April 2021
Column
Keratoknowledge
With regards to keratoconus, almost everything in our field - including this newsletter - typically is devoted to all of the wonderful technical solutions we have for the condition. Much less attention goes towards instructing the patient, it seems. The big question really is: Do patients with keratoconus have minimal disease knowledge? Excellent question, and that is the exact title of an article soon to come out in print by investigators from Switzerland. Experts defined the “minimal keratoconus knowledge (MKK)" with respect to definition, risk factors, symptoms, and possible treatment options of keratoconus. They found that no single subject reached 100% of the desired MKK: the mean MKK was 35% (range 0%-76%). Participants with a university degree had only a moderately higher MKK, and per age decile the MKK declined by 3%. Disease duration, severity of keratoconus in Kmax values, and history of surgical treatment did not significantly increase MKK. Regarding 'triggers,' only 39% of participants reported 'eye-rubbing' as a risk factor. In conclusion, the authors state that there is a substantial mismatch between caregivers’ expectations of patients’ knowledge and patients’ active knowledge regarding their condition. This may lead to inefficient care delivery and to misunderstandings.
Scleral Lens Evaluation On-Eye
Conjunctival Vascular Density
Despite new developments in the scleral lens field, the primary concern continues to be the adverse effects associated with their use, namely infections, inflammatory-related responses and hypoxia-related complications. The introduction of new diagnostic tools can lead to better understanding of the ocular surface, resulting in the formulation of new scleral lens designs and techniques, improving management features related to the fitting relationship with the sclera. This study aimed to evaluate the vascular density of the conjunctiva of keratoconus patients wearing scleral lenses using optical coherence tomography angiography (OCTA). Measurements were made before and after removal of the lens, in addition to investigating the association between vascular density measurements and lens indentation values. The major result of the study is that the vascular density was significantly higher in eyes after removal of the lens. This raises the hypothesis of a possible hidden hypoxia, caused by compression of the lens in the conjunctiva. The results also may raise questions regarding the prolonged use of lenses due to possible alterations in the vascular conjunctival layer, with still unknown consequences. Although limitations apply, OCTA measurement of vessel density seems feasible and reliable. This could provide better means of examination of scleral lenses and could be useful in evaluating the long-term consequences of repetitive use.
Scleral Lens Wear & Corneal Physiology
The February edition of Contact Lens & Anterior Eye was a special on adaptation and adverse responses to lens wear. This included interesting topics related to sclerals and orthokeratology
(next paragraph).
Fluid Reservoir Thickness & Edema
A previous newsletter referred to a paper by Fisher et al on fluid reservoir thickness in the open-eye situation. This new publication is about the closed-eye situation while wearing sclerals. Central corneal edema was primarily stromal in nature and increased with increasing fluid reservoir thickness; the mean total corneal edema was 3.86±0.50%, 4.71±0.28% and 5.04±0.42% for the low (160±7μm), medium (494±17 μm), or high (716±16μm) fluid reservoir thickness, respectively. A significant difference in stromal and total corneal edema was observed between the low and high fluid reservoir thickness conditions only. In conclusion, scleral-induced central corneal edema during closed-eye lens wear increases with increasing fluid reservoir thickness but at a decreased rate compared to theoretical modelling.
Image: Silke Sage/Global Contact
Acute Edema Decades after PK
Murillo et al report three cases of acute corneal edema occurring decades after penetrating keratoplasty (PK) for keratoconus in eyes wearing scleral lenses, with previously clear corneal grafts. The three patients each had a longstanding PK for keratoconus performed between 33–35 years prior to presentation and recurrent ectasia. Each patient presented with an acute, painful eye and reduced vision, one at 3 days, one at 4 months and one at 9 years after refitting into scleral lenses. Each eye had well demarcated focal microcystic epithelial and stromal edema within the graft and crossing the wound margin onto the host cornea. Although a definitive break or detachment of Descemet’s membrane was not visualized, the presentations suggest these were episodes of acute hydrops.
Conjunctival Prolapse
Another paper by Fisher et al investigated the incidence and peak elevation of conjunctival prolapse during short-term open-eye scleral lens wear and its association with lens fitting characteristics. The incidence of conjunctival prolapse was 37% in a group of ten young, healthy adults (mean age±SD, 30±4 years) and was independent of fluid reservoir thickness conditions. Of all participants, 80% exhibited conjunctival prolapse at least once. Prolapse was observed more frequently nasally (73%) than temporally (27%). For the low fluid reservoir thickness condition, eyes with conjunctival prolapse had greater initial limbal clearance (97 μm compared to 43 μm) and more settling after 90 minutes of lens wear (−85 μm compared to −34 μm). In summary: conjunctival prolapse was commonly observed during short-term sealed scleral lens wear in healthy eyes in this study. The peak elevation of the conjunctival prolapse was associated with the extent of limbal settling but not with landing zone tissue compression or with fluid reservoir thickness asymmetry.
Orthokeratology & Safety
Ocular Surface/Dry Eye-Related Cytokines
Yang et al looked at the influence of overnight ortho-k on ocular surface and dry eye-related cytokines in children. According to the authors, some children who use ortho-k may develop symptoms of dry eye discomfort and corneal epithelial staining. It has also been reported that the length of the meibomian glands in children shortens after prolonged ortho-k lens wear. The causes and mechanisms behind this remain controversial. Because ortho-k does not involve open-eye lens wear, and thus, its effect on evaporation, tear film thinning, and partial blinking may be minimal compared with conventional lens wear, the authors speculate that the main reason for these effects may be that the function of the meibomian gland is indeed affected. In summary, they found that as children undergo ortho-k for an extended duration, the stability of the tear film can be reduced; the meibomian glands (especially the upper meibomian glands) can be affected, and ocular surface inflammation can be increased. Therefore, extended ortho-k lens wear in children requires regular examinations of the ocular surface and meibomian glands, and special attention must be paid to children with baseline meibomian gland distortion or a history of allergic conditions.
Incidence of Corneal Adverse Events
In line with the previous article, this one by Hu et al evaluates the overall safety of overnight ortho-k and explores whether factors such as age, refraction and a history of allergic conjunctivitis were associated with corneal adverse events incidence. In this retrospective chart review, a total of 111 eyes (22.7%) had corneal adverse events during the one-year follow-up (corneal staining n=106, corneal infiltration n=5). The incidence of significant adverse events was 6.9%. In conclusion, the investigators state that ortho-k is a safe option for children with myopia. Younger age, higher myopia, and allergic conjunctivitis were risk factors for corneal adverse events in ortho-k wearers, whereas only higher myopia was a risk factor for significant adverse events.
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.