Making sense of refractive surgery in 2001: why, when, for whom, and by whom?

Delayed onset diffuse lamellar keratitis following enhancement LASIK surgery

BACKGROUND

Diffuse lamellar keratitis (DLK) is a relatively uncommon complication of the refractive procedure, laser-assisted in situ keratomileusis (LASIK). If detected and diagnosed in a timely fashion, it can be treated and should resolve with minimal sequelae. If untreated, or misdiagnosed and treated incorrectly, there may be loss of visual acuity. Optometrists should be familiar with this condition, its signs, symptoms and correct treatment protocol.

CASE HISTORY

A 58-year-old male Caucasian developed delayed onset diffuse lamellar keratitis, seemingly in the absence of an epithelial defect, 25 days following an enhancement LASIK procedure to his right eye. The DLK in this patient is delayed longer than typically reported in the literature. Subsequent management with topical steroids was complicated as the patient was a steroid responder and developed a markedly raised intraocular pressure that was managed with a topical anti-glaucoma agent. The diagnosis, pathogenesis and issues relevant to the treatment of this condition are discussed.

CONCLUSION

Optometrists, particularly those actively participating in the shared care of refractive surgery patients, must be familiar with diffuse lamellar keratitis so that diagnosis is not delayed. As the number of cases of refractive surgery in Australia increases, optometrists will encounter this condition more frequently.

Laser in situ keratomileusis (LASİK) in patients with superior steepening on corneal topography: Is it safe and predictable?

BACKGROUND

Attention is usually given to inferior steepening on corneal topography in the evaluation of a patient's suitability for LASIK surgery. The aim of this study is to investigate long-term refractive results with superior steepening.

METHODS

Patients who underwent LASIK surgery between 2015 and 2019 in our refractive surgery department were retrospectively reviewed. The patients with a ≥ 1.0 D superior-inferior (S-I) quadrant difference in the tangential map, using a Scheimpflug camera with a Placido disc topographer (Sirius), were included in the study. Preoperative and postoperative best-corrected and uncorrected visual acuity (Snellen), cylindrical refraction values, and spherical equivalent (SE) values were compared. Adverse events were recorded.

RESULTS

Fifty eyes of 28 patients participated in the study. The mean age of the patients was 27.5 ± 8.0 (19-59). Sixteen patients were female (57.1%), and 12 (42.8%) patients were male. The average follow-up time was 29.8 ± 11.1 months (12-61). Average central corneal thickness was 549.4 ± 26.0 (498-602) μm. Average minimal corneal thickness was 549.1 ± 26.9 (497-598) μm. Preoperative S-I quadrant difference (D) was 1.87 ± 0.7 (1.0-3.99). Posterior elevation (Kvb) was 11.2 ± 1.9 (9-17) μm. The preoperative SE value was - 1.7 ± 2.1 (- 6.25-3.25) and improved to - 0.3 ± 0.44 D (- 1.25-0.75) (p < 0.001). Preoperative cylindrical refraction values were - 2.04 ± 1.7 (- 6.25-0), and postoperative values were - 0.47 ± 0.4 (- 2-0) D (p < 0.001). Uncorrected visual acuity was median 1.0 (0.4-1.0) with 38 eyes (76%) having 20/20 postoperative uncorrected visual acuity. No sight threatening complications or ectasia findings were observed during the 2 years postoperative follow-up time.

CONCLUSIONS

Abnormal corneal topographies with (S-I) asymmetry result in predictable results after LASIK.

Influence of music and its genres on respiratory rate and pupil diameter variations in cats under general anaesthesia: contribution to promoting patient safety

Objectives

The aims of the study were to recognise if there is any auditory sensory stimuli processing in cats under general anaesthesia, and to evaluate changes in respiratory rate (RR) and pupillary diameter (PD) in anaesthetised patients exposed to different music genres, while relating this to the depth of anaesthesia.

Methods

A sample of 12 cats submitted for elective ovariohysterectomy was exposed to 2 min excerpts of three different music genres (classical [CM], pop [PM] and heavy metal [HM]) at three points during surgery (T1 = coeliotomy; T2 = ligature placement and transection of the ovarian pedicle; T3 = ligature placement and transection of the uterine body). A multiparametric medical monitor was used to measure the RR, and a digital calliper was used for PD measurement. Music was delivered through headphones, which fully covered the patient’s ears. P values   <0.05 were considered to be statistically significant.   

Results

Statistically significant differences between stimuli conditions for all surgical points were obtained for RR (T1, P = 0.03; T2, P = 0.00; T3, P = 0.00) and for PD (T1, P = 0.03; T2, P = 0.04; T3, P = 0.00). Most individuals exhibited lower values for RR and PD when exposed to CM, intermediate values to PM and higher values to HM.

Conclusions and relevance

The results suggest that cats under general anaesthesia are likely to perform auditory sensory stimuli processing. The exposure to music induces RR and PD variations modulated by the genre of music and is associated with autonomic nervous system activity. The use of music in the surgical theatre may contribute to allowing a reduced anaesthetic dose, minimising undesirable side effects and thus promoting patient safety.

Topographic Patterns in Refractive Surgery Candidates

PURPOSE

To evaluate the prevalence of different topographic patterns in refractive surgery candidates and to estimate the extent of candidate rejection based on topography alone.

METHODS

We performed a retrospective evaluation of videokeratographies of previously unoperated refractive surgery candidates. The defined topographic patterns of their corneas and the indices computed by the videokeratographer software were registered. The data were evaluated by SPSS/PC statistical software.

RESULTS

One hundred candidate electronic topography records were evaluated. The candidates included 41 women and 59 men whose average age was 32 years (range 17.5-63.5). Their topographic patterns were: spherical (36/200 evaluated eyes), spherocylindrical (60), upper steep (32), lower steep (43), irregular astigmatism (9), decentered (3), suspected keratoconus (11), and probable keratoconus (6 eyes). Rejection from undergoing the procedure was based on topography alone in 27 of the 200 eyes. It was difficult to decide what to do with the 43 eyes with a lower steep pattern, and they were eventually rejected. Of the nine software-calculated indices, only one, "keratoconus index," could distinguish between the spherocylindrical and the lower steep patterns.

CONCLUSIONS

More than one-half of corneal topographies of refractive surgery candidates did not comply with the assumed "normal" spherical or spherocylindrical patterns. The possible continuum of keratoconus-suspected keratoconus-lower steep pattern raises the question of where to draw the line between reasonable and risky when considering corneal refractive surgery.

Ring electrode for radio-frequency heating of the cornea: modelling and in vitro experiments

Radio-frequency thermokeratoplasty (RF-TKP) is a technique used to reshape the cornea curvature by means of thermal lesions using radio-frequency currents. This curvature change allows refractive disorders such as hyperopia to be corrected. A new electrode with ring geometry is proposed for RF-TKP. It was designed to create a single thermal lesion with a full-circle shape. Finite element models were developed, and the temperature distributions in the cornea were analysed for different ring electrode characteristics. The computer results indicated that the maximum temperature in the cornea was located in the vicinity of the ring electrode outer perimeter, and that the lesions had a semi-torus shape. The results also indicated that the electrode thickness, electrode radius and electrode thermal conductivity had a significant influence on the temperature distributions. In addition, in vitro experiments were performed on rabbit eyes. At 5 W power, the lesions were fully circular. Some lesions showed non-uniform characteristics along their circular path. Lesion depth depended on heating duration (60% of corneal thickness for 20 s, and 30% for 10 s). The results suggest that the critical shrinkage temperature (55-63 degrees C) was reached at the central stroma and along the entire circular path in all the cases.