Journal of Refractive Surgery

Therapeutic Refractive Surgery Supplemental Data

Correction of Moderate to High Hyperopia With Implantation of an Allogeneic Refractive Lenticule

Jiawei Wu, MD; Lu Xiong, MD; Zheng Wang, MD; Dan Z. Reinstein, MD, DABO, FRCOphth; Ryan S. Vida, OD; Timothy J. Archer, MA(Oxon), DipCompSci(Cantab), PhD

Abstract

PURPOSE:

To describe the visual outcomes of correcting moderate to high hyperopia after two different surgical procedures of lenticular implantation.

METHODS:

This prospective small case series study used epikeratophakia combined with transepithelial phototherapeutic keratectomy (PTK-EP) and femtosecond laser–assisted lenticule intrastromal keratoplasty (LIKE) using myopic small incision lenticule extraction (SMILE)–derived refractive lenticule for correcting hyperopia ranging from +3.00 to +10.00 diopters (D). The implanted refractive lenticule was matched with the recipient's manifest refraction. The visual, refractive, corneal tomographic, and epithelial thickness outcomes were analyzed after surgery.

RESULTS:

Four eyes underwent PTK-EP and 6 eyes underwent LIKE. At the last postoperative visit, 6 of 10 eyes had uncorrected distance visual acuity equal to or better than the preoperative corrected distance visual acuity (CDVA). No eyes lost one line or more of CDVA postoperatively. Postoperative spherical equivalent was within ±0.50 D of the target for 9 of 10 eyes. Posterior corneal curvature slightly steepened for PTK-EP and LIKE. Postoperative epithelial thickness demonstrated the expected doughnut pattern in both groups characterized by epithelium in the central zone (5 mm) thinner than that in the peripheral zone (5 to 7 mm).

CONCLUSIONS:

Visual outcomes, refraction, posterior corneal surface changes, and epithelial remodeling after PTKEP or LIKE show a potentially useful modality for correcting moderate to high hyperopia.

[J Refract Surg. 2020;36(11):772–779.]

Abstract

PURPOSE:

To describe the visual outcomes of correcting moderate to high hyperopia after two different surgical procedures of lenticular implantation.

METHODS:

This prospective small case series study used epikeratophakia combined with transepithelial phototherapeutic keratectomy (PTK-EP) and femtosecond laser–assisted lenticule intrastromal keratoplasty (LIKE) using myopic small incision lenticule extraction (SMILE)–derived refractive lenticule for correcting hyperopia ranging from +3.00 to +10.00 diopters (D). The implanted refractive lenticule was matched with the recipient's manifest refraction. The visual, refractive, corneal tomographic, and epithelial thickness outcomes were analyzed after surgery.

RESULTS:

Four eyes underwent PTK-EP and 6 eyes underwent LIKE. At the last postoperative visit, 6 of 10 eyes had uncorrected distance visual acuity equal to or better than the preoperative corrected distance visual acuity (CDVA). No eyes lost one line or more of CDVA postoperatively. Postoperative spherical equivalent was within ±0.50 D of the target for 9 of 10 eyes. Posterior corneal curvature slightly steepened for PTK-EP and LIKE. Postoperative epithelial thickness demonstrated the expected doughnut pattern in both groups characterized by epithelium in the central zone (5 mm) thinner than that in the peripheral zone (5 to 7 mm).

CONCLUSIONS:

Visual outcomes, refraction, posterior corneal surface changes, and epithelial remodeling after PTKEP or LIKE show a potentially useful modality for correcting moderate to high hyperopia.

[J Refract Surg. 2020;36(11):772–779.]

Hyperopic corneal refractive surgery was first published by Dausch et al1 in 1993. The U.S. Food and Drug Administration approved laser in situ keratomileusis (LASIK) for hyperopia in 2000.2 However, the predictability and stability of earlier attempts were compromised once the corrected refraction exceeded +3.00 diopters (D).3,4 There have been significant improvements in LASIK for high hyperopia using a larger optical zone and transition zone, updates to the ablation profile design, and the introduction of flying-spot lasers. However, as expected, the refractive stability still decreases for higher corrections along with a reduction in corrected distance visual acuity.5–7 The use of epithelial thickness monitoring has been shown to improve the safety of high hyperopic LASIK.6

By the early 1980s, refractive lamellar keratoplasty was being investigated as a tissue additive procedure to alter corneal refractive power to correct high hyperopic aphakia,8–10 following the descriptions by Barraquer and Rutllán11 of epikeratophakia, in which the lenticule is placed on top of the cornea after epithelium removal. Currently, femtosecond laser technology can accurately create a refractive lenticule. The refractive lenticule extracted from myopic small incision lenticule extraction (SMILE) can be used to correct a refractive error-matched hyperopic correction in a recipient patient according to Barraquer's law of thicknesses.12 Several surgical techniques of refractive lenticular implantation have been developed. Thus, a second method of correcting hyperopia by an additive procedure is endokeratophakia, in which the lenticule is implanted into an intrastromal pocket.13 A third method is femtosecond laser–assisted lenticule intrastromal keratoplasty (LIKE), in which the lenticule is implanted under a corneal LASIK flap.

In 2013, Pradhan et al13 described the endokeratophakia procedure to correct high hyperopia of an aphakic amblyopic eye with +10.50 D. The postoperative refraction at 1 year only reached 50% of the intended correction. Other studies also found there was an undercorrection for high hyperopic treatments using this method.14 The posterior corneal changes were thought to be an important factor for causing the undercorrection, which was also predicted by finite element modeling.15 In a subsequent study, it was postulated that the retention of Bowman's membrane contributed to the posterior cornea changing shape more than the anterior cornea, as originally described by Arffa.16

This phenomenon may be lessened or avoided with epikeratophakia or LIKE as Bowman's layer is severed. We conducted this study to compare the visual outcomes of these procedures for the correction of moderate to high hyperopia.

Patients and Methods

This was a prospective, consecutive, small case series study. Informed consent was obtained from the donors and recipients. The study complied with the tenets of the Declaration of Helsinki and was approved by the hospital ethics committee, and all surgeries were done by one experienced surgeon (ZW). The inclusion criteria for donors and recipients were relevant to age and condition. Inclusion criteria for the tissue recipient were age 18 to 35 years and refractive stability with a change of less than 0.50 D over the previous year. Preoperative minimum spherical refraction was +3.00 to +10.00 D with up to 2.00 D of astigmatism. Inclusion criteria for the donor were spherical equivalent (SEQ) from −3.00 to −10.00 D with up to 2.00 D of astigmatism. The refraction of the donor and the refraction of the recipient were matched to within a reasonable range at the spectacle plane (target postoperative SEQ was within ±1.50 D). The attempted correction of the recipient was limited by the predicted postoperative keratometry, which was not to exceed 51.00 D6 (predicted postoperative keratometry = preoperative simulated keratometry + attempted correction). Theoretically, there is a refractive difference between myopic and hyperopic refraction on the spectacle plane (back vertex distance = 12 mm), and the difference is increased as the attempted correction increases. Calculating the refraction between theoretical and attempted refraction of the lenticule from −3.00 to −10.00 D of myopia may cause an average of 13% undercorrection at the spectacle plane after implantation. But in fact, because the nomogram we used in myopic SMILE is to add in 12% of the intended correction, it may partially compensate for the undercorrection due to the back vertex distance (BVD) between myopia and hyperopia, and the refractive difference caused by BVD may be subtle in this study. All donors were tested for anti-HIV antibody, hepatitis C virus antibody, syphilis serum Treponema pallidium Particle Agglutination (TPPA), hepatitis B virus surface antigen, e-antigen, and core antigen. Exclusion criteria for donors and recipients included any history of ocular disease, surgery, or systemic disease.

Surgical Technique of Lenticule Preparation

Myopic SMILE was performed using the VisuMax femtosecond laser (Carl Zeiss Meditec) in a myopic population. Intended cap thickness was 120 µm, cap diameter was 7 to 7.5 mm, optical zone diameter was 6 to 6.5 mm in all eyes, and incision position was 120 degrees for both eyes. Details of the surgical technique have been previously reported.17 The maximum lenticule thickness from the VisuMax printout was recorded. For patients with astigmatism, the edge of the lenticule at the center of the small incision (ie, at 120 degrees) was marked with the ophthalmic blue marker (Trypan Blue 0.06% Ophthalmic Solution; Auroblue). The lenticule was rinsed with 150 mL of Ringer's solution (Compound Sodium Chloride Injection; Shijiazhuang No. 4 Pharmaceutical Co, Ltd) for 10 minutes, and then immersed in a 1:1000 tobramycin salt solution at room temperature for 20 minutes. The lenticule was implanted into the recipient on the same day.

EpikeraTophakia Combined with Transepithelial Phototherapeutic Keratectomy (PTK-EP)

Corneal topography-guided PTK-EP with the SCHWIND Amaris 1050 RS excimer laser (SCHWIND eye-tech-solutions) was used to automatically center on the corneal vertex18 and remove the corneal epithelium evenly to form a treatment zone. The ablation depth was set to 5 µm deeper than the maximum epithelial thickness measured by anterior segment optical coherence tomography (AS-OCT) (Avanti Optovue, Inc) in the central 7-mm zone. The ablation diameter was set to 0.2 mm larger than that of the implanted lenticule, to facilitate the lenticule positioning. The lenticule was placed on top of the stromal bed after epithelial removal, rotated to the target axis according to the corneal marking (if necessary). The rotation angle of the lenticular mark was determined by the difference between the lenticular astigmatic axis and the target astigmatic axis.19 The lenticule was adequately dehydrated in air, monitored by the built-in optical coherence pachymetry of the excimer laser. A bandage contact lens was placed at the end of the procedure.

LIKE

A 110-µm thick and 8.8- to 9-mm diameter corneal flap was made with the WaveLight FS-200 femtosecond laser (Alcon Laboratories, Inc). The WaveLight EX500 excimer laser (Alcon Laboratories, Inc) was used to correct the residual refractive error if a slight refractive mismatch between the donor and recipient was present. The lenticule was placed on the stromal bed, visually centered on the first Purkinje reflex,20 and rotated to the target axis according to the corneal mark (same method as described for PTK-EP). The lenticule was adequately dehydrated and the corneal flap was replaced. A bandage contact lens was placed at the end of the procedure.

Postoperative Management and Evaluation

All patients were given levofloxacin 0.5% eye drops (Cravit; Santen Pharmaceutical Co, Ltd) four times daily for 1 week. Patients who underwent PTK-EP were also given fluorometholone 0.1% eye drops (Flumetholon; Santen Pharmaceutical Co, Ltd) four times daily for 1 month and decreasing one drop each month over a 4-month period. Patients who underwent LIKE were given loteprednol etabonate ophthalmic suspension 0.5% eye drops (Lotemax; Bausch & Lomb) four times daily for 1 week, then bromfenac sodium 0.1% eye drops (Bronuck; Santen Pharmaceutical Co, Ltd) two times daily for the next 3 weeks, as well as 0.1% sodium hyaluronate (Hylo-tear; Ursapharm) four times daily for 3 months.

Follow-up appointments were scheduled for 1 day, 1 week, 1 month, 3 months, 6 months, and 1 year after surgery. Examination included slit-lamp biomicroscopy, uncorrected distance visual acuity (UDVA), manifest refraction, corrected distance visual acuity (CDVA), corneal topography (Vario Topolyzer; WaveLight, Pentacam tomography (Oculus Optikgeräte), and AS-OCT.

Anterior and posterior corneal simulated keratometry, anterior corneal asphericity (Q-value), spherical aberrations (SA), and root mean square of 3rd to 6th total higher order aberrations (HOAs) were analyzed by Pentacam. Pentacam tangential difference maps before and after surgery were used to analyze the achieved optical zone diameter; the method was previously reported by Reinstein et al,21 which uses a concentric circle to visually align with an accuracy of 0.2 mm and superimpose the best-fitting circle to the optical zone defined as the central zone up to the green/blue power inflection point. AS-OCT produced the epithelial map dividing into three concentric rings, and the average epithelial thickness was calculated by zones of diameter of 0 to 2, 2 to 5, and 5 to 7 mm zones.

Results

Demographic data of the 5 patients enrolled in this study are shown in Table 1. Four eyes of 2 patients underwent the PTK-EP procedure and 6 eyes of 3 patients underwent the LIKE procedure. The average follow-up period was 11 months (range: 8 to 13 months).

Demographic Information

Table 1:

Demographic Information

One week after PTK-EP, the slit-lamp examination revealed that the epithelium was ingrown at the local margin under the lenticule in all 4 eyes (4 of 4), but there was no further deterioration. The bandage contact lens was removed at the 1-week follow-up visit. The epithelium had stabilized at the 1-month follow-up visit.

All LIKE surgeries were uneventful. The flap gutter was wider than that after traditional LASIK surgery, but no epithelial ingrowth occurred. No severe complications were noted during the follow-up period. All lenticules used for both procedures remained transparent at the postoperative visit. One example of each procedure is shown in Figure A (available in the online version of this article).

The top row shows the slit-lamp photography (A) 1 month and (B) 1 year after transepithelial phototherapeutic keratectomy (PTK-EP) and (C) an anterior segment optical coherence tomography (AS-OCT) B-scan 1 year after PTK-EP for eye 3. The black arrows show epithelial ingrowth at the margin of lenticule (A and C). The bottom row shows the slit-lamp photography (D) 1 month and (E) 1 year after PTK-EP and (F) an AS-OCT B-scan 1 year after PTK-EP for eye 5. The * highlights the edge of the lenticule in AS-OCT.

Figure A.

The top row shows the slit-lamp photography (A) 1 month and (B) 1 year after transepithelial phototherapeutic keratectomy (PTK-EP) and (C) an anterior segment optical coherence tomography (AS-OCT) B-scan 1 year after PTK-EP for eye 3. The black arrows show epithelial ingrowth at the margin of lenticule (A and C). The bottom row shows the slit-lamp photography (D) 1 month and (E) 1 year after PTK-EP and (F) an AS-OCT B-scan 1 year after PTK-EP for eye 5. The * highlights the edge of the lenticule in AS-OCT.

Visual Acuity and Refraction

Postoperatively, 6 of 10 eyes had UDVA equal to or better than preoperative CDVA (3 of 4 eyes for PTK-EP and 3 of 6 eyes for LIKE). Four eyes lost one line of postoperative UDVA compared with preoperative CDVA (1 of 4 eyes for PTK-EP and 3 of 6 eyes for LIKE). Three eyes gained one or more lines of postoperative CDVA compared with preoperative CDVA (2 of 4 eyes for PTK-EP and 1 of 6 eyes for LIKE). No eyes lost one line or more of CDVA. Postoperative SEQ was within ±0.50 D of the intended target for 9 eyes (3 of 4 eyes for PTK-EP and 6 of 6 eyes for LIKE), with 1 eye showing an overcorrection of 1.25 D.

Corneal Tomography

Pentacam was used to evaluate the change in corneal anterior and posterior keratometry, Q-value, SA, and total HOAs for both surgery groups, as shown in Table 2. The anterior corneal keratometry steepened in all eyes and the posterior keratometry slightly steep-ened (0.10 D) in 4 eyes postoperatively; the remaining 6 eyes were unchanged. The change of Q-value and total HOAs in the PTK-EP group was greater than that in the LIKE group, except for 1 eye (number 10) due to correcting high astigmatism (2.00 D). But SA in all cases of the LIKE group showed less change than cases in the PTK-EP group. These comparisons were obtained by adjusting the change divided by the attempted refraction because the attempted correction was higher for the PTK-EP eyes. Figure B (available in the online version of this article) shows an example of corneal topography after each procedure. Comparison of tangential difference maps between preoperative and postoperative values showed the larger achieved optical zone diameter was obtained in the LIKE group compared to the PTK-EP group (Figure 1).

Preoperative and Postoperative Outcomes of Tomographya

Table 2:

Preoperative and Postoperative Outcomes of Tomography

Corneal topography maps with transepithelial phototherapeutic keratectomy (PTK-EP) of eye 3 and femtosecond laser–assisted lenticule intrastromal keratoplasty (LIKE) of eye 5 over the follow-up period. (A) Anterior corneal surface topography shows axial curvature from the Alcon WaveLight Topolyzer (Alcon Laboratories, Inc) over time. (B) Anterior corneal surface tomography shows tangential curvature from the Pentacam (Oculus Optikgeräte) over time. (C) Posterior corneal surface elevation from the Pentacam over time. Figure BA shows that the irregularity of the anterior corneal surface gradually becomes regular within 1 year in both groups. Figure BB shows that there is no significant change in the morphology and diameter of the optical zone of the two procedures during the follow-up period. Figure BC shows that there is no significant change of elevation in the posterior corneal surface under the same best-fit sphere during the follow-up period. OD = right eye; OS = left eye

Figure B.

Corneal topography maps with transepithelial phototherapeutic keratectomy (PTK-EP) of eye 3 and femtosecond laser–assisted lenticule intrastromal keratoplasty (LIKE) of eye 5 over the follow-up period. (A) Anterior corneal surface topography shows axial curvature from the Alcon WaveLight Topolyzer (Alcon Laboratories, Inc) over time. (B) Anterior corneal surface tomography shows tangential curvature from the Pentacam (Oculus Optikgeräte) over time. (C) Posterior corneal surface elevation from the Pentacam over time. Figure BA shows that the irregularity of the anterior corneal surface gradually becomes regular within 1 year in both groups. Figure BB shows that there is no significant change in the morphology and diameter of the optical zone of the two procedures during the follow-up period. Figure BC shows that there is no significant change of elevation in the posterior corneal surface under the same best-fit sphere during the follow-up period. OD = right eye; OS = left eye

Pentacam (Oculus Optikgeräte) tangential difference maps for the four transepithelial phototherapeutic keratectomy (PTK-EP) cases and femtosecond laser–assisted lenticule intrastromal keratoplasty (LIKE) cases. The perimeter of the optical zone is identified by the red circle. The center of the optical zone is indicated by the black cross and the corneal vertex is indicated by the white dot. OD = right eye; OS = left eye

Figure 1.

Pentacam (Oculus Optikgeräte) tangential difference maps for the four transepithelial phototherapeutic keratectomy (PTK-EP) cases and femtosecond laser–assisted lenticule intrastromal keratoplasty (LIKE) cases. The perimeter of the optical zone is identified by the red circle. The center of the optical zone is indicated by the black cross and the corneal vertex is indicated by the white dot. OD = right eye; OS = left eye

AS-OCT Observation

AS-OCT B-scan analysis showed the implanted lenticule displayed low reflectivity and a visible demarcation line throughout the follow-up period. As seen in Table 3, in both groups the postoperative epithelial thickness demonstrated a doughnut pattern characterized by epithelium in the central and paracentral zones (5 mm) thinner than that in the peripheral zone (5 to 7 mm). The thinnest epithelial thickness was decreased, and the thickest epithelial thickness was increased in both procedures. Figure C (available in the online version of this article) shows an example of epithelial thickness over time after each procedure.

Preoperative and Postoperative AS-OCT Outcomes

Table 3:

Preoperative and Postoperative AS-OCT Outcomes

Corneal epithelial thickness maps from eyes 3 (transepithelial phototherapeutic keratectomy [PTK-EP]) (top row) and 5 (femtosecond laser–assisted lenticule intrastromal keratoplasty [LIKE]) (bottom row) over the follow-up period. Each map is divided into four annular rings (2, 2 to 5, 5 to 7, and 7 to 9 mm). AS-OCT = anterior segment optical coherence tomography

Figure C.

Corneal epithelial thickness maps from eyes 3 (transepithelial phototherapeutic keratectomy [PTK-EP]) (top row) and 5 (femtosecond laser–assisted lenticule intrastromal keratoplasty [LIKE]) (bottom row) over the follow-up period. Each map is divided into four annular rings (2, 2 to 5, 5 to 7, and 7 to 9 mm). AS-OCT = anterior segment optical coherence tomography

AS-OCT was used to measure the central 2-mm average stromal thickness before and after surgery. As shown in Table 3, the increase in stromal thickness after PTK-EP was less than the predicted thickness (data were available only for 2 eyes, numbers 3 and 4). The increase in stromal thickness after LIKE was close to the predicted thickness, after adjusting the achieved lenticule thickness according to the previously published data by very high-frequency digital ultrasound.22

Discussion

This preliminary study found that two surgical techniques, PTK-EP and LIKE, are promising in the correction of moderate to high hyperopia. There were no severe complications that occurred during the follow-up observation in the study, and there was no obvious opacification observed at the corneal stroma–stromal interface within the central optically active corneal zone by slit-lamp examination and AS-OCT. After PTK-EP, epithelial ingrowth occurred at the margin of the lenticule in 4 eyes, but none of these eyes lost CDVA.

In the current study of 10 eyes, no eye lost even one line of CDVA, and 6 eyes had postoperative UDVA equal to or better than preoperative CDVA. These good refractive results were supported by previous findings described by Ganesh et al14 and Li et al.19 Eight of 9 eyes had postoperative UDVA equal to or better than preoperative CDVA, demonstrated by Ganesh et al. The safety index was 1.50 ± 0.46 and the efficacy index was 1.11 ± 0.11 at 2 years postoperatively, demonstrated by Li et al. The reason for their outcomes of good visual effect by implanting the convex lenticule is unclear.

In the current study, the postoperative SEQ was within ±0.50 D of the intended target in 9 of 10 eyes (3 of 4 eyes in PTK-EP and 6 of 6 eyes in LIKE). Findings from previous studies suggested that a change in the posterior corneal surface affects the postoperative refraction. Pradhan et al13 and Studer et al15 reported only one-half of the intended +10.50 D refractive correction was achieved because of the proportion of curvature change induced by the implanted lenticule on the posterior surface. Ganesh et al14 also reported postoperative SEQ within ±1.00 D in 8 of 9 eyes, and showed undercorrection of hyperopia after endokeratophakia but less, with an average of approximately 21% of intended refraction (mean refraction: +5.39 D). They found that the thicker the myopic lenticule implanted, the more the posterior corneal curvature flattened. Although anterior and posterior curvature alterations increase the corneal refractive power, posterior flattening only provides a minor refractive change (due to the difference in refractive indexes between the cornea and aqueous humor being smaller than those of between air and cornea), which lessened the corrective efficiency of the lenticule. This reduction of lenticular correction by posterior surface flattening effect was confirmed in an ex vivo study.23 In the current study, for both PTK-EP and LIKE, only small changes in posterior corneal curvature were noted despite the relatively high power of the implanted lenticules (mean lenticular refraction: +6.43 D). Thus, PTK-EP and LIKE achieve superior efficacy because most of the curvature changes induced by the lenticule implantation result in anterior surface curvature changes. The advantage of either adding the lenticule to the corneal surface or implanting this under a flap results in anterior curvature changes without exerting forces that cause posterior corneal curvature flattening. This is understandable, because no anteroposterior forces are exerted by the lenticule implantation, as has been seen in endokeratophakia, due to the circular cutting and release of Bowman's layer and stroma in the flap.24

Another factor that may affect postoperative refraction is epithelial thickness remodeling. Pradhan et al13 found the expected epithelial thinning centrally within 6 mm after 1 year of implanting the lenticule. Ganesh et al14 found that the corneal epithelium in the paracentral zone (2 to 5 mm) was thinner than in the central zone (2 mm) postoperatively, but the results were not compared with those before surgery. In the current study, postoperative epithelial thickness demonstrated a slight doughnut pattern characterized by epithelium in the central zone (5 mm) thinner than that in the peripheral zone (5 to 7 mm), which is markedly different from preoperatively. In the current study, as for the Pradhan et al study, we observed the doughnut pattern with thinner epithelium centrally than peripherally. However, the average difference between central and peripheral epithelial thickness was greater for the PTK-EP group (39 µm – 69 µm = −30 µm) than the LIKE group (41 µm – 61 µm = −20 µm). Changes in LASIK for hyperopia previously reported by Reinstein et al25 for similar levels of hyperopic correction using 7-mm optical zones (1.8 mm transition) with the MEL80 laser showed an even higher differential between the thinnest and thickest zones (40 µm – 89 µm = −49 µm). Transition zones with excimer lasers are known to be affected by projection errors, probably explaining the larger epithelial compensation seen after LASIK.26 In contrast, the change in curvature gradient in the peripheral zone for PTK-EP and LIKE is probably relatively lower and hence causes less epithelial compensation (as shown in Figure D, available in the online version of this article).

The diagram shows three refractive surgeries to correct the same refraction of hyperopia. The optical zone of surgeries is 6.5 mm and corneal flap diameter is 9 mm as treatment zone. The treatment zone of transepithelial phototherapeutic keratectomy (PTK-EP) is the area of removal corneal epithelium. (A) Hyperopic laser in situ keratomileusis (LASIK), the mid-peripheral corneal tissue is ablated (dotted line area). (B) In PTK-EP, the refractive lenticule is placed on top of the cornea after epithelium removal (blue area). (C) In femtosecond laser–assisted lenticule intrastromal keratoplasty (LIKE), the refractive lenticule (blue area) is implanted under the corneal LASIK flap (yellow dotted line).

Figure D.

The diagram shows three refractive surgeries to correct the same refraction of hyperopia. The optical zone of surgeries is 6.5 mm and corneal flap diameter is 9 mm as treatment zone. The treatment zone of transepithelial phototherapeutic keratectomy (PTK-EP) is the area of removal corneal epithelium. (A) Hyperopic laser in situ keratomileusis (LASIK), the mid-peripheral corneal tissue is ablated (dotted line area). (B) In PTK-EP, the refractive lenticule is placed on top of the cornea after epithelium removal (blue area). (C) In femtosecond laser–assisted lenticule intrastromal keratoplasty (LIKE), the refractive lenticule (blue area) is implanted under the corneal LASIK flap (yellow dotted line).

For the refractive outcomes in the current series, the achieved SEQ was close to the attempted SEQ, from which we may conclude that the refractive regression generated by doughnut-shaped changes in the epithelium may be counterbalanced with a part of overcorrection expected by the implanted lenticule. Previously, Li et al19 reported that an overcorrection was exhibited after lenticular implantation under the corneal flap, but no obvious changes in epithelial thickness were found in their study.

We note that changes in Q-value, SA, and total HOAs in the LIKE group were less than those in the PTK-EP group, and observed that the difference between the intended and achieved optical zone was smaller for the LIKE group than for the PTK-EP group. This advantage may not only be related to lower intended correction, but also may relate to the wider transition zone and larger optical zone created in the LIKE group. In this group, the large flap created by the femtosecond laser extended approximately 1 mm around the lenticule edge. First, the large flap could fully cover the lenticule, which increases the contact area between flap and stroma bed to improve the adhesion strength,27 reducing the risk of movement of flap and lenticule after surgery. Second, it can form a transition zone around the lenticule, which may reduce the rate of change of curvature that reduced the epithelial remodeling at the edge of the lenticule. Theoretically, the combination of a smoother transition and less epithelial remodeling would result in less reduction in the topographical optical zone and induction in the SA and total HOAs of the front corneal surface. The correction of hyperopic laser refractive surgery was to sever a series of lamellae in the mid-periphery, implying that biomechanical alterations at the peripheral zone resulted in corneal steepening and reduced the accuracy correction.28 Also, there is a case report that 2 patients with both normal or abnormal preoperative topography had corneal ectasia following hyperopic LASIK.29 Thus, the lenticular implantation can effectively retain the stromal thickness and alter the corneal biomechanics in the mid-peripheral zone less. It is reversible for changing corneal shape by lenticule implantation, and the implanted lenticule can be removed to restore the corneal shape when cataract extraction is required.

For the two recipients in the PTK-EP group with high hyperopia, preoperative consideration of predicted curvature was set not to exceed 51.00 D to prevent excessive thinning of the postoperative central minimum epithelial thickness to less than 28 µm,6 which can lead to epitheliopathy or apical syndrome.30 By the use of corneal epithelial thickness mapping and monitoring, it may be possible to further steepen these corneas by excimer laser re-treatment to correct the residual refraction given the characteristics described by Reinstein et al.6

The widespread application of PTK-EP and LIKE poses logistical challenges. For example, having to identify the matching refractions for donor and recipient, completing all serological preoperative testing from the donor in advance, and then scheduling of donors and recipients for surgery on the same day requires significant cooperation, particularly from the donor patients. The donor patient also is exposed to counseling and potential repercussions of the results of serology testing if positive. It may transpire that a “refractive eye bank” that provides long-term storage of lenticules may be helpful, and acellular allograft corneal donor material shaped by the excimer laser could also form a basis for a preferred source of lenticule donor tissue.31

Although no severe complications such as haze from the PTK, decentration of lenticule, or visually significant epithelial ingrowth occurred in our study, the sample size was small. This small case series study demonstrated good visual outcomes in correcting moderate to high hyperopia by PTK-EP and LIKE. These outcomes may be due to less change of posterior corneal surface shape and corneal epithelium thickness remodeling, which reduces the possibility of refractive regression and effectively corrects hyperopia. The objective measurement of whole eye scatter and aberrations will be considered in a future study. A larger case series enrolling different degrees of refraction into both groups and longer-term follow-up are required to further validate the safety and stability of these techniques.

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Demographic Information

No.Age (y)/GenderEyeSurgeryLast Visit (mo)PreoperativeOperativePostoperative



MR (D)SEQ (D)CDVAAddition Ablation (D)Lenticular Refraction (D)TC (D)Target SEQ (D)LMT (μm)MR (D)SEQ (D)UDVACDVAEC (%)a
126/FODPTK-EP13+8.25 +1.00 × 80°+8.7520/40+7.00+1.25 +1.00 × 80°1.75111+1.50 +0.50 × 70°+1.7520/4020/40100.0
226/FOSPTK-EP13+9.00 +1.25 × 95°+9.6320/40+7.00+2.00 +1.25 × 95°2.63111+2.00 +1.00 × 110°+2.5020/5020/40101.8
319/MODPTK-EP13+8.00 +1.50 × 35°+8.7520/40+7.00 +1.00 × 180°+1.00 +0.50 × 35°1.251390.000.0020/2520/25116.7
419/MOSPTK-EP13+8.00 +1.75 × 130°+8.8820/40+8.25 +0.75 × 175°−0.25 +1.00 × 130°0.25143−0.75 +1.25 × 110°−0.1320/2520/25104.4
527/MODLIKE10+4.75 +0.50 × 85°+5.0020/20−0.50 +1.00 × 175°+4.50 +1.25 × 175°−0.25 +0.25 × 85°−0.13113−0.25 +0.50 × 140°0.0020/2020/2097.6
627/MOSLIKE10+4.75 +1.00 × 100°+5.2520/20+4.50 +1.50 × 170°−0.25 +0.50 × 10°0.00117−1.00 +1.50 × 100°−0.2520/2520/20104.8
721/MODLIKE10+5.50+5.5020/25+5.00 +0.25 × 85°+0.25 +0.25 × 175°0.38106+0.25+0.2520/2520/25102.4
821/MOSLIKE10+6.25 +0.50 × 180°+6.5020/40+5.50 +0.75 × 175°+0.63 +0.25 × 90°0.75123+0.25 +0.75 × 15°+0.6320/5020/4099.9
921/MODLIKE10+5.75 +0.75 × 60°+6.1320/25+6.00 +1.00 × 10°−0.50 +0.25 × 150°−0.38135−0.50 +1.00 × 70°0.0020/2020/2094.2
1021/MOSLIKE10+5.00 +2.00 × 125°+6.0020/30+1.50 × 125+6.00 +0.50 × 160°−1.00−1.00128−2.25 +1.50 × 130°−1.5020/4020/30107.1

Preoperative and Postoperative Outcomes of Tomographya

EyeSurgeryMean Anterior K (D)Mean Posterior K (D)Q-value (6 mm)SA (6 mm)Total HOAs (6 mm)Optical Zone (mm)






PreopPostopΔPreopPostopΔPreopPostopΔbPreopPostopΔbPreopPostopΔbProgrammedAchievedΔ
1PTK-EP45.4050.405.00−6.90−6.900.00−0.35−1.18−0.770.186−0.291−0.4430.4631.0710.5656.04.2−1.8
2PTK-EP45.3050.505.20−6.80−6.90−0.10−0.35−1.19−0.780.198−0.279−0.4430.6071.5770.9016.04.2−1.8
3PTK-EP39.4047.307.90−5.80−5.800.00−0.24−1.92−1.460.164−0.831−0.8620.5521.0640.4446.34.2−2.1
4PTK-EP39.0048.209.20−5.80−5.800.00−0.21−2.30−1.580.197−1.321−1.1440.3631.4930.8526.14.0−2.1
5LIKE41.0045.504.50−6.00−6.10−0.10−0.26−0.75−0.620.1840.2930.1380.3170.6640.4406.55.2−1.3
6LIKE40.8045.604.80−6.10−6.100.00−0.19−0.73−0.670.2070.2160.0110.3940.363−0.0386.55.2−1.3
7LIKE41.4046.505.10−6.10−6.20−0.10−0.20−0.79−0.750.2110.146−0.0820.3370.4950.2006.55.0−1.5
8LIKE40.8046.405.60−6.00−6.10−0.10−0.13−0.71−0.640.2520.2570.0060.3090.3510.0466.55.2−1.3
9LIKE41.3047.105.80−6.10−6.100.00−0.25−0.72−0.470.2420.2900.0480.4190.4550.0366.55.4−1.1
10LIKE41.7049.407.70−6.10−6.20−0.10−0.25−1.19−0.870.224−0.094−0.2950.3140.9100.5536.54.8−1.7

Preoperative and Postoperative AS-OCT Outcomes

EyeSurgery0 to 2 mm (μm)2 to 5 mm (μm)5 to 7 mm (μm)Thinnest Point (μm)Thickest Point (μm)Stromal Thickness (μm)LMT (μm)a






PreopPostopΔPreopPostopΔPreopPostopΔPreopPostopΔPreopPostopΔPreopPostopΔ
1PTK-EP4445.4450.383974574103
2PTK-EP4446.6751.883966581103
3PTK-EP5049−150.6348.44−2.1951.5059.007.504939−10547016495603108131
4PTK-EP5247−552.5047.00−5.5052.2558.636.384839−957669491608117135
5LIKE4845−349.5051.001.5050.6350.50−0.134740−75558344053999105
6LIKE4845−348.5044.56−3.9448.6347.38−1.254637−952597437537100109
7LIKE5350−353.7549.00−4.7552.5053.501.004744−35661548058210298
8LIKE5350−352.8848.22−4.6652.7550.88−1.874945−455605473592119115
9LIKE5449−553.6346.11−7.5251.7547.88−3.874441−357636511633122127
10LIKE5949−1058.6346.89−11.7456.0052.13−3.874837−1161665500633133120
Authors

From Aier School of Ophthalmology, Central South University, Changsha, China (JW, ZW); Guangzhou Aier Eye Hospital, Guangzhou, China (JW, LX, ZW); London Vision Clinic, London, United Kingdom (DZR, RSV, TJA); Columbia University Medical Center, New York, New York (DZR); Sorbonne Université, Paris, France (DZR); and Biomedical Science Research Institute, Ulster University, Coleraine, United Kingdom (DZR).

Supported by the Aier Eye Hospital Scientific Research Project (Grant No. AM1909D1) and Medical Scientific Research Fundation of Guangdong Province of China (Grant No. C2020098).

Dr. Reinstein is a consultant for Carl Zeiss Meditec and has a proprietary interest in the Artemis Insight 100 technology (ArcScan, Inc) through patents administered by the Cornell Center for Technology Enterprise and Commercialization, Ithaca, New York. The remaining authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (ZW); data collection (JW, LX); analysis and interpretation of data (JW, ZW, DZR, RSV, TJA); writing of the manuscript (JW, ZW, DZR, RSV); critical revision of the manuscript (JW, LX, ZW, DZR, TJA); administrative, technical, or material support (JW, ZW); supervision (JW, ZW)

Correspondence: Zheng Wang, MD, Department of Refractive Surgery, Guangzhou Aier Eye Hospital, Huanshi Middle Road, Guangzhou, China. Email: gzstwang@gmail.com

Received: February 13, 2020
Accepted: August 19, 2020

10.3928/1081597X-20200826-01

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