Scarry - Not Scary
Not everything is or can be evidence-based in our specialty lens arena. Not everything is logical or makes sense even. For example, with corneal scars, the visual performance oftentimes clears up so dramatically, even when the scar (or opacity) is centrally located on the cornea. Consider this the scar (t)issue: see the mini case report below by our colleague from Portugal, Rodolfo Moura. It concerns a patient with keratoconus and large central opacities. The patient was warned that the visual recovery could be limited. Surprisingly, with a scleral trial lens, vision increased from less than 0.05 (or 20/400) to 0.7 (20/30+). Needless to say, it was a “sea of ​​smiles” in the office. Don’t be scared to try a scleral lens on a scarred cornea: it’s scarry, not scary. A quote from the original 2011 Guide to Scleral Lens Fitting reads: "Eyes with significant scarring due to trauma can achieve excellent vision with scleral lenses — often to the surprise of both the patient and the practitioner." That is still true today apparently. Rodolfo ends the case report with 'I love my job'. What else can I say?
The Scar (t)Issue
Short case report by Rodolfo Moura from the Centro Hospitalar Universitário São João (Porto, Portugal). A patient diagnosed with bilateral keratoconus was corrected with hydrophilic contact lenses and developed, a few years back, a microbial keratitis, possibly from a fungal infection. This resulted in central and paracentral leukomas. Her treating ophthalmologist did not permit her to wear contact lenses until recently, and we gave it a try with scleral lenses. The thick central leukoma and its high reflectivity in the scheimpflug images took away all the expectations of a successful outcome; but surprisingly, after placing a scleral lens, the visual acuity improved dramatically from 0.05 (or 20/400) to 0.7 (20/30+). The photo on the left clearly shows the central leukoma over the visual axis; the photo on the right is an optical section behind the slit lamp showing the thickness of the leukoma, which reaches almost 50% of the cornea.
Midday Fogging in Scleral Lenses
OMG, Is It NHLs Causing MDF?
A new paper in IOVS by Maria Walker et al is a pearl in the clinical and epidemiological department with regard to MDF (mid-day fogging). The natural tear film is approximately 5-10 microns thick and contains proteins, lipids, electrolytes, gases, and metabolites. But once a scleral lens is applied to the eye and the filling solution mixes with the tears to become the fluid reservoir (FR), the thickness of the FR expands from 10 to more than 100 microns, inherently altering the physical properties of the fluid and also impacting the composition and concentration of the tear analytes. The study confirms the presence of several lipid classes and species in the FR during scleral lens wear and suggests that specifically nonpolar hydrophobic lipids (NHLs) secreted primarily by the Meibomian glands contribute to MDF. Some of the NHLs have a tendency to change phase in aqueous solution, existing as a solid, a liquid or an intermediate crystalline state, in the latter of which they appear turbid rather than clear. This state can be affected by temperature, pressure, and interactions with other lipids and surrounding fluid, so it is plausible that the physical characteristics of the FR change the state of the NHLs, contributing to the turbidity observed during MDF. While this may not immediately solve or prevent MDF, it may be the key ingredient to understand MDF and to find solutions for it. Such as solutions, potentially, that could dissolve or change the sate of the NHLs.
Rigid Lens Materials
Protein Deposition on Rigid Lenses
Research on rigid lens deposits and care systems is a rarity, but scientists at the Centre for Ocular Research & Education (CORE) have applied a novel method to answer a long-held question: how much protein is really deposited on rigid gas permeable lens materials? Historically, rigid lens protein deposits have been difficult to measure because of test-sensitivity limitations. To overcome that challenge, a unique approach incorporating radiolabeled lysozyme into an artificial tear solution and then determining on-lens protein sensitively through radioactive counts was applied. While this has been used for soft lens deposition in the past, this was a first for rigid lenses. Seven common rigid lens materials were soaked in the radioactive artificial tear solution for 16 hours, followed by eight hours of exposure to a 3% one-step hydrogen peroxide solution. The deposits were minimal, ranging from 1.2±0.2μg to 3.2±0.7μg per lens without use of a cleaning solution. Moreover, the peroxide solution significantly reduced the amount of radioactive lysozyme present on the majority of rigid lens materials after 30 alternating incubating and cleaning cycles when compared to using phosphate-buffered saline. They found that all tested lens-solution combinations were compatible with each other and within ISO-specified tolerances (such as lens curvature, back vertex power, spectral transmittance, physical appearance). The lysozyme deposits was small in general, and a 3% one-step hydrogen peroxide was successful in significantly reducing the amount of radioactive lysozyme present on the majority matierals, even after several cleaning cycles - suggesting that it can be effective in removing protein deposits. This post on the CORE website by Alex Hui explains the technique, and the outcome of this study, in more detail.
Specialty Contact Lens & Anterior Eye
The February edition of Contact Lens & Anterior Eye is a special issue on specialty lens research with guest editors Stephen Vincent and Pauline Cho, as mentioned in the last issue of I-site newsletter. The focus in this edition is on optical (zone size) improvements in ortho-k.
All images in this section courtesy of Antonio Calossi (optometrist, Florence - Italy)
Orthokeratology, Myopia & BOZD
A study by Na et el looked at the effect of back optic zone diameter on relative corneal refractive power distribution and corneal higher-order aberrations in ortho-k. They found that ortho-k lenses designed with smaller back optic zone diameters (BOZDs) increased myopia control efficacy, induced a steeper distribution of the relative corneal refractive power profile within the pupillary diameter, and induced greater increases in total corneal higher-order aberrations and horizontal coma - which may result in a better myopia control effect.
Another study from China by Zhang et al investigated the effect of corneal power distribution on axial elongation in children using three different ortho-k lens designs. A total of 137 subjects were included: 42 with Euclid lenses, 28 with DRL (Double Reservoir Lens) lenses, and 67 with Corneal Refractive Therapy (CRT) lenses. They found a smaller and more aspheric treatment zone to potentially be more beneficial for reducing axial elongation in children undergoing ortho-k treatment, regardless of their baseline myopic refractive error.
Sun et al studied whether biometric factors and orthokeratology lens parameters can influence the treatment zone diameter on corneal topography in corneal refractive therapy lens wearers. They conclude that adjustments to corneal refractive therapy lens parameters may indeed influence the treatment zone diameter on corneal topography; a higher reverse zone depth 2, a smaller landing zone angle 1, and a larger lens overall diameter can lead to a smaller treatment zone for corneal refractive therapy treatment.
To investigate the effectiveness of ortho-k lenses and corneal changes with increased compression factor for myopia control, Lau et al recruited 75 participants (mean age 9.3±1.0 years) and followed them for two years. The myopia control effectiveness was determined by axial elongation. They found that ortho-k lenses of increased compression factor further slowed axial elongation by 34% when compared with the conventional compression factor, without compromising corneal health.
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.