success and help to decrease bleb fibrosis.
Table 10.5
Steroid management in postoperative trabeculectomy for normal tension glaucoma
Steroid management in postoperative trabeculectomy with MMC for NTG |
|---|
• Taper based on clinical signs of inflammation |
• History of severe postoperative uveitis |
• Patient at high risk of bleb failure
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