Pulsed electron avalanche knife (PEAK) for intraocular surgery.

PURPOSE: To develop a better and more economical instrument for precise, tractionless, "cold" cutting during intraocular surgery. The use of highly localized electric fields rather than laser light as the means of tissue dissection was investigated. METHODS: A high electric field at the tip of a fine wire can, like lasers, initiate plasma formation. Micrometer-length plasma streamers are generated when an insulated 25 micron (microm) wire, exposed to physiological medium at one end, is subjected to nanosecond electrical pulses between 1 and 8 kV in magnitude. The explosive evaporation of water in the vicinity of these streamers cuts soft tissue without heat deposition into surrounding material (cold cutting). Streamers of plasma and the dynamics of water evaporation were imaged using an inverted microscope and fast flash photography. Cutting effectiveness was evaluated on both polyacrylamide gels, on different tissues from excised bovine eyes, and in vivo on rabbit retina. Standard histology techniques were used to examine the tissue. RESULTS: Electric pulses with energies between 150 and 670 microJ produced plasma streamers in saline between 10 and 200 microm in length. Application of electric discharges to dense (10%) polyacrylamide gels resulted in fracturing of the gel without ejection of bulk material. In both dense and softer (6%) gels, layer by layer shaving was possible with pulse energy rather than number of pulses as the determinant of ultimate cutting depth. The instrument made precise partial or full-thickness cuts of retina, iris, lens, and lens capsule without any evidence of thermal damage. Because different tissues require distinct energies for dissection, tissue-selective cutting on complex structures can be performed if the appropriate pulse energies are used; for example, retina can be dissected without damage to the major retinal vessels. CONCLUSIONS: This instrument, called the Pulsed Electron Avalanche Knife (PEAK), can quickly and precisely cut intraocular tissues without traction. The small delivery probe and modest cost make it promising for many ophthalmic applications, including retinal, cataract, and glaucoma surgery. In addition, the instrument may be useful in nonophthalmic procedures such as intravascular surgery and neurosurgery.

Corticosteroid therapy for optic disc neovascularization secondary to chronic uveitis.

PURPOSE: To report successful corticosteroid treatment of optic disc neovascularization associated with uveitis. METHODS: Retrospective review of medical records. RESULTS: Nine patients were identified with chronic uveitis and optic disc neovascularization without clinical or angiographic evidence of retinal ischemia. Ages ranged from 14 to 37 years (median age, 27). All patients were treated with either oral and/or subtenon's corticosteroids. Partial regression of the neovascularization was observed in all patients within 2 to 6 weeks (median, 5 weeks) after initiating treatment. Eight of nine patients had complete resolution of disc neovascularization at a median of 3 months (range, 2 to 42 months) after initiation of treatment and a median follow-up of 24 months (range, 7 to 144 months). Recurrence of disc neovascularization occurred in two patients, but it regressed again after further corticosteroid therapy. CONCLUSIONS: Optic disc neovascularization may occur in patients with chronic uveitis in the absence of retinal ischemia. This neovascularization can be successfully treated with corticosteroids.

Optic nerve head neovascularization in a patient with inactive cytomegalovirus retinitis and immune recovery.

PURPOSE: To report a case of optic nerve head neovascularization in a patient with acquired immunodeficiency syndrome (AIDS) associated with inactive cytomegalovirus retinitis and immune recovery. METHOD: Case report. RESULTS: We examined a 29-year-old man with AIDS and inactive cytomegalovirus retinitis and found vitritis and prominent optic nerve head neovascularization. The patient had been treated with reverse transcriptase and protease inhibitors, resulting in a notable rise in CD4+ lymphocyte count and an undetectable human immunodeficiency virus (HIV)-RNA viral load. No cause of neovascularization other than intraocular inflammation was detected. CONCLUSION: Immune recovery in a setting of inactive cytomegalovirus retinitis can result in optic nerve head neovascularization, as seen in our patient.

Dilute topical proparacaine for pain relief after photorefractive keratectomy.

PURPOSE: The purpose of the study is to determine whether there is a nonanesthetic and nontoxic concentration of topical proparacaine that can be applied repeatedly to the cornea to reduce pain after photorefractive keratectomy (PRK). METHODS: Part I: To determine a nonanesthetic concentration, the corneal sensitivity of 50 healthy volunteers was assessed using aesthesiometry before and after a drop of either 0.01%, 0.025%, 0.05%, 0.1%, or 0.2% topical proparacaine. Ten volunteers similarly were tested with multiple doses of 0.05% proparacaine. To evaluate toxicity, ten healthy volunteers self-administered 0.05% proparacaine to one eye and placebo to the other eye every 15 minutes for 12 hours on day 1 and every hour for 12 hours on days 2 through 7. Subjects were assessed throughout the week using visual acuity, slitlamp examination, aesthesiometry, and ultrasonic pachometry. Part II: In a prospective, double-masked study, 34 patients who underwent PRK (48 eyes) self-administered either topical 0.05% proparacaine or placebo for 1 week after PRK as needed to reduce pain. Patients recorded their pain score before and after drop use and answered a pain-relief questionnaire. RESULTS: Part I: Proparacaine concentrations greater than or equal to 0.1% eliminated sensation from some corneas; concentrations of less than or equal to 0.05% were never fully anesthetic. No corneal toxicity was observed except for some minimal punctate staining in both treatment and placebo eyes. Part II: Patients in the treatment group had significantly more pain relief (P < 0.001) for a longer period (P < 0.001) than did patients in the control group. Average change in pain score was significantly greater in the treatment group (P < 0.002). No significant difference in the number of days needed to reach complete epithelial healing was found between the two groups (P < 0.18). CONCLUSIONS: Dilute (0.05%) topical proparacaine is nonanesthetic and nontoxic, and can be used safely for at least 1 week to reduce pain after PRK.

Contrast sensitivity measurements with the Echelon diffractive bifocal contact lens as compared to bifocal spectacles.

We examined the contrast sensitivity function of presbyopic subjects wearing the Hydron Echelon diffractive bifocal contact lens. Contrast sensitivity with the Echelon lens was compared to contrast sensitivity with bifocal spectacle correction. Each eye was tested for near and distance vision with the Echelon contact lens and with spectacle correction. Most subjects achieved a visual acuity of 20/20 with the Echelon lens; however, on average, contrast sensitivity was found to be significantly decreased with the contact lens as compared to spectacles for both distance and near vision. The largest decrease in contrast sensitivity was seen for mid-range spatial frequencies (4 to 16 cycles/degree). Although most subjects experienced a significant decrease in contrast sensitivity, two experienced only small decreases with the Echelon lens. Only one subject who met entry criteria reported that vision was as good with the Echelon lens as with spectacles. The decreased contrast sensitivity may result from contact lens decentration as well as inherent optical characteristics of the Echelon lens.

Effect of contact lens correction of sine wave contrast sensitivity in keratoconus patients after penetrating keratoplasty.

Contrast sensitivity testing reveals visual deficits not detected by standard acuity tests, providing a more sensitive measure of visual performance. Sine wave contrast sensitivity functions were examined for spectacle and contract lens correction of keratoconic eyes after penetrating keratoplasty (PKP). Contrast sensitivity was significantly higher for middle and high spatial frequencies with a rigid gas permeable contact lens than with glasses, even when Snellen acuity was identical for both forms of correction. Contrast performance correlated with subjective assessments of vision quality. This may be related to the quality of the keratometry mire images and suggests that mild irregularities in graft contour may be affecting contrast sensitivity. When considering the options for optical correction of grafted eyes, an evaluation of contrast sensitivity may help determine whether contact lens correction would optimize visual performance.