April 2023
Column
A Great Fit
Digging into some historical literature on the early days of contact lenses, I came across this paper in the Nederlands Tijdschrift voor Geneeskunde (Dutch Journal of Health Care) dated September 3, 1938. A couple of really interesting things popped up. The author—or presenter, actually, as this was a conference coverage, which was a common way to communicate knowledge in the day—Petrus Thier described his experience with (glass blown) scleral lenses. He explains that if the lens does not align with the ocular surface, it gives rise to air bubbles creeping in, 'something that never happens if the glass fits perfectly'. Especially in the line of the position of the musculus rectus interus and externus insertion, he experiences air bubbles 'inserting' behind the bowl. Thier also notes that for three years they have been experimenting with 'harsprodukten' (plastic) to replace glass for their scleral lenses. He describes this as very advantageous for the eye, the main benefit being that it is much lighter than glass. The fact that 'the temperature of the eye is used to mold the lens to the shape of the ocular surface' is seen as another advantage. Bottom line here: better aligning the lens to the eye shape has been known to have great benefits from the very early days of lens fitting. Furthermore, the use of plastic instead of glass really surfaced the road to start thinking about corneal lenses (see Caroline & Norman, Contact Lens Spectrum February 2023). It is not a surprise that the first known patent application for corneal lenses by Dennis England came just a few years later in 1945. Interestingly, though, aligning a corneal lens with the ocular surface again turned out to be very advantageous. An advantage that continues today but is now spurred by corneal topographers. This I-site newsletter is an ode to aligning lenses better to the ocular surface with various lens modalities.
Eef van der Worp
Rigid Corneal Lenses
Going from the history of the corneal lens to today: the biggest development and advantage is the use of corneal topography. See Gaurav Prakash's contribution to the Eyewiki website of the American Academy of Ophthalmology (updated March 12, 2023). The opportunity to better align the corneal lens with the ocular surface was highlighted in a session by Patrick Caroline and Randy Kojima at the recent Global Specialty Lens Symposium (see conference coverage in the April 2023 issue of Contact Lens Spectrum). Also see the February issue of I-site newsletter on using elevation data to decide when to fit a corneal versus a scleral lens. In many ways, we are fortunate to have the instruments and the tools to align our rigid lenses better with the cornea, something that is actually difficult when it comes to soft lens fitting: the fitting relationship between cornea and lens is weak at best for soft, with hardly any (or no) correlation between central corneal data and lens behaviour on-eye. Photo: Antonio Calossi (Florence - Italy)
Orthokeratology
What Topography Data Do I Need to Fit Orthokeratology Lenses?
It is pretty safe to say that orthokeratology (ortho-k) would not be where it is today without corneal topography. The sole purpose of ortho-k is to subtly reduce the central zone (by as little as 6.13±1.67μm, according to Zhang et al, see I-site newsletter Oct 2021). However, this controlled change cannot occur without knowing the exact shape of the ocular surface. Many software programs increasingly can perform this automatically, but what do you need to know about the topography data to understand ortho-k lens fitting? In the February Myopia Profile, Jeanne Saw and Kate Gifford explain this, covering everything from HVID, apical corneal curvature, sagittal height, pupil size, corneal asphericity,  and corneal astigmatism. Astigmatism is important in topography measurement, not only to determine whether the patient is a good candidate for ortho-k but also to decide on the type of lens (spherical or toric). The generally agreed cutoff point is around 1.50D of corneal toricity. Identifying whether the refractive astigmatism is due to the cornea (modifiable with ortho-k) or due to internal eye structures (posterior cornea and lens, not modifiable) is also important. In children with low-to-moderate myopia and healthy eyes, internal astigmatism typically compensates for anterior corneal astigmatism, so correcting the latter with ortho-k can expose the former as residual after treatment. This means that children (or adults) with a close match between refractive (total) and corneal astigmatism are likely to be better candidates for ortho-k. In order for ortho-k lenses to maintain alignment, the lens must land 360 degrees around the peripheral cornea. If a patient has high astigmatism, limbal-to-limbal astigmatism or irregular astigmatism, the lens will have a tendency to decentre. A toric lens will most likely be required to combat this.
Photo: Angel García (Madrid - Spain)
Ortho-k Treatment Zone Decentration
To follow up on 'controlling the topography' in the last item, another interesting question is whether ortho-k treatment zone decentration can be effective at controlling myopia progression. This was investigated in 46 children with myopia (25 boys, 21 girls; age 11.12±0.33 years) who were treated for 1 year with ortho-k decentration lenses in one eye and centered lenses in the other. Axial length was measured before lens fit and at 6 months and 12 months after the initial lens fit. Corneal topography was measured at baseline and at 1 month after lens wear. The corneal topography obtained from the 1-month visit was used to quantify treatment zone decentration (TZD) for each subject. This intrasubject study showed that when the uncorrected visual acuity is acceptable and there are no apparent complications, ortho-k decentration may be beneficial in better controlling the progression of myopia. The TZD ranged from 0.5mm to 1.5mm. Axial elongation became slower in children with a higher baseline spherical equivalent and with a larger TZD. Photo: Randy Kojima (Vancouver - Canada)
Scleral Lenses
Scheimpflug Imaging & Corneo-Scleral Profiles in Different Quadrants
The corneo-scleral profile (CSP) describes the transition from cornea to sclera, while the corneo-scleral junction angle (CSJ) is the angle formed between the cornea and the sclera. Both are instrumental in scleral lens fitting and design. The aims of this study were to analyze the CSP and CSJ in different quadrants to test correlation and repeatability of an established observational grading and measurement method using Scheimpflug images. The nasal, temporal, superior and inferior CSPs of 35 healthy-eyes participants were imaged using the corneo-scleral-profile module of the Pentacam (Oculus, Wetzlar, Germany), and the captured Scheimpflug CSP images were also subjectively graded into five different corneo-scleral transitions using the Meier grading scale (profile 1, fluid-convex; profile 2, fluid-tangential; profile 3, marked-convex; profile 4, marked-tangential; profile 5, concave). Conclusions: The subjective CSP grading showed poorer repeatability compared to the objective CSJ measurement, which did not detect any differences in angles between the meridians. The weak association between CSP grading and CSJ measurement is likely caused by the limited intra-observer reliability of the Meier grading scale. Furthermore, the CSP grading scale seems to take other aspects beside the CSJ angle, such as scleral radius, into account. 
Advancements in Scleral Lenses
"Advancements in Scleral Lenses" was presented by 
Greg DeNaeyer as a GPLI webinar on Tuesday, February 21st. Increasing popularity of scleral lenses over the last 10 years has been a driver for significant innovation for this contact lens category. This has resulted in increased fitting success of scleral lenses for managing both corneal irregularity and ocular surface disease. This course reviews the latest advancements in scleral lens materials, design, optics, and surface treatments. But a big 'chunk' is dedicated to aligning the scleral lens better with the ocular surface (see column above). 
GPLI
Become a Member
The GPLI Eye Care Professional Membership is a new program that gives eye care practitioners access to premier resources to help you advance your specialty contact lens practice at a low annual fee. The membership supports the ongoing efforts of the GP Lens Institute, and member benefits include: free printed materials (US only), coding and billing module, staff module, building your practice with rigid lens multifocals, archived webinars, free quarterly COPE-approved webinars, bi-monthly member newsletter, access to recent cornea and contact lens residents’ symposium presentations, quarterly GPLI podcast (“GPLI Radio”), member directory, and more.
BCLA Clinical Conference 2023
The BCLA hosts the UK’s largest Clinical Conference and Exhibition dedicated to contact lenses and the anterior eye every two years. This highly regarded three-day event attracts more than 900 UK and international contact lens professionals at all stages of their career.
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. Disclosure: I-site's editor Eef van der Worp, optometrist PhD FAAO FBCLA FIACLE FSLS, receives educational grants from a number of industry partners but is not related to any specific company.