Hyperopic Shift In Refraction Research Articles

Refractive Changes during 72-hour Exposure to High Altitude after Refractive Surgery

The authors prospectively analyzed refractive and pachymetric parameters during exposure to high altitude after radial keratotomy (RK) and photorefractive keratectomy (PRK). The authors measured manifest and cycloplegic refraction, keratometry, computed video keratography, and central and peripheral pachymetry in six subjects who have undergone RK (11 eyes), six who have undergone PRK (12 eyes), and nine with myopia (17 eyes) at sea level and on three consecutive days at 14,100 feet. All measurements were repeated 1 week after subjects returned to sea level. Subjects who have undergone RK demonstrated a significant and progressive increase in spherical equivalence (+0.30 +/- 0.50 diopters on day 1 and +1.52 +/- 1.01 diopters on day 3; P < 0.001) and a decrease in keratometry values during exposure to altitude when compared with control subjects with myopia. Healthy subjects and those who have had PRK demonstrated no significant change in refractive error. Pachymetry measurements demonstrated significant peripheral corneal thickening in all three groups (RK, P < 0.004; PRK, P < 0.007; control subjects, P = 0.0006) by day 3 at high altitude. Refraction, keratometry, and pachymetry returned to baseline (P = 1.000) after return to sea level. Seventy-two-hour exposure to high altitude in subjects who have had RK induces a significant, progressive, and reversible hyperopic shift in refraction with corresponding video keratographic and keratometric changes. The authors hypothesize that the high-altitude hypoxic environment causes increased corneal hydration in the area of the RK incisions, which may lead to central corneal flattening and a hyperopic shift in refractive error. Subjects who have had PRK and those with myopia are not susceptible to this refractive shift. The authors' RK data suggest that the time since surgery and the amount of surgery are related to the degree of hyperopic shift during altitude exposure.

A Prospective Multicenter Trial of Excimer Laser Phototherapeutic Keratectomy for Corneal Vision Los

The 193-nm argon fluoride excimer laser can remove corneal scars and smooth corneal irregularities, obviating corneal transplantation. We conducted a prospective multicenter trial of excimer laser phototherapeutic keratectomy for corneal vision loss as a basis for Food and Drug Administration premarket approval. We treated 232 eyes of 211 patients with corneal vision loss. All had corneal pathology in the anterior 100 microns of the stroma. Mean postoperative follow-up was 10 +/- 8 months. The primary outcome variable was change in best spectacle-corrected visual acuity. At postoperative month 12, best spectacle-corrected visual acuity improved in 46 (45%) of 103 eyes and worsened in nine (9%) of 103 eyes by 2 or more Snellen lines. Best spectacle-corrected visual acuity improved by a mean of 1.6 +/- 2.8 Snellen lines (95% confidence interval, 1.1 to 2.1 lines). Every postoperative visit confirmed statistically significant improvement of mean best spectacle-corrected acuity. At month 12, treated eyes had a mean hyperopic shift in refraction of 0.87 diopter and a mean reduction in astigmatism of 0.36 diopter. Treatment appeared most effective in eyes with hereditary corneal dystrophies, Salzmann's nodular degeneration, and corneal scars, and least effective in eyes with calcific band keratopathy. Complications included recurrence of underlying pathology, corneal graft rejection, and bacterial keratitis. Argon fluoride excimer laser phototherapeutic keratectomy is effective, with relatively few complications, for treating vision loss from corneal opacification or irregularity. Efficacy, however, varies widely depending upon individual eyes and underlying diagnoses.

Phototherapeutic Keratectomy: Strategies and Results in 12 Eyes

As part of a multicenter study of excimer laser procedures, we performed phototherapeutic keratectomy (PTK) on 12 eyes in 11 patients. Three eyes had superficial corneal scarring, two Salzmann's degeneration, two Reis-Bückler's dystrophy; and one each with recurrent lattice dystrophy in a corneal graft, band keratopathy, recurrent erosion syndrome, after pterygium scarring, and contact-lens related keratopathy. Indications for treatment included poor visual acuity, severe glare symptoms, ocular surface discomfort, recurrent erosions, and monocular diplopia. Follow up ranged from 1 to 4 months. Best spectacle corrected visual acuity improved in ten eyes with no eyes suffering loss of best spectacle corrected visual acuity. A hyperopic refractive shift was found in eight of 12 treated eyes. Corneal surface regularity improved in six of 12 eyes and worsened in one eye as measured by computerized corneal topographic analysis. Ten patients (11 eyes) noted improvement in their visual perception and subjective symptoms. We review various strategies of phototherapeutic keratectomy designed to treat particular corneal disorders: patient selection criteria to optimize clinical outcome are reviewed as well.