Use of viscoelastic substance in ophthalmic surgery - focus on sodium hyaluronate

Among viscoelastic substances, sodium hyaluronate has become the most popular for intraocular surgeries since the introduction of Healon^® (sodium hyaluronate 1%, 4 × 10⁶ daltons) in 1979. This review focuses on the recent development of a new generation of sodium hyaluronate agents with new rheologic properties and the relevant new techniques used in cataract, glaucoma, corneal, and vitreoretinal surgeries. The introduction of sodium hyaluronate agents with different rheologic properties has improved the safety and reliability of intraocular surgeries. Although there have been numerous studies reporting the effectiveness of viscoelastic substances in intraocular surgeries, rigorous validation by multi-center randomized control trials is lacking in many cases. At present, no single viscoelastic agent is most suitable to all of the various intraocular surgical techniques. Therefore, ophthalmologic surgeons should keep up with recent developments of viscoelastic agents and relevant surgical techniques for better patient care.

Local treatment with alpha-melanocyte stimulating hormone reduces corneal allorejection

BACKGROUND

Corneal grafting is by far the most common form of transplantation. Many grafts suffer from immune rejection and current therapies are associated with many side effects, requiring more effective and safe therapies. alpha-Melanocyte stimulating hormone (alpha-MSH) is a neuropeptide that suppresses host inflammatory defense mechanisms. The purpose of this study was to determine the role of local therapy with alpha-MSH on corneal allograft survival, and the mechanisms by which it may influence graft outcome.

METHODS

Orthotopic corneal transplantation was performed, with recipients receiving subconjunctival alpha-MSH or sham injections twice weekly. Grafts were followed up for 70 days, and graft inflammation/opacification was compared between the two groups in a masked fashion. Graft infiltration and ocular gene expression of select inflammatory cytokines was evaluated at different timepoints. Additionally, allospecific delayed-type hypersensitivity was compared among the groups 3 weeks posttransplantation.

RESULTS

Results showed a significant increase in corneal graft survival in alpha-MSH-treated recipients compared with controls. Although 75% of allografts in alpha-MSH-treated hosts survived at 70 days, 43% survived in controls (P=0.04). Graft infiltration studies demonstrated a significant decrease in the number of mononuclear and polymorphonuclear cells in alpha-MSH-treated mice compared with controls at days 7 and 14 after transplantation. Furthermore, allospecific delayed-type hypersensitivity and gene expression of interferon-gamma and interleukin-2 showed a significantly reduced expression in alpha-MSH-treated mice compared with controls.

CONCLUSIONS

This study provides for the first time, in vivo evidence that treatment with local alpha-MSH may significantly reduce allorejection of orthotopic transplants.

Systemic cyclosporin A in high failure risk, repeated corneal transplantation

AIM

To evaluate the efficacy of oral cyclosporin A in the prevention and treatment of immune graft rejection in heavily vascularised, repeated keratoplasties with high risk for failure.

METHODS

21 consecutive patients with 28 repeated corneal transplants and four quadrant vascularised recipient bed were treated with oral cyclosporin A for an average period of 12 months (range 1-41 months) and followed for an average period of 26.6 months (range 6-106 months). The average cyclosporin A blood level was 325 ng/ml (range 180-421 ng/ml). Within this group of 21 patients, another 12 regrafts were not treated with cyclosporin A and served as a control group.

RESULTS

Nine of the 28 regrafts (32%) treated with cyclosporin A remained clear. The Kaplan-Meier curve showed a constant decline in survival of the treated grafts, although the survival proportion during the first year of treatment was statistically higher for the treated group compared with the untreated group. Once immune regraft rejection occurred, the regraft failed despite treatment with cyclosporin A and extensive topical and systemic corticosteroids. Nine regrafts (32%) had immune graft rejection and all ultimately failed compared with five in the untreated regrafts (42%, p = NS). Ten other regrafts (36%) in the treatment group failed due to causes other than immune regraft rejection.

CONCLUSIONS

Systemic cyclosporin A has a limited beneficial effect in preventing immune graft rejection in repeated corneal transplants in a highly vascularised corneal bed. When immune graft rejection occurs in such regrafts, the prognosis is poor despite aggressive medical treatment. Causes other than immune regraft rejection may also result in poor visual outcome in patients with clear regrafts.

Analysing the various obstacles to cornea postmortem procurement

AIMS

In many countries the number of corneal donations is far too low to graft all patients on waiting lists within reasonable time. The aim of this study was to define specifically what practical changes are to be implemented to fully meet corneal graft demand.

METHODS

The list of potential donors drawn by the coordination team from 1 January to 31 December 1999 was compared with that of all patients who had died during the same period. In each identified record, the parameters which permitted or precluded effective collection of cornea specimens were analysed, and the reasons why other records were not identified were investigated.

RESULTS

Among the 1112 patients who died in 1999, coordinating nurses were able to identify 451 records (40.5 %) including 329 patients aged between 18 and 85 years (29.5%). After excluding 184 patients (55.9 %) who presented with medical contraindications, the coordinating nurses were able to meet the relatives of only 55 out of 145 patients (38%) and obtained their agreement in 39 cases (71% approval rate). Therefore, relatives' refusal was the cause for the absence of collection in only 5.5% of cases (16/290). The number of corneas procured amounted to 11.8% of identified records and 3.5% of all deceased patients.

CONCLUSION

French law and regulations regarding tissue collection are based on consent presumption but it requires that verifications be made with the relatives to ensure that potential donors were not, before their death, opposed to such tissue procurement. That provision implies a high degree of organisation on the part of coordinating teams. It was demonstrated that donation shortage is no longer the result of relatives' refusal but rather because of logistical difficulties (potential donors not identified and problems in reaching relatives). It appears necessary therefore to strengthen coordinating teams with sufficient staff levels for wider donor identification. Those teams should also find ways to keep closer contact with relatives, so as to meet the maximum transparency targets required by public opinion and regulations and to graft all patients awaiting corneal transplantation.

The outcome of corneal grafting in patients with stromal keratitis of herpetic and non-herpetic origin

AIM

To evaluate the outcome of corneal grafting in patients with stromal keratitis of herpetic (HSK) and non-herpetic origin, using predefined diagnostic criteria and standardised postoperative therapeutic strategies.

METHODS

384 adult immunocompetent recipients of a corneal graft for herpetic (n = 186) or non-herpetic (n = 198) keratitis were followed up prospectively for up to 5 years.

RESULTS

The herpetic group displayed significantly more corneal vascularisation (p = 0.013), more epithelial defects (p = 0.049), lower corneal sensitivity (p <0.001), more graft rejection episodes (p = 0.002), and required larger grafts (p<0.001). However, the postoperative course of visual acuity, endothelial cell numerical density, and rate of graft failures were similar in both groups. After 5 years, cumulative probability of graft survival in HSK patients (40.85%) was similar to that observed in individuals with non-herpetic keratitis (50.15%; log rank = 0.874; relative risk: 1.04).

CONCLUSION

Despite a markedly higher preoperative risk profile in herpetic eyes, the functional outcomes of grafts in individuals with keratitis of herpetic or non-herpetic origin were similar. Probably the most important contribution is a consequent close follow up and a therapeutic strategy including systemic prophylaxis of viral recurrence and of graft rejection by well adopted local steroid therapy.