Akilesh Gokul

Quantitative Analysis of Corneal Energy Dissipation and Corneal and Orbital Deformation in Response to an Air-Pulse in Healthy Eyes

PURPOSE To examine and evaluate ocular biomechanical metrics and additionally derived corneal and orbital components using a noncontact Scheimpflug-based tonometer (CorVis ST) in a population of healthy eyes. METHODS A total of 152 eyes of 152 participants were examined by slit-lamp biomicroscopy, corneal tomography, and the CorVis ST (CST). This determined the distribution of outputs from the CST, such as deformation amplitude (DA), and additionally derived parameters, including maximum corneal deformation (MCD), maximum orbital deformation (MOD), and corneal energy dissipation (CED). RESULTS The mean age of participants was 35.88 ± 13.8 years. Deformation amplitude significantly correlated with age (r = 0.24, P = 0.002) but not sex or ethnicity (P > 0.05). Multiple linear regression analysis revealed significant correlations between DA and age (r = 0.19, P = 0.006) and DA and IOP (r = -0.59, P < 0.001). Age correlated with MCD (r = 0.20, P = 0.01), MOD (r = 0.18, P = 0.03), and CED (r = 0.39, P < 0.001). Males had a lower MOD than females (0.24 vs. 0.26 mm, respectively, P = 0.01); however, there were no differences in MCD or CED between sexes (P > 0.05). There were no significant differences between ethnicities for MCD, MOD, and CED (P > 0.05). Multiple linear regression analysis revealed significant correlations between MCD and IOP (r = -0.65, P < 0.001), CED and age (r = 0.41, P < 0.001), CED and IOP (r = 0.28, P = 0.001), and between CED and central corneal thickness (CCT) (r = -0.36, P < 0.001). CONCLUSIONS The isolation of the corneal component (MCD) should be used when analyzing deformation characteristics in diseases that only affect the cornea. This study establishes a baseline for a population of healthy eyes. Future publications will identify differences in MCD, MOD, and CED between healthy and diseased populations.

Temperature profiles of patient-applied eyelid warming therapies.

PURPOSE To compare temperature profile characteristics (on and off eye) of two patient-applied heat therapies for meibomian gland dysfunction (MGD): an eye mask containing disposable warming units (EyeGiene(®)) and a microwave-heated flaxseed eye bag(®) (MGDRx EyeBag(®)). METHODS In vitro evaluation: surface temperature profiles of activated eye masks and heated eye bags(®) (both n=10), were tracked every 10s until return to ambient temperature. Heat-transfer assessment: outer and inner eyelid temperature profiles throughout the eye mask and eye bag(®) treatment application period (10min) were investigated in triplicate. The devices were applied for 12 different time intervals in a randomised order, with a cool-down period in between to ensure ocular temperatures returned to baseline. Temperature measurements were taken before and immediately after each application. RESULTS In vitro evaluation: on profile, the eye bag(®) surface temperature peaked earlier (0±0 s vs. 100±20 s, p<0.001), cooled more slowly and displayed less variability than the eye mask (all p<0.05). Heat-transfer assessment: the eye bag(®) effected higher peak inner eyelid temperatures (38.1±0.4°C vs. 37.4±0.2°C, p=0.04), as well as larger inner eyelid temperature increases over the first 2 min, and between 9 and 10 min (all p<0.05). CONCLUSIONS The eye bag(®) surface temperature profile displayed greater uniformity and slower cooling than the eye mask, and was demonstrated to be significantly more effective in raising ocular temperatures than the eye mask, both statistically and clinically. This has implications for MGD treatment, where the melting points of meibomian secretions are likely to be higher with increasing disease severity.

Dr John Nottingham's 1854 Landmark Treatise on Conical Cornea Considered in the Context of the Current Knowledge of Keratoconus.

Abstract: John Nottingham has been widely credited with the first accurate description of keratoconus in his treatise on conical cornea, published in 1854. Contained within the 270-page treatise are accounts and theories of keratoconus postulated by authors such as Scarpa, von Carion, von Ammon, and Mackenzie, synthesized by Nottingham in a treatise containing his own original observations. Nottinghams work delves deeply into keratoconus, with coverage reminiscent of a modern review, albeit in a far less succinct manner. He extensively describes the epidemiology, clinical presentation, underlying cause, and treatment of keratoconus. However, the concepts put forth are limited largely by the contemporary lack of understanding of the underlying anatomy and physiology of the eye, and the observations, by technological limitations. He postulates a similar treatment algorithm to that used today; optical devices being the management option of choice in the mild stages with surgery being a last resort. None of the surgical methods discussed are used in the modern era, but he does make reference to the possible efficacy of corneal transplantation. Nottinghams treatise was published over 160 years ago, yet his ideas and observations are surprisingly accurate. It is very possible that he was the first person to publish an accurate, comprehensive description of keratoconus.

In vivo ocular biomechanical compliance in thyroid eye disease

Background/aims To compare the ocular biomechanical properties in patients with thyroid eye disease (TED) and healthy participants using a non-contact Scheimpflug-based tonometer (CorVis ST). Methods All eyes were examined by slit lamp biomicroscopy, corneal tomography and the CorVis ST (CST). Patients with TED were examined by a fellowship trained oculoplastics specialist to determine status and assess severity. The outputs from CST and additionally derived parameters, including maximum orbital deformation (MOD), were compared between healthy participants and patients with TED using Students t-test. Furthermore, a multiple linear regression analysis was used to control for various factors known to influence ocular biomechanical responses to an air pulse. Results This study included 20 patients with TED and compared them with a cohort of 152 healthy participants. The mean age of patients with TED was 46.7±19.0 years and the mean age of healthy participants was 35.9±13.8 years (p=0.03). There were no statistically significant differences in gender distributions between both groups (p>0.05). Several CST parameters were significantly different between groups (p<0.05). Of note, however, MOD was significantly lower in patients with TED (0.16±0.04 mm) compared with the healthy participants (0.25±0.05 mm, p<0.001). This dissimilarity remained even after controlling for the various cofactors. Receiver-operating characteristic analysis revealed an area under the curve of 0.91±0.04 (95% CI 0.84 to 0.98, p<0.001) for MOD. Conclusions The in vivo ocular biomechanics as measured by the CST reflects a reduced orbital compliance. This method of ocular biomechanical assessment may aid in the categorisation of TED severity and assist in monitoring and/or diagnosing TED.

Persisting extreme acute corneal hydrops with a giant intrastromal cleft secondary to keratoconus

Acute corneal hydrops (hydrops corneae) is an incompletely understood complication of keratoconus and other corneal ectatic disorders, including keratoglobus and pellucid marginal corneal degeneration. Keratoconus is a relatively common condition; its prevalence is estimated to lie between 6.8 and 86 per 100,000 with considerable variation among international studies. With an estimated prevalence of 2.8 per cent among patients with keratoconus, corneal hydrops is considerably less common than keratoconus per se. There appears to be a gender predisposition toward males with typical age of onset around 25 years. Earlier age, poorer visual acuity and steeper keratometry at diagnosis of keratoconus, as well as severe allergic eye disease and eye rubbing, have been identified as risk factors for developing corneal hydrops. Interestingly, a history of atopy and contact lens wear do not demonstrate an increased likelihood of developing hydrops, while having a family history of keratoconus appears to have a negative correlation. Acute corneal hydrops is characterised by the development of significant corneal oedema, typically due to a spontaneous break in Desçemet’s membrane and the overlying corneal endothelium, which allows aqueous humour to migrate into the corneal stroma and epithelium. It is hypothesised that the resolution of acute corneal hydrops requires two steps. The first involves re-attachment of the detached Desçemet’s membrane to the posterior stroma, while the second involves the migration of endothelial cells to cover the gap between the edges of the two borders of the break in Desçemet’s membrane. The time taken for the first step to occur is dependent on the depth of detachment of Desçemet’s membrane and can be hastened by anterior chamber paracentesis and intra-cameral injection of non-expansile gas such as sulphur hexafluoride (SF6) speeding up the time to resolution. The second step is dependent on the size of the break in Desçemet’s membrane and the time taken for this step to occur cannot currently be shortened. The corneal oedema associated with acute corneal hydrops is self-limiting, usually resolving within six to 14 weeks in the majority of cases; however, it often leaves a visually debilitating scar in its wake. Scarring of the cornea may necessitate corneal transplantation by penetrating keratoplasty (PKP) or deep anterior lamellar keratoplasty (DALK); however, in practice, the extent of scarring dictates which procedure should be carried out. In cases where there is extensive corneal scarring, PKP is the procedure of choice due to the increased likelihood of perforation when attempting DALK.

The natural history of corneal topographic progression of keratoconus after age 30 years in non-contact lens wearers

Background/aims To determine if significant progression of disease occurs in older, non-contact lens wearing, subjects with keratoconus and to identify potential predictive factors. Methods Clinical and computerised corneal topography records of subjects with keratoconus attending a specialist optometry practice were retrospectively analysed to identify those aged ≥30 years, with ≥2 consultations ≥12 months apart, no contact lens wear and no corneal scarring, surgery or corneal hydrops. Topographic parameters assessed included: maximum keratometry (Kmax), steep keratometry (Ksteep), flat keratometry (Kflat), inferior-superior (I-S) ratio and the surface asymmetry and regularity (surface asymmetry index and surface regularity index) indices. Results Of the 449 subjects with keratoconus assessed, 43 eyes of 27 patients (6.01%) met inclusion criteria, with median age 38.45 (12.86) years at baseline and median follow-up 4.36 (8.68) years. There was a significant increase in Kmax (0.30 (1.21) D), Ksteep (0.27 (0.90) D), Kflat (0.34 (1.12) D) and I-S (0.26 (0.82) D) between baseline and final review, p<0.05. Notably, 18.6%–25.6% of eyes demonstrated ≥1.00 D increase in one or more of four principal topographic parameters (Kmax, Ksteep, Kflat, I-S ratio), while 18.5%–37.0% of subjects had ≥1.00 D increase in the aforementioned parameters in at least one eye over the study period. However, <10% of eyes exhibited ≥1.00 D increase/year in all topographic parameters. The only significant predictor of progression was follow-up time. Conclusions This study confirms that keratoconus may continue to progress beyond age 30. Older subjects with keratoconus should be monitored for progression, particularly with respect to possible corneal collagen cross-linking or astigmatic correction in cataract surgery.

Tear lipid supplement prophylaxis against dry eye in adverse environments

PURPOSE To compare the prophylactic efficacy of single application of lipid and non-lipid containing tear supplements, prior to exposure of symptomatic dry eye subjects to a simulated adverse environment. METHODS Thirty subjects with mild-to-moderate dry eye symptoms participated in the prospective, randomised, double-masked, paired-eye trial. A lipomimetic drop (Systane® Balance) was applied to one eye (randomised), and a non-lipid containing drop (Systane® Ultra) applied simultaneously to the contralateral eye. Subjects were subsequently exposed to a validated simulated adverse environment model created by a standing fan directed towards the eye, at a distance of 1m, for 2.5min. Low contrast glare acuity, lipid layer grade (LLG), non-invasive tear break-up time (NIBUT), temperature variation factor (TVF), and tear meniscus height (TMH) were evaluated at baseline, following eye drop instillation and following simulated adverse environment exposure. RESULTS Both therapies resulted in increased NIBUT (both p<0.001), and prevented its decline below baseline with simulated adverse environment exposure (both p>0.05). However, only the lipomimetic drop increased LLG (p<0.001) and precluded its fall below baseline post-adverse environment exposure (p=0.15). Furthermore, post-instillation and post-exposure LLGs and NIBUT were significantly higher in the lipomimetic group (all p<0.05). No significant changes were observed in glare acuity, TVF and TMH (all p>0.05). More subjects (67%) reported greater ocular comfort in the eye receiving the lipomimetic. CONCLUSIONS Single application of both lipid and non-lipid containing eye drops conferred protective effects against exposure to adverse environmental conditions in subjects with mild-to-moderate dry eye, although the lipomimetic demonstrated superior prophylactic efficacy.