Phakic eyes

Ayyala RS, Cruz DA, Margo CE, Harman LE, Pautler SE, Misch DM, Mines JA, Richards DW. Cystoid macular edema associated with latanoprost in aphakic and pseudo-phakic eyes. Am J Ophthalmol 1998 126(4) 602-4. 

Presence of cataract Patients younger than 40 years of age Neovascular and uveitic glaucoma History of retinal detachment Asthma or history of asthma Phakic eyes°... 

The half-life of anteriorly excreted drugs is also decreased by inflammation, although the mechanism is not clear. Studies of amikacin demonstrated that in phakic eyes the half-life was diminished from 25.5 to 15.5 hours by inducing inflammation, while the aphakic eye half-life was reduced from 14.3 to 7.4 hours (17). Studies of gentamicin showed inflammation decreased the half-life from 32 to 19 hours (18). It is possible that inflammation increases posterior permeability and thereby allows these drugs to be eliminated by both anterior and posterior routes, accounting for the observed increase in the rate of elimination. 

The half-life of vancomycin following intraocular injection is long, and ranges from 25.5 to 56 hours (14,15). Removal of the lens dramatically decreases the half-life to 9.8 hours (14). In inflamed eyes the half-life is slightly longer in the phakic eye and is slightly shorter in a model of infection (14,15). 

Clearance of first-generation cephalosporins after intravitreal injection suggests a posterior clearance route (23). Newer agents may be removed by the anterior route or by the combined posterior and anterior route (30). In phakic eyes, the half-life of cefazolin in the monkey and the rabbit is 6.5 7 hours (22,45). The half-life is decreased by inflammation, presumably by interference with active transport across posterior structures. In studies of third-generation agents (ceftizoxime and ceftriaxone), there was increased drug half-lives in infected rabbit eyes as compared to controls (30). Ceftazadime has a half-life of 13.8 20 hours in the rabbit, but the half-life is dramatically lowered by removal of the lens and vitreous (46). 

Amikacin is eliminated anteriorly and has a half-life similar to that of vancomycin at 25.5 hours in the normal phakic eye (49). Inflammation decreases the half-life and removal of the lens significantly reduces the half-life to 14.3 hours in the rabbit although the effect is not quite as marked as the changes for vancomycin. Amikacin is a concentration-dependent antibiotic with a postantibiotic effect that is, there is prolonged activity even after its concentrations have fallen below therapeutic levels. 

In another trial, triamcinolone acetonide was injected into the vitreous cavity of 14 eyes within six weeks of PDT (53). Eleven received one initial combined treatment and three received an additional combined treatment after six months. Median follow-up was 18 months (range 12-25 months). Overall, 7% gained 30 or more letters, 50% maintained stable vision, 14% lost 15-29 letters, and 29% lost 30 or more letters. The mean number of PDT treatments during the first year was 2.57. Side effects were mild and included IOP elevation in 28.5% and cataract progression in 50% of phakic eyes. 

Kerr Muir MG, Sherrard ES, Andrews V, Steel ADM. Air, methylcellulose, sodium hyaluronate and the corneal endothelium endothelial protective agents. Eye 1987 1 480-486 Kim JH. Intraocular inflammation of denatured viscoelastic substance in cases of cataract extraction and lens implantation. J Cataract Refract Surg 1987 13 537-542 Kirkby GR, Gregor ZJ. The removal of silicone oil from the anterior chamber in phakic eyes. Arch Ophthalmol 1987 105 1592... 

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