Laser in situ keratomileusis flap stability during simulated aircraft ejection in a rabbit model

Photorefractive Keratectomy in Student Naval Aviators: Outcomes of the U.S. Navy Accessioning Study

PURPOSE

To present the outcomes of the U.S. Navy photorefractive keratectomy (PRK) accessioning study conducted between 2000 and 2005 that helped lead to the acceptance of laser vision correction within the U.S. aviation industry.

METHODS

In this prospective masked study, a total of 301 students who had PRK and underwent naval flight training were compared to 4,368 untreated peers. Three training pipelines were compared: propeller/jet transport, jet fighters, and helicopters. The evaluated metrics were flight and academic performance (assessed for the primary and advanced stage of the training as normalized Navy Standard Score [NSS]), as well as the student attrition rate from training.

RESULTS

The attrition rate was lower in the PRK group compared to controls (15.9% vs 23.2%; P = .004). In the primary stage of training, students who had PRK outperformed controls in flight training performance in the propeller/jet transport pipeline (average NSS after PRK: 52.4 ± 7.5 vs controls: 50.7 ± 6.4, P = .02), but the flight performance in the jet fighter and helicopter pipelines was comparable between the two groups. Academic performance in the primary stage of training was approximately 7% to 13% higher in students who had PRK for all training pipelines. During the advanced training stage, there was no difference in the flight performance between the groups in any of the presented pipelines. Academic performance was significantly better for students who had PRK in the helicopter pipeline (51.2 ± 11.0 vs 46.7 ± 11.7 P < .001) but comparable between the two groups in the remaining pipelines.

CONCLUSIONS

Refractive surgery did not have adverse effects on flight performance metrics. Pilots who had PRK had comparable or better outcomes than their untreated peers. [J Refract Surg. 2024:40(3):e173-e181.].

Small-incision lenticule extraction in the U.S. military: prospective study of visual and military task performance

PURPOSE

To assess early visual outcomes and military task performance after small-incision lenticule extraction (SMILE) among U.S. military service members.

SETTING

Warfighter Refractive Eye Surgery Program and Research Center and Night Vision and Electronic Sensors Directorate, Fort Belvoir, Virginia.

DESIGN

Single-center, prospective, observational study.

METHODS

The study was composed of active duty service members (n = 37) electing to undergo SMILE for myopia or myopic astigmatism. Testing performed preoperatively and at 1 month and 3 months postoperatively included uncorrected (UDVA) and corrected (CDVA) distance visual acuities, wavefront aberrometry, low-contrast visual acuity (LCVA), contrast sensitivity, and vision-related questionnaire. 14 participants underwent rifle marksmanship with spectacle correction before and without correction at 6 to 8 weeks postoperatively.

RESULTS

At 3 months postoperatively, the efficacy index was 0.96 and the safety index was 1.03. UDVA was ≥20/20 in 69 (96%) of eyes. LCVA change from baseline was significant under night vision condition. Eye problems contributed to 10% work and 20% activity impairments, both of which decreased to 0% (P = .001). The overall satisfaction rating for SMILE was high at 90.9 (95% CI, 85.3 to 96.5), and 95% of participants would be willing to undergo the procedure again. The median scores between preoperative and 6 to 8 weeks postoperative firing performance were comparable (34 vs 35, with and without correction, respectively; P = .247).

CONCLUSIONS

After the early recovery period, SMILE seems to preserve quality of vision, which appears to facilitate the accomplishment of tasks related to their work as military service members as well as performing activities outside of work.

Visual outcomes after SMILE from the first-year experience at a U.S. military refractive surgery center and comparison with PRK and LASIK outcomes

PURPOSE

To assess the visual outcomes of small-incision lenticule extraction (SMILE) after the first year of treatments at a military refractive surgery center and compare with photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) outcomes during the same period.

SETTING

Warfighter Refractive Eye Surgery Program and Research Center, Fort Belvoir, VA.

DESIGN

Retrospective study.

METHODS

Records of service members who underwent SMILE, PRK, or LASIK for myopia from March 2017 to February 2018 were reviewed. Preoperative and up to 6-month postoperative data were collected. Visual outcomes were compared between treatments.

RESULTS

Of 563 treated eyes, 173 (30.7%) underwent SMILE, 304 (54.0%) PRK, and 86 (15.3%) LASIK. In comparing SMILE with PRK 1 month postoperatively, SMILE (145 eyes [87.9%]) attained uncorrected distance visual acuity (UDVA) ≥20/20 more vs PRK (214 eyes [73.8%]; P < .01). Similarly, SMILE (152 eyes [94.4%]) achieved more eyes with manifest spherical equivalent (MSE) within ±0.50 diopters (D) from intended target vs PRK (250 eyes [85.9%]; P = .01). None lost ≥1 line of corrected distance visual acuity in SMILE vs PRK (16 eyes [5.5%]; P < .01). Thereafter, there were no other significant differences except SMILE had 117 eyes (95.1%) vs PRK with 224 eyes (99.6%) achieving UDVA ≥20/20 at 3 months postoperatively (P = .01). In assessing SMILE vs LASIK, all parameters were comparable; however, 77 SMILE eyes (96.3%) had MSE within ±0.50 D from target vs 31 LASIK eyes (83.8%) at 6 months postoperatively (P = .02).

CONCLUSIONS

The first year after SMILE treatments in a U.S. military center demonstrated early postoperative outcomes superior to PRK. SMILE seemed more predictable compared with LASIK.

Laser in situ keratomileusis flap stability in an aviator following aircraft ejection

We present the case of a 28-year-old male F/A-18F Super Hornet naval flight officer who ejected from an aircraft at 13 000 feet at a speed in excess of 350 knots 7 years after uneventful laser in situ keratomileusis (LASIK). The patient was evaluated the day after the ejection. No LASIK flap complications or epithelial defects were found, and the corrected distance visual acuity was 20/15 in both eyes.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

Globe Rupture of a Post-LASIK Keratectasia Eye From Blunt Trauma

PURPOSE

To report a case of globe rupture in a patient with post-laser in situ keratomileusis (LASIK) ectasia after blunt trauma.

METHODS

Observational case report.

RESULTS

A 42-year-old man with a history of post-LASIK ectasia sustained paracentral corneal rupture secondary to blunt trauma from a fist to his left eye (OS). Slit-lamp examination revealed rupture in the posterior stroma (inferior paracentral) of the OS with an overlying intact LASIK flap; however, the inferior edges of the LASIK flap were Seidel positive. The anterior chamber was flat. Although he was initially managed with cyanoacrylate glue and a bandage contact lens, the patient eventually required tectonic penetrating keratoplasty. The postoperative course was unremarkable, and over 1 year later, the visual acuity OS was 20/25 with -7.50 + 2.00 × 0.50.

CONCLUSIONS

Globe rupture from blunt trauma has not been shown to be more common in patients with a history of LASIK. Although blunt trauma to the post-LASIK globe would generally incur a similar risk of rupture to that of the normal eye, keratectasia after LASIK may predispose the globe to rupture.

When case report became case series: 45 cases of late traumatic flap complications after laser-assisted in situ keratomileusis and review of Chinese literature

OBJECTIVE

To report 45 cases of late traumatic flap complications after laser-assisted in situ keratomileusis (LASIK) and discuss the continually increasing number of cases in China.

METHODS

A multicentre retrospective survey of eye injuries was carried in 31 military hospitals from January 2006 to December 2011. Detailed information from the medical records of all 92 cases with a history of prior LASIK treatment were collected and summarised, with respect to visual acuity (VA), flap condition, treatment and final outcome. All Chinese publications relevant to late traumatic flap complications in Chinese patients were retrieved and summarised.

RESULTS

92 inpatients (92 eyes) underwent LASIK surgery; 45 of these had traumatic LASIK flap complications. Flap dislocation was the commonest and most needed surgical repair. VA after treatment was good and no statistically significant difference was observed when compared with the 47 cases without flap complications. 109 articles related to late traumatic flap complications after LASIK were retrieved from four Chinese document databases. There were 550 cases of late traumatic flap complications. From 2004, case reports became more common; 10 or more cases were reported in some case series. VA of most cases was good and there was no remarkable vision loss after treatment.

CONCLUSIONS

Late traumatic flap complications after LASIK have become more frequent in China, although the prognosis of most cases is good.

Early flap displacement after LASIK

PURPOSE

To evaluate the risks of flap displacement after LASIK.

DESIGN

Retrospective case series.

PARTICIPANTS

We included 41 845 consecutive adults who underwent LASIK surgery at Optical Express in the United Kingdom, including 81 238 eyes, of which 14 555 were hyperopic and 66 681 myopic or mixed astigmatic. We treated 57 241 eyes with the IntraLase FS-60 femtosecond laser and 23 997 with the Moria S.A. ONE Use-Plus automated microkeratome.

METHODS

We calculated the incidence of all flap displacements in the study population during an observational time period of ≥12 months after surgery. Independent variables were entered into logistic regression models to identify risk factors. Postoperative outcomes were assessed.

MAIN OUTCOME MEASURES

The incidence and odds ratios (OR) of flap displacement in the study population and in categories of refractive error and flap surgery technique.

RESULTS

The incidence of flap displacements was 10 in 81 238 LASIK procedures (0.012%), including 8 hyperopic eyes (0.055%) and 2 myopic eyes (0.003%). All flap displacements occurred within 48 hours of surgery and none were preceded by ocular trauma. They were classified as "early flap displacements" (EFD). The incidence of EFD after microkeratome surgery was 0.033% (n = 8), and after femtosecond laser it was 0.003% (n = 2). In hyperopic eyes having microkeratome surgery, the incidence was 0.179% (n = 7). In a logistic regression model, the strongest predictor of EFD after LASIK was hyperopia, recording an OR of 19.29 (P<0.001). The OR of developing an EFD after microkeratomy was 10.53 times higher than after femtosecond laser (P<0.005). In hyperopes, the OR of an EFD was 18.87 times higher after microkeratomy than after femtosecond treatment. Four of 10 displaced flaps needed secondary surgery, and 1 eye lost 2 lines of best-corrected visual acuity.

CONCLUSIONS

The incidence of flap displacements during a 12-month period after LASIK was extremely low (0.012%). Although the small number of displacements with the femtosecond laser limits conclusions, the risk of EFD was higher after microkeratome surgery than femtosecond laser.

Traumatic Corneal Flap Dislocation One to Six Years After LASIK in Nine Eyes With a Favorable Outcome

PURPOSE

To report our experience treating eye trauma after LASIK refractive surgery.

METHODS

Nine eyes of eight patients (one woman and seven men) were treated for ocular trauma: blunt trauma (n=5), sharp instrument trauma (n=2,) and trauma from inflation of automobile air bags during a traffic accident (n=2). The time from LASIK varied between 3 months and 6 years. All patients were hospitalized as a result of severe decrease in visual acuity and pain.

RESULTS

Seven of nine LASIK flaps had some degree of dislocation and were lifted, irrigated, and repositioned. Two flaps were edematous without dislocation. Intensive topical steroids and antibiotics were used in all patients up to 3 weeks after trauma. Three months after trauma, five eyes regained their pre-trauma visual acuity (between 20/20 and 20/40), and three eyes lost one line of best spectacle-corrected visual acuity.

CONCLUSIONS

Trauma occurring several months or years after LASIK may cause flap injury. Adequate and prompt treatment usually is successful.

Stability of the laser in situ keratomileusis corneal flap in rabbit eyes

PURPOSE

To quantify the force required to dislodge a laser in situ keratomileusis (LASIK) corneal flap in rabbits and correlate that force with sources of injury to LASIK corneal flaps in humans.

SETTING

Animal Vivarium and Department of Ophthalmology, Naval Medical Center, San Diego, California, USA.

METHODS

Corneal flaps were cut in 56 eyes of 30 rabbits. A -8.00 diopter excimer ablation was also performed in 32 of the eyes. Injury testing, using a burst of CO2 from a modified paintball gun, was conducted from 1 to 9 days postoperatively. Impact force was compared to that generated by mechanical trauma (fingers and a small tree branch) striking a force gauge.

RESULTS

Of 43 eyes tested for injury, flaps could not be dislocated in 11 eyes (26%). There was no significant difference between eyes treated with flap only and those that also had ablation. When flaps were dislodged, the required force generally resulted in extensive intraocular injury. There was no significant difference between the force required for flap dislocation on postoperative days 1 and 9.

CONCLUSIONS

In rabbits, LASIK corneal flaps were very resistant to high-speed wind trauma as early as 24 hours postoperatively. Flap stability was robust prior to the formation of collagen scar tissue, probably due to epithelial bridging at the edge of the flap and an osmotic gradient across the flap-stromal bed interface. Although this study used a rabbit model, it seems likely that both these flap adhesion mechanisms would also provide stability to the LASIK flap in humans.

Traumatic Late Flap Dehiscence and Enterobacter Keratitis Following LASIK

PURPOSE

To report a case of traumatic flap dehiscence and Enterobacter keratitis 34 months after LASIK.

METHODS

A 36-year-old man sustained a flap dehiscence following traumatic right eye gouging by a seagull claw. He presented the following day with uncorrected visual acuity (UCVA) in the affected eye of 3/200 and organic foreign body deposits underneath the flap. Systemic and topical antibiotics were administered and urgent surgical debridement and replacement of the LASIK flap was performed. An Enterobacter species was cultured from an intraoperative swab.

RESULTS

After a prolonged postoperative course, including administration of topical ofloxacin, tobramycin, chloramphenicol, and dexamethasone, UCVA returned to 20/20.

CONCLUSIONS

Good visual outcome after early debridement and appropriate antibiotics was achieved. Patients should be injury advised to seek prompt ophthalmic consultation after LASIK.

Using the Freiburg Acuity and Contrast Test to measure visual performance in USAF personnel after PRK

PURPOSE

Photorefractive keratectomy (PRK) may be an alternative to spectacle and contact lens wear for United States Air Force (USAF) aircrew and may offer some distinct advantages in operational situations. However, any residual corneal haze or scar formation from PRK could exacerbate the disabling effects of a bright glare source on a complex visual task. The USAF recently completed a longitudinal clinical evaluation of the long-term effects of PRK on visual performance, including the experiment described herein.

METHODS

After baseline data were collected, 20 nonflying active duty USAF personnel underwent PRK. Visual performance was then measured at 6, 12, and 24 months after PRK. Visual acuity (VA) and contrast sensitivity (CS) data were collected by using the Freiburg Acuity and Contrast Test (FrACT), with the subject viewing half of the runs through a polycarbonate windscreen. Experimental runs were completed under 3 glare conditions: no glare source and with either a broadband or a green laser (532-nm) glare annulus (luminance approximately 6090 cd/m) surrounding the Landolt C stimulus.

RESULTS

Systematic effects of PRK on VA relative to baseline were not identified. However, VA was almost 2 full Snellen lines worse with the laser glare source in place versus the broadband glare source. A significant drop-off was observed in CS performance after PRK under conditions of no glare and broadband glare; this was the case both with and without the windscreen. As with VA, laser glare disrupted CS performance significantly and more than broadband glare did.

CONCLUSIONS

PRK does not appear to have affected VA, but the changes in CS might represent a true decline in visual performance. The greater disruptive effects from laser versus broadband glare may be a result of increased masking from coherent spatial noise (speckle) surrounding the laser stimulus.