Pressure Induced Stromal Keratopathy (Pisk) After Small Incision Lenticule Extraction (Smile)

To report the occurrence of Pressure Induced Stromal Keratopathy  (PISK) occurring after Small Incision Lenticule Extraction (SMILE) in a 29 year old male patient

 Refractive Services of a tertiary care ophthalmology institute:

A 29 year old male  underwent  SMILE for a  manifest refractive spherical equivalent (MRSE ) of -9.00 D OD and -6.75 D OS.  IOP on NCT was 22mm Hg OU ; cornea compensated IOP ( IOP CC) on Ocular Response Analyser was 16.9 mm Hg OD and 19.1 mm Hg OS.  Uncorrected distance visual acuity (UDVA) on post operative day 1 was 20/30 OU .Dexamethasone eye drops 6times /day postoperatively were prescribed to be tapered over 2 weeks

He presented  1 month postoperatively with headache and blurring of vision OU for 4 days. UDVA was 20/120 OU ; corrected distance visual acuity (CDVA) was 20/30 OU with an MRSE of -2.25 D OD and -2.25 D OS. Slit lamp biomicroscopy revealed diffuse interface haze in the  lenticule area and a subtle widening of the gap between cap and bed stromal interface.  A  differential diagnosis of PISK and diffuse lamellar keratitis was considered .The patient admitted to   continuing topical steroid drops for the last 34 days without tapering.

 IOP CC on ORA  was recorded as 32 mmHg and 31 mm Hg OD and OS respectively while on  NCT it was recorded as  11mm and 14 mm OD and OS respectively. On anterior segment OCT multiple small hyporeflective pockets close to the cap/stromal bed interface were seen. A definitive diagnosis of PISK was made, topical steroids stopped antiglaucoma medication started.  At 1 month UDVA had improved to 20/30 OU, MRSE had regressed to -0.50 D OU and IOP CC was recorded as 14 mm Hg OU. Serial densitometry on the Pentacam showed an increase above baseline levels in the 0-2 and 2-6 mm annuli during the episode of PISK which resolved to baseline levels after normalization of IOP.

Though far less commonly reported than LASIK, PISK can occur even after SMILE. Differentiation from diffuse lamellar keratitis (DLK) is important.  History of headaches, blurring of vision, regression of refractive error, and appearance of fluid pockets at the flap/stromal bed interface are important clinical clues to arrive at a diagnosis of PISK. NCT may underestimate the  IOP  and should not be relied on as the sole modality. ASOCT is useful to document  and serially evaluate the interface fluid, though the changes may be more subtle as compared to LASIK. Corneal densitometry is another useful imaging modality which can be used to detect and evaluate resolution of PISK, especially if changes on ASOCT are equivocal.