Gene therapy for retinal diseases

Gene therapy has a growing research potential particularly in the field of ophthalmic and retinal diseases owing to three main characteristics of the eye; accessibility in terms of injections and surgical interventions, its immune-privileged status facilitating the accommodation to the antigenicity of a viral vector, and tight blood-ocular barriers which save other organs from unwanted contamination. Gene therapy has tremendous potential for different ocular diseases. In fact, the perspective of gene therapy in the field of eye research does not confine to exclusive monogenic ophthalmic problems and it has the potential to include gene based pharmacotherapies for non-monogenic problems such as age related macular disease and diabetic retinopathy. The present article has focused on how gene transfer into the eye has been developed and used to treat retinal disorders with no available therapy at present.

Intravitreal bevacizumab for pseudophakic cystoid macular edema; a systematic review

Cystoid macular edema (CME) is a major cause of decreased vision after complicated or uncomplicated cataract surgery. This paper reviews the use of intravitreal bevacizumab (IVB) injection for treatment of pseudophakic CME. In a literature search of all articles available on Medline and Scopus databases, 11 studies including one prospective and 4 retrospective studies, 4 case reports, one letter to editor and one review article were identified. All articles except one, reported the use of IVB for chronic CME unresponsive to at least one conventional treatment modality. The level of evidence for all studies was categorized as low or very low. Although intravitreal bevacizumab might be effective for many cases of pseudophakic CME, its use should be reserved for eyes unresponsive to conventional treatment modalities.

Intravitreal erythropoietin injection for the treatment of non-arteritic anterior ischaemic optic neuropathy

AIM

To evaluate the effect of intravitreal injection of erythropoietin for the treatment of non-arteritic anterior ischaemic optic neuropathy (NAION).

METHODS

In this prospective interventional case series, 31 eyes of 31 patients with NAION were included. Patients received intravitreal injection of 2000 unit (0.2 cm³) of erythropoietin within 1 month of the onset of the disease. Visual acuity and visual field were recorded before injections and 1 week, 1 month, 3 months and 6 months after the injections.

RESULTS

The mean duration of symptoms before injections was 11.2 ± 5.5 days. Six months after injections, visual acuity improved in 27 eyes (87%), and 17 eyes (54.8%) had ≥ 3 lines of visual improvement. The mean preinjection visual acuity was 1.01 ± 0.88 logMAR and 0.58 ± 0.58 logMAR (p<0.001) at last follow-up. Visual acuity improvement occurred in 61.2% of patients within the first month. It followed a biphasic pattern in which there was continuous improvement up to 3 months and then started to deteriorate, although it remained significantly better than baseline until the last follow-up. No patient lost any lines of visual acuity compared with the baseline values. The mean of mean deviations of visual field was -19.6 ± 5.7 dB at baseline and -18.6 ± 6.3 dB (p = 0.6) at last follow-up.

CONCLUSIONS

Intravitreal injection of erythropoietin may be safe and effective in the treatment of NAION. The effect may last for a few months and then decline.

Contribution of pneumolysin and autolysin to the pathogenesis of experimental pneumococcal endophthalmitis

PURPOSE

To determine the contribution of pneumolysin and autolysin, two putative pneumococcal virulence proteins, to the pathogenesis of Streptococcus pneumoniae endophthalmitis.

METHODS

Endophthalmitis was established in Lewis rats by intravitreal injection of pneumococcal strains at an inoculum of 10 organisms. The virulence of three closely related type 2 S. pneumoniae strains were compared: a pneumolysin-deficient derivative (PLN-A), an autolysin-deficient derivative (AL-6), and their isogenic wild-type parent (D 39). Clinical and histologic inflammation scores were compared 24 hours and 48 hours after inoculation.

RESULTS

Eyes infected with PLN-A and AL-6 strains showed less anterior segment inflammation clinically at 24 hours than did eyes infected with the wild-type strain. Histologic examination at 24 hours showed significantly less corneal infiltration and vitritis and more relative preservation of retinal tissue in eyes infected with PLN-A and AL-6 strains than in eyes infected with the wild-type strain. At 48 hours, no observable differences between PLN-A and wild-type strains were present clinically or histologically. Histologically, however, the AL-6 strain caused less retinal damage than did the wild-type strain.

CONCLUSIONS

Intraocular infection with pneumolysin-deficient S. pneumoniae results in less severe tissue damage in the first 24 hours of disease compared with infection with pneumolysin-producing S. pneumoniae. Autolysin-deficient S. pneumoniae shows a similar degree of attenuated virulence. Pneumolysin and autolysin may contribute to the early pathogenesis of pneumococcal endophthalmitis.

Management of retained intravitreal lens fragments after cataract surgery

With the rise of popularity of phacoemulsification as the preferred surgical method for cataract extraction, there has been an increased incidence of posterior dislocation of lens fragments. The appropriate management of this complication both during and after cataract extraction is discussed in this review. It is suggested that vigorous attempts by the cataract surgeon to retrieve intravitreal lens fragments should be avoided. Timely referral to a posterior segment surgeon for pars plana vitrectomy and removal of lens fragments can result in good visual outcome. Complications, such as glaucoma and retinal detachment, may develop in some cases. The importance of careful clinical follow-up is emphasized.

Treatment of experimental Staphylococcus epidermidis endophthalmitis with oral trovafloxacin

PURPOSE

To investigate the ocular pharmacokinetics and efficacy of oral trovafloxacin, a novel fluoroquinolone antibiotic, in Staphylococcus epidermidis endophthalmitis.

METHODS

Albino rabbits (n = 20) were infected with an intravitreal inoculum of S epidermidis (1.0 x 10(8) colony-forming units [CFU/0.1 ml) and 24 hours later received a single oral dose of trovafloxacin (250 mg/kg). Serum and intraocular samples from infected and control (noninfected) eyes were obtained up to 24 hours after antibiotic administration for measurement of trovafloxacin levels. A second group of rabbits (n = 72) was infected intraocularly and randomized 24 hours later to oral trovafloxacin (250 mg/kg twice a day) for 6 days or no treatment (control). Treatment efficacy was assessed by vitreous culture, clinical examination, and histopathology.

RESULTS

Following a single dose of trovafloxacin, maximal vitreous levels were achieved at 8 hours in infected eyes, with a penetration ratio of 36%. Vitreous levels were greater than 15 times the minimum inhibitory concentration of the strain employed. In animals with established endophthalmitis, treated eyes were sterilized after 5 days (P = .0495) compared with control eyes, which autosterilized at 14 days. Clinical and histologic examination revealed significant amelioration of anterior segment inflammation in treated eyes, although severe destruction of posterior segment structures occurred in both groups after 6 days of therapy.

CONCLUSIONS

These data support trovafloxacin as a potential oral agent for treatment or prophylaxis of S epidermidis endophthalmitis, although retinal alterations that occur over the period required for vitreous sterilization suggest that it will not replace intravitreal therapy in established endophthalmitis.

Implication of pneumolysin as a virulence factor in Streptococcus pneumoniae endophthalmitis

PURPOSE

To determine if pneumolysin, a multifunctional cytotoxin produced by Streptococcus pneumoniae, may be a virulence determinant in the pathogenesis of pneumococcal endophthalmitis.

METHODS

Lewis rats (n = 20) were injected intravitreally with purified recombinant pneumolysin at the following doses; 3.9 hemolytic units (HU), 39 HU, 390 HU, 3.9 x 10(3) HU, and 3.9 x 10(4) HU. After 24 hours, eyes were examined clinically and enucleated for histopathologic examination to elucidate the dose-response relationship. To determine the temporal progression of the disease model, a second group of rats (n = 8) were injected intravitreally with 390 HU of pneumolysin. At 6 and 48 hours, eyes were examined clinically and enucleated for histopathology.

RESULTS

Eyes injected with pneumolysin demonstrated increasing anterior and posterior segment inflammation in response to increasing doses of administered toxin. The onset of inflammation and tissue damage occurred rapidly, and was maximal at 24 to 48 hours. The clinical and histopathologic changes observed mimicked those of S. pneumoniae endophthalmitis. Histopathologic analysis demonstrated rapid onset of iridocyclitis and vitritis with polymorphonuclear leukocyte influx, inner retinal necrosis, and retinal detachment. Retinal pigment epithelial necrosis and choroiditis were noted at the highest doses administered. Inflamed eyes were shown to be sterile.

CONCLUSIONS

Pneumolysin injected intravitreally induces many of the clinical and histopathologic features of pneumococcal endophthalmitis, and may play an important role in the inflammation and tissue damage that occurs in pneumococcal endophthalmitis.

Optic nerve avulsion

OBJECTIVE

To characterize the presentation, role of diagnostic imaging, and course in patients with optic nerve avulsion.

METHODS

A retrospective review of medical records of all 6 patients with optic nerve avulsion who were seen at the Massachusetts Eye and Ear Infirmary, Boston, from January 1, 1991, to July 31, 1995.

RESULTS

The initial visual acuity ranged from 20/100 to no light perception. All 6 patients underwent neuroimaging, including computed tomography, magnetic resonance imaging, or both. B-scan ultrasonography was performed on 4 patients, and the condition of 1 patient was evaluated with color Doppler ultrasonography to assess the optic nerve vasculature. In 1 patient, a computed tomographic scan was suggestive of an optic nerve avulsion. Neuroimaging in the other 5 patients, including 2 patients who underwent magnetic resonance imaging, failed to demonstrate an avulsion. During a follow-up period of up to 25 months, 4 patients showed no improvement in visual acuity, 1 patient improved from no light perception to bare light perception, and 1 patient improved from 20/100 to 20/25.

CONCLUSIONS

These data suggest that final visual outcome was dependent on initial postinjury visual acuity. Neuroimaging, B-scans, and Doppler ultrasonography were usually not helpful in establishing the presence of optic nerve avulsion, although they may be useful in evaluating comorbid conditions.

Inhaled steroids: effect on intraocular pressure in patients without glaucoma

OBJECTIVE

To evaluate the risk of intraocular pressure (IOP) elevation in patients receiving inhaled steroid therapy.

DESIGN

Prospective study.

SETTING

Four private practices in New Jersey.

PATIENTS

A total of 187 patients (99 men and 88 women) with no documented history of glaucoma about to begin inhaled steroid therapy for various pulmonary conditions were enrolled. Of the 187, 183 were followed at 12 weeks.

INTERVENTIONS

Measurement of the IOP with the Tono-Pen before therapy was started and 12 weeks after therapy was started.

OUTCOME MEASURE

IOP.

RESULTS

No significant rise in IOP was observed. No patient had a rise in IOP greater than 4 mm Hg.

CONCLUSIONS

Although isolated case reports indicate a definite risk of glaucoma in the presence of inhaled steroid therapy, the risk appears to be small.

Endogenous fungal endophthalmitis

Endogenous fungal endophthalmitis has increased in the past half-century because of the advent of antibiotics and indwelling catheters. The disease process can produce highly suggestive, though nonpathognomonic, ocular signs that assist the clinician in reaching a diagnosis. Intraocular inflammation, especially if it is granulomatous in nature in a patient with one or more of the risk factors already discussed, should raise the suspicion of fungal endophthalmitis. If a diagnosis remains elusive, vitreous biopsy is indicated for proper identification of a fungal organism. Although a particular therapeutic regimen has not yet been prospectively established, compelling arguments can be made to treat nearly all patients with endogenous fungal endophthalmitis with a systemic antifungal such as amphotericin B or fluconazole. A possible exception includes an IVDA-related endophthalmitis in a patient with negative blood cultures and without other evidence of fungemia. Vitrectomy and intravitreal amphotericin B (with or without intravitreal corticosteroid) should be considered in cases of endogenous fungal endophthalmitis in which there is substantial vitreous involvement, and also in cases in which there is clear progression of disease despite initial therapy with an appropriate systemic antifungal agent. Prompt therapy following early diagnosis will help reduce significant visual loss in all forms of fungal endophthalmitis.

Effect of intravitreal dexamethasone in treatment of pneumococcal endophthalmitis in rabbits

PURPOSE

To investigate whether corticosteroid therapy would decrease the inflammation and tissue damage associated with pneumococcal endophthalmitis.

METHODS

Albino rabbits were injected intravitreally with 1000 live organisms of Streptococcus pneumoniae and randomized after 24 hours to treatment with intravitreal vancomycin hydrochloride alone (n = 10), combination intravitreal vancomycin and intravitreal dexamethasone (n = 10), or no treatment (n = 10). After 2 weeks, the eyes were examined clinically and enucleated for histopathologic examination.

RESULTS

Eyes treated with vancomycin and dexamethasone had significantly less intraocular inflammation and more preservation of retinal tissue than untreated eyes or eyes treated with vancomycin alone (P < .05, Fisher's exact test). Untreated and vancomycin-treated eyes were indistinguishable on clinical and histologic examination. Marked anterior and posterior segment inflammation with total retinal necrosis was noted in eyes from both groups.

CONCLUSION

Intravitreal corticosteroid therapy may play an important role in minimizing the inflammation and tissue damage associated with pneumococcal endophthalmitis.

Differential activation of yeast adenylate cyclase by wild-type and mutant RAS proteins

In these experiments we demonstrate that purified RAS proteins, whether derived from the yeast RAS1 or RAS2 or the human H-ras genes, activate yeast adenylate cyclase in the presence of guanine nucleotides. These results confirm the prediction of earlier genetic and biochemical data and for the first time provide a complete biochemical assay for RAS protein function. Furthermore, we observe a biochemical difference between the RAS2 and RAS2val19 proteins in their ability to activate adenylate cyclase after preincubation with GTP.