Effects of chalazia on corneal astigmatism

A chalazion is a meibomian gland lipogranuloma which accompanies swelling on the eyelid and eyelid tenderness [1]. It is a common eyelid disease that causes eye morbidity due to inflammation and cosmetic disfigurement [2]. A variety of factors are believed to be associated with the development of chalazia including meibomian gland dysfunction, chronic blepharitis, seborrheic dermatitis, gastritis, and smoking [1]. Chalazia treatment includes medical treatments, such as warm compression and topical antibiotic eye drops or ointment, and surgical incision and curettage, with or without triamcinolone intralesional injection [3].

Corneal topographic changes are important factors in corneal refractive surgery, intraocular lens power calculations for cataract surgery, and visual acuity assessments [4‐6]. In addition, amblyopia may develop in children with corneal astigmatism [7]. It has been reported that the pressure of an upper lid chalazion induces hyperopia and astigmatism.7 Chalazia can increase higher-order aberrations (HOAs), as measured by the Hartmann–Shack aberrometer; these can affect the preoperative evaluation and refractive surgery outcomes, especially wavefront-guided approaches [8]. In addition, decreased vision due to a chalazion of the upper eyelid has been documented in a patient following laser-assisted in situ keratomileusis (LASIK) [9]. Furthermore, corneal aberration has been reported to contribute to the visual function [10, 11]. The changes in corneal astigmatism according to chalazion size and location is necessary for better outcome of ocular surgery.

However, the effects of chalazia on corneal astigmatism have not been thoroughly investigated. In this study, we investigated changes in corneal astigmatism according to chalazion size and location.

This study adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of Hallym University Medical Center. Medical charts of a total of 114 eyes from 64 patients were reviewed retrospectively in this study between July 2013 and April 2015 at the Hallym University Gangnam Sacred Heart Hospital, Seoul, South Korea. Forty four eyes from 33 patients exhibiting an eyelid chalazion were assigned to the chalazion group. The control group comprised 22 contralateral normal eyes of chalazion patients and 48 eyes from 24 patients without a chalazion, randomly selected and matched for age and sex. Patient medical history including diabetes mellitus and hypertension was obtained and a physical examination of eye and eyelid was performed prior to study procedures. Patients in the control group did not have a history of ophthalmic surgery including eyelid surgery and were not using topical or systemic medications on examination.

Chalazia were classified according to their site (upper, lower, or both eyelid groups) and location (nasal, middle, temporal, or whole area of eyelid). They also were classified into groups according to their size; small (≤1/5 of eyelid), medium (2/5–3/5), or large (>4/5).

An autokeratorefractometer (ARK; KR8100, Topcon; Japan) was utilized to measure keratometric values (K) including mean K, flat and steep K, astigmatism, and axis. Central corneal thickness (CCT), corneal topographic data, and wavefront aberration data were obtained using a Galilei™ dual-Scheimpflug analyzer (Ziemer Group; Port, Switzerland). Simulated K (simK) were obtained from the central 3-mm zone of the corneas including flat and steep K, mean K, astigmatism (difference between steep and flat Ks), and the axis of the steep meridian.

Corneal wavefront aberrations were analyzed, including total root mean square (RMS, in microns) of the total high order aberration, second order aberration, oblique astigmatism (Z⁻² ₂), defocus (Z⁰ ₂), vertical astigmatism (Z² ₂), third order aberration, vertical trefoil (Z⁻³ ₃), vertical coma (Z⁻¹ ₃), horizontal coma (Z¹ ₃), oblique trefoil (Z³ ₃), fourth order aberration, oblique quadrefoil (Z⁻⁴ ₄), secondary oblique astigmatism (Z⁻² ₄), primary spherical aberration (Z⁰ ₄), vertical secondary astigmatism (Z² ₄), and vertical quadrefoil (Z⁴ ₄).

A total 114 eyes from 64 patients were included in this study: 44 eyes in the chalazion group and 70 eyes in the control group (Table 1). Mean patient age was 40.0 ± 13.9 years in the chalazion group and 43.4 ± 14.0 years in the control group. The chalazion group was divided into the following subgroups: 1) according to site of the chalazion, the upper eyelid (n = 22), lower eyelid (n = 16), and both eyelids (n = 6), 2) according to the location of the chalazion, the nasal eyelid (n = 10), middle eyelid (n = 25), temporal eyelid (n = 4), and whole eyelid (n = 3), and 3) according to the size of the chalazion, small (n = 14), medium (n = 17), and large (n = 11) (Additional file 1).

Corneal topographic data for the chalazion and control groups are presented in Fig. 1 and Table 2. There was no difference in CCT different between the two groups. Astigmatism measured by ARK was not significantly different between the chalazion and control groups (p = 0.074; independent t-test). Oblique astigmatism (Z⁻² ₂) was greater in the chalazion group compared with the control group (p = 0.013; independent t-test). Other topographic data were similar between the chalazion and control groups.

The CCT was not significantly different between the chalazion site subgroups (Fig. 2, Table 3). However, astigmatism by simK, steep K by simK, total RMS, second order aberration, Z⁻² ₂, and Z² ₂ were significantly different between these subgroups (p = 0.001, 0.022, 0.002, <0.001, 0.009, and 0.001, respectively; ANOVA). Astigmatism by simK was greater in the upper eyelid group compared with the control and lower eyelid groups (p = 0.001 and 0.004, respectively; Tukey post hoc test). Steep K by simK significantly differed between upper and lower lids (p = 0.011; Tukey post hoc test). Total RMS was greater in the upper eyelid group compared with the control and lower eyelid groups (p = 0.004 and 0.003, respectively; Tukey post hoc test). Second order aberration was greater in the upper eyelid group compared with the control, lower eyelid, and whole eyelid groups (p = 0.001, <0.001, and 0.019, respectively; Tukey post hoc test). The Z⁻² ₂ was greater in the upper eyelid group compared with the control (p = 0.06, Tukey post hoc test). The Z² ₂ was greater in the upper eyelid group compared with the control and lower eyelid group, and lower in the upper eyelid group compared with whole eyelid group (p = 0.002, 0.008 and, 0.028, respectively; Tukey post hoc test).

Corneal topographic changes according to chalazion location are presented in Fig. 3 and Table 4. The CCT was also not significantly different between chalazion location subgroups. Astigmatism by ARK, Z⁻² ₂, Z⁰ ₂, and Z⁻² ₄ were significantly different between groups (p = 0.046, 0.033, 0.003, and 0.015, respectively; ANOVA). Astigmatism by ARK was significantly different between the control and temporal area groups or between middle and temporal area group (p = 0.019 and 0.025; Tukey post hoc test). The Z⁰ ₂ was greater in the whole area group compared with the control, nasal, middle, and temporal area groups (p = 0.002, 0.021, 0.001, and 0.004, respectively; Tukey post hoc test). There was a significant difference in Z⁻² ₄ between temporal and whole area groups (p = 0.018; Tukey post hoc test).

Corneal topographic changes according to chalazion size are presented in Fig. 4 and Table 5. The CCT was not significantly different between chalazion size subgroups. Astigmatism by simK, second order aberration, Z⁻² ₂, and Z² ₂ were greater in the large-sized chalazion group (p = 0.037, 0.036, 0.006, and 0.002, respectively; ANOVA). Astigmatism by simK and second order aberration was greater in the large-sized chalazion group compared with the control (p = 0.049 for both; Tukey post hoc test). There was a significantly greater Z⁻² ₂ in the large-sized chalazion group compared with the control (p = 0.003; Tukey post hoc test). Z² ₂ was greater in the large-sized chalazion group compared with the control and small-sized chalazion groups (p = 0.015 and 0.004, respectively; Tukey post hoc test).

A chalazion is a common eyelid disease, affecting individuals of all ages, caused by plugged meibomian glands and chronic lipogranulomatous inflammation [12]. Chalazia have been reported to increase corneal astigmatism and HOAs [7, 8, 13, 14]. In this study, we evaluated the effects of chalazia on the cornea according to chalazia site, location, and size using corneal topography and wavefront analysis. This study systematically revealed the mechanical effects of chalazia on corneal astigmatism. In this study, a large-sized chalazion in the whole upper eyelid induced changes in the corneal topographical and wavefront assessments. The mechanisms behind the effects of chalazia on corneal astigmatism can be suggested as follow. Firstly, with regards to the biomechanical properties of the cornea, it has been reported that its tensile strength is 3.81 ± 0.40 MPa and its stress-strain is α = 42.81 ± 11.67 and β = 2.97 ± 0.21 [15]. Compressive pressure of chalazia in excessive of these levels can induce the corneal astigmatism. In contrast, cornea under reduced strain by corneal refractive surgery (such as LASIK) may be more affected by lower pressure [9]. Secondly, lamellar orientation in human corneas has been shown to be related to mechanical properties [16, 17]. The mechanical effects increase in the meridian direction as they become closer to the center of the cornea [17]. Variations in the regional elastic performance of the human cornea have been reported; the pressure-induced meridional strains were smallest at the corneal paracenter and periphery, with the largest recorded at the limbus [18]. The circumferential strains varied less between regions with the para-centre straining to the greatest extent. In the meridional direction, Young’s modulus of elasticity was greatest at the central and para-central corneal regions, while the greatest circumferential elastic modulus was found at the limbus [17, 18]. Some authors have suggested the notion of circumferentially orientated reinforcing structures in human limbal tissue [18]. The para-central region of the human cornea was found to be stiffer in the meridional direction compared with the circumferential direction, suggesting a meridionally-orientated reinforcement of the para-central parts of the human cornea [18]. Furthermore, the human corneal stroma exhibit a preferred collagen orientation in the inferior-superior and nasal-temporal directions. However, at the limbus, the preferred orientation is tangential to the cornea [19]. Therefore, it is difficult for the pressure on the sclera to have an effect on the cornea in the meridian direction. Chalazia in the middle eyelid can more easily induce corneal astigmatism in the meridian direction because it is located superior to the cornea and close to the center of the cornea. The mass effect of a chalazion could increase with size. Chalazia generally affected Z⁻², an aberration of off-axis rays. Furthermore, HOAs influence sensitivity to contrast to varying degrees at different orientations [20].

These findings may have implications in pediatric patients at risk of amblyopia [13]. In addition, transient chalazion-induced astigmatism can disturb the visual acuity, mislead intraocular lens calculation before cataract surgery, and result in serious error during refractive surgery. Therefore, in these cases, chalazia should be treated in the early phase. Long-term chalazia may induce the remodeling of corneal stroma through the secretion of inflammatory mediators including matrix metalloproteinases. Chalazia excision can decrease corneal astigmatism and irregularity; this is more prominent in single, firm, and central upper eyelid lesions [14]. Treatment modality includes incision and curettage, intralesional triamcinolone injection, and intralesional botulinum injection.

Large-sized chalazia in the whole upper eyelid should be treated in the early phase because they induced the greatest change in corneal topography. Chalazion should be treated before corneal topography is performed preoperatively and before the diagnosis of corneal diseases.