Mechanical devices to the rescue

September 1, 2014

Prof. Dick discusses the challenges posed by a small pupil in femtosecond laser cataract surgery and the options that are available to surgeons to overcome pupil constriction.

The 'threat' of a small pupil

Occurrence of miosis

Sometimes, however, the sudden occurrence of miosis might be connected to femtosecond laser technology or rather to the way it has been applied. After having initially achieved a pupil diameter sufficiently larger than the intended capsulotomy, a constriction can happen within just minutes and right during the process of femtosecond laser treatment. In these cases, a failure of the mydriatic can be ruled out: the pupil at the beginning of the intervention has obviously been larger (usually greater than 5.0 mm) than the safety margins set for a safe capsulotomy (otherwise, the surgeon, or rather the system, would not have been able to perform accurate and safe laser pretreatment). Roberts et al. reported an incidence of 9.5% for their first 200 femtosecond laser-assisted procedures and a decrease to 1.23% in the subsequent 1300 cases by additional instillation of a drop of 10% phenylephrine immediately after laser treatment.2 However, in our experience the incidence without the preoperative use of topical nonsteroidal anti-inflammatory drugs was 5% (n = 100) and decreased to 1% (n = 100) with nonsteroidal anti-inflammatory drug pretreatment.

The phenomenon of postoperative laser miosis is under evaluation; its causes are being discussed. Possible explanations are a sudden rise in the aqueous humour's temperature immediately after the laser has been applied and the release of inflammatory mediators as a result of this temperature rise or of collateral effects of laser-induced shock waves. It seems from case reports that the more time elapses between laser pretreatment and the beginning of intraocular surgery, the narrower these pupils become.3

Time, as so often in life, is the key. Any delay caused by, for instance, shuttling patients to and from so-called laser suites to the operating theatre puts them at risks; this is one of the central arguments of our plea for laser (pre-)treatment and phacoemulsification/IOL implantation in the same room.4