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Year : 2019  |  Volume : 11  |  Issue : 2  |  Page : 42-47

Effect of mesopic pupil size on aberrometric outcomes after femtolaser-assisted intracorneal ring implantation in keratoconus

Department of Ophthalmology, Faculty of Medicine, Sohag University, Sohag, Egypt

Date of Submission10-Nov-2019
Date of Decision13-Jan-2020
Date of Acceptance29-Dec-2019
Date of Web Publication09-Mar-2020

Correspondence Address:
Dr. Amr Mounir
Department of Ophthalmology, Sohag Faculty of Medicine, Sohag University, Sohag 82524
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DOI: 10.4103/sjopthal.sjopthal_29_19

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Purpose: This study aimed to evaluate the effect of mesopic pupil size on corneal high-order aberrations in keratoconic eyes implanted with femtosecond laser-assisted intracorneal ring segments (ICRS) implantation procedure. Design: The study design involves a retrospective, consecutive case series. Patients and Methods: A total of 160 consecutive eyes of 133 patients with the diagnosis of keratoconus (93 eyes with keratoconus Grade 2 and 67 with keratoconus Grade 3) were included in the study. Keraring (Mediphacos, Belo Horizonte, Brazil) implantations were performed using femtosecond-assisted laser in Sohag Refractive Center, Sohag, Egypt, between September 2015 and September 2017. Pupil size and anterior corneal aberrations were measured by Scheimpflug placido topography (Sirius, CSO, Italy). Results: There were statistically significant changes between corneal aberrations preoperatively and postoperatively in both groups. Mesopic pupil size had no significant correlation with all corneal aberrations. Conclusion: Mesopic pupil size did not prove to be affecting corneal aberrations after femtosecond laser-assisted ICRS implantation for keratoconus.

Keywords: Corneal aberrations, femtosecond laser, kerarings, keratoconus, pupil size

How to cite this article:
Mounir A, Mostafa EM. Effect of mesopic pupil size on aberrometric outcomes after femtolaser-assisted intracorneal ring implantation in keratoconus. Sudanese J Ophthalmol 2019;11:42-7

How to cite this URL:
Mounir A, Mostafa EM. Effect of mesopic pupil size on aberrometric outcomes after femtolaser-assisted intracorneal ring implantation in keratoconus. Sudanese J Ophthalmol [serial online] 2019 [cited 2021 Apr 19];11:42-7. Available from: https://www.sjopthal.net/text.asp?2019/11/2/42/280247

  Introduction Top

Keratoconus is an ectatic debilitating corneal disorder, characterized by a progressive corneal thinning that results in corneal protrusion, myopia, and irregular astigmatism.[1] Diverse lines of management have been described for keratoconus such as rigid gas-permeable contact lenses,[2] corneal collagen cross linking,[3] intracorneal ring segment (ICRS) implantation,[4],[5] or keratoplasty.[6]

The pupil forms the physical aperture that controls the retinal image quality.[7],[8],[9] The retinal image quality of the corrected eye is optimum at pupil sizes of about 3–5 mm.[9] Diffraction and higher-order aberrations (HOAs) cause deterioration in quality below 3 mm and above 5 mm, respectively.[10],[11] Thus, pupil size is a major contributor of optical quality in refractive procedures,[12],[13],[14],[15] as it plays an important role in HOAs.[16],[17] Therefore, incorporating measuring pupil size preoperatively, especially in low-light illumination conditions, is warranted.[18]

Implantation of ICRS was proved to enhance the visual acuity and diminish refractive errors along with mean keratometry (K) values.[19] ICRS are polymethyl methacrylate rings implanted at the corneal mid-periphery thus inducing a flattening of the central portion of the anterior cornea because of the morphological structure of the corneal lamellae (arc-shortening effect).[20] The main benefits of ICRS include stability, reversibility, and safety while preserving the integrity of the central cornea.[21],[22],[23] Corneal tunnelization for ICRS was first done by the mechanical dissection,[24],[25] which is nowadays replaced by the femtosecond laser.[26] Femtosecond laser allows an accurate depth of tunnelization at a predetermined depth with a high degree of precision.[27] The effectiveness and safety of ICRS in the management of different stages keratoconus have been the subject of a number of studies with satisfactory refractive results.[23] However, their effect on HOAs was controversial among studies where some studies reported their increase.[23],[27] To the best of our knowledge, pupil size after ICRS was not previously investigated. Hence, we focused on the pupil size and its relation to postoperative HOA. Furthermore, the aberrometric changes of kerarings implantation using femtosecond laser in keratoconus patients were investigated.

  Patients and Methods Top

This retrospective interventional study was conducted at the Sohag Refractive Center, Sohag, Egypt, on 160 consecutive keratoconic eyes of 133 patients treated with ICRS implantation for Grade 2 and Grade 3 (according to Amsler–Krumeich grading system)[28] with clear central cornea and age between 18 and 40 years. Kerarings (Mediphacos, Belo Horizonte, Brazil) were implanted in all eyes with femtosecond laser tunnel creation (IntraLase; Advanced Medical Optics, Santa Ana, California, USA) between September 2015 and September 2017. The exclusion criteria included patients with corneal scarring, history of previous corneal surgeries or ocular pathology, systemic medications that affect corneal wound healing, collagen vascular diseases, corneal dystrophies, pregnant or lactating females, or patients with follow-up <6 months.

All patients underwent comprehensive examination, including uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA) (decimal notion), spherical equivalent, slit-lamp biomicroscopy, and fundus examination.

Corneal topography, pachymetry, corneal aberrometry, and mesopic pupil diameter were evaluated using Sirius Scheimpflug placido topography (CSO, Florence, Italy). The CSO topography system analyzes a total of 6144 corneal points of a corneal area enclosed in a circular annulus defined by an inner radius of 0.33 and an outer radius of 10 mm with respect to the corneal vertex. Mesopic pupil diameter was acquired by Sirius in a dark room with the disc illuminated in a manner to bring ambient light intensity to 4.0 lux as advised by the manufacturer.[29]

Data collected from Sirius were corneal dioptric power in the flattest meridian (Kf) and steepest meridian (Ks) for the 3-mm central zone and maximum corneal power in the 6-mm zone (KM). Corneal aberrometry data were collected from the Sirius as well included total higher-order root mean square (RMS) (computed for third to seventh Zernike terms), coma-like RMS (third-, fifth-, and seventh-order Zernike terms), spherical-like RMS (computed for fourth- and sixth-order Zernike terms), and secondary astigmatism (fourth-order Zernike terms). HOAs were reported in microns. The minimum thickness for implantation was 400 um, with implantation at 80% depth at the insertion site. All procedures were done under topical anesthesia under complete aseptic measures by two surgeons (AM, EM). Corneal tunnelization was performed with a 30 kHz femtosecond system (IntraLase, IntraLase Corp., Irvine, California). The femtotunnel creation parameters included inner diameter 5.00 mm and outer diameter 5.90 mm and entry cut length 1.40 mm and entry cut thickness 1 mm. The incision was created at the steepest axis. KeraRings (Mediphacos) were used in all cases. The selection of the number (1 or 2), arc-length, and thickness of Kerarings segments was performed following the nomogram defined by the manufacturer.[4] Only one ring segment was implanted in 31 eyes (19.37%), whereas two segments were necessary for the other 129 eyes (80.63%).

The incision site was on the steepest meridian in all eyes. The incision was opened by a Sinski hook, and the tunnel was dilated by blunt dilator before ring insertion. After ring insertion, a soft bandage contact lens was applied. No intraoperative complications were reported. The postoperative medication included topical antibiotics eye drops (e.g., gatifloxacin 0.3% five times/day for 1 week), topical steroid eye drops (e.g., prednisolone acetate 1%) five times/day for 1 week, lubricant eye drops, and systemic nonsteroidal anti-inflammatory drugs. Postoperative follow-up was scheduled at the 1st day, 1st week and then 1, 3, and 6 months. Postoperative complications were minimal, including segment migration in three eyes. Follow-up included manifest UCVA, BCVA, sphere, cylinder, corneal topography, and aberrometry. Our study adhered to the Tenants of Helsinki and the Ethical Board Committee approval of our institution (Sohag Faculty of Medicine) was obtained.

Statistical analysis

SPSS software for Windows was used for the statistical analysis (version 15.0.1 SPSS Inc., Chicago, IL, USA). The mean values and standard deviations were calculated for every parameter during the follow-up. The normal distribution of all data samples was checked by the Kolmogorov–Smirnov test. If a parametric analysis was possible, the paired Student's t-test was performed for comparisons between the data obtained in the preoperative and postoperative examinations or consecutive postoperative visits. When a parametric analysis was not possible, the Wilcoxon rank-sum test was applied. The level of statistical significance used was (P < 0.05).

  Results Top

This study included 160 consecutive keratoconus eyes of 133 patients treated with femtosecond keraring implantation; 66 were male and 67 were female, ranging in age from 10 to 42 years (mean age: 24.37 ± 6.35 years). Of the 160 eyes, 93 eyes (58.1%) were classified as Grade 2 keratoconus (Group I) and 67 (41.9%) eyes classified as Grade III (Group II). The refractive outcomes of both groups are reported in [Table 1].
Table 1: Refractive outcomes pre- and post-Keraring femtosecond implantation

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Mean mesopic pupil diameter preoperatively and postoperatively was 4.35 ± 0.54 mm and 4.42 ± 0.66, respectively.

There was no statistically significant difference between pre- and post-operative mesopic pupil diameter (P = 0.3). There was no correlation between age and pupil size (P = 0.97).

Corneal aberrations in Group II are higher than Group I with a significance of 0.02. All HOAs were significantly reduced in both groups, as shown in [Table 2] [Figure 1] and [Figure 2].
Table 2: Changes in keratometric and corneal high-order aberrations in both groups of keratoconus

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Figure 1: Change in high-order aberrations within 5 mm pupil diameter (a) High-order aberrations before intracorneal ring implantation (b) High-order aberrations after intracorneal ring implantation

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Figure 2: Change in high-order aberrations within 6 mm pupil diameter (a) High-order aberrations before intracorneal ring implantation (b) High-order aberrations after intracorneal ring implantation

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Our results show that pupil diameter did not have any correlation with corneal aberrations either preoperatively or post-operatively.

  Discussion Top

The first reported results of ICRS in keratoconus was in 2000 by Colin et al.[30] who detected a decrease in the corneal steepening and astigmatism. Since then, several studies[31],[32] established the efficacy and safety of ICRS on both the short term and long term. The cornea is a major contributing factor in the aberrated eyes of keratoconus. Thus, the main scope in our study was investigating the effect of pupil size on corneal aberrations in keratoconus after implantation of ICRS which eventually has an impact on the degree of visual gain. Furthermore, some studies[19] have challenged the concept that the smaller diameter of ring segments (Kerarings) that are near the border of the pupil could adversely affect the visual quality. Therefore, studying the effect of pupil diameter on corneal aberrations after keraring implantation was further challenged in this study. To the best of our knowledge, pupil size effect was not tested previously. The mesopic pupil is the size that is most prevalent indoors. The mesopic pupil diameter in our study is comparable to other studies.[33],[34]

Automated pupillometry has been subjected to test and proved to be accurate, repeatable, and superior to mechanical devices.[29]

However, on comparing Sirius with two other automated pupillometers (NeurOptics® Pupillometer and Ocular Wavefront Analyzer®), Sirius proved to obtain relatively larger measurements of the pupil.[35]

There was no influence of pupil size on corneal aberrations either before or after keraring implantation which concurs well with several studies[12],[15],[18] that concluded that pupil size does not positively or negatively correlate with any of postoperative visual symptoms 12 months after laser in situ keratomileusis.

We are aware that our study might have some limitations. Studying the anterior corneal aberrations, instead of total ocular aberrations may be considered limiting. However, we believe that as the kerarings act on the corneal plane thus affecting the anterior corneal aberrations with minor effect on the posterior corneal surface and the internal optics of the eye (mainly the crystalline lens).[36],[37]

Further studies would be beneficial to investigate the impact of pupil size after ICRS on contrast sensitivity and subjective symptoms as the role of mesopic pupil size as a risk factor in predicting night vision complaints is still controversial. It would also be interesting to analyze the effect of increment increase pupil size on corneal aberrations. This study could be a good basis to detect if the pupil size could be incorporated as one of the predictive factors of the prognosis in cases of keratoconus managed by ICRS to help optimize the treatment outcomes.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2]


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