Clinical News: MEDICAL AND PRODUCT UPDATES

BACTERIA AND BIOFILM
Infected punctal plugs may be a common problem

A recent study conducted in Kyoto, Japan, and Lancaster, in the United Kingdom, found that punctal plugs are prone to bacterial infection. Evidence suggests that this often includes bacterial biofilm, which is known to make infections highly resistant to treatment.

The study involved 21 patients with dry eye whose puncta had been occluded for at least 3 months and who used artificial tears six times a day. Material from the occluded puncta was analyzed using bacterial culture, scanning electron microscopy and transmission electron microscopy. No evidence of conjunctivitis was present when the samples were taken. (During the course of the study, a number of punctal plugs were removed for reasons not related to the study. These plugs were examined as well.)

A punctal plug heavily colonized by bacteria.

Of the 18 material samples analyzed, eight (44%) tested positive for bacteria; six contained S. epidermis; two contained S. aureus. (The study found no correlation between the presence of bacteria and the length of time the plug had been inserted.)

Of the 15 removed punctal plugs that were analyzed, more than half were contaminated with bacteria: five were heavily coated with bacterial biofilm, three were moderately covered. Four of the remaining plugs couldn't be analyzed because of surface debris.

The authors were unable to explain why some puncta became infected and others did not. However, the authors recommend careful monitoring of punctal plug patients for material accumulating in or on the plug. In these cases, the authors suggest considering replacement of the plug, clearing of the hole or an alternative treatment.

MYOPIA AND HYPEROPIA
Genomes and nightlights

Recent studies suggest that a child's poor eyesight may have a lot to do with the parents' eyesight -- and little to do with the use of a nightlight.

A study of more than 500 British twins at St Thomas' Hospital in London found that about 85% of cases of myopia and hyperopia appeared to be inherited, as did half of the cases of astigmatism.

While this provides strong evidence for the effect of heredity, other evidence, such as the explosion of myopia within a single generation in the Far East, led the researchers to stress that the environment must also play an important role. Christopher Hammond, M.D., a co-investigator in the study, believes that the trigger for poor eyesight is probably extensive close work combined with a genetic predisposition to poor vision.

Researchers hope to identify the susceptibility gene, which may make it possible to take preventive action.

Meanwhile, a U.S. study concerning the impact of nightlight use during infancy -- which has been connected to myopia in previous studies -- found that nine infant rhesus monkeys reared with constant light exposure up to 6 months of age were no more susceptible to myopia than 23 monkeys reared with a normal diurnal lighting cycle. No significant differences were found in lens thickness, corneal radius or thickness, vitreous chamber depth or anterior chamber depth.

One previous study found a fivefold increase in the incidence of myopia among children who slept with room lights on, although these findings were not replicated by a follow-up study using a different population. Another study found that corneal radius of curvature and vitreous chamber depth were increased in chickens who were raised under constant light.

The twin and primate studies were reported in Investigative Ophthalmology and Visual Science.

LASIK AND DRY EYE
Severed nerves or fewer tears?

A recent study conducted by Steven E. Wilson, M.D., suggests that the problem of dry eye after laser-assisted in situ keratomileusis (LASIK) is most likely the result of the severing of corneal nerves -- LASIK-induced neurotrophic epitheliopathy, or LNE -- rather than diminished tear production.

The study compared the eyes of 19 patients with moderate-to-severe cor-neal epithelium erosion at 1 to 3 months post-LASIK, to eyes of 19 patients who failed to develop any erosion. (Patients with dry eye symptoms before surgery were excluded from the study.)

Dr. Wilson found no difference in tear production at 1, 3 or 6 months, and no significant difference in corneal irregularity or refractive correction. On the other hand, the signs and symptoms of LNE tended to resolve after about 6 months -- when is about when corneal nerves finish regenerating into the flap.

The study was reported in the June 2001 issue of Ophthalmology Management.