Is soft toric contact lenses fitting a feasible option to improve optical quality and visual performance in corneal ectasia?

Abstract

Objectives

To assess the feasibility of fitting soft toric contact lenses (STCL) in corneal ectasias and their impact on optical quality and visual performance.

Methods

A total of 22 eyes were fitted with a molded STCL: 11 eyes/9 subjects with corneal ectasia and 11 healthy eyes/11 subjects. Wavefront aberrations were analyzed using a Hartmann-Shack aberrometer. Visual performance was measured under photopic (85 cd/m 2) and mesopic (≤3 cd/m 2) conditions. High-(96 %) and low- (10 %) contrast VA (HCVA and LCVA respectively) were assessed using the ETDRS charts and contrast sensitivity (CS) using the Pelli-Robson chart.

Results

After STCL fitting in the ectatic corneas, oblique astigmatism increased 0.15±0.17 μm and 0.34 ± 0.36 μm for 3 mm- and mesopic pupil diameters, respectively.

Mean defocus decreased 1.41 ± 0.36 μm and 2.17 ± 0.85 μm for the same pupil diameters. More positive values of vertical coma were found with a change of 0.05 ± 0.06 μm and 0.12 ± 0.10 μm for 3 mm and mesopic pupil diameters, respectively. Comparing changes between both groups, with a 3 mm pupil aperture, statistically significant differences (p < 0.05) were detected in oblique astigmatism, defocus, vertical secondary trefoil and horizontal secondary coma. In the group with corneal ectasia, photopic HCVA and LCVA improved 0.09 ± 0.11 logMAR and 0.12 ± 0.15 logMAR respectively. In mesopic conditions, HCVA, LCVA and CS improved 0.11 ± 0.12 logMAR, 0.18 ± 0.15 logMAR and 0.11 ± 0.07 log. units, respectively.

Conclusions

The analyzed molded soft toric contact lens is a feasible option for good vision in corneal ectasia with moderate irregularity and negative vertical coma.

Introduction

The term corneal ectasia includes a group of conditions characterized by progressive thinning, bulging and distortion of the cornea. Keratoconus (KC) is the most prevalent corneal ectasia which affects the surface, structure and transparency contributing towards the conical shape of the cornea [1]. Laser-assisted refractive procedures have become very popular in the last decades. As a result, some patients present altered corneal properties. Similar to KC, ectasia after refractive surgery shows topographic asymmetric inferior corneal steepening [2].

The progression of ectasia increases low-order aberrations (LOA), including myopic spherocylindrical refractive values, and high-order aberrations (HOA). This mainly produces vertical coma aberration due to the loss of rotational symmetry of corneal surfaces. When the cone is displaced inferiorly, the vertical coma is negative, which is induced by the anterior corneal surface [3]. The increase in HOA, reduces the optical quality and therefore the quality of life in comparison with healthy subjects [4]. Surgery treatments, with the goal of stabilization include cross-linking, intrastromal corneal ring segments (ICRS) and keratoplasty. The fitting of rigid gas permeable contact lenses (RGP) is the gold standard treatment of ectasias. The front surface of corneal RGP on an ectatic cornea provides a refractive surface much more regular profile and a post-RGP lens tear film that has the capability to mask both LOA and HOA [[5], [6], [7]]. However, it is difficult for some patients to tolerate these lenses for enough hours to perform their activities [8]. When this occurs, the alternative contact lens options include soft contact lenses (SCL), piggy-back, hybrid and scleral lenses.

In recent years, scleral RGP prescribing has increased due to significant advantages over corneal RGP including improved comfort and stability. Scleral RGP are designed to vault over the cornea and limbus. This create a fluid reservoir between the lens and the cornea neutralizing surface irregularities [9]. While scleral lenses offer several advantages, in some cases their size and application and removal sometimes pose a problem.

Previous studies have shown that the visual acuity (VA) achieved using a SCL is often better than the outcome predicted by aberrometry coefficients. Moreover, they can achieve higher comfort levels compared to other lenses [[10], [11], [12]]. Carballo-Alvarez et al. [13] reported that soft toric contact lenses (STCL) are a viable option for good vision in keratoconic eyes with moderate irregularity after ICRS implantation. Several reports indicate that a high central thickness of the SCL seems to decrease the HOA and to improve the visual function in irregular cornea [7,[14], [15], [16]]. To fully correct the HOA of both anterior and posterior corneal surfaces in keratoconic patients, customized wavefront-guided contact lens designs have been developed as an option to improve optical quality in KC [12,[17], [18], [19], [20], [21], [22]]. Other authors used asymmetric SCL to correct vertical coma aberration in keratoconic patients [[23], [24], [25]].

As previously observed in eyes with an irregular cornea [10,11], the clinical experience indicates that in some patients, STCL besides offering high comfort, leads to better visual function than predicted by corneal HOA indicators and could be an alternative to RGP lens. The purpose of this study was to assess the feasibility of STCL fitting in corneal ectasias and their impact on optical quality and visual performance.