Surface Disease and the Corneal Ectasias
5.4 Recent Advances: Corneal Ectasia
5.4.1 Soft Lens
In the last several years, specialty soft lenses of SiHy material have been introduced with reports of better comfort and increased tolerance compared to RGP
lenses in the early stages of keratoconus (Ozkurt et al. 2012 ). The newer lenses of higher Dk material would presumably reduce the likelihood of hypoxic complications seen with hydrogel lenses in which a tight fi t might have been accepted for mechanical stability and comfort on that basis. Soft specialty lenses are generally available at lower cost than other specialty lenses. Ultimately as ectasia pro- gresses, soft lenses may not be adequate to neutral- ize irregular astigmatism as they essentially drape over rather than neutralize any local steepening.
5.4.2 Rigid Gas-Permeable Corneal Lenses
Inferior steepening and absolute steepening of
>52 D are predictors of less stable fi t. Faced with a choice between a tight fi t with apical bearing or a loose fi t which is unstable and can result in lost lenses, there are many patients who are main- tained in tight fi t till scarring occurs, at which time keratoplasty is required. In the last decade, many options including introduction of higher Dk RGP materials and increased appreciation of back surface toric designs have allowed for increased mechanical stability without excessive bearing apically on the fl atter meridian.
5.4.3 Piggyback Systems
Modern piggyback systems use a high-Dk sili- cone hydrogel lens underneath the RGP lens in
Fig. 5.3 Piggyback lens system in patient with keratoco- nus and history of Stevens-Johnson syndrome
a b
Fig. 5.2 ( a ) RGP corneal lens with optimal fi t: “lid attachment”. ( b ) RGP corneal lens with adequate fi t:
“intra-palpebral”
an attempt to overcome past issues with hypoxia related to the total thickness of the system. The overall Dk of the piggyback system varies with the Dk thickness of both lenses. Recent report suggests that negative-powered soft lenses may be optically for use in piggyback systems because of reduced aberrations related to local fl attening (Romero-Jimenez et al. 2013 ).
5.4.4 Hybrid Lenses
Hybrid lenses technology has advanced to incor- porate higher Dk materials in both the rigid center and the hydrogel skirt. There are new specialty designs to accommodate apical cones and corneas with reverse geometry (central fl attening) after cornea transplant or refractive surgery. Earlier problems with hybrid lenses have been addressed with the newer designs and materials of the last decade, with two studies fi nding 79.5 and 86 % success rates in patients with moderate or advanced disease (Nau 2008 ; Abdalla et al. 2010 ). A study from the Cornea Service at Wills Eye Institute administered the Contact Lens Impact on Quality of Life Questionnaire (CLIQ) on 71 consecutive patients who wore soft toric, RGP, or hybrid lenses in at least one eye with keratoconus and found that there was no difference in quality of life among the three groups (Erdurmus et al. 2009 ). There is an argument that the reason for the slow acceptance of modern hybrid lenses is the relatively high cost compared to RGP corneal or soft lenses and the assertion that they do not improve visual acuity or comfort when compared to RGP corneal contact lenses (Romero-Jimenez et al. 2010 ).
Corneal complications even with the new- est designs have been reported (Fernandez- Velazquez 2011 ), with clinical experience suggesting that these lenses can develop suction and adherence that may not be detected in the ini- tial fi tting process.
5.4.5 RGP Mini-scleral and Scleral Lens
Mini-scleral lenses are reported as a good option for visual rehabilitation after placement
of intrastromal corneal ring segments (Karlgard et al. 2004 ). Any of these larger RGP lenses would have the advantage over corneal RGP lenses in that bearing on the thin cornea directly over the segment is less likely. A reported compli- cation of mini-scleral contact lens wear is nonul- cerative keratitis perhaps related to compression from peripheral seal or lens hygiene or care product (Bruce and Nguyen 2013 ). Advances in lens design and manufacture to incorporate back- surface toricity allowing for alignment with toric sclerae increase the likelihood of success with large diameter RGP lenses (Visser et al. 2006 ; Baran et al. 2012 ).
Reports from the United States and Israel demonstrate that RGP scleral lenses are a good alternative to surgery for patients with keratoco- nus, with success in a majority of patients who might otherwise have proceeded to surgery (Schornack and Patel 2010 ; Severinsky and Millodot 2010 ).
5.4.6 PROSE Treatment
PROSE treatment is an effective option for the treatment of corneal ectasia and astigmatism. As described previously, the devices used in PROSE treatment are made of highly gas-permeable material; the fi t is typically characterized by fl uid ventilation, minimal movement, and no contact with the cornea (Fig. 5.4a, b ). The latter features account for the excellent optics and comfort achieved in PROSE treatment for patients with corneal ectasia. A study of patients who were referred having failed contact lens rehabilitation found mean change of −0.54 logMAR (approxi- mately 5 lines improvement) in visual acuity compared to habitual correction and mean of 20 points improvement in visual function in the NEI VFQ-25 questionnaire (Stason et al. 2010 ).
A study of a subsequent cohort confi rmed this level of impact on both acuity and visual function and reported that 78/89(88 %) eyes that were fi t- ted with devices were still wearing the PROSE devices and had a mean improvement in VFQ-25 scores of 27.6 ( P < 0.001) on a 100-point scale after 6 months. Eyes that had undergone previous penetrating keratoplasty were included in the
analysis, with similar results. 93.1 % of eyes achieved a visual acuity of 20/40 or better (Baran et al. 2012 ). There was not one candidate eye that could not be fi tted, despite including patients who had failed previous attempts at contact lens treatment using advance technologies such as specialty corneal lenses, hybrid lenses, piggyback systems, and even scleral lenses (Table 5.1 ) (Baran et al. 2012 ).
Recent reports reveal that PROSE treatment can serve as platform for the correction of higher order aberrations. There are reports of
reduction of HOAs across all diagnosis (Gumus et al. 2010 ) and of improvement of low-contrast vision in keratoconus with PROSE treatment (Hussoin et al. 2012 ) using aspheric optics.
Because stability of fi t and capacity for precise registration on the eye, devices used in PROSE treatment are a suitable platform for custom HOA correction in corneal ectasia (Sabesan et al. 2013 ).
The advances in PROSE treatment have caused a paradigm shift in the management of corneal ectasia, because a PROSE device can accommodate any corneal shape. PROSE treat- ment is now widely available across the United States. PROSE treatment is a practical alternative to penetrating keratoplasty for eyes with advanced disease considered to be “contact lens intolerant.”
Furthermore, “axial opacity” is not suffi cient indication for keratoplasty unless vision has been assessed wearing a mechanically stable contact lens or PROSE device.
Sclera
Cornea Liquid reservoir Ectatic cone
Optic zone
Transitional zone Haptic zone
Prosthetic Replacement of the Ocular Surface Ecosystem
b a
Fig. 5.4 ( a ) Slit lamp image of PROSE treatment. Note fl uid-fi lled space behind back surface of prosthetic device and front surface of cornea. ( b ) Corresponding schematic diagram of PROSE device in cross-section over ectatic cornea
Table 5.1 Contact lens history in patients referred for PROSE treatment
90 % of patients had tried contact lenses
75 % of patients had tried rigid gas-permeable lenses 22 % of patients had tried piggyback lenses 17 % of patients had tried hybrid lenses Prosthetic devices could be dispensed in all cases