Laparoscopic surgery has become the preferred approach for a wide range of abdominal procedures because of reduced postoperative pain, shorter hospital stay, earlier recovery, and better cosmetic outcomes. Despite these benefits, it is associated with unique physiological changes resulting from carbon dioxide pneumoperitoneum (CO₂ inflation of the abdomen) and patient positioning, particularly the Trendelenburg position (a head-down tilt of the operating table). These changes influence cardiovascular, respiratory, cerebral, and ocular physiology and have implications for perioperative patient safety. Carbon dioxide insufflation increases intra-abdominal pressure, reducing venous return from the abdomen and impairing cerebral and episcleral venous drainage (outflow of blood from the veins over the white of the eye). Simultaneously, Trendelenburg positioning increases hydrostatic pressure within the cranial and orbital venous systems. Together these factors can produce transient elevations in intracranial pressure (ICP) and intraocular pressure (IOP). Raised end-tidal carbon dioxide (EtCO₂, the CO₂ concentration measured at the end of each exhaled breath), prolonged pneumoperitoneum, and increased central venous pressure may further augment these changes. Although usually well tolerated in healthy individuals, they may become clinically relevant in patients with impaired ocular autoregulation, glaucoma (optic nerve damage typically associated with raised eye pressure), or reduced optic nerve reserve. Optic nerve sheath diameter (ONSD), measured by bedside ocular ultrasonography, has emerged as a reliable, rapid, non-invasive surrogate marker for raised intracranial pressure. Because the subarachnoid space surrounding the optic nerve communicates directly with the intracranial cerebrospinal fluid compartment, a rise in intracranial pressure produces measurable expansion of the optic nerve sheath. Simultaneous assessment of ONSD and IOP therefore provides complementary information on ocular and intracranial responses during laparoscopic surgery. Previous studies have demonstrated transient increases in IOP during laparoscopic procedures, particularly those requiring prolonged pneumoperitoneum and steep Trendelenburg positioning. However, most evaluated individual procedures or assessed either IOP or ONSD alone. Comparative evaluation of different laparoscopic abdominal procedures using a standardised anaesthetic technique and simultaneous measurement of both parameters remains limited, and data in glaucoma-suspect patients are scarce. The present study was undertaken to compare perioperative changes in IOP and ONSD among patients undergoing laparoscopic cholecystectomy, appendectomy, and TAPP/TEP inguinal hernia repair, to evaluate recovery kinetics, and to compare responses between glaucoma-suspect and non-glaucoma patients. We hypothesized that procedures requiring prolonged pneumoperitoneum and steeper Trendelenburg positioning would produce greater increases in IOP and ONSD than procedures with shorter operative duration and less extreme positioning.

Study Design and Setting This prospective observational comparative study was conducted in the Departments of General Surgery and Ophthalmology of a tertiary care teaching hospital in North India, in accordance with the STARD 2015 guidelines (Standards for Reporting of Diagnostic Accuracy Studies — a reporting checklist for studies that use a test, here ONSD, as a marker) and the Declaration of Helsinki, after Institutional Ethics Committee approval and registration with the Clinical Trials Registry–India. Written informed consent was obtained from all participants before enrolment. Study Population A total of 150 adult patients scheduled for elective laparoscopic abdominal surgery were enrolled consecutively between 20 January 2023 and 30 April 2024. Patients were allocated into three equal groups — laparoscopic cholecystectomy, laparoscopic appendectomy, and laparoscopic TAPP/TEP inguinal hernia repair — with 50 patients in each group. Sample Size Sample size was based on previously reported differences in IOP during laparoscopic surgery. Assuming a standard deviation of 6 mmHg, a clinically significant difference of 3.5 mmHg, a two-sided α error of 0.05 (Zα/2 = 1.96) and a power of 80% (Zβ = 0.84), the minimum required sample was approximately 46 patients per group. To allow for exclusions and incomplete data, 50 patients were included per group, giving 150 participants in total. Inclusion Criteria Patients aged 18–65 years undergoing elective laparoscopic cholecystectomy, appendectomy, or TAPP/TEP inguinal hernia repair were eligible. All participants underwent preoperative ophthalmological evaluation and had normal intraocular pressure, a healthy optic disc, and no other significant ocular pathology. Exclusion Criteria Patients with established glaucoma, previous ocular surgery, active ocular inflammation, corneal pathology interfering with tonometry, orbital disease, or contraindications to ocular ultrasonography were excluded, as were patients with neurological disorders known to affect intracranial pressure. Glaucoma-suspect patients were eligible and were defined as individuals with ocular hypertension (IOP > 21 mmHg) and/or suspicious optic disc or retinal nerve fibre layer findings without a confirmed diagnosis of glaucoma; they were analysed separately per the predefined protocol. Patients with only a positive family history of glaucoma, in the absence of clinical findings, were not classified as glaucoma suspects. Anaesthetic and Surgical Protocol All patients received a single standardised general anaesthesia protocol administered by experienced anaesthesiologists. Pneumoperitoneum was established with carbon dioxide insufflation according to institutional practice. Laparoscopic cholecystectomy was performed in reverse Trendelenburg (approximately 15–20° head-up), appendectomy in moderate Trendelenburg (approximately 15° head-down), and TAPP/TEP hernia repair in steep Trendelenburg (approximately 30–45° head-down). Measurement of Intraocular Pressure and Optic Nerve Sheath Diameter Intraocular pressure was measured with a calibrated handheld Tono-Pen tonometer (a pen-shaped device that touches the anaesthetised cornea to read eye pressure) after topical ocular anaesthesia. Optic nerve sheath diameter was measured by high-frequency ocular ultrasonography using a closed-eyelid technique with sterile coupling gel, 3 mm posterior to the globe in the transverse plane. Three measurements were recorded from each eye and the mean of both eyes was used for analysis. All measurements were performed by a single experienced ophthalmologist to minimise interobserver variability. Measurements were obtained at baseline before induction, immediately after induction, during pneumoperitoneum (15 and 30 minutes), at the end of surgery, and during the postoperative recovery period according to the predefined protocol. Outcome Measures The primary outcome was the change in IOP and ONSD during laparoscopic surgery. Secondary outcomes were comparison among the three procedures, assessment of recovery kinetics, and subgroup analysis of glaucoma-suspect patients. Statistical Analysis Statistical analysis was performed using SPSS version 25.0. Continuous variables are presented as mean ± standard deviation and categorical variables as frequencies and percentages. Normality was assessed with the Shapiro–Wilk test. Between-group comparisons used one-way analysis of variance (ANOVA) or the Kruskal–Wallis test as appropriate, and serial perioperative measurements were analysed by repeated-measures ANOVA. Optimal ONSD/IOP thresholds were derived using the Youden index (a statistic that identifies the cut-off maximising sensitivity plus specificity). Effect sizes and 95% confidence intervals. A two-sided p value < 0.05 was considered statistically significant.

Baseline Characteristics A total of 150 patients were enrolled and completed the study, with 50 each undergoing laparoscopic cholecystectomy, appendectomy, and TAPP/TEP inguinal hernia repair (Table 1). The groups were comparable for age, BMI, ASA physical status, hypertension, diabetes mellitus, and the proportion of glaucoma suspects (all p > 0.05). A significant difference was seen in sex distribution, with a marked male predominance in the TAPP/TEP group (86%) compared with cholecystectomy (42%) and appendectomy (56%) (p < 0.001); this is addressed in the Discussion. Table 1. Baseline demographic and clinical characteristics according to surgical procedure Characteristic Cholecystectomy (n=50) Appendectomy (n=50) TAPP/TEP (n=50) p-value Age (years), mean ± SD 44.8 ± 12.3 38.6 ± 13.1 46.2 ± 11.8 0.062 Male sex, n (%) 21 (42.0) 28 (56.0) 43 (86.0) <0.001 BMI (kg/m²), mean ± SD 25.6 ± 3.8 24.9 ± 3.5 25.3 ± 3.9 0.648 Hypertension, n (%) 12 (24.0) 8 (16.0) 10 (20.0) 0.602 Diabetes mellitus, n (%) 9 (18.0) 6 (12.0) 7 (14.0) 0.726 ASA I/II/III, n 18/26/6 22/24/4 17/28/5 0.791 Glaucoma suspects, n (%) 10 (20.0) 10 (20.0) 10 (20.0) 1.000 Perioperative Characteristics Perioperative characteristics are shown in Table 2. TAPP/TEP repair had significantly longer operative duration and pneumoperitoneum time than cholecystectomy or appendectomy (both p < 0.001), and higher peak EtCO₂ (p = 0.009). Steep Trendelenburg positioning was used predominantly during TAPP/TEP (78%), whereas only a small proportion of cholecystectomy or appendectomy patients required a head-down position (p < 0.001). Mean pneumoperitoneum pressure was comparable across procedures. Table 2. Perioperative characteristics according to surgical procedure Variable Cholecystectomy (n=50) Appendectomy (n=50) TAPP/TEP (n=50) p-value Duration of surgery (min) 72 ± 18 58 ± 16 94 ± 22 <0.001 Duration of pneumoperitoneum (min) 58 ± 15 46 ± 14 82 ± 19 <0.001 Pneumoperitoneum pressure (mmHg) 12.5 ± 1.0 12.2 ± 0.8 12.8 ± 1.1 0.071 Peak EtCO₂ (mmHg) 37.4 ± 3.2 36.8 ± 3.5 39.1 ± 3.7 0.009 Head-down (Trendelenburg) tilt used, n (%) 4 (8.0) 6 (12.0) 39 (78.0) <0.001 Changes in Intraocular Pressure Serial intraoperative IOP changes are shown in Table 3. Baseline IOP was comparable across groups. After induction, IOP fell slightly in all patients. After pneumoperitoneum a progressive rise occurred, peaking at 30 minutes of pneumoperitoneum. The greatest increase was in TAPP/TEP, where mean IOP rose from 15.0 ± 2.2 mmHg at baseline to 21.2 ± 3.5 mmHg (p < 0.001); cholecystectomy and appendectomy showed smaller but significant increases. After release of pneumoperitoneum, IOP declined toward baseline, and by 30 minutes after extubation had nearly returned to preoperative levels in all groups. Table 3. Changes in intraocular pressure during laparoscopic procedures (mmHg) Time point Cholecystectomy Appendectomy TAPP/TEP p-value Baseline 15.1 ± 2.3 14.8 ± 2.4 15.0 ± 2.2 0.812 After induction 13.4 ± 2.1 13.2 ± 2.0 13.1 ± 2.1 0.754 15 min pneumoperitoneum 17.2 ± 2.8 16.5 ± 2.7 18.9 ± 3.1 0.001 30 min pneumoperitoneum 18.4 ± 3.0 17.3 ± 2.9 21.2 ± 3.5 <0.001 End of surgery 17.1 ± 2.9 16.4 ± 2.6 19.8 ± 3.2 <0.001 30 min post-extubation 15.6 ± 2.4 15.2 ± 2.2 16.3 ± 2.7 0.083 Changes in Optic Nerve Sheath Diameter Serial ONSD changes are shown in Table 4. Baseline ONSD did not differ across groups. As with IOP, ONSD rose progressively after pneumoperitoneum, peaking during surgery before declining during recovery. The largest increase was in TAPP/TEP, where mean ONSD rose from 4.67 ± 0.31 mm to 5.26 ± 0.39 mm (p < 0.001), with smaller increases during cholecystectomy and appendectomy. Most patients showed near-complete normalisation of ONSD by 30 minutes after extubation. Table 4. Changes in optic nerve sheath diameter during laparoscopic procedures (mm) Time point Cholecystectomy Appendectomy TAPP/TEP p-value Baseline 4.68 ± 0.32 4.64 ± 0.29 4.67 ± 0.31 0.874 After induction 4.59 ± 0.28 4.57 ± 0.27 4.60 ± 0.30 0.912 15 min pneumoperitoneum 4.89 ± 0.34 4.81 ± 0.31 5.08 ± 0.37 0.002 30 min pneumoperitoneum 5.01 ± 0.35 4.90 ± 0.33 5.26 ± 0.39 <0.001 End of surgery 4.92 ± 0.34 4.85 ± 0.31 5.15 ± 0.36 <0.001 30 min post-extubation 4.72 ± 0.30 4.69 ± 0.28 4.79 ± 0.32 0.275 Subgroup analysis revealed that glaucoma-suspect patients exhibited significantly higher baseline and peak intraocular pressure values compared with non-glaucoma patients. Additionally, glaucoma suspects demonstrated greater increases in optic nerve sheath diameter and required a longer duration for normalization of perioperative changes (Table 5). Glaucoma-Suspect Subgroup Analysis Thirty patients met the predefined criteria for glaucoma suspicion (Table 5). Compared with non-glaucoma patients, they had significantly higher baseline IOP (17.2 ± 2.4 vs 14.5 ± 2.1 mmHg, p < 0.001) and higher peak intraoperative IOP (23.8 ± 3.2 vs 18.9 ± 3.1 mmHg, p < 0.001). Baseline ONSD was comparable, but glaucoma suspects had a greater rise in ONSD during surgery (mean rise 0.57 vs 0.36 mm) and significantly delayed recovery, requiring 48 ± 15 minutes to normalise versus 33 ± 12 minutes (p < 0.001). These findings indicate greater perioperative ocular physiological stress in glaucoma-suspect patients. Table 5. Peak IOP and ONSD in glaucoma suspects versus non-glaucoma patients Parameter Glaucoma suspects (n=30) Non-glaucoma (n=120) p-value Baseline IOP (mmHg) 17.2 ± 2.4 14.5 ± 2.1 <0.001 Peak IOP (mmHg) 23.8 ± 3.2 18.9 ± 3.1 <0.001 Increase in IOP (mmHg) 6.6 ± 2.1 4.4 ± 1.8 <0.001 Baseline ONSD (mm) 4.72 ± 0.30 4.65 ± 0.31 0.284 Peak ONSD (mm) 5.29 ± 0.35 5.01 ± 0.36 0.001 Time to normalisation (min) 48 ± 15 33 ± 12 <0.001

This prospective comparative study demonstrated that laparoscopic abdominal surgery produces significant but reversible increases in both IOP and ONSD. Of the three procedures, TAPP/TEP inguinal hernia repair produced the greatest changes and appendectomy the smallest. Glaucoma-suspect patients showed significantly greater increases in both parameters together with delayed recovery. The rise in IOP is consistent with the known consequences of carbon dioxide pneumoperitoneum. Raised intra-abdominal pressure increases intrathoracic and central venous pressure, impairing episcleral venous drainage; the resulting reduction in aqueous humour outflow transiently raises IOP. At the same time, carbon dioxide absorption during prolonged pneumoperitoneum can cause cerebral vasodilatation, increasing intracranial blood volume and pressure, which is reflected by enlargement of the optic nerve sheath. The head-down position appears to contribute independently to the rise in IOP and ONSD. The single largest intraoperative increase occurs immediately after assuming the Trendelenburg position and rises further with time, over and above the effect of pneumoperitoneum alone. Because this effect is both degree- and time-dependent, the steep Trendelenburg used for TAPP/TEP provides a coherent explanation for the marked elevations in this group, in which longer operative duration, prolonged pneumoperitoneum, higher EtCO₂ and steep positioning likely act synergistically to impair cerebral and orbital venous drainage. Comparison with Previous Literature The magnitude and direction of the changes observed here are consistent with the published literature, and the procedure-specific gradient we found fits neatly between the low-Trendelenburg and steep-Trendelenburg extremes reported by others (Table 6). In laparoscopic colorectal surgery, standard pneumoperitoneum produced only a mild, reversible IOP rise of about 4 mmHg, with a larger rise when the Trendelenburg position was used, mirroring the modest increases we saw in cholecystectomy and appendectomy. At the opposite extreme, robot-assisted radical prostatectomy in steep Trendelenburg has repeatedly produced much larger increases — on the order of 13 mmHg above pre-induction values, with peak intraoperative pressures reaching 30–36 mmHg — exceeding even our TAPP/TEP group, in which the head-down tilt is steep but the operative duration is shorter than a typical prostatectomy. Studies using ONSD during laparoscopic cholecystectomy have likewise shown that the sheath widens in direct proportion to the intra-abdominal pressure applied, supporting our parallel IOP and ONSD findings. The peak IOP in our glaucoma-suspect subgroup (23.8 mmHg) is comparable to the peak pressures reported in glaucomatous eyes during steep-Trendelenburg surgery, reinforcing the view that these patients have reduced ocular reserve. Table 6. Comparison of the present findings with selected published studies The fall in IOP immediately after induction, seen in all three groups, is also consistent with previous work: general anaesthetic agents reduce sympathetic activity, lower extraocular muscle tone, and decrease aqueous humour production, producing a transient fall in IOP before the effects of pneumoperitoneum appear. Simultaneous measurement of ONSD and IOP is a strength of this study. IOP reflects changes within the eye, whereas ONSD gives an indirect assessment of intracranial pressure; the parallel rise in both supports the view that pneumoperitoneum and positioning affect ocular and intracranial venous haemodynamics together. The glaucoma-suspect subgroup deserves particular attention. Despite having no established diagnosis, these patients showed higher baseline and peak IOP and delayed recovery, suggesting reduced ocular physiological reserve. Although the transient elevations seen here are unlikely to cause clinically significant visual impairment in healthy individuals, susceptible patients may benefit from individualised anaesthetic management, avoidance of unnecessarily prolonged steep Trendelenburg, maintenance of normocapnia (normal blood CO₂ levels), and the lowest effective pneumoperitoneum pressure. Sex Distribution The three groups differed significantly in sex distribution, with a marked male predominance in the TAPP/TEP group (86%) compared with cholecystectomy (42%) and appendectomy (56%). We acknowledge this as an unadjusted between-group difference. However, it reflects the true epidemiology of the underlying disease rather than a selection or recruitment bias: inguinal hernia is far more common in men than in women, with a reported lifetime risk of approximately 27% in men versus 3% in women, and men account for the large majority of inguinal hernia repairs worldwide (for example, roughly 90% of repairs in a nationwide Danish cohort), giving an approximate male-to-female ratio of about 8–9:1. A predominantly male TAPP/TEP group is therefore expected and representative of patients who actually undergo this operation. Nonetheless, because sex was not balanced across groups and multivariable adjustment was not performed, the possibility that sex contributed to the observed between-group differences cannot be fully excluded; this is noted among the limitations.

Laparoscopic abdominal surgery causes significant but reversible increases in intraocular pressure and optic nerve sheath diameter, reflecting transient alterations in ocular and intracranial physiology associated with carbon dioxide pneumoperitoneum and surgical positioning. Among the three procedures, TAPP/TEP inguinal hernia repair produced the greatest elevations in both parameters, likely because of prolonged pneumoperitoneum, higher end-tidal carbon dioxide, and routine steep Trendelenburg positioning. Glaucoma-suspect patients showed significantly greater increases in IOP and ONSD together with delayed recovery, suggesting reduced ocular reserve and increased susceptibility to perioperative haemodynamic change. Although the changes were transient and resolved postoperatively, the findings support procedure-specific perioperative risk assessment and reinforce the importance of minimising pneumoperitoneum pressure, limiting steep Trendelenburg time where feasible, and maintaining optimal intraoperative ventilation. Future multicentre studies with longer follow-up are warranted to determine whether repeated or prolonged exposure has any long-term significance in susceptible patients. CLINICAL IMPLICATIONS These findings have practical implications for surgeons and anaesthesiologists. Patients undergoing prolonged laparoscopic procedures, particularly TAPP/TEP repair requiring steep Trendelenburg positioning, experience greater ocular physiological stress than those undergoing shorter procedures. A brief preoperative ophthalmological screen to identify glaucoma suspects is reasonable before prolonged steep-Trendelenburg laparoscopy. In such patients, maintaining normocapnia, avoiding unnecessarily prolonged pneumoperitoneum, using the lowest effective insufflation pressure, and limiting steep head-down time may reduce transient elevations in intraocular and intracranial pressure. In selected high-risk patients, perioperative monitoring with ocular ultrasonography or tonometry may allow early recognition of exaggerated responses. These measures are low-cost and feasible in most Indian operating theatres. STRENGTHS OF THE STUDY This study has several methodological strengths. First, it used a prospective design, which reduces recall and selection bias compared with retrospective work. Second, sample sizes were equal across the three surgical groups (50 each), improving the fairness of between-group comparison. Third, a single standardised general anaesthesia protocol was applied to every patient, removing anaesthetic technique as a confounding variable. Fourth, and distinctively, IOP and ONSD were assessed simultaneously, providing a more comprehensive picture of combined ocular and intracranial physiological change than studies evaluating either parameter alone. Fifth, all measurements were performed by a single experienced ophthalmologist using standardised techniques, maximising internal measurement consistency. Sixth, the inclusion of a predefined, clinically relevant glaucoma-suspect subgroup adds information that has been inadequately explored in previous studies. LIMITATIONS Several limitations should be acknowledged. First, this was a single-centre study, which may limit generalisability. Second, optic nerve sheath diameter is an indirect surrogate for intracranial pressure rather than a direct measurement. Third, all ONSD and IOP measurements were performed by a single observer; while this maximises internal consistency, no formal interobserver reliability assessment (for example an intraclass correlation coefficient, ICC, or Cohen's kappa — statistics that quantify how closely independent observers agree) was undertaken, so the reproducibility of the measurements across different operators cannot be confirmed. Fourth, follow-up was limited to the immediate perioperative period, so long-term ophthalmic outcomes were not assessed, and no formal postoperative visual outcome assessment (such as visual acuity, visual fields, or retinal nerve fibre layer imaging) was performed; established glaucoma and confirmed glaucoma suspects were excluded. Fifth, although a standardised anaesthetic protocol was used, the groups differed in operative duration, pneumoperitoneum time, EtCO₂ and sex, and multivariable adjustment was not performed effect sizes and 95% confidence intervals were not calculated. Finally, the glaucoma-suspect subgroup was relatively small and heterogeneous, and larger multicentre studies are required to validate these findings.

1. Litynski GS. Highlights in the history of laparoscopy. Surg Innov. 1998;5(1):16-31. 2. Grabowski JE, Talamini MA. Physiological effects of pneumoperitoneum. Journal of Gastrointestinal Surgery. 2009 May;13(5):1009-16. 3. Weinreb RN, Khaw PT. Primary open-angle glaucoma. The lancet. 2004 May 22;363(9422):1711-20. 4. Hwang JW, Oh AY, Hwang DW, Jeon YT, Kim YB, Park SH. Does intraocular pressure increase during laparoscopic surgeries? It depends on anesthetic drugs and the surgical position. Surgical Laparoscopy Endoscopy & Percutaneous Techniques. 2013 Apr 1;23(2):229-32. 5. Van Wicklin SA. Systematic review and meta-analysis of the effect of Trendelenburg position on intraocular pressure in adults undergoing surgery. Ann Laparosc Endosc Surg 2019;4. 6. Van Wicklin SA. Systematic review and meta-analysis of prone position on intraocular pressure in adults undergoing surgery. International journal of spine surgery. 2020 Apr 30;14(2):195-9. 7. Ben-Haim M, Rosenthal RJ. Causes of arterial hypertension and splachnic ischemia during acute elevations in intra-abdominal pressure with CO2 pneumoperitoneum: a complex central nervous system mediated response. International journal of colorectal disease. 1999 Dec;14(4):227-36. 8. Kim EJ, Koo BN, Choi SH, Park K, Kim MS. Ultrasonographic optic nerve sheath diameter for predicting elevated intracranial pressure during laparoscopic surgery: a systematic review and meta-analysis. Surgical Endoscopy. 2018 Jan;32(1):175-82. 9. Lee YY, Lee H, Park HS, Kim WJ, Baik HJ, Kim DY. Optic nerve sheath diameter changes during gynecologic surgery in the Trendelenburg position: comparison of propofol-based total intravenous anesthesia and sevoflurane anesthesia. Anesth Pain Med (Seoul). 2019 Oct 31;14(4):393-400. 10. Adisa AO, Onakpoya OH, Adenekan AT, Awe OO. Intraocular Pressure Changes With Positioning During Laparoscopy. JSLS. 2016 Oct-Dec;20(4):e2016.00078. 11. Kaur G, Sharma M, Kalra P, Purohit S, Chauhan K. Intraocular Pressure Changes during Laparoscopic Surgery in Trendelenburg Position in Patients Anesthetized with Propofol-based Total Intravenous Anesthesia Compared to Sevoflurane Anesthesia: A Comparative Study. Anesth Essays Res. 2018 Jan-Mar;12(1):67-72. 12. Bossuyt PM, et al. STARD 2015: an updated list of essential items for reporting diagnostic accuracy studies. BMJ 2015;351:h5527. Add the inguinal-hernia incidence reference(s) cited in the Discussion (e.g. Kingsnorth & LeBlanc 2003; Burcharth et al. 2013).