Laser speckle contrast imaging enables perfusion monitoring of the anterior segment during strabismus surgery: a study on the horizontal rectus muscles.

BACKGROUND: A dreaded complication of strabismus surgery is anterior segment ischaemia (ASI), caused by damage to the anterior ciliary arteries. To avoid ASI, a maximum of two rectus muscles are operated on at a time. However, these surgical protocols are based on empirical observations of clinical outcome, rather than objective perfusion measurements. There is no method available for perioperative, real-time perfusion measurements during ocular muscle surgery. The aims of this study were to investigate whether laser speckle contrast imaging (LSCI) could be used for such measurements, and to monitor perfusion during strabismus surgery on one or two horizontal rectus muscles. METHODS: Forty-four eyes in 44 patients with horizontal strabismus underwent corrective surgery involving medial and/or lateral rectus muscle detachment. Perfusion in the adjacent paralimbal and iris tissue was monitored with LSCI. RESULTS: When the first horizontal rectus muscle was detached perfusion in the adjacent paralimbal tissue decreased by 23% (p<0.0001), and by 12% (p<0.0001) when the second muscle was detached. The iris perfusion decreased by 5% (p<0.05) when the first muscle was detached but showed no significant decrease as the second muscle was cut. CONCLUSION: This is the first study showing that perfusion of the anterior segment can be monitored non-invasively with LSCI during strabismus surgery. In this cohort, two horizontal rectus muscles were detached with only a small decrease in the anterior segment circulation. Future studies are required for complete mapping of the effect of surgery on multiple ocular muscles on the anterior segment circulation.

Erratum to: Successful repair of a full upper eyelid defect following traumatic amputation by simply suturing it back in place, JPRAS Open volume 19, March 2019, pages 73-76.

[This corrects the article DOI: 10.1016/j.jpra.2018.12.002.].

The Success of Unilateral Surgery for Constant and Intermittent Exotropia and Factors Affecting It in a Large Scandinavian Case Series.

PURPOSE: To compare the results of surgery for constant and intermittent exotropia, to determine factors affecting surgical success, and to evaluate the effect of horizontal rectus muscle surgery on distance-near incomitance. METHODS: In this retrospective study of 291 Scandinavian patients, inclusion criteria were surgery for constant (n = 101) or intermittent (n = 190) exotropia with no vertical deviation, no previous strabismus surgery, and available postoperative follow-up data. Medical records of patients (age: 3 to 85 years) undergoing surgery were reviewed. Surgical success was defined as postoperative esodeviation of less than 5 prism diopters (PD) to exodeviation of 10 PD or less. RESULTS: Surgical success was 70% in constant exotropia and 80% in intermittent exotropia (P > .05). At follow-up 1.5 years after surgery, a significant drift was found in intermittent exotropia (P < .05). Different surgeons, spherical equivalents, anisometropia, amblyopia, gender, and age had no effect on surgical success (P > .05). The surgical success rate increased with decreasing preoperative angle (P < .05). Resection of the medial rectus muscle had a greater effect on the near deviation, whereas recession of the lateral rectus muscle had a greater effect on the distance deviation (P < .05). CONCLUSIONS: Surgical success was equally good in constant and intermittent exotropia, but better long-term stability was observed following surgery for constant exotropia. The only factor affecting surgical success was the preoperative deviation, with smaller deviations having a better outcome. A distance-near incomitance may be an important consideration in choosing the magnitude of medial versus lateral rectus muscle surgery. [J Pediatr Ophthalmol Strabismus. 2021;58(1):34-41.].

The impact of vision screening in preschool children on visual function in the Swedish adult population.

BACKGROUND: Amblyopia is the most common monocular visual impairment in Scandinavia. A visual screening programme for preschool children was introduced in Sweden in the 1970s to reduce the prevalence of amblyopia. The purpose of this study was to investigate the impact of this visual screening programme in adult men recruited to the armed forces in Sweden. METHODS: The prevalence of amblyopia was compared in recruits born in 1956-1957 (n = 1500), before the introduction of the visual screening programme (unscreened), and those born in 1977-1979 (n = 2626), after the visual screening programme was introduced (screened). Amblyopia was defined as bilateral, if the bilateral best corrected visual acuity (BCVA) was <0.5 (20/40), and unilateral if there was a ≥2-line interocular difference and BCVA was <0.625 (20/32) in the worse eye. Subgroup analysis was performed on recruits with hyperopia, myopia and anisometropia. RESULTS: The prevalence of amblyopia was significantly lower after the introduction of the Swedish visual screening programme. Forty-seven (3.3%) of the unscreened and 23 (0.9%) of the screened recruits had unilateral amblyopia (p < 0.0001, OR = 0.26 (95%CI 0.16-0.43)). The risk for developing amblyopia was markedly reduced by screening in recruits with hyperopia (≥2D) (p < 0.0001 and OR 0.034 (95% CI 0.003-0.207)) and anisometropia (≥1.5D interocular difference) (p < 0.01 and OR 0.20 (95% CI 0.08-0.66)). Only a few recruits with myopia had amblyopia. CONCLUSIONS: The results demonstrate the value of the Swedish visual screening programme for preschool children in preventing amblyopia. Anisometropia or high hyperopic refractive errors can be identified by screening and corrected to prevent amblyopia.

Successful repair of a full upper eyelid defect following traumatic amputation by simply suturing it back in place.

There is a general belief that a full-thickness eyelid defect is best repaired using a vascularized flap in combination with a free graft, and that a free full-thickness eyelid graft would not survive due to poor blood perfusion. However, we describe a case in which an upper eyelid was traumatically amputated. The eyelid was sutured in place and healed well in situ. The long-term outcome was good regarding motility and function. This raises the question of whether a blood-supplying pedicle is necessary for the survival of the graft when repairing large eyelid defects.

Clinical evidence supporting the use of donor sclera as spacer material in complicated cases of strabismus surgery - retrospective evaluation of surgical results in 117 patients with thyroid-associated ophthalmopathy or congenital strabismus.

PURPOSE: To examine the outcome of the use of donor sclera as spacer material in complicated cases of strabismus surgery. METHODS: A retrospective cohort study on patients with complicated thyroid-associated ophthalmopathy (TAO) (n = 42) or congenital strabismus (n = 75). Patients underwent strabismus surgery during 1994-2014. The surgical results were evaluated in terms of the reduction in the angle of deviation, the need for re-operation, complications and patient satisfaction. RESULTS: The majority of the TAO patients underwent surgery for vertical strabismus (n = 25). The vertical angle of deviation in the primary position was significantly reduced from a median of 23 prism dioptres (PD) to 2 PD (n = 35, p < 0.001). The horizontal angle of deviation in primary position for TAO patients with esotropia was significantly reduced, from a median of 35 PD to 2 PD (n = 17, p < 0.001). The majority of the congenital cases had horizontal strabismus (esotropia = 29, exotropia = 27). The angle of deviation in esotropia was reduced from a median of 29 PD to 8 PD (n = 36, p < 0.001) and in exotropia from 30 PD to 10 PD (n = 34, p < 0.001). Most of the patients were satisfied with the outcome of surgery, and only 12% required re-operation within 2 years. CONCLUSION: This is the first clinical study on the use of donor sclera as spacer material in complicated cases of strabismus surgery. The surgical results were good in terms of the reduction in the angle of deviation, the need for re-operation, complications and patient satisfaction, supporting the use of donor sclera for strabismus surgery.

Comparison of a new digital KM screen test with conventional Hess and Lees screen tests in the mapping of ocular deviations.

PURPOSE: To evaluate the digital KM screen computerized ocular motility test and to compare it with conventional nondigital techniques using the Hess and Lees screens. METHODS: Patients with known ocular deviations and a visual acuity of at least 20/100 underwent testing using the digital KM screen and the Hess and Lees screen tests. The examination duration, the subjectively perceived difficulty, and the patient's method of choice were compared for the three tests. The accuracy of test results was compared using Bland-Altman plots between testing methods. RESULTS: A total of 19 patients were included. Examination with the digital KM screen test was less time-consuming than tests with the Hess and Lees screens (P < 0.001 and P = 0.003, resp., compared with the digital KM screen). Patients found the test with the digital KM screen easier to perform than the Lees screen test (P = 0.009) but of similar difficulty to the Hess screen test (P = 0.203). The majority of the patients (83%) preferred the digital KM screen test to both of the other screen methods (P = 0.008). Bland-Altman plots showed that the results obtained with all three tests were similar. CONCLUSIONS: The digital KM screen is accurate and time saving and provides similar results to Lees and Hess screen testing. It also has the advantage of a digital data analysis and registration.

A novel surgical technique employing donor sclera in strabismus surgery.

We describe a novel surgical technique employing donor sclera as a spacer to solve the problem encountered in complicated cases of restrictive strabismus surgery when no more muscle or tendon is available for surgical extension of the eye muscle to correct the angle of deviation. This is often the case in patients who have previously undergone extensive surgery and in patients with mechanical restrictions, such as thyroid-associated orbitopathy (TAO).

Blood Perfusion in a Full-Thickness Eyelid Flap, Investigated by Laser Doppler Velocimetry, Laser Speckle Contrast Imaging, and Thermography.

Purpose: The eyelid is commonly dissected and divided in the process of, for example, blepharotomy, entropion repair, or when preparing a full-thickness eyelid flap to reconstruct a tumor defect. No study has yet been conducted to examine how perfusion in an eyelid is affected by dissection, using modern imaging techniques. Methods: The eyelid was divided with a 10-mm vertical incision, 5 mm from the medial canthus, and the incision was extended horizontally by 30 mm to provide a full-thickness eyelid. Blood perfusion was measured along the length of the free dissected eyelid using both laser Doppler velocimetry and laser speckle contrast imaging. Tissue temperature was visualized using a high-resolution infrared camera (thermography). Results: Measurements using laser speckle contrast imaging showed that blood flow decreased gradually from the pedicel base to the tip of the free dissected eyelid: 83% at 10 mm, stabilizing at 80% at 20 mm from the pedicel base. These results were supported by laser Doppler velocimetry, showing a reduction in perfusion to 67%, 15 mm from the pedicel base. Thermographic imaging showed a corresponding decrease in temperature from the tip to the pedicel base compared with nondissected eyelids. Conclusions: Dissection of an eyelid, to provide a full-thickness eyelid flap, results in only a slight decrease in blood flow. The results support the view that plastic surgery of the eyelids is permissive, and the rich vascularization of the eyelid due to the anastomotic network of vessels in the tarsal plate may increase the likelihood of flap survival and surgical success.

Optimal Epinephrine Concentration and Time Delay to Minimize Perfusion in Eyelid Surgery: Measured by Laser-Based Methods and a Novel Form of Extended-Wavelength Diffuse Reflectance Spectroscopy.

OBJECTIVE: This study investigates the hypoperfusion effects of epinephrine in local anesthesia in eyelid surgery. A novel form of extended-wavelength diffuse reflectance spectroscopy was evaluated. METHODS: Blood perfusion in porcine eyelid flaps was measured using laser Doppler velocimetry and laser speckle contrast imaging, whereas the tissue response was measured using diffuse reflectance spectroscopy with a broad spectrum (450-1550 nm). Epinephrine was either injected cumulatively, 0.1 (1:10,000,000), 1.0 (1:1,000,000), 10 (1:100 000), and 100 µg/ml (1:10 000), to determine the dose-response relation, or given as a single dose (10 µg/ml). Control experiments were performed with saline or lidocaine. RESULTS: Increasing concentrations of epinephrine resulted in a gradual decrease in tissue perfusion, measured by laser Doppler velocimetry and laser speckle contrast imaging, approaching a minimum after the injection of 10 µg/ml. Similar tissue response was observed with diffuse reflectance spectroscopy. The time from the injection of epinephrine (10 µg/ml) to the stabilization of hypoperfusion was 75 seconds. After administration of 10 µg/ml epinephrine, about 20% of the blood perfusion remained, supporting the use of epinephrine in eyelid flaps with a narrow pedicle. CONCLUSIONS: 10 µg/ml epinephrine appears to be adequate for vasoconstriction before oculoplastic surgery. Incisions need only be delayed for about 1 minute. Extended-wavelength diffuse reflectance spectroscopy appears to be a promising technique for monitoring the tissue response following changes in blood perfusion in plastic surgery reconstructions. However, more rigorous validation of the technique is required before it can be implemented in clinical practice.

Hypoperfusion in response to epinephrine in local anaesthetics: Investigation of dependence on epinephrine concentration, spread of hypoperfusion and time to maximal cutaneous vasoconstriction.

OBJECTIVES: The present study aimed to examine hypoperfusion in response to epinephrine following the administration of a local anaesthetic. The concentration of epinephrine that causes maximal hypoperfusion, the spread of hypoperfusion in the tissue and the time to the stabilization of hypoperfusion were investigated. METHODS: Blood perfusion was monitored using laser Doppler velocimetry and laser speckle contrast imaging of random-pattern advancement flaps (1 × 4 cm) or intact skin on the pig flank. Epinephrine was either injected cumulatively (0.1, 1.0, 10 or 100 µg/ml) after injecting 20 mg/ml lidocaine, to determine the concentration response, or given as a single dose (12.5 µg/ml epinephrine+20 mg/ml lidocaine). Control experiments were performed with saline or lidocaine (without epinephrine). RESULTS: Increasing concentrations of epinephrine resulted in a gradual decrease in skin perfusion, approaching a minimum after injecting 10 µg/ml. The area of hypoperfusion was 12 mm in radius, and the time from the injection to the stabilization of hypoperfusion was approximately 120 s. After the administration of 10 µg/ml epinephrine in flaps with small pedicle, 25% blood perfusion still remained. CONCLUSIONS: Local anaesthetic with an epinephrine concentration of approximately 10 µg/ml appears to be adequate for vasoconstriction before surgery. Incisions were required to be delayed only for 2 min following local anaesthetic with epinephrine in pigs. The remaining 25% blood perfusion observed after the administration of epinephrine supports the use of epinephrine in flaps with a small pedicle. Obviously, these experimental findings must be clinically assessed before being considered for infiltration anaesthesia during plastic surgery procedures.

Perfusion and Oxygenation of Random Advancement Skin Flaps Depend More on the Length and Thickness of the Flap Than on the Width to Length Ratio.

OBJECTIVE: The aim was to investigate the relationship between the dimensions (length, width, and thickness) of random advancement skin flaps and retained tissue perfusion and oxygenation. METHODS: Flaps were raised on the flanks of pigs. The flaps were either 0.5 or 1.0 cm wide, thin (dissected halfway through the subcutaneous tissue) or thick (dissected down to the muscle fascia). Tissue perfusion was measured by laser Doppler velocimetry, and tissue oxygenation (pO2) was measured using a Licox system, every 0.5 cm along the flaps' length. Tissue temperature was visualized by high-resolution infrared camera. RESULTS: Perfusion and oxygenation decreased gradually from the base to the tip of the flap, reaching approximately 40% of presurgical values (2.0 cm) and approximately 20% (2.5 cm) from the base of the flap. There was virtually no blood flow, nor oxygen tension, 3.0 cm from the base of the flap. The width to length ratio of the flap did not determine blood flow or oxygenation, being approximately 30% in a 0.5 cm wide and 2 cm long flap, and 0% in a 1.0 cm wide and 4 cm long flap, both with a width to length ratio of 1:4. Blood flow and oxygenation were preserved to a greater extent in the thick flaps (∼40%) than in the thin flaps (∼20%), in a 0.5 cm wide and 2 cm long flap. CONCLUSIONS: The dissection of a random advancement flap results in hypoperfusion and oxygenation that cannot be predicted by the width to length ratio but depend on the length and thickness of the flap.

Evaluation of the Microvascular Blood Flow, Oxygenation, and Survival of Tarsoconjunctival Flaps Following the Modified Hughes Procedure.

PURPOSE: For the modified Hughes procedure, a tarsoconjunctival flap from the upper eyelid is used to reconstruct large, full-thickness, lower eyelid defects. The conjunctival pedicle is divided once vascularization is deemed to be adequate. The importance of maintaining a flap pedicle to ensure adequate perfusion of the graft has been questioned. The purpose of the study was to investigate the microvascular blood flow, oxygenation, and survival of a tarsoconjunctival flap in an experimental porcine model of the modified Hughes procedure. METHODS: The modified Hughes procedure was performed in 9 pigs. Microvascular blood flow was measured by laser Doppler velocimetry. Tissue oxygenation was measured using a Licox system, and tissue survival was determined by analyzing histologic sections of biopsy specimens from the lower edge of the flap. RESULTS: Blood flow and the oxygenation of the tissue decreased gradually during dissection and advancement of the tarsoconjunctival flap. At the time when the flap was sutured into place, there was virtually no blood flow or oxygenation of the tissue. However, flap survival did not seem to be compromised, as shown by the absence of pyknotic cell nuclei necrosis in the biopsy specimens, 12 hours after the procedure. CONCLUSIONS: The pedicle of the tarsoconjunctival flap does not seem to contribute to the nourishment of the tarsoconjunctival flap. Nourishment may be supplied by the rich vascularization of the remaining eyelid and tear film. If this is the case, single-stage grafting of a free tarsal plate may be performed, thus avoiding the eyelid-sharing stage of the procedure, without compromising the survival of the graft.