Traction on the retina induced by saccadic eye movements in the presence of posterior vitreous detachment

CLINICAL OUTCOMES OF RHEGMATOGENOUS RETINAL DETACHMENT REPAIR IN PATIENTS WITH NYSTAGMUS

PURPOSE

To report the anatomical and visual outcomes of rhegmatogenous retinal detachment repair in patients with congenital or acquired nystagmus.

METHODS

This was a case series involving a retrospective review of medical records from January 1, 2015, to April 1, 2021, of eight eyes of eight patients (seven men and one woman) with documented nystagmus who underwent rhegmatogenous retinal detachment repair. Primary outcomes included final reattachment rate and single surgery anatomical success at three months postoperatively. Secondary outcomes included final visual acuity and mean number of additional procedures required for retinal reattachment.

RESULTS

Mean age was 52.1 years (range: 14-77 years), and mean follow-up time was 18.6 months (range: 2.8-32.9 months). Pars plana vitrectomy (PPV) was performed in four patients (50.0%), scleral buckle in 3 (37.5%), and PPV/scleral buckle in 1 (12.5%). A repeat PPV was required in three eyes (37.5%) because of proliferative vitreoretinopathy, two of which initially underwent PPV, and one had PPV/scleral buckle. Two eyes (25%) required a third PPV because of proliferative vitreoretinopathy or retinal breaks. Mean time to first redetachment was 29 days. Single surgery anatomic success at three months was achieved in five patients (62.5%). Complete final retinal reattachment was achieved in all patients. Final visual acuity improved or stabilized in seven eyes (87.5%).

CONCLUSION

Despite a 100% final retinal reattachment rate, rhegmatogenous retinal detachment repair can be challenging among patients with nystagmus, including postoperative complications such as recurrent retinal detachment because of retinal breaks. No silicone oil emulsification or related complications were observed in our series.

A mechanical model of ocular bulb vibrations and implications for acoustic tonometry

In this study, we propose a comprehensive mechanical model of ocular bulb vibrations and discuss its implications for acoustic tonometry. The model describes the eye wall as a spherical, pre-stressed elastic shell containing a viscoelastic material and accounts for the interaction between the elastic corneoscleral shell and the viscoelastic vitreous humor. We investigate the natural frequencies of the system and the corresponding vibration modes, expanding the solution in terms of scalar and vector spherical harmonics. From a quantitative point of view, our findings reveal that the eyebulb vibration frequencies significantly depend on IOP. This dependency has two origins: "geometric" stiffening, due to an increase of the pre-stress, and "material" stiffening, due to the nonlinearity of the stress-strain curve of the sclera. The model shows that the second effect is by far dominant. We also find that the oscillation frequencies depend on ocular rigidity, but this dependency is important only at relatively large values of IOP. Thus close to physiological conditions, IOP is the main determinant of ocular vibration frequencies. The vitreous rheological properties are found to mostly influence vibration damping. This study contributes to the understanding of the mechanical behavior of the eye under dynamic conditions and thus has implications for non-contact intraocular pressure measurement techniques, such as acoustic tonometry. The model can also be relevant for other ocular pathological conditions, such as traumatic retinal detachment, which are believed to be influenced by the dynamic behavior of the eye.

PNEUMATIC WITHOUT PEXY: A CASE REPORT OF A RETINAL DETACHMENT REPAIR

PURPOSE

To present a case of pneumatic retinal detachment repair that did not require retinal pexy.

METHODS

Report of a case and review of the literature.

RESULTS

Pneumatic retinopexy was performed with a plan for photocoagulation of the retinal tear once the retina was reattached. During postoperative evaluation, the superotemporal retinal tear had operculated and the retina was reattached. No laser or cryopexy was performed, and the retina remained attached during long-term follow-up.

DISCUSSION

Addressing traction on the retina and intraocular microcurrents that allow subretinal fluid accumulation is the core principle of detachment repair; if the traction is released, pexy may not be necessary.

Ocular Fluid Mechanics and Drug Delivery: A Review of Mathematical and Computational Models

The human eye is a complex biomechanical structure with a range of biomechanical processes involved in various physiological as well as pathological conditions. Fluid flow inside different domains of the eye is one of the most significant biomechanical processes that tend to perform a wide variety of functions and when combined with other biophysical processes play a crucial role in ocular drug delivery. However, it is quite difficult to comprehend the effect of these processes on drug transport and associated treatment experimentally because of ethical constraints and economic feasibility. Computational modeling on the other hand is an excellent means to understand the associated complexity between these aforementioned processes and drug delivery. A wide range of computational models specific to different types of fluids present in different domains of the eye as well as varying drug delivery modes has been established to understand the fluid flow behavior and drug transport phenomenon in an insilico manner. These computational models have been used as a non-invasive tool to aid ophthalmologists in identifying the challenges associated with a particular drug delivery mode while treating particular eye diseases and to advance the understanding of the biomechanical behavior of the eye. In this regard, the author attempts to summarize the existing computational and mathematical approaches proposed in the last two decades for understanding the fluid mechanics and drug transport associated with different domains of the eye, together with their application to modify the existing treatment processes.

The effects of aging on the mechanical properties of the vitreous

The vitreous body is a viscoelastic gel-like network that fills the space between the lens and the retina in the eye. With aging, the vitreous undergoes a liquefaction process in which liquid pockets form in the gel network, thereby motivating the detachment of the vitreous from the retina in a process known as posterior vitreous detachment (PVD). The PVD process may lead to the formation of floaters and even result in partial or complete loss of vision. Experiments show that the liquefaction and the PVD processes alter the mechanical properties of the vitreous. In this work, we propose a microscopically motivated model that characterizes the changes in the mechanical properties of the vitreous due to aging. To this end, we distinguish between four vitreous states: a homogeneous vitreous, a liquefied vitreous, a vitreous that undergoes partial PVD, and a vitreous with full PVD. The model predicts the time-dependent and the steady-state response of the vitreous in each of the four states. The proposed framework is validated through a comparison with various experimental findings and captures the softening of the vitreous due to aging. We illustrate the importance of the age at which the PVD process begins and of the rate of the detachment process. In addition, we introduce a quantifiable parameter that describes the stage of PVD in the eye. Lastly, we employ our model to investigate the possibility of restoring the mechanical properties of a vitreous that has undergone PVD through the addition of reinforcing fibers to the gel. This work provides insight into the consequences of the age-related changes in the microstructure of the eye and serves as a motivation for new therapeutic measures.

Changing clinical patterns of Rhegmatogeneous Retinal Detachments during the COVID19 pandemic lockdown in the North West of the UK

INTRODUCTION

The UK Government imposed a COVID19 lockdown (LD) restricting all but essential activities from 24th March 2020. Subsequently, there has been a significant reduction in casualty attendances nationwide including for ophthalmic emergencies. We aim to study the presentation of rhegmatogenous retinal detachments (RRD) and significant vitreous haemorrhage caused by posterior vitreous detachment (PVD-VH) in three tertiary centres covering most of the North West of England in the 6 weeks before and during the lockdown.

METHODS

A retrospective multicenter non-randomised consecutive case series study was designed to collect information on all cases of RRD and PVD-VH requiring surgery presenting to the vitreoretinal departments of Manchester Royal Eye Hospital, East Lancashire NHS Foundation Trust and the Lancashire NHS Foundation Trust from 11th February to 4th May 2020.

RESULTS

A total of 137 eyes of 137 patients were identified between the three centres of which 132 eyes were operated for RRD. Of these, 86 (64.7%) were operated pre-LD compared with 46 eyes (34.8%) during LD. Forty-five out of 86 eyes (52.3%) were macula-off pre-LD compared with 31 out of 46 eyes (67.3%) during LD (p = 0.06). There was lower proportion of non-PVD related RRD during LD (11 pre-LD to 1 during LD, p = 0.05). PVR was present in four cases during LD compared to 2 before (p = 0.19).

CONCLUSION

There was a clinically significant reduction in the overall incidence of RRD in our centres with an increase in the proportion of macula-off and proliferative vitreoretinopathy during the LD period compared to a similar period before.

Flow dynamics of vitreous humour during saccadic eye movements

In this work, we reveal the flow dynamics of Vitreous Humour (VH) gel and liquid phases during saccadic movements of the eye, considering the biofluids viscoelastic character as well as realistic eye chamber geometry and taking into account the saccade profile. We quantify the differences in the flow dynamics of VH gel and liquid phases using viscoelastic rheological models that are able to model the VH shear rheology, considering different amplitudes of saccadic movements (10^∘, 20^∘, 30^∘ and 40^∘). For this purpose, the computational fluid dynamics (CFD) open source software OpenFOAM® was used. The results portray a distinct flow behaviour for the VH gel and liquid phases, with inertial effects being more significant for the VH liquid phase. Moreover, the Wall Shear Stress (WSS) values produced by the VH gel phase are more than twice of those generated by the VH liquid phase. Results also show that for different amplitudes of eye movement both the velocity magnitude in the vitreous cavity and the shear stresses on the cavity walls rise with increasing saccadic movement displacement.

On the mechanics of myopia and its influence on retinal detachment

A mechanics-based mathematical model of retinal detachment due to the geometric changes of the eye associated with the evolution of myopia is developed. This includes deformation of the retina due to biological growth of the retina, as well as elastic deformation imposed on the retina by the myopic change in shape of the much stiffer choroid and sclera. The problem is formulated as a propagating boundary value problem in the calculus of variations, which yields self-consistent governing equations, boundary conditions, and transversality conditions that establish the location of the propagating boundaries that correspond to equilibrium configurations of the detaching ocular system. Axisymmetric conditions are considered, and exact, analytical solutions to the corresponding boundary value problem are obtained for detaching retinas with and without a tear. Based upon application of the model presented herein to the emmetropic retina, a value of the bond energy of the retina to retinal pigment epithelium interface is estimated using material properties found in the literature. Simulations based on the analytical solutions are performed for a detachment in the retina located at either the posterior or superior pole of the eye. The results support the clinical finding of an increased prevalence of retinal detachment in myopic eyes and provide insight into the potential causation for the increased prevalence.

The Influence of Prolongation of Interruptions of Preoperative Posturing and Other Clinical Factors on the Progress of Macula-On Retinal Detachment

PURPOSE

To evaluate whether prolongation of interruptions of preoperative posturing by sitting upright influences retinal detachment (RD) progression. The secondary objective was to find clinical factors to identify patients with a high risk for RD progression.

DESIGN

Prospective cohort study.

PARTICIPANTS

One hundred ninety-eight patients divided among 3 cohorts of patients with macula-on RD were included. Inclusion criteria were volume OCT scans of sufficient quality and smallest distance from the fovea to the detachment border of at least 1.25 mm. In the second and third cohort, 50 patients with only superior temporal RD were included.

METHODS

Patients were admitted to the ward in anticipation of surgery. Preoperative bed rest and positioning were prescribed. The position of the RD border was determined based on OCT imaging performed at baseline, before and after the usual interruptions for meals or toilet visits. The duration of interruptions was prolonged with sitting upright for 20 minutes in cohort 2 and for 40 minutes in cohort 3. Various secondary outcome measures were defined, such as the baseline area of subretinal fluid (SRF) as measured on ultrasound images in the third cohort.

MAIN OUTCOME MEASURES

The RD border displacement was determined. The worst RD progression from baseline was given by the shortest distance to the fovea in any of the OCT scans during follow-up. The worst relative RD progression from baseline was defined as the worst RD progression from baseline as a percentage of the baseline distance between RD border and fovea.

RESULTS

The median duration of interruptions was 22, 41, and 58 minutes in cohorts 1, 2, and 3, respectively. The median RD border displacement during interruptions in patients with superior temporal RD was not significantly different among the cohorts (P = 0.28). The correlation coefficient between the SRF area at baseline and worst relative RD progression from baseline was 0.37 (95% confidence interval, 0.04-0.66; P = 0.009).

CONCLUSIONS

We did not find a significant increase in RD progression after prolongation of interruptions by sitting upright. Patients with a larger area of SRF on ultrasound showed more RD progression from baseline.

The Effect of Compliance With Preoperative Posturing Advice and Head Movements on the Progression of Macula-On Retinal Detachment

Purpose

The aim of this study was to explore the relationship between compliance with preoperative posturing advice and progression of macula-on retinal detachment (RD) and to evaluate whether head positioning or head motility contributes most to RD progression.

Methods

Sixteen patients with macula-on RD were enrolled, admitted to the ward, and instructed to posture preoperatively. The primary outcome parameter was compliance, which was defined as the average head orientation deviation from advised positioning. Secondary outcome parameters included the average rotational and linear head acceleration. The head orientation and acceleration were measured with a head-mounted inertial measurement unit (IMU). Optical coherence tomography (OCT) imaging was performed at baseline and during natural interruptions of posturing for meals and toilet visits to measure RD progression toward the fovea.

Results

The Spearman correlation coefficient with RD progression was 0.37 (P = 0.001, r_s² = 0.13) for compliance, 0.52 (P < 0.001, r_s² = 0.27) for rotational acceleration, and 0.49 (P < 0.001, r_s² = 0.24) for linear acceleration. The correlation coefficient between RD progression and rotational acceleration was statistically significantly higher than the correlation coefficient between RD progression and compliance (P = 0.034).

Conclusion

The strength of the correlation between RD progression and compliance was moderate. However, the correlation between RD progression and rotational and linear acceleration was much stronger. Preoperative posturing is effective by reducing head movements rather than enforcing head positioning.

Translational Relevance

Monitoring the efficacy of preoperative posturing in macula-on RD using OCT and IMU measurements shows that a new and combined application of these technologies leads to clinically relevant insights.

Retinal detachment in albinism

Purpose

To report the visual and anatomic outcomes of albino retinal detachment (ARD) repair.

Methods

Collaborative retrospective analysis of ARD. Outcome measures were number of surgical interventions, final retinal reattachment, and best corrected visual acuity (BCVA) at last follow-up.

Results

Seventeen eyes of 16 patients (12 males; mean age =37.8 years) had the following complications at presentation: macula off (14), total (7) or inferior detachment (5), proliferative vitreoretinopathy (5), detectable break (16), lattice (5), horseshoe tears (9), and giant tear or dialysis (4). Mean number of interventions was 1.8 (range =1–5) and included cryopexy (15) with scleral buckle (11), and/or vitrectomy (8). Mean initial BCVA was counting finger (CF) 1 m and at last follow-up (mean 77 months) CF4m with mean improvement of 4.5 lines (early treatment diabetic retinopathy study) (P=0.05). Intraoperative choroidal hemorrhage occurred in three eyes. The retina was finally attached in 14 eyes, with residual inferior detachment in three eyes with silicone oil in situ. Silicone oil was kept in six of seven eyes because of residual inferior detachment (3) and removal of silicone oil, which led to redetachment (1) or fear of redetachment (2).

Conclusion

Repair of ARD may require several interventions, with the need to keep silicone oil in several cases due to nystagmus and reduced melanin pigment.

Intraocular currents, Bernoulli's principle and non-drainage scleral buckling for rhegmatogenous retinal detachment

For many years, it is not fully understood how non-drainage scleral buckling surgery brings about spontaneous reattachment of the detached retina when retinal breaks remain open at the end of surgery. Various explanations have been put forward, but none more interesting than the effect of fluid currents associated with eye movements. One such explanation involved the physics of the Bernoulli's principle. Daniel Bernoulli was an eighteenth century Swiss mathematician and he described an equation based on the conservation of energy. The sum of pressure energy, potential energy and kinetic energy remains constant. Bernoulli's equation usually applies to closed system such as the flow of fluid through pipes. When fluid flows through a constriction, the speed of fluid increases, the kinetic energy increases. If there was no change in elevation (potential energy), then the increase in kinetic energy must be accompanied by a decrease in pressure energy. In ophthalmic surgery, the Bernoulli's effect is the basis for venturi pumps that drive vitrectomy and phacoemulsification machines. This essay expounds on how Bernoulli's effect might be relevant to scleral buckling for retinal detachment repair. In the era when vitrectomy is increasing the primary surgical operation for retinal detachment, the pervasive advice is to emphasise the importance of patient adopting head posture and remaining still postoperatively. The exception is non-drainage scleral buckling surgery. Early postoperative mobilisation may be vital to achieve reattachment.

Preoperative Posturing of Patients with Macula-On Retinal Detachment Reduces Progression Toward the Fovea

PURPOSE

Traditionally, preoperative posturing consisting of bed rest and positioning is prescribed to patients with macula-on retinal detachment (RD) to prevent RD progression and detachment of the fovea. Execution of such advice can be cumbersome and expensive. This study aimed to investigate if preoperative posturing affects the progression of RD.

DESIGN

Prospective cohort study.

PARTICIPANTS

Ninety-eight patients with macula-on RD were included. Inclusion criteria were volume optical coherence tomography (OCT) scans could be obtained with sufficient quality; and the smallest distance from the fovea to the detachment border was 1.25 mm or more.

METHODS

Patients were admitted to the ward for bed rest in anticipation of surgery and were positioned on the side where the RD was mainly located. At baseline and before and after each interruption for meals or toilet visits, a 37°×45° OCT volume scan was performed using a wide-angle Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany). The distance between the nearest point of the RD border and fovea was measured using a custom-built measuring tool.

MAIN OUTCOME MEASURES

The RD border displacement and the average RD border displacement velocity moving toward (negative) or away (positive) from the fovea were determined for intervals of posturing and interruptions.

RESULTS

The median duration of intervals of posturing was 3.0 hours (interquartile range [IQR], 1.8-14.0 hours; n = 202) and of interruptions 0.37 hours (IQR, 0.26-0.50 hours; n = 197). The median RD border displacement was 2 μm (IQR, -65 to +251 μm) during posturing and -61 μm (IQR, -140 to 0 μm) during interruptions, a statistically significant difference (P < 0.001, Mann-Whitney U test). The median RD border displacement velocity was +1 μm/hour (IQR, -21 to +49 μm/hour) during posturing and -149 μm/hour (IQR, -406 to +1 μm/hour) during interruptions, a statistically significant difference (P < 0.001).

CONCLUSIONS

By making use of usual interruptions of preoperative posturing we were able to show, in a prospective and ethically acceptable manner, that RD stabilizes during posturing and progresses during interruptions in patients with macula-on RD. Preoperative posturing is effective in reducing progression of RD.

Traumatic retinal detachment--the difficulty and importance of correct diagnosis

Accurate characterization of a retinal detachment as traumatic is often difficult, but is important because it may instigate a careful search for occult coexistent traumatic pathology, affect the prognosis and the treatment of both eyes, influence insurance coverage benefits and medical-legal determinations, and is essential for epidemiologic studies. We review the epidemiology and pathophysiology of traumatic retinal detachment, common obstacles to correct diagnosis, diagnostic guidelines, and outline categories of traumatic causal relationships. Because there is no generally accepted definition of traumatic retinal detachment, we offer a practical one. Categorization as traumatic should be based on the particular history and physical examination rather than epidemiologic criteria.

An experimental model of vitreous motion induced by eye rotations

BACKGROUND

During eye rotations the vitreous humour moves with respect to the eye globe. This relative motion has been suggested to possibly have an important role in inducing degradation of the gel structure, which might lead to vitreous liquefaction and/or posterior vitreous detachment. Aim of the present work is to study the characteristics of vitreous motion induced by eye rotations.

METHODS

We use an experimental setup, consisting of a Perspex model of the vitreous chamber that, for simplicity, is taken to have a spherical shape. The model is filled with an artificial vitreous humour, prepared as a solution of agar powder and hyaluronic acid sodium salt in deionised water, which has viscoelastic mechanical properties similar to those of the real vitreous. The model rotates about an axis passing through the centre of the sphere and velocity measurements are taken on the equatorial plane orthogonal to the axis of rotation, using an optical technique.

RESULTS

The results show that fluid viscoelasticity has a strong influence on flow characteristics. In particular, at certain frequencies of oscillation of the eye model, fluid motion can be resonantly excited. This means that fluid velocity within the domain can be significantly larger than that of the wall.

CONCLUSIONS

The frequencies for which resonant excitation occurs are within the range of possible eye rotations frequencies. Therefore, the present results suggest that resonant excitation of vitreous motion is likely to occur in practice. This, in turn, implies that eye rotations produce large stresses on the retina and within the vitreous that may contribute to the disruption of the vitreous gel structure. The present results also have implications for the choice of the ideal properties for vitreous substitute fluids.

Mechanical models of the dynamics of vitreous substitutes

We discuss some aspects of the fluid dynamics of vitreous substitutes in the vitreous chamber, focussing on the flow induced by rotations of the eye bulb. We use simple, yet not trivial, theoretical models to highlight mechanical concepts that are relevant to understand the dynamics of vitreous substitutes and also to identify ideal properties for vitreous replacement fluids. We first recall results by previous authors, showing that the maximum shear stress on the retina grows with increasing viscosity of the fluid up to a saturation value. We then investigate how the wall shear stress changes if a thin layer of aqueous humour is present in the vitreous chamber, separating the retina from the vitreous replacement fluid. The theoretical predictions show that the existence of a thin layer of aqueous is sufficient to substantially decrease the shear stress on the retina. We finally discuss a theoretical model that predicts the stability conditions of the interface between the aqueous and a vitreous substitute. We discuss the implications of this model to understand the mechanisms leading to the formation of emulsion in the vitreous chamber, showing that instability of the interface is possible in a range of parameters relevant for the human eye.

Tamponade or filling effect: changes of forces in myopic eyes

Myopia is the most common ocular abnormality. Its high and growing prevalence has contributed to a recent surge in surgical interest in the disorder, since retinal detachment in eyes with high myopia differs from that in emmetropic eyes or eyes with low myopia. The myopic eye, because of its specific anatomy, poses special challenges that need to be overcome to ensure the appropriate use of vitreous substitutes. However, intraocular tamponades have shown great potential for revolutionizing retinal detachment surgery and vitreomacular surgery in general in myopic eyes. We provide an updated review of the clinical use of vitreous substitutes in the myopic eye, paying particular attention to analyzing the ideal function of endotamponade agents and comparing the effects of these agents on the physical and biological properties of the eye.

Enzymatic degradation identifies components responsible for the structural properties of the vitreous body

PURPOSE

Vitreous degeneration contributes to several age-related eye diseases, including retinal detachment, macular hole, macular traction syndrome, and nuclear cataracts. Remarkably little is understood about the molecular interactions responsible for maintaining vitreous structure. The purpose of this study was to measure the structural properties of the vitreous body after enzymatic degradation of selected macromolecules.

METHODS

Mechanical properties of plugs of bovine and porcine vitreous were analyzed using a rheometer. Oscillatory and extensional tests measured vitreous stiffness and adhesivity, respectively. Major structural components of the vitreous were degraded by incubation overnight in collagenase, trypsin, or hyaluronidase, singly or in combination. Vitreous bodies were also incubated in hyper- or hypotonic saline. Effects of these treatments on the mechanical properties of the vitreous were measured by rheometry.

RESULTS

Enzymatic digestion of each class of macromolecules decreased the stiffness of bovine vitreous by approximately half (P < 0.05). Differential effects were observed on the damping capacity of the vitreous (P < 0.05), which was shown to correlate with material behavior in extension (P < 0.01). Digestion of hyaluronan significantly decreased the damping capacity of the vitreous and increased adhesivity. Collagen degradation resulted in the opposite effect, whereas digestion of proteins and proteoglycans with trypsin did not alter behavior relative to controls. Osmotic perturbations and double-enzyme treatments further implicated hyaluronan and hyaluronan-associated water as a primary regulator of adhesivity and material behavior in extension.

CONCLUSIONS

Collagen, hyaluronan, and proteoglycans act synergistically to maintain vitreous stiffness. Hyaluronan is a key mediator of vitreous adhesivity, and mechanical damping is an important factor influencing dynamic vitreous behavior.