ASSESSMENT OF SIMULATED SURGICAL DEXTERITY AFTER MODIFIABLE EXTERNAL EXPOSURES AMONG NOVICE VERSUS EXPERIENCED VITREORETINAL SURGEONS.

PURPOSE: To evaluate novice and senior vitreoretinal surgeons after various exposures. Multiple comparisons ranked the importance of these exposures for surgical dexterity based on experience. METHODS: This prospective cohort study included 15 novice and 11 senior vitreoretinal surgeons (<2 and >10 years' practice, respectively). Eyesi-simulator tasks were performed after each exposure. Day 1, placebo, 2.5 mg/kg caffeine, and 5.0 mg/kg caffeine; day 2, placebo, 0.2 mg/kg propranolol, and 0.6 mg/kg propranolol; day 3, baseline simulation, breathalyzer readings of 0.06% to 0.10% and 0.11% to 0.15% blood alcohol concentrations; day 4, baseline simulation, push-up sets with 50% and 85% repetitions maximum; and day 5, 3-hour sleep deprivation. Eyesi-generated score (0-700, worst-best), out-of-tolerance tremor (0-100, best-worst), task completion time (minutes), and intraocular pathway (in millimeters) were measured. RESULTS: Novice surgeons performed worse after caffeine (-29.53, 95% confidence interval [CI]: -57.80 to -1.27, P = 0.041) and alcohol (-51.33, 95% CI: -80.49 to -22.16, P = 0.001) consumption. Alcohol caused longer intraocular instrument movement pathways (212.84 mm, 95% CI: 34.03-391.65 mm, P = 0.02) and greater tremor (7.72, 95% CI: 0.74-14.70, P = 0.003) among novices. Sleep deprivation negatively affected novice performance time (2.57 minutes, 95% CI: 1.09-4.05 minutes, P = 0.001) and tremor (8.62, 95% CI: 0.80-16.45, P = 0.03); however, their speed increased after propranolol (-1.43 minutes, 95% CI: -2.71 to -0.15 minutes, P = 0.029). Senior surgeons' scores deteriorated only following alcohol consumption (-47.36, 95% CI: -80.37 to -14.36, P = 0.005). CONCLUSION: Alcohol compromised all participants despite their expertise level. Experience negated the effects of caffeine, propranolol, exercise, and sleep deprivation on surgical skills.

A Polysomnographic Study of Effects of Sleep Deprivation on Novice and Senior Surgeons during Simulated Vitreoretinal Surgery.

PURPOSE: To assess the impact of a 3-hour polysomnography (PSG)-recorded night of sleep deprivation on next-morning simulated microsurgical skills among vitreoretinal (VR) surgeons with different levels of surgical experience and associate the sleep parameters obtained by PSG with Eyesi-generated performance. DESIGN: Self-controlled cohort study. PARTICIPANTS: Eleven junior VR surgery fellows with < 2 years of surgical experience and 11 senior surgeons with > 10 years of surgical practice. METHODS: Surgical performance was assessed at 7am after a 3-hour sleep-deprived night using the Eyesi simulator and compared with each subject's baseline performance. MAIN OUTCOME MEASURES: Changes in Eyesi-generated score (0-700, worst to best), time for task completion (minutes), tremor-specific score (0-100, worst to best), and out-of-tolerance tremor percentage. Polysomnography was recorded during sleep deprivation. RESULTS: Novice surgeons had worse simulated surgical performance after sleep deprivation compared with self-controlled baseline dexterity in the total score (559.1 ± 39.3 vs. 593.8 ± 31.7; P = 0.041), time for task completion (13.59 ± 3.87 minutes vs. 10.96 ± 1.95 minutes; P = 0.027), tremor-specific score (53.8 ± 19.7 vs. 70.0 ± 15.3; P = 0.031), and out-of-tolerance tremor (37.7% ± 11.9% vs. 28.0% ± 9.2%; P = 0.031), whereas no performance differences were detected in those parameters among the senior surgeons before and after sleep deprivation (P ≥ 0.05). Time for task completion increased by 26% (P = 0.048) in the post-sleep deprivation simulation sessions for all participants with a high apnea-hypopnea index (AHI) and by 37% (P = 0.008) among surgeons with fragmented sleep compared with those with normal AHI and < 10 arousals per hour, respectively. Fragmented sleep was the only polysomnographic parameter associated with a worse Eyesi-generated score, with a 10% (P = 0.005) decrease the following morning. CONCLUSIONS: This study detected impaired simulated surgical dexterity among novice surgeons after acute sleep deprivation, whereas senior surgeons maintained their surgical performance, suggesting that the impact of poor sleep quality on surgical skills is offset by increased experience. When considering the 2 study groups together, sleep fragmentation and AHI were associated with jeopardized surgical performance after sleep deprivation. FINANCIAL DISCLOSURE(S): The authors have no proprietary or commercial interest in any materials discussed in this article.

Effects of fetal haemoglobin on systemic oxygenation in preterm infants and the development of retinopathy of prematurity PacIFiHER Report No. 2.

BACKGROUND/AIMS: Fetal haemoglobin (HbF) has an oxyhaemoglobin dissociation curve that may affect systemic oxygenation and the development of retinopathy of prematurity (ROP). The study aim is to characterise the effects of HbF levels on systemic oxygenation and ROP development. METHODS: Prospective study conducted from 1 September 2017 through 31 December 2018 at the Johns Hopkins NICU. Preterm infants with HbF measured at birth, 31, 34 and 37 weeks post-menstrual age (PMA), complete blood gas and SpO2 recorded up to 42 weeks PMA, and at least one ROP exam were included. RESULTS: Sixty-four preterm infants were enrolled. Higher HbF was associated with significantly higher SpO2, lower PCO2, lower FiO2 from birth to 31 weeks PMA and 31 to 34 weeks PMA (rs=0.51, rs=-0.62 and rs=-0.63; p<0.0001 and rs=0.71, rs=-0.58 and rs=-0.79; p<0.0001, respectively). To maintain oxygen saturation goals set by the neonatal intensive care unit, higher median FiO2 was required for HbF in the lowest tercile from birth compared with HbF in the highest tercile to 31 weeks and 31 to 34 weeks PMA; FiO2=35 (21-100) versus 21 (21-30) p<0.006 and FiO2=30 (28-100) versus 21 (21-30) p<0.001, respectively. Preterm infants with ROP had poorer indices of systemic oxygenation, as measured by median levels of SpO2 and PCO2, and lower levels of HbF (p<0.039 and p<0.0001, respectively) up to 34 weeks PMA. CONCLUSION: Low HbF levels correlated with poor oxygenation indices and increased risk for ROP. O2 saturation goals to prevent ROP may need to incorporate relative amount of HbF.

Mechanistic Insights into the Pathogenesis of Proliferative and Nonproliferative Vitreomacular Traction.

PURPOSE: To describe the vitreoretinal interface in vitreomacular traction (VMT) by using novel optical coherence tomography (OCT) methods; wide-angle montage, and pseudomotion OCT imaging systems. DESIGN: Observational case series. METHODS: Wide-angle montage OCT images of horizontal and vertical scans through the fovea were acquired in 50 eyes of 46 consecutive patients with VMT. Baseline fundus scans were obtained. These were followed by scans acquired with an eye-tracking system performed immediately after vertical and horizontal eye movements. Three scans were then superimposed to compare changes in the contour and position of the posterior vitreous. RESULTS: The subjects were classified as VMT with ("proliferative"; 48.0%) and without ("nonproliferative"; 52.0%) thickened posterior vitreous. Epiretinal membrane was observed in 26.9% of nonproliferative and 95.8% of proliferative VMT eyes (P = 3.6 × 10-7). No eye of proliferative and 57.7% of nonproliferative VMT eyes had wavy contoured posterior vitreous (P = 4.0 × 10-6). None with proliferative VMT, but 91.7% of nonproliferative VMT eyes, showed motion induced changes of posterior vitreous following eye movement (P = 2.0 × 10-8). The posterior vitreous detachment extended beyond the scanned area in 34.6% of nonproliferative and 8.3% of proliferative VMT eyes (P = .040). CONCLUSIONS: By dynamically evaluating the vitreoretinal interface of patients with VMT, the static contraction forces of a thickened posterior vitreous at the macula are implicated in proliferative VMT. This contractile force is not strongly implicated in the majority of VMT eyes with nontaut and more mobile vitreous (nonproliferative VMT). VMT and its associated complications are determined by at least 2 different pathophysiological mechanisms.

Posterior Vitreous Detachment in Normal Healthy Subjects Younger Than Age Twenty.

Purpose: To describe the initiation of posterior vitreous detachment (PVD) in the eyes of normal individuals, under 20 years of age, using wide-angle optical coherence tomography (OCT). Methods: This is an observational cross-sectional study. Montaged images of horizontal and vertical OCT scans were obtained in 63 healthy eyes of 35 consecutive subjects ranging in age from 4 to 17 years. Results: Forty-five eyes (71.4%) had obvious PVD, defined as a contiguous line of posterior cortical vitreous separated from the surface of the retina. Eighteen eyes (28.6%) had no PVD. The mean age of the individuals without PVD was significantly younger than those with PVD (P = 0.008). The spatial distribution of PVD initiation was highest in the superior quadrants, with the nasal, inferior, septum papillomaculae, and temporal quadrants following in descending order of frequency (P < 0.001). PVD was observed to begin anterior to the premacular liquefied lacuna, where the vitreous gel directly adheres to the vitreoretinal interface. In the majority of subjects (80.6%), PVD was initiated anterior to the vascular arcades. Conclusions: PVD can be observed by OCT to begin in the first and second decade of life. It begins in the mid-peripheral vitreous, most frequently in the superior quadrants anterior to the vascular arcades. In this study, all PVDs originated outside of the macular liquefied lacunae, where the vitreous gel adheres directly to the retina.

Current and novel multi-imaging modalities to assess retinal oxygenation and blood flow.

Retinal ischemia characterizes the underlying pathology in a multitude of retinal diseases that can ultimately lead to vision loss. A variety of novel imaging modalities have been developed to characterize retinal ischemia by measuring retinal oxygenation and blood flow in-vivo. These technologies offer valuable insight into the earliest pathophysiologic changes within the retina and provide physicians and researchers with new diagnostic and monitoring capabilities. Future retinal imaging technologies with the capability to provide affordable, noninvasive, and comprehensive data on oxygen saturation, vasculature, and blood flow mechanics are needed. This review will highlight current and future trends in multimodal imaging to assess retinal blood flow and oxygenation.

A Comparison of Manual and Robot Assisted Retinal Vein Cannulation in Chicken Chorioallantoic Membrane.

Retinal vein occlusion (RVO) is a vision threatening condition occurring in the central or the branch retinal veins. Risk factors include but are not limited to hypercoagulability, thrombus or other cause of low blood flow. Current clinically proven treatment options limit complications of vein occlusion without treating the causative occlusion. In recent years, a more direct approach called Retinal Vein Cannulation (RVC) has been explored both in animal and human eye models. Though RVC has demonstrated potential efficacy, it remains a challenging and risky procedure that demands precise needle manipulation to achieve safely. During RVC, a thin cannula (diameter 70-110 µm) is delicately inserted into a retinal vein. Its intraluminal position is maintained for up to 2 minutes while infusion of a therapeutic drug occurs. Because the tool-tissue interaction forces at the needle tip are well below human tactile perception, a robotic assistant combined with a force sensing microneedle could alleviate the challenges of RVC. In this paper we present a comparative study of manual and robot assisted retinal vein cannulation in chicken chorioallantoic membrane (CAM) using a force sensing microneedle tool. The results indicate that the average puncture force and average force during the infusion period are larger in manual mode than in robot assisted mode. Moreover, retinal vein cannulation was more stable during infusion, in robot assisted mode.

Prediction error in iris suture fixated intraocular lenses and long-term stability.

IMPORTANCE: Little evidence exists for prediction error in iris-sutured intraocular lenses. BACKGROUND: To determine the magnitude of prediction error in iris-sutured intraocular lenses, associated factors and their long-term stability. DESIGN: Retrospective, nonrandomized, noncomparative case series conducted at the Wilmer Eye Institute (Baltimore, Maryland, United States). PARTICIPANTS: Adult patients with subluxated intraocular lenses that underwent iris-suture fixation between January 2000 and December 2014 by a single surgeon. Pregnant women, children (below the age of 18) and cases with follow-up under 1 month were excluded. METHODS: Prediction error was calculated in 60 eyes and survival analysis was performed on 99 eyes. MAIN OUTCOME MEASURES: Prediction error (the difference between the postoperative manifest refraction in spherical equivalent and the spherical equivalent predicted by the Barrett Universal II, Holladay 2 and SRK/T formulas), preoperative and postoperative distance-corrected visual acuity, manifest refraction, frequency of postoperative complications and time until re-subluxation. RESULTS: Mean prediction error using the Barrett formula was -0.35 ± 1.0 D. Higher axial length (≥25.5 mm) was associated with greater prediction error (-0.72 ± 1.11 D vs -0.18 ± 0.91 D, P = .048). Twelve re-subluxations occurred over a mean follow-up period of 30.28 ± 41.86 months. The predicted 50% survival of iris-sutured lenses was 114.25 months. CONCLUSIONS AND RELEVANCE: Iris-suture fixation may require moderate lens power adjustment to compensate for prediction error, especially in eyes with higher axial length. Longer follow-up demonstrates that iris-suture fixation remains a viable technique, yet re-subluxations require routine monitoring of such eyes.

Robotic Retinal Surgery Impacts on Scleral Forces: In Vivo Study.

Purpose: This study aims to map force interaction between instrument and sclera of in vivo rabbits during retinal procedures, and verify if a robotic active force control could prevent unwanted increase of forces on the sclera. Methods: Experiments consisted in the performance of intraocular movements of a force sensing instrument, adjacent to the retinal surface, in radial directions, from the center to the periphery and back, and compared manual manipulations with robotic assistance and also robotic assistance with an active force control. This protocol was approved by the Animal Use and Ethical Committee and experiments were according to ARVO Statement of Animal Use. Results: Mean forces using manual manipulations were 115 ± 51 mN. Using robotic assistance, mean forces were 118 ± 49 mN. Using an active force control method, overall mean forces reduced to 69 ± 15, with a statistical difference compared with other methods (P < 0.001). Comparing intraocular directions, superior sector required higher forces and the force control method reduced differences in forces between users and retained the same force pattern between them. Conclusions: Results validate that the introduction of robotic assistance might increase the dynamic interactions between instrument and sclera, and the addition of an active force control method reduces the forces at levels lower than manual manipulations. Translational Relevance: All marketing benefits from extreme accuracy and stability from robots, however, redundancy of safety mechanisms during intraocular manipulations, especially on force control and surgical awareness, would allow all utility of robotic assistance in ophthalmology.

Hybrid Robot-assisted Frameworks for Endomicroscopy Scanning in Retinal Surgeries.

High-resolution real-time intraocular imaging of retina at the cellular level is very challenging due to the vulnerable and confined space within the eyeball as well as the limited availability of appropriate modalities. A probe-based confocal laser endomicroscopy (pCLE) system, can be a potential imaging modality for improved diagnosis. The ability to visualize the retina at the cellular level could provide information that may predict surgical outcomes. The adoption of intraocular pCLE scanning is currently limited due to the narrow field of view and the micron-scale range of focus. In the absence of motion compensation, physiological tremors of the surgeons' hand and patient movements also contribute to the deterioration of the image quality. Therefore, an image-based hybrid control strategy is proposed to mitigate the above challenges. The proposed hybrid control strategy enables a shared control of the pCLE probe between surgeons and robots to scan the retina precisely, with the absence of hand tremors and with the advantages of an image-based auto-focus algorithm that optimizes the quality of pCLE images. The hybrid control strategy is deployed on two frameworks - cooperative and teleoperated. Better image quality, smoother motion, and reduced workload are all achieved in a statistically significant manner with the hybrid control frameworks.

Robot-assisted tremor control for performance enhancement of retinal microsurgeons.

Pars plana vitrectomy is a challenging, minimally invasive microsurgical procedure due to its intrinsic manoeuvres and physiological limits that constrain human capability. An important human limitation is physiological hand tremor, which can significantly increase the risk of iatrogenic retinal damage resulting from unintentional manoeuvres that affect anatomical and functional surgical outcomes. The limitations imposed by normal physiological tremor are more evident and challenging during 'micron-scale' manoeuvres such as epiretinal membrane and internal limiting membrane peeling, and delicate procedures requiring coordinated bimanual surgery such as tractional retinal detachment repair. Therefore, over the previous three decades, attention has turned to robot-assisted surgical devices to overcome these challenges. Several systems have been developed to improve microsurgical accuracy by cancelling hand tremor and facilitating faster, safer and more effective microsurgeries. By markedly reducing tremor, microsurgical precision is improved to a level beyond present human capabilities. In conclusion, robotics offers potential advantages over free-hand microsurgery as it is currently performed during ophthalmic surgery and opens the door to a new class of revolutionary microsurgical modalities. The skills transfer that is beyond human capabilities to robotic technology is a logical next step in microsurgical evolution.

Artificial intelligence, robotics and eye surgery: are we overfitted?

Eye surgery, specifically retinal micro-surgery involves sensory and motor skill that approaches human boundaries and physiological limits for steadiness, accuracy, and the ability to detect the small forces involved. Despite assumptions as to the benefit of robots in surgery and also despite great development effort, numerous challenges to the full development and adoption of robotic assistance in surgical ophthalmology, remain. Historically, the first in-human-robot-assisted retinal surgery occurred nearly 30 years after the first experimental papers on the subject. Similarly, artificial intelligence emerged decades ago and it is only now being more fully realized in ophthalmology. The delay between conception and application has in part been due to the necessary technological advances required to implement new processing strategies. Chief among these has been the better matched processing power of specialty graphics processing units for machine learning. Transcending the classic concept of robots performing repetitive tasks, artificial intelligence and machine learning are related concepts that has proven their abilities to design concepts and solve problems. The implication of such abilities being that future machines may further intrude on the domain of heretofore "human-reserved" tasks. Although the potential of artificial intelligence/machine learning is profound, present marketing promises and hype exceeds its stage of development, analogous to the seventieth century mathematical "boom" with algebra. Nevertheless robotic systems augmented by machine learning may eventually improve robot-assisted retinal surgery and could potentially transform the discipline. This commentary analyzes advances in retinal robotic surgery, its current drawbacks and limitations, and the potential role of artificial intelligence in robotic retinal surgery.

A Novel Semi-Autonomous Control Framework for Retina Confocal Endomicroscopy Scanning.

In this paper, a novel semi-autonomous control framework is presented for enabling probe-based confocal laser endomicroscopy (pCLE) scan of the retinal tissue. With pCLE, retinal layers such as nerve fiber layer (NFL) and retinal ganglion cell (RGC) can be scanned and characterized in real-time for an improved diagnosis and surgical outcome prediction. However, the limited field of view of the pCLE system and the micron-scale optimal focus distance of the probe, which are in the order of physiological hand tremor, act as barriers to successful manual scan of retinal tissue. Therefore, a novel sensorless framework is proposed for real-time semi-autonomous endomicroscopy scanning during retinal surgery. The framework consists of the Steady-Hand Eye Robot (SHER) integrated with a pCLE system, where the motion of the probe is controlled semi-autonomously. Through a hybrid motion control strategy, the system autonomously controls the confocal probe to optimize the sharpness and quality of the pCLE images, while providing the surgeon with the ability to scan the tissue in a tremor-free manner. Effectiveness of the proposed architecture is validated through experimental evaluations as well as a user study involving 9 participants. It is shown through statistical analyses that the proposed framework can reduce the work load experienced by the users in a statistically-significant manner, while also enhancing their performance in retaining pCLE images with optimized quality.

The Question of a Role for Statins in Age-Related Macular Degeneration.

Age-related macular degeneration (AMD) is the leading cause of irreversible central vision loss in patients over the age of 65 years in industrialized countries. Epidemiologic studies suggest that high dietary fat intake is a risk factor for the development and progression of both vascular and retinal disease. These, and other associations, suggest a hypothesis linking elevated cholesterol and AMD progression. It follows, therefore, that cholesterol-lowering medications, such as statins, may influence the onset and progression of AMD. However, the findings have been inconclusive as to whether statins play a role in AMD. Due to the significant public health implications of a potential inhibitory effect of statins on the onset and progression of AMD, it is important to continually evaluate emerging findings germane to this question.

Posterior Vitreous Detachment as Observed by Wide-Angle OCT Imaging.

PURPOSE: Posterior vitreous detachment (PVD) plays an important role in vitreoretinal interface disorders. Historically, observations of PVD using OCT have been limited to the macular region. The purpose of this study is to image the wide-angle vitreoretinal interface after PVD in normal subjects using montaged OCT images. DESIGN: An observational cross-sectional study. PARTICIPANTS: A total of 144 healthy eyes of 98 normal subjects aged 21 to 95 years (51.4±22.0 [mean ± standard deviation]). METHODS: Montaged images of horizontal and vertical OCT scans through the fovea were obtained in each subject. MAIN OUTCOME MEASURES: Montaged OCT images. RESULTS: By using wide-angle OCT, we imaged the vitreoretinal interface from the macula to the periphery. PVD was classified into 5 stages: stage 0, no PVD (2 eyes, both aged 21 years); stage 1, peripheral PVD limited to paramacular to peripheral zones (88 eyes, mean age 38.9±16.2 years, mean ± standard deviation); stage 2, perifoveal PVD extending to the periphery (12 eyes, mean age 67.9±8.4 years); stage 3, peripapillary PVD with persistent vitreopapillary adhesion alone (7 eyes, mean age 70.9±11.9 years); stage 4, complete PVD (35 eyes, mean age 75.1±10.1 years). All stage 1 PVDs (100%) were observed in the paramacular to peripheral region where the vitreous gel adheres directly to the cortical vitreous and retinal surface. After progression to stage 2 PVD, the area of PVD extends posteriorly to the perifovea and anteriorly to the periphery. Vitreoschisis was observed in 41.2% at PVD initiation (stage 1a). CONCLUSIONS: Whereas prior work suggests that PVD originates in the perifoveal region and after the sixth decade, our observations demonstrate that (1) PVD first appears even in the third decade of life and gradually appears more extensively throughout life; (2) more than 40% of eyes without fundus diseases at their PVD initiation are associated with vitreoschisis; and (3) PVD is first noted primarily in the paramacular-peripheral region where vitreous gel adheres to the retinal surface and is noted to be more extensive in older ages to ultimately involve the fovea.

Robot-assisted vitreoretinal surgery: current perspectives.

Vitreoretinal microsurgery is among the most technically challenging of the minimally invasive surgical techniques. Exceptional precision is required to operate on micron scale targets presented by the retina while also maneuvering in a tightly constrained and fragile workspace. These challenges are compounded by inherent limitations of the unassisted human hand with regard to dexterity, tremor and precision in positioning instruments. The limited human ability to visually resolve targets on the single-digit micron scale is a further limitation. The inherent attributes of robotic approaches therefore, provide logical, strategic and promising solutions to the numerous challenges associated with retinal microsurgery. Robotic retinal surgery is a rapidly emerging technology that has witnessed an exponential growth in capabilities and applications over the last decade. There is now a worldwide movement toward evaluating robotic systems in an expanding number of clinical applications. Coincident with this expanding application is growth in the number of laboratories committed to "robotic medicine". Recent technological advances in conventional retina surgery have also led to tremendous progress in the surgeon's capabilities, enhanced outcomes, a reduction of patient discomfort, limited hospitalization and improved safety. The emergence of robotic technology into this rapidly advancing domain is expected to further enhance important aspects of the retinal surgery experience for the patients, surgeons and society.

Towards Bimanual Robot-Assisted Retinal Surgery: Tool-to-Sclera Force Evaluation.

The performance of retinal microsurgery often requires the coordinated use of both hands. During bimanual retinal surgery, dominant hand performance may be negatively impacted by poor non-dominant hand assistance. Therefore understanding bimanual latent determinants, and establishing safety criteria for bimanual manipulation is relevant to robotic development and to eventual patient care. In this paper, we present a preliminary study to quantitatively evaluate one aspect of bimanual tool use in retinal surgery. Two force sensing tools were designed and fabricated using fiber Bragg grating sensors. Tool-to-sclera contact force is measured using the developed tools and analyzed. The tool forces were recorded during five basic surgical maneuvers typical of retinal surgery. Two subjects are involved in experiments, including one clinician and one engineer. For comparison, all manipulations were replicated under robot-assisted conditions. The results indicate that the average tool-to-sclera force recorded from the dominant hand tool is significantly higher than that from the non-dominant hand tool (p = 0.004). Moreover, the average forces under robot-assisted conditions with the present steady hand robot is notably higher than freehand conditions(p = 0.01). The forces obtained from the dominant and not-dominant hand instruments indicate a weak correlation.

User Behavior Evaluation in Robot-Assisted Retinal Surgery.

Retinal microsurgery is technically demanding and requires high surgical skill with very little room for manipulation error. The introduction of robotic assistance has the potential to enhance and expand a surgeon's manipulation capabilities during retinal surgery, i.e., improve precision, cancel physiological hand tremor, and provide sensing information. However, surgeon performance may also be negatively impacted by robotic assistance due to robot structural stiffness and nonintuitive controls. In complying with robotic constraints, the surgeon loses the dexterity of the human hand. In this paper, we present a preliminary experimental study to evaluate user behavior when affected by robotic assistance during mock retinal surgery. In these experiments user behavior is characterized by measuring the forces applied by the user to the sclera, the tool insertion/retraction speed, the tool insertion depth relative to the scleral entry point, and the duration of surgery. The users' behavior data is collected during three mock retinal surgery tasks with four users. Each task is conducted using both freehand and robot-assisted techniques. The univariate user behavior and the correlations of multiple parameters of user behavior are analyzed. The results show that robot assistance prolongs the duration of the surgery and increases the manipulation forces applied to sclera, but refines the insertion velocity and eliminates hand tremor.