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- Haemophilus influenzae type b
- Streptococcus pneumoniae
Trabeculectomy is the most common non-laser surgical procedure performed for treatment of all forms of glaucoma. It involves the fashioning of a fistula from the anterior chamber of the eye to the subconjunctival space. This allows for extra drainage of aqueous humour to the subconjunctival space. This produces a localised elevation of the conjunctiva in the area of the trabeculectomy called a “filtering bleb.” Antimetabolites may be used intraoperatively and perioperatively to increase the success of glaucoma filtering surgery by their action on wound healing. 5-Fluorouracil or mitomycin C is administered to the scleral flap during the procedure. Postoperatively; subconjunctival injections of 5-fluorouracil may be given. This is known as an augmented trabeculectomy.
Infective endophthalmitis is a recognised complication of glaucoma filtering surgery. It may occur in the early postoperative period or it may happen years after surgery. Another entity, possibly a precursor to endophthalmitis has been described as blebitis.1 Blebitis is an infection of the trabeculectomy bleb without vitreous involvement.
Clinical features of blebitis include pain, photophobia, conjunctival discharge, and severe conjunctival injection centred on an opalescent filtering bleb. A Siedel test may be positive (this indicates aqueous leakage from the bleb) and there may be an anterior chamber reaction. There is no vitritis.2
As many as one per 100 patients/year may develop infection of the bleb.3 Factors associated with increased risk of bleb related endophthalmitis include increased axial length, thin leaky bleb, conjunctivitis, upper respiratory tract infection, hibernal occurrence, trauma, and vitreous wicks.4, 5 With the increased use of antimetabolites in glaucoma surgery, the incidence of thin walled cystic blebs seems to be increasing.6 These blebs are more prone to leakage.7 Some studies conclude the incidence of bleb related endophthalmitis is higher when antimetabolites are used.8 This is more common with inferior limbal trabeculectomy.7, 8 However, some studies show equal incidence in augmented trabeculectomy and trabeculectomy without antimetabolite augmentation.5
There are few data available for the incidence of blebitis. In most reported cases conjunctival swabs were performed for culture and sensitivity, but organisms causing endophthalmitis may only be present transiently on the ocular surface. In many reports, ocular surface cultures came back positive for Staphylococcus epidermidis and S aureus, which may both be found on healthy normal eyes.
The microbiology of bleb associated endophthalmitis is different from other causes of endophthalmitis. Clinicians should not extrapolate the results of the Endophthalmitis Vitrectomy study to the post-filtration surgery endophthalmitis given the differing pathogenesis and unique spectrum of organisms.2 The most common organisms are Streptococcus species.6 The second most common is Haemophilus influenzae type b at over 23%.8 Of the streptococci, S pneumoniae may account for approximately 12%.9 Between them H influenzae type b and S pneumoniae probably cause more than 35% of blebitis and bleb associated endophthalmitis.
The treatment of endophthalmitis is expensive. It usually involves admission of the patient and frequent use of expensive drops as well as surgical intervention. Inpatient treatment for blebitis has been priced at US$892 (approximately £540) per 24 hours.10 This can work out to more than £5000 for a 10 day stay in hospital. Furthermore, the cost of follow up visits and the morbidity that is involved need to be taken into account. Frequently these patients have pre-existing visual compromise and an episode of endophthalmitis may result in partially sighted or blind registration, an individual disaster with wider social implications.
H influenzae type b vaccine is licensed for use in infants. However, its use is allowed in those patients considered to be at risk for invasive H influenzae type b disease such as sickle cell disease and those receiving treatment for malignancy.11 After the age of 13 months the vaccine is effective after a single dose. This vaccine has already shown benefit in ophthalmology by the dramatic decrease in the incidence of orbital cellulitis in immunised children.12 It consists of a capsular polysaccharide of H influenzae type b conjugated to a protein carrier. Side effects of the vaccine include fever, headache, malaise, irritability, loss of appetite, vomiting, diarrhoea, rash, urticaria, convulsions, erythema multiforme, and transient cyanosis of the lower limbs.11 Its cost to the NHS is as low as £8.83 for a single dose of 0.5 ml.11
Pneumococcal vaccine is available. It is a polyvalent pneumococcal polysaccharide from each of 23 capsular types of S pneumoniae. The vaccine is recommended from the age of 2 for people with the following conditions: homozygous sickle cell disease, asplenia or dysfunction of the spleen, chronic renal disease, nephrotic syndrome, immunodeficiency, immunosuppression, chronic heart disease, chronic lung disease, chronic liver disease, and diabetes mellitus. It is effective after a single dose if the strains of S pneumoniae prevalent in the community are reflected in the polysaccharides contained in the vaccine. Its cost to the NHS is £9.49 for a 0.5 ml vial.11
There have been no reports of epidemics of infective blebitis. If it were contagious, there would have been epidemics or clustering in our glaucoma clinics. We can find no evidence of case to case transmission. In fact, all reported cases and series appear sporadic. The association with upper respiratory tract infections and hibernal occurrence are strongly suggestive of respiratory infection with consequent spread to the predisposed eye.4, 5 We are uncertain whether this is systemic or droplet spread. However, the need for topical antibody protection is negated by the presence of systemic antibodies against the specific bacteria. We believe that by minimising the possibility of systemic infections with these agents we diminish the likelihood of blebitis.
It is possible that these vaccines could be given to patients who are destined for trabeculectomy. The cost for both vaccines would be less than £20.00.
Two hundred and fifty vaccinations could be paid for by the price of a single episode of bleb associated endophthalmitis. Assuming a long term infection rate of 2%, these vaccines could possibly prevent two cases of bleb associated endophthalmitis, representing a saving of £5000 to the NHS.
Apart from the cost, vaccination has the potential to prevent significant ocular morbidity. At the very least, these vaccines should be considered in high risk patients undergoing augmented trabeculectomy. We plan to conduct a prospective study of the effect of these vaccinations upon the incidence of blebitis and bleb related endophthalmitis.
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