Early Posterior Corneal Changes and Belin/Ambrósio Scores Following Photorefractive Keratectomy: A Pentacam Study

Abstract

Introduction

To evaluate early postoperative changes in the posterior corneal surface, anterior chamber parameters, and Belin/Ambrósio Enhanced Ectasia Display (BAD) scores following photorefractive keratectomy (PRK) using Pentacam tomography.

Methods

This observational study included 102 eyes of 51 patients (mean age 28.43 ± 6.27 years) undergoing alcohol-assisted PRK for myopia and/or astigmatism. Preoperative and 1-month postoperative assessments were performed using the Pentacam system, measuring, anterior chamber depth (ACD), anterior chamber volume (ACV), central corneal thickness, posterior keratometry, posterior elevation, and BAD scores. PRK was conducted with a WaveLight^® EX 500 excimer laser, followed by mitomycin-C application. Statistical analysis utilized paired t-tests and Pearson’s correlation.

Results

At 1 month post-PRK, ACV significantly decreased (p < 0.01), while ACD reduction was not significant (p = 0.40). Posterior keratometry (K1, K2, Kmean) and astigmatism decreased (p < 0.01), with a mean posterior elevation increase of −2.50 ± 2.94 µm (p < 0.01). A weak negative correlation was observed between maximum posterior elevation difference and ablation depth (p = 0.03, r = −0.20) and ablation depth/preoperative pachymetry ratio (p = 0.03, r = −0.20). BAD-D scores (Dp, Dt, Da, total D) significantly increased (p < 0.01), except for Df (p = 0.41). No correlation was found with preoperative pachymetry or residual stroma.

Conclusions

PRK induces minimal posterior corneal protrusion and BAD score changes at 1 month, potentially mimicking early ectasia. Multimodal testing is advised for accurate ectasia detection. Larger, longer-term studies are needed to validate these findings.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40123-025-01199-8.

Key Summary Points

Why carry out this study?

Iatrogenic ectasia is one of the most concerning complications associated with refractive surgery. Postoperative ectasia was identified by assessing elevation of the posterior corneal surface using topography/tomography.

Studies utilizing the Orbscan system have documented significant anterior displacement of the posterior corneal surface following refractive surgery. It is crucial to acknowledge that the Orbscan system inaccurately measures both corneal thickness and posterior surface elevation in post-refractive surgery cases.

What was learned from the study?

The present study demonstrated significant alterations in the posterior corneal surface and Belin/Ambrósio Enhanced Ectasia Display (BAD) scores at 1 month after photorefractive keratectomy (PRK) using Pentacam device. However, these changes were not as pronounced as those observed with the Orbscan but may mimic ectasia. Therefore, these changes should be considered when evaluating postoperative ectasia utilizing Pentacam tomography.

Introduction

The primary objective of corneal refractive surgery is to reshape the cornea to alter its refractive properties and ultimately achieve emmetropia. Photorefractive keratectomy (PRK), utilizing an excimer laser, modifies the refractive power of the cornea through precise photo ablation of its superficial layers. However, this procedure, along with the disruption of Bowman’s layer integrity, significantly compromises the structural stability of the cornea. As a result, such corneas are prone to anterior displacement even under physiological intraocular pressure levels [1–3]. This forward shift may destabilize the refractive outcomes following laser treatment and may resemble the characteristics of keratectasia.

Iatrogenic keratectasia is a notable postoperative complication of laser-based refractive procedures, characterized by progressive corneal thinning and steepening, leading to diminished visual acuity owing to advancing myopia and irregular astigmatism [4, 5]. Since the introduction of PRK and laser in situ keratomileusis (LASIK) in clinical practice, an increased incidence of postoperative ectasia has been reported [6]. While ectasia typically manifests between 6 months and 1 year post-surgery, reports indicate its potential onset as early as 1 month after the procedure [7]. The precise evaluation of the cornea is crucial for preoperative risk assessment and the early identification of post-refractive surgery ectasia. Various technologies have been developed to assess the characteristics of the corneal surface in both healthy individuals and patients with keratoconus. These technologies include Placido disc-based topography, slit-scanning topography, and Scheimpflug tomography. In the context of early keratoconus detection, a Scheimpflug tomography device known as the Pentacam (Oculus Inc., Wetzlar, Germany) was developed, demonstrating greater sensitivity across multiple parameters compared to Placido disc-based topography [8–10]. This device is currently regarded as a highly sensitive tool for the early detection of keratoconus and ectatic disorders [11–13]. Belin/Ambrósio Enhanced Ectasia Display (BAD) scores offers a comprehensive representation of the corneal tomographic structure in Pentacam corneal tomography system. This was achieved through the integration of the enhanced elevation approach, as delineated by Belin, along with pachymetric and curvature data [11]. The BAD assesses deviations from normality across various parameters, where a value of zero corresponds to the mean of the normal population, and a value of one indicates one standard deviation toward the ectasia value. The final ‘D’ value is derived through a regression analysis, which assigns different weights to the parameters. In the Pentacam display system, each parameter is marked in yellow (indicating suspicion) if it is ≥ 1.6 standard deviations from the mean, or in red (indicating abnormality) if it is ≥ 2.6 standard deviations from the mean. The final D value is derived from a regression analysis, which optimizes the accuracy of ectasia detection.

This study aimed to evaluate changes in the posterior corneal surface, anterior chamber depth and anterior chamber volume and D scores on the BAD at 1 month post-PRK using the Pentacam corneal topography/tomography system equipped with rotating Scheimpflug imaging technology. We hypothesized that PRK induces measurable early changes in posterior corneal elevation, anterior chamber parameters, and BAD scores, detectable by Pentacam at 1 month post-surgery, and that these changes may correlate with ablation depth or preoperative corneal thickness, potentially resembling early ectatic patterns.

Methods

The study protocol received approval from the Ethical Committee of Ondokuz Mayıs University (B.30.2.ODM.0.20.08/256) and adhered to the principles outlined in the Declaration of Helsinki. Informed consent was obtained from all participants.

This observational study involved 102 eyes from 51 patients, aged 18 to 41 years, who underwent alcohol-assisted PRK for the correction of myopia and/or astigmatism. All participants underwent a comprehensive preoperative examination, which included assessments of best-corrected visual acuity, manifest and cycloplegic autorefraction error, tonometry, slit lamp biomicroscopy, and fundoscopy. Both preoperative and postoperative corneal topography/tomography were conducted using a Pentacam device.

Pentacam is a corneal tomographic device extensively utilized in clinical environments. This technology employs a 360° rotating Scheimpflug camera to capture high-resolution cross-sectional images of the anterior segment [14]. Within a maximum duration of 2 s, Pentacam constructs a three-dimensional model of the anterior segment, capturing data from up to 25,000 elevation points and 138,000 elevation points in the Pentacam HR. The data obtained from this device include topography/tomography, pachymetry, anterior chamber angle, anterior chamber volume (ACV), anterior chamber depth (ACD), lens densitometry, and various other ocular indices. The reliance on elevation mapping as the primary data source distinguishes the Pentacam from other modalities [15]. ACV is calculated by integrating the volume of the anterior chamber based on the three-dimensional (3D) model constructed from Scheimpflug images. The system defines the anterior chamber boundaries from the posterior corneal surface to the anterior lens surface (or iris plane in aphakic eyes) within a specified corneal diameter (typically 12 mm). The software uses elevation data to compute the volume enclosed within these boundaries, expressed in cubic millimeters (mm³). ACD is measured as the axial distance from the posterior corneal surface (endothelium) to the anterior surface of the lens (or iris plane) along the optical axis. The Pentacam software identifies these anatomical landmarks using edge-detection algorithms and calculates the distance based on the Scheimpflug-derived 3D model, reported in millimeters (mm). Posterior corneal elevation (PCE) is determined relative to a best-fit sphere (BFS) calculated for the posterior corneal surface, typically within an 8.0-mm central zone. The software constructs the BFS by fitting a sphere to the posterior corneal elevation data, minimizing deviations. PCE is then quantified as the perpendicular distance (in micrometers, µm) from the posterior corneal surface to the BFS at specific points, with positive values indicating protrusion above the BFS and negative values indicating forward displacement (protrusion toward the anterior chamber). Each eye’s preoperative Pentacam measurements served as an internal baseline, allowing assessment of postoperative changes within the same cohort, though without an external control group for comparison.

Patient measurements were conducted by a single technician under scotopic conditions, without the use of pupil dilation. Consistent scans were obtained for all participants utilizing the automatic release mode, and the scan of the highest quality, as indicated by an “OK” score, was selected for statistical analysis.

All the PRK surgeries performed by same surgeon (KY) using a WaveLight^® EX 500 (Alcon Inc., Ft Worth, Texas, USA) device in a 6.5 mm optical zone. The corneal epithelium was removed using a hockey stick blade following %20 alcohol application. After excimer laser PRK, mitomycin-C was applied at a concentration of 0.02% for 30 s on the corneal stromal bed, and the eye was irrigated with 30 cc of BSS. Subsequently, a 0.5% drop of moxifloxacin (Vigamox^®; Alcon Laboratories, Inc, Texas, USA) was instilled directly onto the cornea. Following this procedure, a bandage contact lens was placed on each eye. The postoperative medication plan included administration of 0.5% loteprednol (Lotemax, Bausch & Lomb Inc. USA) five times daily in both eyes, moxifloxacin 0.5% (Vigamox; Alcon Laboratories, Inc., Texas, USA) five times daily in both eyes, and preservative-free artificial tears with 0.15% sodium hyaluronate (Eyestil; SIFI, Italy) eight times daily. On the fifth day, the physician who performed the procedure (KY) removed the bandage contact lenses. At the first month visit, Pentacam corneal tomography was repeated.

The study measured several variables, including central corneal thickness, ACD, ACV, anterior and posterior keratometry (K1, K2 and Kmean), elevation in the BFS, and maximum posterior elevation difference (MPED). The BFS was calculated using the central 8.0-mm zone of the cornea prior to surgery, and this calculation was consistently applied to both preoperative and postoperative maps. The change in MPED was defined as the greatest forward protrusion of the posterior cornea above the BFS within the 4.0-mm zone. To ascertain the MPED, the preoperative elevation data were subtracted from the postoperative elevation data, with a focus on the maximum difference in the central 4.0-mm zone. Forward protrusion of the posterior cornea was recorded as negative. Additionally, BAD-D values, representing the standard deviation of the front elevation difference (Df), deviation of back elevation difference (Db), deviation of average pachymetric progression (Dp), deviation of minimum thickness (Dt), and deviation of ARTmax (Da), as well as a final D score (D), were also recorded and compared.

Statistical analyses were conducted using SPSS software (version 21.0; Chicago, IL, USA). Initially, the normality of the data distribution was evaluated using the Kolmogorov–Smirnov test. Continuous variables that adhered to a normal distribution are reported as mean ± standard deviation, whereas those that did not conform to a normal distribution are presented as median (minimum–maximum). Categorical data are expressed as frequencies and percentages. A paired t-test was employed to assess the differences in measured values before and after laser refractive surgery. Pearson’s linear correlation was utilized to examine the association between the amount of forward movement of the posterior corneal surface (maximum elevation back difference) and preoperative pachymetry, ablation depth, residual stroma and ablation depth/preoperative pachymetry ratio (AD/P).To address the inter-eye correlation present in bilateral eye data, generalized estimating equations (GEE) were employed, utilizing an exchangeable working correlation structure to model the impact of PRK on posterior corneal elevation and BAD scores (Supplementary Material).

Results

The study included 102 eyes from 51 patients who underwent alcohol-assisted PRK for myopia and myopic astigmatism. The mean age of the patients was 28.43 ± 6.27 years, ranging from 18 to 41 years. In total, 19 patients were male (37.3%), while 31 were female (62.7%). The mean preoperative spherical equivalent (SE) refraction was −3.02 D ± 1.80 D, and the mean ablation depth was 50.02 ± 25.14 µm. The mean postoperative residual stromal thickness was 438 ± 25.14 µm with the lowest residual stromal thickness recorded as 345 µm. All demographic data of the patients are summarized in Table 1.

Table 1.

Patient demographics

	Mean ± Std dev.	Minimum	Maximum
Age (years)	28.43 ± 6.27	18	41
Preoperative sphere	−2.59 ± 1.78	−7.00	0.75
Preoperative astigmatism	−0.87 ± 1.06	−5.00	−1.50
Preoperative SE	−3.02 ± 1.80	−7.75	0.13
Preoperative K1 (anterior)	43.14 ± 1.54	39.50	47.50
Preoperative K2 (anterior)	44.25 ± 1.66	40.25	48.25
Preoperative Kmean (anterior)	39.87 ± 1.55	39.87	47.87
Preoperative pachymetry	538.54 ± 36.06	442	605
Ablation depth	50.02 ± 25.14	11.65	121.15
Residual stroma	438.11 ± 42.19	345	519

SE spherical equivalent, K1 flattest keratometry, K2 steepest keratometry, Kmean mean keratometry

Both ACD and ACV decreased following PRK at 1st month, but this change statistically significant only in ACV (p < 0.01). These changes was shown in Fig. 1.

Fig. 1.

Both ACD and ACV decreased following photorefractive keratectomy, but this change was significant only in ACV (p < 0.01). ACD anterior chamber depth, ACV anterior chamber volume

The posterior flattest (K1), steepest (K2), mean astigmatism (K1 + K2/2) and posterior corneal astigmatism (K2-K1) values were significantly decreased (p < 0.01). Additionally, there was a statistically significant increase in the posterior surface elevation in the BFS map at postoperative first month (p < 0.01). The mean increase in posterior elevation was −2.50 ± 2.94 µm. Number of patients and MPED values was shown in Fig. 2.

Fig. 2.

Maximum posterior elevation difference values and number of patients

No correlation was observed between the maximum elevation back difference (MEBD) and preoperative pachymetry (p = 0.51) or residual stroma (p = 0.52). However, a weak negative correlation was identified between MEBD and ablation depth (p = 0.03, r = −0.20); ablation depth/preoperative pachymetry ratio (AD/P) (p = 0.03, r = −0.20); preoperative anterior keratometric values (K1, K2, Kmean; p < 0.01, r = −0.31, −0.38, −0.36), respectively.

ACD difference was weakly positively correlated with preoperative sphere (p < 0.01, r = 0.30), preoperative SE (p < 0.01 r = 0.32), preoperative pachymetry (p < 0.01, r = 0.25), ablation depth (p < 0.01, r = 0.33), and AD/P (p < 0.01 r = 0.36). ACD difference was weakly negatively correlated with residual stroma (p < 0.01, r = −0.35).

There were no significant correlation between ACV difference and preoperative demographic data.

These correlations are shown in Table 2. Correlation between MEBD and ablation depth and AD/P illustrated in Fig. 3. In this negative correlation, as the amount of ablation increases, the MEBD decreases in the direction of the negative value, indicating that the cornea is actually elevated forward that much. In other words, increasing amount of ablation and the ratio of ablation to preoperative pachymetry were weakly correlated with posterior corneal elevation. (p = 0.03, r = −0.20).

Table 2.

Correlation of MEBD, ACD, and ACV difference with preoperative and postoperative data

	MEBD		ACD difference		ACV difference
	r	p*	R	p*	r	p*
Age	0.05	0.63	0.10	0.27	−0.01	0.98
Preoperative sphere	0.12	0.23	0.30	< 0.01	0.05	0.61
Preoperative astigmatism	0.04	0.71	0.12	0.21	−0.06	0.51
Preoperative SE	0.19	0.05	0.32	< 0.01	0.05	0.66
Preoperative K1 (anterior)	−0.31	< 0.01	−0.06	0.56	0.06	0.58
Preoperative K2 (anterior)	−0.38	< 0.01	−0.07	0.50	0.04	0.72
Preoperative Kmean (anterior)	−0.36	< 0.01	−0.06	0.58	0.03	0.74
Preoperative pachymetry	−0.06	0.51	0.25	< 0.01	0.05	0.62
Ablation depth	−0.20	0.03	0.33	< 0.01	−0.06	0.55
Residual stroma	0.06	0.52	−0.35	< 0.01	0.05	0.59
AD/P	−0.20	0.03	0.36	< 0.01	0.02	0.87

MEBD maximum elevation back difference, ACD anterior chamber depth, ACV anterior chamber volume, SE spherical equivalent, K1 flattest keratometry, K2 steepest keratometry, Kmean mean keratometry, AD/P ablation depth/preoperative pachymetry

*Pearson correlation analysis. Correlation is significant at p < 0.05 level, with significant p-values highlighted in bold within the table

Fig. 3.

Correlations between maximum elevation back difference, ablation depth, and ablation depth/pachymetry ratio

Preoperatively, all 102 eyes were screened to exclude ectatic disorders, with only 2 eyes (1.96%) having total D ≥ 1.6 (suspicious) and none ≥ 2.6 (abnormal). For individual parameters: Dp had 7 eyes (6.86%) ≥ 1.6 and 1 eye (0.98%) ≥ 2.6; Dt had 4 eyes (3.92%) ≥ 1.6 and 2 eyes (1.96%) ≥ 2.6; Da had 4 eyes (3.92%) ≥ 1.6 and 1 eye (0.98%) ≥ 2.6; Df had 10 eyes (9.80%) ≥ 1.6 and 2 eyes (1.96%) ≥ 2.6; Db had 5 eyes (4.90%) ≥ 1.6 and 2 eyes (1.96%) ≥ 2.6. This confirms that preoperative BAD scores were predominantly normal. Among the D scores postoperatively, statistically significant differences were found in the Dp, Dt, Da, and total D scores (p < 0.01), but no statistically significant change was found in the Df value following surgery (p = 0.41). These findings are summarized in Table 3.

Table 3.

Comparison of the posterior corneal measurements and Belin–Ambrósio enhanced ectasia analysis scores following PRK at the first month

Parameter	Preoperative		Postoperative		p*
	Mean	Min–Max	Mean	Min–Max
ACD	3.22 ± 0.29	2.43/3.98	3.17 ± 0.30	2.27/3.99	0.40
ACV	205.49 ± 35.84	110/283	199.53 ± 36.06	107/287	< 0.01
K1 (posterior)	−6.15 ± 0.26	−6.8/−5.60	−6.12 ± 0.25	−6.80/−5.60	< 0.01
K2 (posterior)	−6.56 ± 0.30	−7.3/−6.00	−6.51 ± 0.27	−7.30/−6.00	< 0.01
Kmean (posterior)	−6.35 ± 0.27	−7.0/−5.90	−6.32 ± 0.25	−7.00/−5.90	< 0.01
Astigmatism posterior	0.40 ± 0.16	0.1/0.9	0.37 ± 0.17	−0.6/0.8	0.04
Df	0.63 ± 1.10	−1.28/4.80	0.85 ± 2.44	−1.82/10.09	0.41
Db	0.19 ± 1.03	−1.34/3.88	0 ± 1	−1.46/3.36	< 0.01
Dp	1.03 ± 0.79	−0.80/2.89	4.67 ± 2.86	−0.05/14.60	< 0.01
Dt	0.06 ± 1.07	−1.70/3.35	1.85 ± 1.68	−0.85/6.47	< 0.01
Da	0.66 ± 0.62	−0.71/2.04	2.01 ± 0.70	0.37/3.49	< 0.01
D	1.24 ± 0.60	−0.34/2.65	2.35 ± 1.15	0.45/6.34	< 0.01
Posterior elevation	6.35 ± 5.48	−2/26	3.88 ± 5.40	−7/24	< 0.01

ACD anterior chamber depth, ACV anterior chamber volume, PRK photorefractive keratectomy, K1 flattest keratometry, K2 steepest keratometry, Kmean mean keratometry, Df deviation of front elevation difference, Db deviation of back elevation difference, Dp deviation of average pachymetric progression, Dt deviation of minimum thickness, Da deviation of ARTmax, D final D score

*Paired t-test, a p-value of <0.05 is significant, with significant p-values highlighted in bold in the table

Table 4 summarizes preoperative and postoperative BAD values, their changes (ΔD), and the correlations between preoperative values and ΔD. At 1 month post-PRK, total D increased by 1.11 (from 1.24 ± 0.60 to 2.35 ± 1.15), with Dp showing the largest change (ΔDp = 3.64). There were no significant correlations between the change in BAD-D values and their preop values. This suggests that surgical factors play much more role than baseline corneal characteristics.

Table 4.

Preoperative and postoperative Belin–Ambrósio enhanced ectasia analysis scores values

Parameter	Preop mean ± SD	Postop mean ± SD	ΔD (Postop −Preop)	Correlation (Preop versus ΔD)	p-value* (correlation)
Df	0.63 ± 1.10	0.85 ± 2.44	0.22 ± 2.31	r = 0.07*	0.55
Db	0.19 ± 1.03	0.00 ± 1.00	−0.19 ± 0.92	r = 0.06*	0.61
Dp	1.03 ± 0.79	4.67 ± 2.86	3.64 ± 2.83	r = 0.06*	0.65
Dt	0.06 ± 1.07	1.85 ± 1.68	1.79 ± 1.54	r = 0.06*	0.59
Da	0.66 ± 0.62	2.01 ± 0.70	1.35 ± 0.82	r = 0.04*	0.68
D	1.24 ± 0.60	2.35 ± 1.15	1.11 ± 1.04	r = 0.17*	0.09

ΔD and correlation analysis. ΔD = Delta D: (Postop D value −Preop D value)

Df deviation of front elevation difference, Db Deviation of back elevation difference, Dp deviation of average pachymetric progression, Dt deviation of minimum thickness, Da deviation of ARTmax, D final D score

*Pearson correlation analysis. Correlation is significant at p < 0.05 level, with significant p-values highlighted in bold within the table

Discussion

This observational study investigated changes in the posterior corneal surface and BAD scores in 102 eyes of 51 patients who underwent PRK for the correction of myopia and/or astigmatism in the first month postoperatively using Pentacam tomography device.

The impact of excimer laser keratorefractive surgery on the posterior corneal surface has been a subject of investigation since the initial report of the serious complication of keratectasia. Numerous studies have utilized corneal topography devices to assess the forward displacement of the posterior corneal surface, as it is considered an early indicator of ectasia [1–4, 14, 15].

In the present study following PRK surgery, a reduction in both ACD and ACV was observed; however, statistical significance was achieved solely in the ACV group (p < 0.01). Similarly, Nishimura et al. reported a decrease in ACD and ACV within the first month postoperatively after LASIK, although this change did not reach statistical significance, as assessed using the Pentacam [16]. This reduction has also been documented in earlier studies employing Orbscan topography and IOL master biometry devices [17, 18]. Nawa posited that the observed reduction in ACD can be attributed to alterations in the magnification effect on the anterior lens surface images caused by post-LASIK corneal changes [19]. The post-LASIK cornea induces a steeper appearance of the posterior corneal surface. According to the Pentacam manufacturer, adjustments have been implemented to address this post-LASIK issue and accurately assess the true posterior curvature through ray tracing. Sun et al. posited that the reduction in the ACD may be partially attributable to the patient’s accommodative response. The ACD diminishes with increased accommodative effort, as the patient must exert greater accommodation to focus on a near target following the correction of myopic refractive error through laser refractive surgery [20]. Rosa et al. suggested that the reduction in the ACD following PRK is attributable not only to alterations in the cornea but also to the remodeling of the anterior segment [21]. The observed decrease in ACV despite an increase in PCE appears counterintuitive, as a forward shift of the posterior corneal surface might be expected to increase anterior chamber volume. We hypothesize that this finding results from a combination of corneal biomechanical changes, anterior segment remodeling, and potential measurement artifacts. PRK-induced stromal thinning and curvature flattening may reduce the anterior chamber’s effective volume, while subtle shifts in the iris-lens diaphragm or accommodative effects could further contribute to ACV reduction without significantly altering ACD. Additionally, early postoperative corneal changes, such as haze or edema, may affect Pentacam’s boundary detection, influencing ACV calculations. These findings underscore the complexity of anterior segment dynamics post-PRK and the need for multimodal imaging to validate such changes.

Alterations in the posterior corneal surface are commonly observed following keratorefractive procedures, leading to changes in posterior corneal elevation, curvature, asphericity, and posterior K-values [22, 23]. These changes occur indirectly as a result of corneal remodeling following anterior corneal flattening, resulting in varied outcomes in the posterior cornea [24, 25]. In the present study, it was observed that posterior corneal astigmatism values, including the steepest, flattest, mean, and back astigmatism values, decreased following PRK within the first month. Khairat et al. did not observe significant alterations in the keratometric power of the posterior cornea 3 months post-LASIK, as assessed using Pentacam [26]. However, Seitz et al. [23] and Kim et al. [27] reported a notable increase in the negative corneal power of the posterior cornea after the LASIK procedure, utilizing Orbscan and Galilei devices, respectively. The discrepancy between the current study and previous reports on posterior keratometry measurements may be attributed to variations in the type of laser surgery and topography system employed.

Previous studies have documented anterior displacement of the posterior corneal surface following laser surface ablation for myopia using Orbscan [28–30]. Anterior displacement of the posterior cornea following laser-assisted subepithelial keratectomy (LASEK) was reported in a study conducted by Kim et al. by 25.90 μm 1 or 2 weeks postoperatively [28]. Kamiya et al. reported an anterior movement of the posterior corneal surface by 29.5 ± 1.9 μm at 1 week, by 34.4 ± 3.4 μm at 1 month, and by 54.3 ± 4.0 μm at 3 months after PRK [29]. Miyata et al. also found a mean anterior shift of the posterior cornea 36.6 ± 25.3 μm post-PRK at 1 week, which progressively raised to 55.1 ± 46.1 μm at 1 year postoperatively utilizing Orbscan topography [30]. However, Orbscan may inaccurately assess the postoperative posterior surface elevation. In contrast, Pentacam can obtain precise data on posterior corneal elevation and corneal thickness. Measurements of posterior corneal protrusion obtained with Pentacam after laser refractive surgery was found to be lower than that acquired using Orbscan [31]. Ciolino and Belin documented an average forward protrusion of 0.88 ± 4.64 μm 2 months following PRK, with a mean ablation depth of 53.2 μm, as assessed by Pentacam. This finding indicates a protrusion amount comparable to that observed in the present study [32]. Sun et al. [20] reported a mean difference in posterior corneal elevation of − 0.47 ± 4.23 μm following PRK and LASEK, which is consistent with the findings of both our study and those of Ciolino and Belin. In addition, there was a significant correlation between the amount of forward shift and residual bed thickness in many previous reports [33, 34]. Eyes characterized by a thinner cornea and higher levels of myopia, necessitating increased ablation and resulting in a thinner residual stromal bed, exhibited a greater predisposition to the anterior displacement of the posterior corneal surface. This condition contributed to the propensity for myopic regression following excimer laser surgery. The present study identified a correlation between ablation depth and the ablation depth/preoperative pachymetry ratio with posterior corneal elevation, measuring a modest −2.50 ± 2.94 µm. Recent investigations have reported fewer alterations in the posterior corneal surface, similar to those presented here, in contrast to previous research findings [34, 35]. This discrepancy may be attributed to variations in study methodologies, follow-up durations, and the utilization of different topography/tomography systems.

Corneal topography/tomography is essential prerequisites for refractive surgery procedures to differentiate subclinical keratoconus from normal corneal conditions, thereby preventing iatrogenic ectasia. Currently, Scheimpflug technology and optical coherence tomography are recognized as the most effective tools for screening keratoconus or ectatic disorders [36, 37].

In the current study among the BAD scores, a statistically significant difference (p < 0.01) was found for all D scores (Dp, Dt, Da, and total D), except Df value (p = 0.41) postoperatively at the first month. Shams et al. examined the influence of preoperative BAD-D scores on the 2-year refractive outcomes PRK in patients with low-to-moderate myopia [38]. The study cohort was divided into two groups: those with BAD-D < 1.60 (low BAD-D, normal) and those with BAD-D ≥ 1.60 (high BAD-D, suspicious). It was observed that 85% of patients in the high BAD-D group and 97% of patients in the low BAD-D group experienced no loss of postoperative corrected distance visual acuity (CDVA) compared with their preoperative CDVA. Notably, patients with lower preoperative BAD-D scores demonstrated a stronger linear correlation between attempted and achieved SE (r = 0.98 versus r = 0.73). Furthermore, a higher proportion of patients with normal preoperative BAD-D exhibited postoperative SE and refractive astigmatism within ± 0.50 diopters. The findings indicate that, despite no reduction in visual acuity and acceptable levels of safety and efficacy, patients in the low BAD-D group exhibited a more predictable correction of refractive error in terms of SE and refractive astigmatism. Özdoğan and colleagues investigated the biomechanical characteristics of corneas 25 years after myopic PRK, utilizing the Corvis ST (Oculus, Wetzlar, Germany) and Pentacam tomography [39]. The corneal biomechanical index (CBI) was grouped according to ectasia risk levels: low (< 0.25), moderate (0.25–0.50), and high (> 0.50). BAD values from the Pentacam were considered normal if below 2.3 (under 1.6 as truly normal, 1.61–2.3 as a normal variant) and indicative of pathology if above 2.3 (2.3–2.7 as moderately suspicious, above 2.7 as confirmed disease). Individuals with BAD scores under 2.3 served as the control group. In the PRK cohort, the average CBI was 0.91 ± 0.11, compared with 0.50 ± 0.27 in the control group (p < 0.01). BAD values were 3.34 ± 1.53 in the PRK group and 1.1 ± 0.70 in controls (p < 0.01). Among PRK-treated eyes, 71.9% fell into the “high-risk CBI with diseased BAD” category, while 25% were labeled as “high-risk CBI with normal BAD.” The researchers noted that refractive surgery complicates ectasia detection, as standardized methods for these patients remain undefined. Diagnosing ectasia after PRK is more challenging than identifying keratoconus. Although CBI and BAD were designed to spot keratoconus, they are also applied to detect early ectasia following laser refractive procedures. However, in this study, CBI classified 96% of normal post-PRK eyes—except for one case—as “high risk for ectasia.” The elevated CBI scores in otherwise normal post-PRK eyes suggest that this shift may stem from PRK’s impact. Consequently, CBI appears inadequate for distinguishing ectasia from typical post-PRK corneas. A similar limitation applies to BAD, with 71.9% of normal post-PRK eyes flagged as “diseased” on the basis of BAD values. While BAD’s false-positive rate is lower than CBI’s, it remains notably high, potentially undermining its utility in separating normal post-PRK eyes from those with ectasia. The study’s long follow-up period, exceeding 25 years post-PRK, indicates these corneas are resistant to ectasia, further supporting the idea that CBI and BAD yield false positives in this context. In the current study, the absence of correlation between preoperative BAD-D values and their postoperative changes (ΔD) (r = 0.03–0.07, p = 0.55–0.72) indicates that PRK-induced BAD score elevations (e.g., ΔTotal D = 1.11 ± 1.04) are driven by surgical factors rather than baseline corneal traits. This, combined with the high postoperative proportion of suspicious (53.92%) and abnormal (23.53%) total D scores, suggests that BAD scores may mimic ectasia early post-PRK, necessitating multimodal testing to ensure accurate ectasia detection. The long-term outcomes of PRK in Özdoğan et al.’s study were consistent with the findings of the present study. To the best of the authors’ knowledge, the current study is the first to document early changes in the BAD score following PRK.

Limitations

There are certain limitations to this study. Firstly, the sample size is relatively small, and the lack of a control group represents a constraint. Secondly, the Pentacam calculates ACV, ACD, and PCE using Scheimpflug-derived 3D models, integrating elevation and curvature data. However, measurements may be influenced by postoperative corneal changes, patient-related artifacts, or limitations in edge-detection algorithms, potentially affecting precision.

Conclusions

The main take-home messages of our study are the significant early changes in posterior corneal parameters and BAD scores post-PRK, their potential to mimic ectasia, and the need for multimodal testing to ensure accurate diagnosis. While the lack of a control group is a limitation, the objective data provide a valuable foundation for understanding PRK’s early effects and guide clinical practice toward cautious interpretation of postoperative tomography. These findings underscore the importance of further research with controlled designs to elucidate the long-term implications of these changes.

Supplementary Information

Below is the link to the electronic supplementary material.

Authors Contributions

Konuralp Yakar was responsible for the design of the study. Both Konuralp Yakar and Gökhan Özgür undertook the data collection. The data analysis was conducted by Gökhan Özgür and Konuralp Yakar. The interpretation of the data was carried out by Konuralp Yakar and Göksu Alaçamlı. The drafting of the manuscript was the responsibility of Konuralp Yakar and Göksu Alaçamlı. The critical revision of the manuscript was performed by Konuralp Yakar, Göksu Alaçamlı, and Gökhan Özgür. All authors reviewed and approved the final version of the paper.

Funding

No funding or sponsorship was received for this study or publication of this article. The Rapid Service Fee was funded by the authors.

Data Availability

The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Conflict of Interest

Konuralp Yakar, Göksu Alaçamlı, and Gökhan Özgür have nothing to disclose.

Ethical Approval

The study protocol received approval from the Ethical Committee of Ondokuz Mayıs University (B.30.2.ODM.0.20.08/256) and adhered to the principles outlined in the Declaration of Helsinki. Informed consent was obtained from all participants.