The demise and ultimate “death” of corneal GP lenses has been a topic of conversation over the past few decades as alternative contact lens materials and designs continue to improve and take over the market. This being said, contact lens practitioners are well aware of the many advantages that corneal GPs have over other modalities, including quality of optical performance, resistance to microbial binding and contamination, optimization of oxygen transmission, and lens durability. Of course, the ongoing challenge is initial and long-term lens comfort when compared to other contact lens modalities.

There continues to be a place and a need for corneal GP contact lenses. This article will discuss some of the more contemporary studies pertaining corneal GP lenses that emphasize this position.

It’s All About the Vision

Michaud et al (2018) looked at the clinical and subjective performance of a large-diameter GP (LGP) lens in subjects who had low-to-moderate (0.75D to 2.75D) refractive astigmatism. The multi-site, prospective, cross-over clinical study recruited 40 asymptomatic contact lens wearers who were randomly assigned to group A or group B. Group A wore comfilcon A soft toric lenses for two weeks and then crossed over to LGP lenses (Boston XO [Bausch + Lomb], 14.3mm diameter mini-scleral lens). Group B initially wore the LGP lenses and then crossed over to the soft toric lenses. For each lens type, low-contrast and high-contrast visual acuity (VA) were evaluated at distance. After two months, all subjects completed a questionnaire regarding their lens preference and the quality of vision in day-to-day activities.

Results showed that 75% preferred the vision of the LGP lenses as compared to the soft toric lenses, and 53% expressed a preference to continue with this modality. Wear time, subjective comfort, and subjective vision ratings exhibited no significant difference between the two groups. The conclusion was that in a population of asymptomatic lens wearers, LGP lenses can be a good alternative to soft toric lenses to correct refractive astigmatism.

De Jong et al (2017) looked at the effects of corneal scars and their treatment with GP lenses on quality of vision, including straylight. Straylight and best-corrected visual acuity (BCVA) were measured during and after GP lens wear in 23 patients who had corneal scars. Contralateral eyes were used as controls.

The scarred-eye straylight values were 1.53 log(s) without a contact lens and 1.60 log(s) with a contact lens (P = 0.043). Healthy eyes without a contact lens had a mean straylight value of 1.13 log(s), corresponding to age-normal values. VA improved from 0.66 logarithm of minimal angle of resolution (logMAR) to 0.19 logMAR with contact lens wear in eyes with a corneal scar (P < 0.001). The authors concluded that corneal scars can have a strong effect on quality of vision by diminishing visual acuity and increasing straylight. Contact lens treatment did not improve straylight; in fact, there was a minimal increase. As the recovery of VA with contact lens wear far exceeded straylight increase, contact lenses remain a clinically useful treatment option in most patients who have corneal scars.

Yamaguchi et al (2017) studied corneal diseases that resulted in corneal opacities, scarring, and edema, which caused reduced VA and loss of vision. They performed a detailed analysis of high-order aberrations (HOAs) of the anterior and posterior corneal surface as well as total corneal HOAs in these diseases using an anterior segment imaging system combined with a ray-tracing method. They also conducted a correlation analysis between visual acuity and these HOAs.

The results indicated that corneal HOAs directly degrade VA in corneal diseases characterized by mild-to-moderate corneal opacities. The researchers also stated that correcting corneal HOAs with GP lenses is useful in cases in which the posterior corneal surface is relatively smooth and lacking posterior-corneal-induced HOAs. The results further demonstrate the clinical relevance of irregular astigmatism of the posterior corneal surface when assessing the visual function of diseased eyes.

Bagheri et al (2017) evaluated the effect of corneal GPs on involuntary eye movements and VA for patients who have infantile nystagmus syndrome. Thirty-two eyes of 16 patients with a mean age of 18.6 ± 4.9 years were enrolled. Monocular BCVA improved from 0.56 ± 0.23 logMAR to 0.51 ± 0.23 logMAR (P = 0.007), and binocular BCVA improved from 0.54 ± 0.25 logMAR to 0.48 ± 0.24 logMAR (P = 0.01) after fitting corneal GP contact lenses.

Corneal GP wear significantly improved contrast sensitivity at low (P = 0.02) and intermediate (P < 0.001) frequencies but not at high frequencies (P = 0.6). The frequency, amplitude, and intensity of nystagmus were decreased significantly after corneal GP wear (P < 0.001). The authors concluded that corneal GPs improved monocular and binocular BCVA and contrast sensitivity in patients who have infantile nystagmus syndrome. Motor indices of nystagmus (frequency, amplitude, and intensity) were also significantly improved.

Keratoconus and Corneal GPs

Corneal cross-linking (CXL) as a means to control progression in keratoconus has created a true paradigm shift in our approach to the disease’s management. Singh et al (2018) looked at the influence of CXL on corneal GP lens fitting characteristics and success. The objective was to evaluate changes in lens fit post-CXL and to correlate these changes with alterations in corneal topographic parameters. The prospective intervention study of 20 keratoconic eyes of 14 patients (age > 18 years) who underwent CXL showed an improvement in VA by one Snellen line, both uncorrected VA and BCVA, and a decrease in flat/mean/apical K by 0.8D, 0.8D, and 1.3D, respectively. CXL also resulted in significant improvement in GP lens fit and improved subjective comfort and duration of lens wear.

Nilagiri et al (2018) investigated binocular vision performance and depth perception in patients wearing corneal GP lenses. The objective was to compare changes in logMAR acuity and stereoacuity from best-corrected spherocylindrical spectacles to GP contact lenses in bilateral and unilateral keratoconus vis-à-vis age-matched control subjects. Monocular and binocular logMAR acuity and random-dot stereoacuity were determined in subjects who had bilateral (n = 30; 18 to 24 years) and unilateral (n = 10; 18 to 24 years) keratoconus and in 20 control subjects.

The median monocular and binocular logMAR acuity and stereoacuity improved significantly from spectacles to GP lenses in the bilateral keratoconus cohort (P < 0.001). Only monocular logMAR acuity of the affected eye and stereoacuity improved from spectacles to GP lenses in the unilateral keratoconus cohort (P < 0.001). The magnitude of improvement in binocular logMAR acuity and stereoacuity was also greater for the bilateral compared with the unilateral keratoconus cohort. The researchers concluded that binocular resolution and stereoacuity improve from spectacles to GP contact lenses in bilateral keratoconus, whereas only stereoacuity improves in unilateral keratoconus. The magnitude of improvement is greater for the binocular compared with the unilateral keratoconus cohort.

The Initial GP Lens Experience

Gill et al (2017) investigated the effect of topical anesthetic (TA) during corneal GP lens fitting on subjective and objective measures of patient anxiety. Forty-seven subjects were randomly assigned to Group A or B and attended on two occasions that were one week apart. First visit: subjects received bilaterally either a single drop of TA (0.5% proxymetacaine) (Group A) or placebo (0.9% saline) (Group B) prior to GP lens application. No drops were instilled at the second visit. At each visit, patient anxiety was assessed, either subjectively (visual analogue scale [VAS]) or objectively (skin conductance [SC]), as was anterior ocular health.

At visit 1, the GP lens trial produced small increases in hyperemia and corneal staining, but no difference associated with TA use. At visit 2, increases in staining and hyperemia were observed, but hyperemic responses were significantly less than at visit 1 for both groups. Corneal staining was also less but was not statistically significant. VAS scores indicated that subjects who received TA during visit 1 were significantly less anxious at visit 2.

At visit 2, comfort was slightly reduced for subjects who received TA at visit 1 and was significantly increased for subjects who received placebo. TA use reduced anxiety during the lens adaptation period compared with placebo.

The conclusions suggested that TA use during GP lens fitting has potential patient benefits of improved first-time GP lens wear comfort, reduced anxiety during adaptation, and reduced anxiety prior to subsequent GP lens wear.

Concluding Remarks

Corneal GPs have taken quite a hit over the past years, especially in their consideration as a first-fit option. We should keep in mind that corneal GPs offer numerous advantages, and we should continue to work on the issues that limit their current use and acceptance. CLS

For references, please visit www.clspectrum.com/references and click on document #275.