Excimer laser photorefractive keratectomy for high myopia: four-year experience with a multiple zone technique

Twelve-Month Outcomes of the Wavefront-Optimized Photorefractive Keratectomy for High Myopic Correction Compared with Low-to-Moderate Myopia

Purpose

To evaluate the 12-months outcomes of photorefractive keratectomy (PRK) in patients with high myopia (≥ 6.0 diopters, D) compared with low-to-moderate myopia (< 6.0 D).

Patients and Methods

Records of 46 patients (69 eyes) who underwent PRK for myopic and astigmatic correction between October 2015 and December 2018 were reviewed. High myopic eyes (29 eyes) were compared with low-to-moderate myopic eyes (40 eyes). All surgeries were adjunct with 0.02% mitomycin C intraoperatively. Measured outcomes included postoperative uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent, corneal haze rate, and any complications.

Results

At 12 months post-PRK, 26 eyes (89.7%) in the high myopia and 39 eyes (97.5%) in the low-to-moderate myopia group had UDVA ≥ 20/20, (p=0.30). Average postoperative logMAR UDVA at 12 months was −0.04 (20/18) and −0.11 (20/15) for the high myopia and low-to-moderate myopia groups, respectively. No eyes in either group had residual refractive errors >1 D. No eyes in both groups developed significant corneal haze at month 12. No eyes had a loss of greater than two Snellen lines of CDVA at 12 months post-surgery. The efficacy and safety indices at 12 months post-surgery were not significantly different between groups (1.06±0.26 vs.1.14±0.27, p =0.25 and 1.14±0.27 vs 1.17±0.26, p=0.60 for low-to-moderate myopia vs high myopia groups, respectively).

Conclusion

PRK with high myopic correction provides excellent refractive outcomes and is safe, compared to those of low-to-moderate myopic correction.

Corneal Aberrations, Contrast Sensitivity, and Light Distortion in Orthokeratology Patients: 1-Year Results

Purpose. To evaluate the corneal higher-order aberrations (HOA), contrast sensitivity function (CSF), and light distortion (LD) in patients undergoing orthokeratology (OK). Methods. Twenty healthy subjects (mean age: 21.40 ± 8 years) with mean spherical equivalent refractive error M = −2.19 ± 0.97 D were evaluated at 1 day, 1 month, and 1 year after starting OK treatment. Monocular LD, photopic monocular CSF, and corneal HOA for 6 mm pupil size were measured. Results. LD showed an increase after the first night (p < 0.05) and recovery to baseline after 1 month, remaining stable after 1 year (p > 0.05). Spherical-like, coma-like, and secondary astigmatism HOA RMS increased significantly (p ≤ 0.022) from baseline to 1-month visit, remaining unchanged over the follow-up. Contrast sensitivity for medium frequencies (3.0, 4.24, and 6.00 cpd) was significantly correlated with LD parameters at baseline (r ≤ −0.529, p < 0.001). However, after 1 year of treatment, this correlation was only statistically significant for 12 cpd spatial frequency (r ≤ −0.565, p < 0.001). Spherical-like RMS for 6 mm pupil size correlated with irregularity of the LD (r = −0.420, p < 0.05) at the 1-year visit. Conclusion. LD experienced by OK patients recovers after one month of treatment and remains stable in the long term while optical aberrations remain significantly higher than baseline.

Mesopic Functional Visual Acuity in Normal Subjects

To evaluate mesopic functional visual acuity (FVA) with a newly developed system in normal subjects and to compare the results with photopic FVA, sixty-eight healthy volunteers (24.03 ± 4.42 [mean ± standard deviation] years) were enrolled in this study. A commercially available FVA measurement system (AS-28; Kowa, Aichi, Japan) was modified to measure FVA under mesopic conditions as well as photopic conditions. Measurements were performed monocularly in photopic conditions during 60 seconds. After dark adaptation for 15 minutes, the same measurements were repeated in mesopic conditions. Outcomes included starting visual acuity (VA), FVA (the average of VAs), visual maintenance ratio (VMR), maximum VA, minimum VA, and numbers of blinks during the 60-second measurement session, and were compared between mesopic and photopic conditions. Starting VA was –0.11 ± 0.08 and 0.39 ± 0.12 logarithm of the minimum angle of resolution (logMAR) in photopic and mesopic conditions, respectively. FVA was –0.06 ± 0.09 and 0.52 ± 0.14 logMAR, VMR was 0.98 ± 0.02 and 0.94 ± 0.04, maximum VA was –0.15 ± 0.06 and 0.33 ± 0.12 logMAR, the minimum VA was 0.05 ± 0.12 and 0.78 ± 0.20 logMAR, and the number of blinks was 8.23 ± 7.54 and 7.23 ± 6.20, respectively. All these parameters except the number of blinks were significantly different between the two conditions (P < 0.001). Besides, the difference between maximum and minimum VAs and standard deviation of VA were significantly larger in mesopic than in photopic conditions (P < 0.001). This study revealed that not only overall visual function decline but also instability of vision under mesopic conditions even in healthy subjects.

Mesopic contrast sensitivity and ocular higher-order aberrations after overnight orthokeratology

PURPOSE

To investigate mesopic contrast sensitivity and night driving ability in eyes undergoing overnight orthokeratology, and to analyze the relationship among mesopic contrast sensitivity, ocular higher-order aberrations, and myopic correction.

DESIGN

Prospective, noncomparative, consecutive case series.

METHODS

In 44 eyes of 22 subjects (mean age +/- standard deviation [SD], 24.0 +/- 3.2 years) with orthokeratology, ocular aberrations and mesopic contrast sensitivity were determined before and three months after commencement of the procedure. Mean spherical equivalent refraction +/- SD was -2.34 +/- 0.99 diopters at baseline. Mesopic contrast sensitivity with and without glare was assessed using the Mesotest II (Oculus, Wetzlar, Germany).

RESULTS

Orthokeratology significantly reduced the log mesopic contrast sensitivity from 0.25 +/- 0.08 to 0.08 +/- 0.10 without glare (P < .0001, Wilcoxon) and from 0.21 +/- 0.11 to 0.07 +/- 0.10 with glare (P < .0001). The proportion of eyes that fulfilled the German standard recommendation level for night driving was 36%. The induced changes in log mesopic contrast sensitivity showed significant negative correlation with the changes in third-order (r = -0.490, P = .0013 without glare; r = -0.362, P = .0177 with glare; Spearman rank correlation coefficient) and fourth-order root mean square (r = -0.586, P = .0001 and r = -0.306, P = .0450, respectively). Furthermore, significant correlation was found between the amount of myopic correction and the induced changes in log mesopic contrast sensitivity (r = -0.442, P = .0038 without glare; r = -0.464, P = .0024 with glare). The induced changes in higher-order aberrations significantly correlated with the amount of myopic correction (P < .0001, Pearson correlation coefficient).

CONCLUSIONS

Mesopic contrast sensitivity after overnight orthokeratology is deteriorated significantly as ocular higher-order aberrations increase, and these changes depend on the amount of myopic correction.

Technical Improvements in Photorefractive Keratectomy for Correction of High Myopia

PURPOSE

To evaluate the effects of hardware and software improvements in photorefractive keratectomy (PRK) for the treatment of highly myopic eyes.

METHODS

A retrospective study was carried out in 554 patients (582 eyes) with myopia between -7.00 and -17.00 D (mean -11.20 +/- 3.60 D) who had undergone PRK using the Aesculap Meditec laser. Group 1 with a 5-mm-diameter single ablation zone; Group 2 with a 5-mm-diameter single zone surrounded by a 2-mm tapered transitional zone; Group 3 and Group 4, same as Group 2 but with the laser upgraded with a smoke aspiration control system (Group 3), and with a computer-controlled fluence (Group 4).

RESULTS

In Group 1 at 2 years after PRK (50 eyes), 10 eyes (20%) were within +/-1.00 D of attempted correction and 13 eyes (26%) were within +/-2.00 D. In Group 2 at 2 years (118 eyes), 42 eyes (36%) were within +/-1.00 D of attempted correction and 65 eyes (55%) were within +/-2.00 D. In Group 3 at 2 years (43 eyes), 18 eyes (42%) were within +/-1.00 D of attempted correction and 28 eyes (65%) were within +/-2.00 D. In Group 4 at 2 years (47 eyes), 25 eyes (53%) were within +/-1.00 D of attempted correction and 29 eyes (62%) were within +/-2.00 D.

CONCLUSIONS

Software and hardware improvements facilitated PRK correction of high myopia with reasonable predictability, especially if a tapered transition zone was used. At 12 and 24-month follow-up, only the use of a tapered transition zone was associated with a statistically significant improvement in predictability.

Quality of vision after laser in situ keratomileusis: influence of dioptric correction and pupil size on visual function

PURPOSE

To determine the influence of pupil size and the amount of ablation on visual performance and on the patient's perception of glare or halo after laser in situ keratomileusis (LASIK).

SETTING

Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan.

METHODS

This study included a random cross-section of 50 eyes of 32 patients with "uniform" topography at least 6 months after LASIK and 51 eyes of 28 patients who had normal corneas. Each LASIK patient completed a survey rating adverse effects such as symptoms of night glare and halo. Pupil diameter and best spectacle-corrected visual acuity (BSCVA) were measured under photopic and scotopic conditions. Contrast sensitivity was measured with an MCT 8000 (Vistech Consultants, Inc.) under daytime and nighttime and with night glare conditions. A Technomed C-scan (Technomed Technology) was performed, and the potential corneal visual acuity (PCVA) was calculated after the settings for the pupil size were changed to the values measured under bright-light or dim-light conditions.

RESULTS

No significant difference was found between the post-LASIK and normal cornea groups in photopic or scotopic BSCVA (P>.05). In cases of moderate myopia, the post-LASIK group had decreased PCVA and contrast sensitivity (P<.05). In cases of high myopia, the post-LASIK group had decreased contrast sensitivity at spatial frequencies of 1.5 cycles per degree (cpd) under daytime conditions and 3 cpd under nighttime conditions (P<.05). Glare or halo symptoms did not correlate with scotopic BSCVA, PCVA, or nighttime contrast sensitivity with or without glare (P>.05). Pupil size was not significantly correlated with glare or halo symptoms, BSCVA, or contrast sensitivity under scotopic or photopic conditions (P>.05). In moderate myopia, the amount of attempted correction of the spherical equivalent (SE) was correlated with halo symptoms (P<.05; adjusted r(2) = 0.17). In high myopia, the amount of attempted astigmatism correction was correlated with the development of glare symptoms (P<.05; adjusted r(2) = 0.16).

CONCLUSIONS

There was a decrease in contrast sensitivity in post-LASIK eyes. The amount of attempted correction of the SE or astigmatism was correlated with the development of glare and halo symptoms. Pupil size was not significantly correlated with glare or halo symptoms, BSCVA, or contrast sensitivity in post-LASIK patients with "uniform" topography who had scotopic pupils not larger than 7.0 mm.

Iris-claw Phakic Intraocular Lens for High Myopia

PURPOSE

To evaluate the efficacy, safety, predictability, and stability of implanting a polymethylmethacrylate (PMMA) phakic intraocular lens (PIOL) (the Artisan myopia lens) to correct high myopia.

METHODS

An Artisan myopia lens was implanted in 78 consecutive eyes of 49 patients with preoperative myopia that ranged from -6.25 to -28.00 D. Mean patient age was 42.4 years. Mean follow-up was 10.7 months and all patients were followed for at least 6 months; 45 eyes had follow-up of 12 months, and 10 eyes had 24 months. The desired outcome was emmetropia in all eyes except for those eyes with preoperative myopia greater then -23.00 D.

RESULTS

Fifty-three eyes (67.9%) had a postoperative refraction at the last follow-up examination within +/-1.00 D of emmetropia, and 39 eyes (50.0%) had a postoperative refraction +/- within 0.50 D of emmetropia. The postoperative refraction remained stable during the entire follow-up period. Mean spectacle-corrected visual acuity improved from 20/32 preoperatively to 20/25 postoperatively. Mean postoperative uncorrected visual acuity was 20/32. There was no significant change in endothelial cell density from baseline. We did not encounter major complications.

CONCLUSION

Implantation of the Artisan myopia lens to correct high myopia resulted in a stable and fairly predictable refractive outcome. A significant endothelial cell change was not detected.

Functional outcome and satisfaction after photorefractive keratectomy. Part 2: survey of 690 patients

PURPOSE

To document patient satisfaction and self-perceived quality of vision after bilateral photorefractive keratectomy (PRK).

DESIGN

Noncomparative, interventional case series.

PARTICIPANTS

Consecutive patients who underwent bilateral PRK from May 1994 through May 1997 by the 12 surgeons of four collaborating centers with a minimum of 4 months since the last surgery and up to 30 months since the first surgery.

METHODS

A questionnaire with known psychometric properties was self-administered by the patients.

MAIN OUTCOME MEASURES

Responses to individual questions and scale scores.

RESULTS

A total of 929 questionnaires were sent, of which 690 were answered and returned (74.3% response rate). The preoperative spherical equivalent ranged from -0.38 diopters [D] to -27.75 D (mean, -5.32 D; standard deviation, 2.85 D). Although 91.8% of the patients were satisfied or very satisfied with their surgery, 96.3% considered that their main goal had been reached, and 95.7% would still choose to have surgery if they had it to do over. The degree of satisfaction was proportional to the postoperative uncorrected visual acuity in the best eye expressed in LogMAR (r = -0.18, P: = 0. 0001) and was negatively correlated with the importance of the corneal haze (r = -0.23, P = 0.0001). Daytime glare was reported to be greater than before surgery by 55.1% of patients. A decrease in night vision was reported by 31.7% of patients, and 31.1% of patients reported increased difficulty driving at night because of their vision.

CONCLUSIONS

Overall satisfaction after PRK for low to severe myopia appears to be very good. Glare and night vision disturbance, particularly bothersome for night driving, seem to constitute significant secondary effects that deserve further investigation and should be kept in mind for future improvements in the technique.

Advances in refractive surgery: 1975 to the present

PURPOSE

To review the major advances in the field of refractive surgery occurring over the past 25 years.

METHODS

Literature review.

RESULTS

The major developments in refractive surgery over the past 25 years are reviewed.

CONCLUSIONS

The past 25 years have witnessed great changes in refractive surgery. As a result of advancements in technology, instrumentation, and technique, we have seen improvements in the treatment of all types of ametropias. In this article, we review some of the successes and failures of the past quarter-century.

Contrast sensitivity measured by 2 methods after photorefractive keratectomy

PURPOSE

To study contrast sensitivity in eyes that had flying-spot excimer laser photorefractive keratectomy (PRK) and to compare a subjective method (Vision Contrast Test System [VCTS] 6500) and an objective method (visual evoked potential [VEP]) of measuring contrast sensitivity.

SETTING

Istituto Clinica Oculistica, Università degli Studi, Bari, Italy.

METHODS

Contrast sensitivity changes over time were evaluated in 26 eyes. The baseline values were compared with measurements 3, 6, and 12 months after PRK using the VCTS 6500 and VEP. Contrast threshold and VEP amplitude were classified by myopic correction.

RESULTS

Contrast threshold values changed significantly over time (P <.001). Significant differences were found between mean contrast threshold preoperatively and 12 months postoperatively (P <.001) at all spatial frequencies. A significant relationship was established between baseline and 12 month measurements at 18 cycles per degree. Mean VEP amplitude measurements also changed significantly over time (P <.001) and showed a significant relationship between baseline and 12 month measurements (P <.001). A significant relationship was also established between baseline and 12 month VEP amplitude values at 100% of grating contrast. Patients with high myopia complained significantly more at a lower contrast threshold and at lower VEP amplitude values than patients with low myopia.

CONCLUSIONS

Three months after PRK, contrast threshold and VEP amplitude values were reduced. Partial recovery was established at 6 months, although patients reported permanent impairment under low-contrast conditions, especially if the myopia correction was more than 6.0 diopters.

Retinal nerve fiber layer measurements using scanning laser polarimetry after photorefractive keratectomy

PURPOSE

To assess the effects of corneal depth changes on retinal nerve fiber layer (RNFL) postoperative measurements in myopic patients who had undergone photorefractive keratectomy (PRK).

METHODS

A total of 120 myopic patients underwent PRK for myopia (range -2 to -10 diopters) and were divided into three groups according to their myopic correction: lower than 3 diopters (low myopia group), between 3 and 6 diopters (medium myopia group), over 6 diopters (high myopia group). RNFL parameters were evaluated preoperatively and 5 days, 3 months and 6 months after surgery, using a GDx NFA II scanning laser ophthalmoscope.

RESULTS

Significant changes were seen in the symmetry, superior maximum, and average thickness, comparing baseline with six-month measurements (p=0.008, 0.027, 0.015 respectively). Dividing the sample according to attempted myopic correction, it was found that mean postoperative RNFL thickness was significantly lower after PRK only in the high myopia group. Mean RNFL thickness did not change with time (p=0.884). Ablation depth was correlated with a change in RNFL thickness by the sixth postoperative month for each group. These variables were significantly related only in the high myopia group (p=0.003).

CONCLUSIONS

As polarised light penetrates the ablation area, morphological and functional changes might affect Gdx NFA II measurements. It must always be borne in mind that RNFL thickness can decrease either in cases of glaucoma or after PRK for high myopia, so close attention must be paid to interpreting these measurements in patients who have undergone PRK.

Results of bilateral photorefractive keratectomy

OBJECTIVE

To study the refraction and potential risks of bilateral photorefractive keratectomy for myopia.

DESIGN

Retrospective, noncomparative case series.

PARTICIPANTS

Four hundred eighteen consecutive patients (836 eyes) with myopia from -18 to -0.50 diopters (D) had bilateral simultaneous refractive surgery.

INTERVENTION

Refractive surgery was performed with the Nidek EC-5000 slit-scanning excimer laser (Nidek Co., Tokyo, Japan).

MAIN OUTCOME MEASURES

Manifest refraction, Snellen best spectacle-corrected visual acuity (BSCVA) and uncorrected visual acuity, haze, and halos were evaluated for 12 months after surgery. Both eyes of each patient were examined at the same follow-up after initial treatment.

RESULTS

At 12 months after surgery, 95% of eyes were within +/- 1D of emmetropia, and 0.4% of patients had residual anisometropia more than 2 D. Thirty-three eyes (3.9%) were retreated, whereas 5 patients (1.2%) had retreatments in both eyes. Odds ratios between unilateral versus bilateral postoperative events were evaluated for the retreatments (1:0.22; P = 0.001), undercorrections more than 1 D (1:0.17; P < 0.0001), overcorrections more than 1 D (1:0.23; P < 0.0001), loss of 1 line of BSCVA (1:0.44; P < or = 0.002), and loss of 2 lines of BSCVA (1:0.18; P = 0.013). At 12 months after surgery, one eye with a loss of 2 lines of BSCVA was treated for haze more than 1; the fellow eye had haze 0.75. No patient had bilateral haze more than 1. At 12 months after surgery, no patient lost 2 lines of BSCVA in both eyes. There was a higher incidence of halos in both eyes rather than in one eye only (odds ratio: 4.17; P < 0.0001). No postoperative infections occurred.

CONCLUSIONS

Bilateral events occurred approximately 2.5 to 4 times less often than unilateral events, except for the incidence of halos. The calculated odds ratio did not show an increased risk for the fellow eye while performing bilateral surgery, although not exempted from the risk of infection. It may be difficult to predict a complication in the fellow eye based on the results of the first operated eye.

Initial results of photorefractive keratectomy and laser in situ keratomileusis performed by a single surgeon

PURPOSE

To determine the safety and efficacy of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) early in a surgeon's experience.

SETTING

Ophthalmology Department, John A. Moran Eye Center, Salt Lake City, Utah, USA.

METHODS

Between October 1995 and April 1997, a retrospective analysis was performed of 200 eyes in 128 patients who had PRK or LASIK with a follow-up of at least 3 months. The mean age was 38.1 years +/- 10.4 (SD) in the PRK group and 42.3 +/- 10.1 years in the LASIK group. There were 36 women and 30 men in the former and 32 women and 30 men in the latter. Photorefractive keratectomy, PRK/astigmatic keratotomy (AK), LASIK, or LASIK/AK was performed with the Summit Omnimed excimer laser. Preoperative evaluation included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), cycloplegic refraction, tonometry, and computerized videokeratography. At 1, 3, and 6 months, UCVA, BSCVA, mean spherical equivalent (SE), astigmatism, corneal haze, subjective vision (day, night, glare, and halo), and complications were measured.

RESULTS

Mean SE was 0.16 +/- 0.82 diopter (D) in the PRK group and -0.09 +/- 0.63 D in the LASIK group at 1 month (P < .05), -0.18 +/- 0.66 D and -0.16 +/- 0.58 D, respectively, at 3 months, and -0.33 +/- 0.73 D and -0.09 +/- 0.62 D, respectively, at 6 months. Achieved correction was similar in the 2 groups. Mean BSCVA was 22.8 +/- 6.0 in the PRK group and 22.2 +/- 5.3 in the LASIK group at 1 month, 21.1 +/- 6.0 and 21.1 +/- 3.1, respectively, at 3 months, and 19.8 +/- 3.5 and 22.9 +/- 5.2, respectively, at 6 months (P < .005). Mean surface regularity index was 0.68 +/- 0.40 in the PRK group and 0.86 +/- 0.41 in the LASIK group at 1 month, 0.54 +/- 0.26 and 0.72 +/- 0.37, respectively, at 3 months (P < .05), and 0.49 +/- 0.27 and 0.84 +/- 0.42, respectively, at 6 months. Mean surface asymmetry index was 0.71 +/- 0.43 in the PRK group and 0.55 +/- 0.21 in the LASIK group at 1 month (P < .05), 0.53 +/- 0.24 and 0.51 +/- 0.23, respectively, at 3 months, and 0.46 +/- 0.19 and 0.64 +/- 0.54, respectively, at 6 months. The subjective parameters between the groups were significantly different only at 6 months; patients in the PRK group reported better day and night vision.

CONCLUSION

With careful preparation and proper training, PRK and LASIK appear to be safe and efficacious even during the surgeon's early learning phases.