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International Newsletter and Forum on Rigid Gas Permeable Contact Lenses, Corneal Shape, Health and Vision |
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Quantifying
In general, we typically don't realize how lucky we are. What wealth we have we often simply take for granted. The same seems to be true for how lucky we are in the (R)GP lens clinic: what a fun modality to work with. With regard to corneal (R)GPs, we can really measure the shape of the corneal area covered quite accurately. Then, when we want to fit a lens, we 'simply' add fluorescein to see where the lens aligns and where it does not. Within seconds, we have a sense of the quality of the lens fit. To some degree, we can quantify this, too (typically, dark areas in the fluorescein pattern mean less than 20 microns of tear film). For scleral lenses, we have less control of the fitting at this point, but lens evaluation is pretty straightforward: we can quantify the thickness of the clearance behind the lens by measuring it with OCT or by estimating it behind the slit lamp using central lens thickness or the cornea as a reference. The conjunctival fit can be assessed by looking at the conjunctival vessels: compression and blanching. But this is not the case for the 100 million wearers of soft lenses worldwide. We don't actually fit these lenses anymore (we are selecting one at best). Keratometry values (central or peripheral) do not predict soft lens behavior on-eye very well (that is an understatement). And soft lens evaluation on-eye is not really straightforward either: lens movement seems to be a poor indicator of lens alignment and fit. And more so: what does soft lens movement mean? Is it equal to tear film exchange? With about 3 microns of post-lens tear film behind the soft lens, that is questionable. It may be just mucin behind the lens. How nice it is to have a grip on the lens fit and to be able to evaluate that with (R)GPs. Let's count our blessings.
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(R)GPs to Induce Peripheral Myopic Defocus
 The purpose of this work was to evaluate the potential of a novel, custom-designed corneal rigid gas permeable (RGP) contact lens to modify the relative peripheral refractive error in a sample of myopic patients. The experimental (R)GP lens induced a significant change in relative peripheral refractive error compared with the baseline (no lens) beyond the 10 degrees of eccentricity to the nasal and temporal side of the visual field. The maximum effect was achieved at 30 degrees. Wearing the experimental (R)GP lens, 60% of the eyes had peripheral myopia exceeding 1.00D, whereas none of the eyes presented with this feature at baseline. Based on this, the investigators conclude that custom-designed (R)GP lenses can generate a significant degree of relative peripheral myopia in myopic patients regardless of their baseline spherical equivalent refractive error, which appears to be promising for myopia control. |
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Conjunctival, Episcleral and Scleral Changes
OCT images of the anterior eye were captured before, immediately following 3h of wear and then 3h after removal of a mini-scleral contact lens in 10 young (27±5 years) healthy participants (neophyte rigid lens wearers). The aim of the study was to quantify the influence of short-term wear of these lenses on the morphology of the corneo-scleral limbus, conjunctiva, episclera and sclera. Following 3h of lens wear, statistically significant tissue thinning was observed across all quadrants, with a mean decrease in thickness of -24.1±3.6μm, which diminished but did not return to baseline 3h after lens removal (-16.9±1.9μm). The largest tissue compression was observed in the superior quadrant (-49.9±8.5μm) and in the annular zone 1.5mm from the scleral spur (-48.2±5.7μm), corresponding to the approximate edge of the lens' landing zone. Compression of the conjunctiva/episclera accounted for about 70% of the changes. In conclusion, the investigators stated that optimal-fitting mini-scleral contact lenses worn for three hours resulted in significant tissue compression in young healthy eyes, with the greatest thinning observed superiorly, potentially due to the additional force of the eyelid, with a partial recovery of compression 3h after lens removal.
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Axial Length Change vs Spherical Equivalent Refraction
The purpose of this study was to investigate the relationship between axial length increase and baseline spherical equivalent refractive errors in myopic children wearing orthokeratology lenses. One hundred fifteen (115 right eyes) Chinese children wearing orthokeratology lenses were enrolled in this cohort study. Data at baseline and 2 years after wearing the lenses were collected. After uni-variate analysis, a statistically significant relationship was found between change in axial length and baseline spherical equivalent refractive error. Higher spherical equivalent refractive error was associated with smaller increases in axial length. Slower axial length growth in higher ametropia could be helpful in controlling the development of myopia.
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Effect of Ageing on Keratoconic Corneas
Joint investigators from Cardiff (UK)
and Tel Aviv (Israel) explored the potential effect of aging on the corneal curvature and corrected visual acuity in patients with long-term keratoconus. Disease onset was self-reported to be at a mean age of 18.4 years. Mean age of patients at last examination was 53.8 years. Mean central corneal curvature was 6.87mm (48.77D) and 6.56mm (51.09D) at first and last examination, respectively, and statistically significant. However, the last measurement of corneal curvature was found to remain approximately constant over the years from about 20 to 50 years after onset. Mean BCVA was not significantly different between first and last examination and was found to be approximately constant over the years.
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Translating (R)GP Mutifocals are Still in the Game!
In the past, translating gas permeable multifocals were used frequently for presbyopic patients. With new soft multifocal technology and advancement in aspheric-near gas permeable multifocals, translating (R)GP lenses are not utilized as often anymore. But when fit properly, translating (R)GP multifocals allow patients to achieve very clear distance, intermediate and near vision. A 58-year-old male presented to our clinic for his annual eye exam and (R)GP lens fit. With these lenses, he achieved 20/30 distance vision OD and OS with no significant over-refraction. He was wearing reading glasses of an unknown power over his contact lenses for near tasks. We fitted him with a new translating multifocal lens design; this lens is a translating (R)GP multifocal, but there are no lines demarcating the different distance and near zones. He returned three weeks later for a contact lens follow up. He had been wearing the lenses about 12 hours per day. He reported great distance (20/25), intermediate and near vision (20/25). Translating multifocals can offer our presbyopic patients a great option for crisp, clear distance and near vision. For patients with demanding vision needs, we should keep these lens designs in mind!
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Upcoming Events
- VDCO, 18-20 Sept, Berlin (DE)
- AAO, 7-10 Oct, New Orleans (US)
- ECLSO, 16-17 Oct, Izmir (TU)
- CLMA, 28-31 Oct, Miami (US)
- Cornea CL & Cont Vision Care Symp, 5-6 Dec, Houston (US)
- Global Specialty Lens Symposium, 21-24 jan, Las Vegas (US)
- NCC 2016, 13-14 maart, Veldhoven (NL)
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I-site is an educational newsletter that is distributed on a monthly basis and provides an update on rigid gas permeable related topics (scientific research, case reports and other publications worldwide). I-site is objective and non-political. Its editor Eef van der Worp, optometrist, PhD, FAAO, FBCLA, FIACLE, FSLS is a lecturer for a variety of industry partners, but is not related to any specific company. Please contact us at: i-site@netherlens.com.
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