Effect of Scleral Lens Oxygen Permeability on Corneal Physiology.

SIGNIFICANCE: This randomized, masked, crossover clinical study identifies that ≥125 Dk materials should be used for scleral lens daily wear if disruption to corneal oxygen is to be minimized. PURPOSE: Modern scleral lens use has increased and has proven to be successful where other types and materials have previously failed. Although the required oxygen permeability has been modeled, this has not been established clinically. METHODS: Fifteen masked participants aged 20.7 ± 2.3 years (10 female) were bilaterally fitted with five different scleral lenses (65, 100, 125, 163, and 180+ Dk) of the same shape profile and one soft silicone hydrogel lens compared with no lens wear on separate occasions in a randomized order. A masked researcher measured corneal thickness and fluid reservoir depth, corneal curvature, objective bulbar and limbal redness, corneal biomechanics, and ocular surface oxygen consumption before and after 8 hours of wear. In addition, comfort scores were obtained using a visual analog scale. RESULTS: Scleral lenses with oxygen permeability of 65 Dk resulted in greater corneal thickness (1.37 ± 1.25%) after 8 hours of wear versus ≥100 Dk materials (0.58 ± 0.99%; F = 17.215, P < .001) because of stromal thickening; edema with ≥100 Dk materials was associated with fluid reservoir depth (r = 0.231, P = .05). Fluid reservoir depth decreased similarly with all oxygen-permeable lenses from 325.6 ± 99.1 µm to 174.2 ± 100.8 µm after 8 hours of wear (F = 0.961, P = .44). Oxygen consumption reduced with ≤125 Dk lenses (χ = 604.196, P < .001). Soft and scleral lens wear had no effect on corneal curvature, corneal biomechanics, or ocular hyperemia (P > .05). Soft lenses were more comfortable than all the scleral lenses (P < .05), and the 180+ Dk lenses had the best comfort among the sclerals (P < .05). CONCLUSIONS: A ≥125 Dk is advised for safe scleral lens daily wear. Scleral lens wear leads to an increase in corneal thickness, regardless of lens-material oxygen permeability because of the fluid reservoir depth.

Factors Influencing Pseudo-Accommodation-The Difference between Subjectively Reported Range of Clear Focus and Objectively Measured Accommodation Range.

The key determinants of the range of clear focus in pre-presbyopes and their relative contributions to the difference between subjective range of focus and objective accommodation assessments have not been previously quantified. Fifty participants (aged 33.0 ± 6.4 years) underwent simultaneous monocular subjective (visual acuity measured with an electronic test-chart) and objective (dynamic accommodation measured with an Aston open-field aberrometer) defocus curve testing for lenses between +2.00 to -10.00 DS in +0.50 DS steps in a randomized order. Pupil diameter and ocular aberrations (converted to visual metrics normalized for pupil size) at each level of blur were measured. The difference between objective range over which the power of the crystalline lens changes and the subjective range of clear focus was quantified and the results modelled using pupil size, refractive error, tolerance to blur, and ocular aberrations. The subjective range of clear focus was principally accounted for by age (46.4%) and pupil size (19.3%). The objectively assessed accommodative range was also principally accounted for by age (27.6%) and pupil size (15.4%). Over one-quarter (26.0%) of the difference between objective accommodation and subjective range of clear focus was accounted for by age (14.0%) and spherical aberration at maximum accommodation (12.0%). There was no significant change in the objective accommodative response (F = 1.426, p = 0.229) or pupil size (F = 0.799, p = 0.554) of participants for levels of defocus above their amplitude of accommodation. Pre-presbyopes benefit from an increased subjective range of clear vision beyond their objective accommodation due in part to neural factors, resulting in a measured depth-of-focus of, on average, 1.0 D.

Anterior Segment Optical Coherence Tomographic Angiography Assessment of Acute Chemical Injury.

PURPOSE: To compare routine clinical examination with optical coherence tomography angiography (OCTA) for the assessment of limbal conjunctival ischemia following a chemical burn. SETTING: Validity analysis. METHODS: We assessed 10 participants (15 eyes) with an acute chemical injury. Clinical photographs were used to determine the extent of any limbal conjunctival epithelial defect and ischemia. These were compared with the extent of limbal ischemia identified on OCTA images of the ocular surface. Quantitative and longitudinal analysis using the OCTA software were also performed. Correlations with visual outcome were sought using clinical and OCTA-derived variables. RESULTS: The extent of clinically determined limbal ischemia was less than that identified with OCTA (2.3±3.6 clock hours vs 5.1±4.2 clock hours, P = .003), which in turn was less than the size of limbal conjunctival epithelial defect (7.3±5.1 clock hours, P = .03). Longitudinal OCTA analysis showed that mean vessel area increased by 0.2%±0.1% during the study, corresponding to a rate of vascular recovery of 0.9 mm2/d. Significant correlations were found between visual outcome at 3 months and limbal conjunctival fluorescein staining (r = 0.67, P = .006), and limbal conjunctival ischemia on OCTA (r = 0.76, P = .001). CONCLUSIONS: OCTA can objectively identify and monitor the recovery of limbal ischemia following an acute ocular chemical injury. OCTA confirms that limbal ischemia is usually more extensive than is suggested by clinical examination, and the former is highly correlated with visual outcome. OCTA therefore is a useful tool in the management of ocular chemical injury.

Initial experience using a femtosecond laser cataract surgery system at a UK National Health Service cataract surgery day care centre.

OBJECTIVES: To describe the initial outcomes following installation of a cataract surgery laser system. SETTING: National Health Service cataract surgery day care unit in North London, UK. PARTICIPANTS: 158 eyes of 150 patients undergoing laser-assisted cataract surgery. INTERVENTIONS: Laser cataract surgery using the AMO Catalys femtosecond laser platform. PRIMARY OUTCOME MEASURE: intraoperative complications including anterior and posterior capsule tears. SECONDARY OUTCOME MEASURES: docking to the laser platform, successful treatment delivery, postoperative visual acuities. RESULTS: Mean case age was 67.7±10.8 years (range 29-88 years). Docking was successful in 94% (148/158 cases), and in 4% (6/148 cases) of these, the laser delivery was aborted part way during delivery due to patient movement. A total of 32 surgeons, of grades from junior trainee to consultant, performed the surgeries. Median case number per surgeon was 3 (range from 1-20). The anterior capsulotomy was complete in 99.3% of cases, there were no anterior capsule tears (0%). There were 3 cases with posterior capsule rupture requiring anterior vitrectomy, and 1 with zonular dialysis requiring anterior vitrectomy (4/148 eyes, 2.7%). These 4 cases were performed by trainee surgeons, and were either their first laser cataract surgery (2 surgeons) or their first and second laser cataract surgeries (1 surgeon). CONCLUSIONS: Despite the learning curve, docking and laser delivery were successfully performed in almost all cases, and surgical complication rates and visual outcomes were similar to those expected based on national data. Complications were predominately confined to trainee surgeons, and with the exception of intraoperative pupil constriction appeared unrelated to the laser-performed steps.

Evaluating the effect of splitting cylindrical power on improving patient tolerance to toric lens misalignment.

PURPOSE: Evaluating the impact of splitting toric power on patient tolerance to misorientation such as with intraocular lens rotation. SETTING: University vision clinic. METHODS: Healthy, non astigmats had +1.50D astigmatism induced with spectacle lenses at 90°, 135°, 180° and +3.00D at 90°. Two correcting cylindrical lenses of the opposite sign and half the power each were subsequently added to the trial frame misaligned by 0°, 5° or 10° in a random order and misorientated from the initial axis in a clockwise direction by up to 15° in 5° steps. A second group of adapted astigmats with between 1.00 and 3.00DC had their astigmatism corrected with two toric spectacle lenses of half the power separated by 0°, 5° or 10° and misorientated from the initial axis in both directions by up to 15° in 5° steps. Distance, high contrast visual acuity was measured using a computerised test chart at each lens misalignment and misorientation. RESULTS: Misorientation of the split toric lenses caused a statistically significant drop in visual acuity (F=70.341; p<0.001). Comparatively better acuities were observed around 180°, as anticipated (F=3.775; p=0.035). Misaligning the split toric power produced no benefit in visual acuity retention with axis misorientation when subjects had astigmatism induced with a low (F=2.190, p=0.129) or high cylinder (F=0.491, p=0.617) or in the adapted astigmats (F=0.120, p=0.887). CONCLUSION: Misalignment of toric lens power split across the front and back lens surfaces had no beneficial effect on distance visual acuity, but also no negative effect.