Intraoperative miosis is the complication most frequently reported by experienced surgeons performing femtosecond laser-assisted cataract surgery (FLACS). This occurs between the femtosecond laser pretreatment and the actual cataract surgery.
“Intraoperative miosis occurs in between 10 and 32 percent of cases and can significantly reduce the benefits of FLACS by interrupting subsequent nucleofractis, removal of cortical fibres and implantation of the intraocular lens,” said Mihyun Choi MD, of Seoul St. Mary’s Hospital, Seoul, Korea,at the XXXIII Congress of the ESCRS in Barcelona, Spain
Boris Malyugin MD, of the S. Fyodorov Eye Microsurgery Complex Federal State Institution, Moscow, Russia, discussed the results of his study of miosis after FLACS. Dr Malyugin, who uses the LenSx laser (Alcon), included 363 patients (363 eyes) in his study. Pupil diameters were assessed immediately before and 10 minutes after the femtosecond laser steps of the procedure.
“The average pupil diameter decreased from 7.7 mm preoperatively to 6.4mm after FLACS. Significantly, about 13 percent of eyes experienced constriction to 5 mm or less, which makes the subsequent surgical steps quite difficult,” he said.
This miosis occurred despite a preoperative medical protocol that included topical diclofenac 0.1% applied three times per day starting one day preoperatively and cyclopentolate 1% + phenylephrine 2.5% applied topically 60, 45 and 30 minutes before surgery.
“In severe cases, pupil expansion devices were needed during the initial steps of phacoemulsification,” he said.
Dr Choi presented the results of his study of pupil size alterations induced by photodisruption during FLACS, which both sought to evaluate the extent of miosis and determine factors correlated with the phenomenon. Dr Choi’s team used the Catalys Precision Laser System (Abbot Medical Optics) for the surgery. NSAID eyedrops were not applied.
“We divided the potential correlative factors into three groups: patient factors, femtosecond laser pretreatment parameters, and anatomic factors,” said Dr Choi.
These factors included age, gender, co-morbidities and LOCS score, the duration of laser pretreatment, the time between laser pretreatment and phacoemulsification and the distance between capsulotomy and pupillary margins.
In a study that enrolled 56 eyes, images extracted from surgical videos were used to measure the pupil area, allowing quantitative analysis of pupil constriction.
“The mean pupil area decreased by nearly 30 percent during the time it took to shift between procedures, and the extent of pupil constriction was positively correlated with the duration of both femtosecond laser primary incision creation and laser-assisted lens fragmentation,” said Dr Choi.
Pupil constriction was also correlated with patient age and the distance between the laser capsulotomy and the pupillary margin. It was not, however, associated with suction-on time or the so-called shifting time, which is defined as the time between laser pretreatment and phaco surgery.
Dr Choi hypothesized that the longer tissue is exposed to laser emissions, the more prostaglandin is released from intraocular tissues, leading to miosis. Previous studies have shown that PGE2 and total prostaglandin levels are elevated in the aqueous humour after femtosecond surgery.
The shifting time in Dr Choi’s clinic is about 25 minutes, during which prostaglandins cause the iris to constrict. Significantly, Dr Choi’s team did not additionally dilate the patient’s pupil between laser and surgery.
Dr Schultz utilised the hypothesis of prostaglandin increase as the cause of post-femtosecond laser miosis to design a study comparing the effects of specific steps of laser pretreatment on increased prostaglandin concentration in the aqueous humour. Prostaglandin concentrations were measured using an enzyme-linked immunoassay (ELISA) with aqueous humour from 67 patients divided into four groups: control, only capsulotomy, only fragmentation, or both capsulotomy and fragmentation.
“This study identified the anterior capsulotomy as the main trigger for intraocular prostaglandin increase in the aqueous humour immediately after laser-assisted cataract surgery,” said Dr Schultz.
This increase was significantly greater than the increase caused by fragmentation itself, which did not lead to a prostaglandin increase.
“This suggests that optimisation of the laser energy settings, in combination with preoperative use of NSAIDs, might prevent the phenomenon of laser-induced miosis,” he said. Dr Schultz said that same-day NSAID pre-treatment with three drops of diclofenac, can help to block this phenomenon.
All three studies included only patients with senile cataract, and excluded patients with potential confounding factors such as a history of inflammatory eye disease, previous ocular surgery or trauma, pseudoexfoliation or dilated pupil size smaller than 6 mm.
Mihyun Choi: email@example.com