A prospective clinical study was conducted to determine the viability of a novel large diameter RGP corneal CL design for eyes with KC. Patients were recruited from those attending the optometry clinic at the Universitat Politècnica de Catalunya between March 2022 and March 2024, all with a confirmed ophthalmological diagnosis of KC, irrespective of type and stage of the condition. Due to the asymmetric nature of KC,1 which was verified with an intraclass correlation analysis, as reported below, all eyes fitted with CLs were included in the subsequent data analysis. Exclusion criteria were eyes with a history of keratoplasty, refractive surgery, corneal pathologies other than KC, or signs of CL induced corneal warpage.

The study adhered to the tenets of the Declaration of Helsinki (1975, revised in Tokyo in 2013). Written informed consent was obtained from all participants or their legal tutors after providing a detailed explanation of the purpose, potential risks, and consequences of the study. Participants were informed that they could withdraw from the study at any time without repercussions. Ethical approval was granted by the Fundació Assistencial Mútua de Terrassa Ethics Committee for Clinical Research with Drugs (code n. E/22–023).

Rigid gas-permeable corneal KAKC-I CLs (Hecht Contactlinsen GmbH, Freiburg, Germany and Conóptica SL, Barcelona, Spain), manufactured with Boston EO material (Dk = 58 units), and with diameters ranging from 10.30 mm to 11.50 mm were used in eyes with KC. These lenses feature four concentric spherical zones with diameters D0, D1, D2, and D3, and corresponding radii of curvature R0, R1, R2, and R3. The central zone D0 serves as the optic zone, functioning as a dome over the area most affected by KC. The adjacent zone (D0 – D1) transitions to the alignment zone, which is located around the circumference defined by diameter D1. The subsequent zones (D1 – D2, and D2 – D3) create a gradual progression toward the edge lift, which begins at the circumference of diameter D3 (Fig. 1).

Fig. 1.

Sodium fluorescein image of a large diameter rigid gas-permeable corneal CL for keratoconus. The white rings correspond to the different zone changes (D0, D1, D2 and D3), and the yellow ring shows the total lens diameter (DT).

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The determination of the lens parameters was tailored for each patient. For the initial trial lens, the diameters were based on the horizontal visible iris diameter (HVID), measured using the MYAH topographer (Topcon Healthcare, Barcelona, Spain). The total diameter (DT) was set at 90% of the HVID, whereupon the diameters of the concentric zones (D3, D2 and D1) were calculated by subtracting 0.6 mm, 1.2 mm, and 2.8 mm from DT, respectively. The diameter of the central zone (D0) was at least 1 mm smaller than D1, and could adopt one of the following four values: 6.0 mm, 6.5 mm, 7.0 mm, and 7.5 mm. The widest possible D0 was chosen to ensure adequate pupillary coverage in low-light conditions. In order to determine the radii of curvature, the average sagittal heights of the eyes for circles concentric to the pupil corresponding to the previously determined diameters D0, D1, D2 and D3 of the CL were first obtained with the Oculus Pentacam model HR (High Resolution, software version 1.21r65). Secondly, adequate tear thickness values were added to calculate the sagittal heights of the CL for each diameter and at the geometric centre. Finally, the radii of curvature for each zone were obtained through geometrical calculations based on sagittal height and diameter.

Tear thickness values were selected based on clinical experience. Thus, fixed values were considered at the outer transition zone points: 60 µm at the beginning of the edge lift (D3), and 15 µm and 5 µm at the end (D2) and beginning (D1) of the alignment zone, respectively. The topographic location and elevation of the cone apex was used to select adequate tear thickness at the end of the optical zone (D0) and at the geometric centre of the lens, with values ranging from 20 to 60 µm.

Contact lenses with a geometry based on increasing radial values, or with reverse geometry, were employed according to corneal profile and topographic location of the cone apex. Increasing radial geometry is particularly suited for topographically centred ectasias, as these CLs feature a steeper central dome to accommodate the corneal shape. In contrast, reverse geometry lenses are designed with a flatter profile and a higher dome in the paracentral area, making them the preferred choice for eyes with topographically decentred ectasias.

To complete the characterization of the CLs, additional parameters were defined: the sagittal height from the plane described by the circle D1 (SD1), i.e., the height of the CL dome from the alignment zone; and the sagittal height from the plane described by the circle D3 (SD3), which corresponds to the total sagittal height of the CL, excluding the edge lift.

All patients attended an initial baseline visit, followed by one or more evaluation visits, if parameter adjustments were required to optimize fit. Follow-up visits were scheduled at one week (1 W), 15 days and 1 month after lens delivery, and three months later (3 M), although only data from the 1 W and 3 M visits was collected for the purposes of this study. All procedures, including lens fitting and handling training sessions, were performed by the same practitioner and employed the same instrumentation. Briefly, these CL are inserted following the same procedure as an orthokeratology CL. First, a couple of preservative-free artificial tear drops are added into the bowl of the CL to improve comfort and avoid the formation of trapped air bubbles; then, patients are instructed to tilt their heads parallel to the surface of a counter top and to insert the CL by looking directly into the bowl of the CL during the process. Lens removal follows the same procedures as a typical RGP CL. Patients already wearing CLs were required to refrain from using them for one week before participating in the study to ensure reliable topographic measurements.

At the baseline visit, all participants underwent a comprehensive optometric examination that included topographic analysis using the Oculus Pentacam HR, measurement of HVID and pupillary diameter under photopic and scotopic lighting conditions with the Topcon MYAH and slit-lamp anterior ocular surface evaluation (the Efron Grading Scales were used to grade any observed ocular complication18). Monocular visual acuity (VA) and contrast sensitivity (CS) at 3, 6, 12 and 18 cycles per degree (cpd) were determined with a logMAR chart and the CSV-1000 test (VectorVision®, Greenville, OH, US) under photopic conditions (58 cd/m2), respectively, while patients used their habitual correction. In addition, to assist in the assessment of the visual performance with the new CL design, best-corrected visual acuity (BCVA) was obtained while patients wore a KC RGP corneal CL from a trial lens set with the best over-refraction in a trial frame.

At the evaluation visit, CL fit was assessed at least 15 min after lens insertion. The following criteria were defined to evaluate the suitability of the fitting: (1) Visual acuity with the CLs was equal to or greater than the BCVA obtained with the trial lens, and could not be further improved with over-refraction; (2) DT was correct to avoid invading the limbal area, ensuring the lens edge remained within the boundaries of the visible cornea at all times; (3) Adequate vertical movement with blinking was observed, and rapid re-centring of the CL with reference to the geometrical centre of the cornea; (4) Fluorescein pattern showed no bearing at the central cornea or cone apex and uniform alignment across the periphery; (5) Edge lift ensured tear exchange and comfort and showed a symmetrical pattern along the entire perimeter of the lens. In addition, patients were required to demonstrate adequate CL handling and care practices. A 0.05% concentration povidone-iodine based maintenance system was provided to the patients (Cleadew, OPHTECS Europe B.V., Elst, The Netherlands) with the recommendation of wearing the CLs for two hours the first day and to gradually increasing wear time each day over the course of the first week.

If the adaptation was deemed unsatisfactory, new CLs were ordered with the necessary design adjustments, including: (1) An increase or decrease in sagittal height if the dome was found to have insufficient or excessive clearance, respectively; (2) A change in Dᴛ of up to 0.5 mm, or adjustments to radii R₃ and/or R₂, if tear exchange or lens movement was not clinically satisfactory; (3) Adjustments in D₁ by up to 0.5 mm to prioritize a more peripheral bearing or to obtain a wider alignment zone. The number of CLs required to achieve optimum fit for each patient was recorded.

At all follow-up visits, the suitability of the adaptation was reassessed based on the previously described criteria. Visual acuity and CS were measured while patients wore the CLs, using the same tests and lighting conditions as at the baseline visit. After removing the CLs, ocular health was evaluated. Additionally, at the 3 M follow-up visit the number of hours of daily lens wear was recorded, and user satisfaction was assessed with both a 10 cm vertical Visual Analogue Scale (VAS) and the multiple choice question “Over the past three months, how often have you felt satisfied with your contact lenses?" (Possible answers were: a) No response or not certain; b) Never; c) Infrequently; d) Sometimes; e) Most of the time; f) Always).

Keratoconus were classified according to the position of the cone apex as central (apex within the central 3 mm zone), paracentral (apex within the 3–5 mm zone), or peripheral (apex outside the central 5 mm zone).19 For severity, the Topographic Keratoconus Classification (TKC) Index, provided by the Oculus Pentacam software, was used, which evaluates parameters of the anterior corneal surface and assigns one of four increasing severity levels: TKC1, TKC2, TKC3, and TKC4.

The IBM SPSS Statistics v.28 (IBM Corp. NY, US) was used for statistical analysis. Only participants who completed the 3 M follow-up period were included in the analysis. Data normality was assessed with the Kolmogorov-Smirnov test. As the data did not follow a normal distribution, results are presented as median, maximum and minimum values. The Friedman non-parametric test for repeated measures was employed to determine the statistical significance of changes in parameters over time and, when appropriate, pairwise comparisons were conducted with the Conover post-hoc test. The interocular symmetry between the keratoconic eyes of the same patient was assessed with Intraclass Correlation Analysis,20 focusing on the variables rPUPIL (the distance from the corneal apex to the pupillary centre) and dPC (the distance from the pupillary centre to the cone apex). A p-value <0.05 denoted statistical significance.

Fifty-seven eyes from 32 participants were initially recruited for this prospective study. Eight participants (25%) failed to complete the 3 M follow-up, of whom two discontinued due to an unsuccessful adaptation, and the remaining six for personal reasons unrelated to the adaptation process. None of the patients discontinued due to poor visual quality, discomfort or severe adverse events associated with CL wear. The final sample included 41 eyes from 24 participants (9 females) diagnosed with KC, with a median age of 28.5 years (range from 15 to 65 years). Seven patients (13 eyes) were previous CL wearers, including 2 scleral CLs, 7 RGP CLs and 4 soft CLs. None of these patients presented clinically significant corneal or conjunctival alterations at the baseline visit related to their previous CL use. Table 1 presents a summary of relevant ocular parameters of the final study sample.

Distance from the corneal apex to the pupillary centre (rPUPIL) ranged from 0.07 to 1.06 mm, with a median value of 0.32 mm. The distance from the pupillary centre to the cone apex (dPC) varied between 0.25 and 3.83 mm, with a median of 1.20 mm. An analysis of interocular asymmetry revealed intraclass correlation values of 0.20 for rPUPIL and 0.28 for dPC. According to these results, it was deemed safe to include both eyes of the same patient in subsequent analyses.

Thirty-two (78.0%) of the CLs had increasing radial values geometry and the remaining 9 (22.0%) featured a reverse geometry design. Increasing radial values geometry was used in 28 eyes with central KC, and 2 eyes with paracentral and 2 eyes with peripheral KC (to preserve the predefined tear film thicknesses values); Reverse geometry CLs were employed in 6 eyes with paracentral and 3 eyes with peripheral ectasias. Table 2 displays a summary of the parameters of these CLs, including DT, D1, SD3 and SD1 (D3 and D2 are not reported, as these values are derived by subtracting a fixed amount from DT​, as described in the Methods section).

The number of CLs needed to achieve optimal fit ranged from 1 to 10, with a median of 2 and an interquartile range (IQR) of 4.5. As expected, the skill of the practitioner in determining lens parameters improved over time, given the novelty of the CL design and of the method of calculation. Thus, during the second year of the study, while minimum and median values remained unchanged, the IQR and maximum values decreased to 2 and 6, respectively.

Table 3 presents a summary of the values of VA obtained at each visit. Statistically significant differences were found in monocular VA over time (p < 0.001). A post-hoc pairwise analysis revealed a significant improvement in VA with the new CL at the 1 W (p = 0.004) and the 3 M (p = 0.002) follow-ups, as compared with that obtained at the baseline visit. No difference was found between 1 W and 3 M visits.

Monocular CS values at baseline and each follow-up visit are displayed in Fig. 2. A statistically significant change in CS at all frequencies was found (all p < 0.001). Pairwise analysis revealed an improvement in CS over baseline values at the 1 W (p < 0.001 at 3, 6 and 18 cpd; p = 0.004 at 12 cpd), and the 3 M (p < 0.001 at all frequencies) visits. No differences were found between 1 W and 3 M CS values. With the new CL, CS values were equivalent to those reported in the literature for healthy eyes with the CSV-1000 test.21

Fig. 2.

Monocular contrast sensitivity values at baseline (BAS) and three-months (3_M) at spatial frequencies of 3, 6, 12 and 18 cycles per degree (cpd). The shaded area represents normal contrast sensitivity values at each spatial frequency.21 (*) denote atypical values, and correspond to the same patient.

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Fig. 3 presents a box plot of the various ocular complications observed at the baseline visit and after 3 M of CL use. It also includes a reference red line denoting the numerical threshold for clinical significance in the assessed ocular complications, based on the Efron Grading Scale.18 None of the observed complications reached clinical significance at any visit. Comparative analysis of the grades of ocular complications at the three visits revealed statistically significant differences for conjunctival staining (p = 0.007), which increased at 1 W (p = 0.007) and 3 M (p = 0.007), relative to baseline values, and for superior limbic keratoconjunctivitis (p < 0.001), which decreased at the 3 M follow-up, when compared with baseline (p < 0.001) and 1 W (p = 0.001). No statistically significant differences were found for any other ocular complication.

Fig. 3.

Severity of the ocular complications observed at baseline and at the 3-months follow-up, as determined with the Efron Grading Scales.18 A reference red line is shown to denote the threshold for clinical significance for ocular complications (grade 3). Statistically significant differences in severity between baseline and three months are denoted by *.

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The degree of wearer satisfaction after 3 M of using the CLs, assessed with a 10 cm VAS, ranged from 4.8 to 10, with a median score of 9.1 and an IQR of 1.6. Nine users (37.5%) reported feeling “always” satisfied with their CLs, 10 (41.7%) selected “most of the time”, 3 (12.5%) answered “sometimes” and 2 (8.3%) chose “infrequently”. The number of hours per day that patients wore the CLs also emerged as a potential indicator of user satisfaction, ranging from 4 to 16 h, with a median of 9.5 h and an IQR of 6 h.