Misleading tonometry after LASIK

Interface Fluid After Laser in situ Keratomileusis

PURPOSE

To describe a case of interface fluid after laser in situ keratomileusis (LASIK) and review the literature on this rare complication after LASIK.

METHODS

We present a case report and literature review. Articles for this review were chosen from electronic database and manual literature searches. MEDLINE searches were made from 1990 to April 2002, using the key words "interface fluid" and "LASIK."

RESULTS

A 40-year-old man had uneventful LASIK for residual refractive error from previous penetrating keratoplasty in his right eye. Diffuse lamellar keratitis began 1 day postoperatively. Topical corticosteroids were administered. Six weeks after LASIK, a layer of interface fluid developed. Intraocular pressure was 9 mmHg when measured centrally by Goldmann applanation tonometry and 30 mmHg by Tono-pen tonometry. The interface fluid resolved with antiglaucoma agents and corticosteroids combined with cyclosporine.

CONCLUSIONS

This case, along with other reported cases, demonstrate the clinical features of interface fluid after LASIK.

Mismatch between flap and stromal areas after laser in situ keratomileusis as source of flap striae

PURPOSE

To calculate theoretically the magnitude of the excess area between the lower surface of the flap and the underlying ablated stroma.

METHODS

On the initial assumptions of a nonextensible flap and a spherical cornea, flap and ablated stromal areas were determined as a function of myopic correction in the range of 0 to -12 diopters (D) for typical values of corneal radius (7.8 mm) and flap thickness (160 microm), together with a range of ablation zone diameters (4.0 mm, 6.0 mm, 8.0 mm, and 10.0 mm).

RESULTS

Excess flap area increases with the magnitude of the refractive correction and the diameter of the ablated zone. For a -6.0 D correction and an 8.0 mm ablation zone, the excess area is nominally about 1.0 mm(2), giving a potential overlap of the flap at the edge opposite the hinge of about 100 microm. CONCLUSIONS; Excess flap area may cause striae because of wrinkling. Although a nonextensible flap is assumed in the model, any stretching or contraction due to cutting the flap will be independent of the refractive correction. Hence, a mismatch in areas must still occur. This geometric effect may have clinical consequences in optical aberration, refractive regression, or impaired wound healing.

Some possible longer-term ocular changes following excimer laser refractive surgery

While the short- and medium-term refractive and acuity results of excimer laser refractive surgery may now be generally satisfactory, the relatively brief history of the procedures involved (around 10 years or less) means that those concerned with eye care must remain vigilant to the possibility of longer-term problems. This paper reviews some relevant studies of potential post-surgical effects, including imperfect corneal healing and recovery of innervation, reduced corneal sensitivity and dry eye problems, changes in corneal rigidity leading to slow refractive change, possibly misleading reductions in measured intraocular pressure, and retinal and vitreous pathology.