Is superior hinge inferior?

A recent investigation into the effect of hinge position on corneal sensation and dry eye after LASIK suggests that a superior hinge is associated with more dry eye and greater loss of corneal sensation. E. Donnenfeld and colleagues conducted a prospective, randomised, self-controlled trial with 52 patients undergoing bilateral LASIK. Surgeons created a superior-hinge using a Hansatome microkeratome in one eye and the nasal-hinge using an Amadeus microkeratome in the other eye.

In all eyes, the flaps were 160 microns thick, with a diameter of 9.5 mm. Corneal sensation was reduced in eyes with either superior- or nasal-hinge corneal flaps at one week, one month, and three months after surgery (P < 0.001). Compared with preoperative values, a significant reduction in corneal sensation remained at six months in corneas with superior-hinge flaps but not in corneas with nasal-hinge flaps. Mean corneal sensation was greater in corneas with a nasal-hinge flap compared with corneas with a superior-hinge flap at all postoperative visits.

Limbal relaxing incisions for astigmatism

Limbal relaxing incisions are a simple, safe, and effective method to correct primary mixed astigmatism and mixed astigmatism after cataract surgery, Turkish researchers report. The investigators created limbal relaxing incisions to correct astigmatism in 37 eyes of 26 patients with mixed astigmatism. Twenty-four eyes had primary astigmatism, and 13 eyes had astigmatism after cataract surgery. The length, number, and depth of the incisions were determined using the Gills and Gayton nomogram. Follow-up was at least six months in all cases. The mean preoperative and postoperative refractive astigmatism was 3.31 dioptres (D) +/- 1.50 (SD) and 1.59 +/- 1.28 D, respectively (P <.001).

The mean absolute change in refractive astigmatism was 1.72 +/- 0.81 D. No patient lost lines of UCVA or BSCVA. Mean preoperative and postoperative UCVA was 0.29 +/- 0.22 and 0.54 +/- 0.31, respectively (P =.0001) and the mean BSCVA, 0.61 +/- 0.30 and 0.74 +/- 0.30, respectively (P =.0001). There were no serious postoperative complications.

Reduced Daily Eye Patching Effectively Treats Amblyopia

Patching the unaffected eye of children with moderate amblyopia for two hours daily works as well as patching the eye for six hours, suggests a large multicentre study. Researchers in the Pediatric Eye Disease Investigator Group (PEDIG) followed 189 children under seven years of age who were assigned to receive either two hours or six hours of daily patching combined with at least one hour per day of near visual activities during patching.

After four months of patching, the children in the two-hour group had similar improvements in visual acuity as those seen with six hours of daily patching. However, the researchers add that these results do not necessarily apply to all children with amblyopia, noting that children with more severe amblyopia, or who have amblyopia from causes other than crossed eyes or refractive error, may need a different treatment regimen.

Pros and cons of glaucoma interventions

Trabeculectomy with mitomycin C may be more effective than viscocanalostomy in lowering intraocular pressure in patients with primary open-angle glaucoma, while eyes undergoing viscocanalostomy experience a lower incidence of complications, report Japanese researchers. K. Kobayashi and colleagues compared IOP lowering effect and safety of viscocanalostomy and trabeculectomy with mitomycin C in bilateral open-angle glaucoma in a series of 25 patients.

The eyes of each patient were randomly assigned to receive viscocanalostomy in one eye and trabeculectomy with mitomycin C in the other eye. At 12 month follow-up, the mean postoperative IOP was 17.1±1.5 mmHg in viscocanalostomy-treated eyes and 12.6±4.3 mmHg in trabeculectomy-treated eyes. The mean intraocular pressure in viscocanalostomy-treated eyes was significantly higher than that in trabeculectomy-treated eyes at every visit. At 12 months, 16 viscocanalostomy-treated eyes (64%) and 22 trabeculectomy-treated eyes (88%) achieved an intraocular pressure of less than or equal to 20 mmHg without medication. There were fewer complications in viscocanalostomy-treated eyes.

Buffering increases suffering

An investigation to determine whether buffering ocular tetracaine hydrochloride reduces the pain of instillation revealed just the opposite. Sixty patients participated in a prospective, randomised, double-blind, two-treatment, two-period crossover, single center study. Participants were randomized to receive either two drops of buffered or plain tetracaine in a randomly assigned eye. After a mean wash out period of 24 days (range 7 to 54 days), participants returned to have two drops of the other medication instilled in the same eye.

The participants recorded the pain of instillation on a 100 mm visual analog scale (VAS) immediately and five minutes after instillation. Immediately after instillation, the adjusted mean VAS score for buffered tetracaine was 29.1 mm, and the adjusted mean VAS score for plain tetracaine was 16.0 mm. The researchers suggest this indicates that pain with instillation of ocular anesthetics is not dependent on low pH.

Connect the quantum dots

Scientists at Cornell University report using ‘quantum dots’ to grab microscopic, multicolor images of the insides of capillaries of mice. They speculate that future in vivo photo shoots may yield glimpses of tissue and organ function. Daniel Larson and colleagues used a two-photon excitation approach to illuminate quantum dots -- nanometer-scale crystals built to emit specific colors of light. With this method, radiation in the near-infrared range instead of more dangerous ultraviolet wavelengths can be employed. The researchers compared their experimental deep-tissue imaging technique to conventional approaches in skin and adipose tissues in mice.

In the set of experimental images, highly fluorescent, biocompatible quantum dots lit up the mice and provided more detail at lower power magnification than a conventional imaging technique. Imaging highly fluorescent quantum dots via two-photon absorption may lead to biocompatible quantum dots that emit different colors of light (or adhere to different type of tissues) even though the dots are excited by the same infrared radiation.