Photorefractive keratectomy (PRK) has been a common method for the correction of refractive error for some time [
Presbyopia is an on-going challenge for the refractive surgeon, and, as of yet, no single surgical solution has been found. It has been observed in some cases that, following corneal refractive surgery, presbyopic patients appear to develop pseudoaccommodation and have better than expected near visual acuity [
Currently, there is no literature detailing the level of near visual acuity following hyperopic PRK (MEDLINE search with key words “photorefractive keratectomy,” “PRK,” “presbyopia,” “near vision,” “near visual acuity”). A previous study [
This study evaluated the distance and near vision (with best corrected distance vision) in a group of 120 presbyopic posthyperopic PRK eyes with age-matched controls assessing for evidence of the safety, efficacy, and predictability of performing hyperopic PRK on presbyopic eyes.
This retrospective comparative single surgeon (AL) study included presbyopic eyes undergoing hyperopic PRK to correct distance vision with a target postoperative refraction of plano. It also included a control group which received no treatment whatsoever. All treatments were performed in a private practice in Siena, Italy. All patients signed a consent form for hyperopic correction by PRK.
Inclusion criteria were as follows. An age between 45 and 65. A cycloplegic refraction with spherical equivalent between +1.00 and +5.00. Refractive stability for the last 2 years. Absence of any previous corneal or lens surgery. Absence of any corneal, macular, inflammatory, or lens abnormality. Absence of collagen disease or diabetes. Ultrasound central corneal pachymetry greater than 500 microns. Regular corneal topography with no signs of contact lens induced warpage and a central curvature less than 45 dioptres. Keratoconus was ruled out by a combination of topography indexes and pattern, and pachymetry as detailed in angle-supported phakic intraocular lenses in eyes with keratoconus and myopia [ Best spectacle corrected visual acuity (BSCVA) of 0.2 log MAR units was required for an eye to be included. Absence of pseudophakia.
Followup for assessment of near and distance visual acuity was 12 months following the treatment.
Preoperative assessment consisted of uncorrected visual acuity (UCVA), BSCVA, autorefractometry assessed with Retinomax 2 (Nidek), manifest and cycloplegic refraction (by cyclopentolate), undilated and dilated slit lamp evaluation, axial and tangential corneal topography assessed with Oculus Keratograph (Iculus Wetzlar, Germany), tonometry assessed with Goldmann tonometer, dilated funduscopy.
Soft contact lens use was interrupted 1 month before examination and surgery, while rigid contact lens use was interrupted 3 months before examination and surgery.
A Bausch & Lomb Technolas 217z excimer laser was used in Planoscan mode. A 6 mm optical zone was chosen in all eyes. The cycloplegic spherical error was fully treated. The left eye was treated immediately after the right. Laser fluence was calibrated obtaining a fully red area (with tiny aluminum remnants) on the calibration plate with 65 spots. No nomogram adjustments were used.
Before PRK, topical anesthesia comprising 3 to 5 drops of oxybuprocaine 0.4% was administered. After an eyelid speculum was inserted, manual deep ithelialization was performed in a 10.0 mm circular area with a blunt golf-club spatula and the epithelium was discarded. Laser ablation was centred on the visual axis, which was identified by the superimposed Purkinje images.
Ten mL of BSS at 10°C was dripped on the cornea, and the cornea dried by a Merocel sponge. Another Merocel sponge soaked with mitomycin C 0.2 mg/mL (corresponding to 0.02%) (Kyowa Hakko Kogyo Co. Ltd., Tokyo, Japan) was applied on the stromal bed for 45 seconds. Finally, the stromal bed was irrigated with 30 mL of BSS at 10°C. Topical levofloxacin 0.3% and diclofenac were instilled, and a balafilcon a bandage contact lens (Pure Vision, Bausch & Lomb) was applied.
All patients had postoperative examinations at 2, 3, 4, 6, and 30 days as well as 2, 4, 6, and 12 months. A slit lamp examination was performed at all examinations. Manifest BSCVA, UCVA, and tonometry were measured at all visits beginning at 30 days. At the 12 month visit, unaided near visual acuity was assessed. It was not assessed at any other stage in order to remove any possible learning effects. Near visual acuity was also assessed with any distance correction required to negate the effects of under or over correction.
Following the surgery, an assessment of near vision was carried out for all eyes. This assessment was carried out by the same person (AL), with the same reading chart and in the same lighting conditions to ensure no extraneous factors influenced the results. Any eyes where the spherical equivalent was not 0.00 following the PRK had their near vision assessed with their required distance refraction in place, so as to negate any effects of over or under correction. All eyes with a spherical equivalent of 0.00 had their near vision assessed unaided. Near vision was measured using Jaeger notation.
At this stage, the control group had their unaided near visual acuity measured as a comparison.
Statistical analysis was performed by PASW Statistics v.18 (SPSS: An IBM Company). The unit of data analysis used was per eye. An independent
A total of 120 eyes of 60 patients passed the inclusion criteria and gave consent to be included in this study. All eyes had hyperopic PRK to correct distance refractive error and were in an age group affected by presbyopia. A group of age-matched healthy presbyopic emmetropes (cycloplegic refraction in each eye comprised between +0.25 and −0.25 D) was used as a control group. All patients attended for a 12-month followup.
All PRK group patients were in the presbyopic age group with a mean age of 52 and range of 45 to 65 (SD 5.09). The mean age for the control group was 54 with a range of 45 to 65 (SD 5.09). The difference in age was not statistically significant (
Preoperatively, the mean spherical equivalent (SE) of the PRK group was +2.38 with a range of +1.00 to +4.75 (SD 0.71). Preoperatively, the mean BSCVA of the PRK group was 0.003 Log MAR with a range of 0.00 to 0.10 log MAR (SD 0.015).
Predictability was measured by mean SE at 12 months. Postoperatively, the mean SE was −0.10 with a range of +0.25 to −1.00 (SD 0.27). At 12 months, 109 eyes (91%) were within ±0.50 D of the intended correction and 120 eyes (100%) were within ±1.00 D of the intended correction.
Safety was evaluated by changes in BSCVA, observed at 12 months. In the PRK group, mean BSCVA at 12 months was 0.005 log MAR with a range of 0.00 to 0.15 (SD 0.022) log MAR. 2 eyes lost ≥0.1 log MAR acuity with all other eyes maintaining or seeing an increase in BSCVA as seen in Figure
This figure shows pre- and postoperative best spectacle corrected visual acuity (BSCVA) for 120 presbyopic eyes undergoing hyperopic PRK. The operation had a safety index of 0.995 with 2 eyes losing ≥0.1 log MAR and all other eyes maintaining or having an increase in BSCVA.
Efficacy was evaluated by UCVA at 12 months. The mean UCVA that was at 12 months was 0.04 (SD 0.077) log MAR with a range of 0.00 to 0.30 log MAR. Efficacy index (postoperative UCVA/preoperative BSCVA) was 0.92.
Figure
This figure compares the distance corrected near visual acuity (DCNVA) of 120 posthyperopic PRK eyes, which are also presbyopic (PRK group), and the uncorrected near visual acuity (UNVA) of 120 emmetropic presbyopic eyes (control group). The near visual acuity was found to be better to a statistically significant extent (
Almost 50% of the PRK group had a
Summary of near visual acuity (NVA) for PRK and control group.
PRK group | Control group | |
---|---|---|
Number of eyes | 120 | 120 |
Mean NVA | ||
Median NVA | ||
Mode NVA |
NVA = DCNVA for PRK group and UCVA for control group.
This table shows the main NVA findings. The mean NVA following PRK was found to be better to a statistically significant extent (
All eyes selected for this study underwent uneventful PRK with no complications occurring.
This study found PRK to be a safe, predictable, and effective way of correcting low to moderate levels of hyperopia in a presbyopic age group. Hyperopia is the most common refractive error [
In this study, the post-PRK eyes were observed to have significantly better near acuity than would be expected for presbyopic eyes, when compared to a control group which has had no surgery.
It may be that this better than expected near vision is due to an increase in depth of focus (DOF). Depth of focus (DOF) can be defined as “the distance in front and behind the focal point over which the image may be focused without causing a sharpness reduction” [
DOF is affected by several factors which can be separated into two categories; external or internal. External factors include luminance, contrast, wavelength of light, spatial frequency, and target detail [
A well-observed complication following corneal refractive surgery is an increase in higher-order aberrations [
Bakaraju et al. [
This association between SA and DOF in presbyopes was also investigated by Rocha et al. [
The only other study which assessed the level of near vision in presbyopes following a laser corneal refractive procedure was conducted by Artola et al. [
Although multifocal corneal laser surgery has not become widely excepted [
A lot of current research in corneal laser refractive surgery relates to minimising any surgically induced higher order aberrations following surgery such as SA [
None of the authors has conflict of interests with the submission.
The study was performed in a private Italian Institution which is not governed by a Research Ethics Committee. Therefore, ethical approval was obtained from the University of Ulster Local Research Ethics Committee. Informed consent was obtained, and this study followed all the guidelines required by the University of Ulster’s Local Research Ethics Committee.