Splinter Cataract in Patients with Keratoconus and Frequent Eye Rubbing: A Novel Finding

Background

Cataract is defined as any change in crystalline lens clarity that obscures passage of light through the lens to the retina [1]. The changes in the lens transparency and refractive index are a result of a shift in the water content and type of proteins in the crystalline lens [1]. Cataract can be classified according to the area of the lens that is affected (nuclear sclerotic, cortical, or subcapsular) [1]. Multiple risk factors have been associated with cataract formation, including age, trauma, inflammation, smoking, chronic ultraviolet light exposure, metabolic disorders, and use of certain medications [2,3]. The onset of age-related cataract formation typically happens in the fifth and sixth decade of life [4].

Patients with keratoconus are at increased risk of developing cataract at a younger age compared to the normal population, and predisposing factors include atopy and topical steroid use [5,6]. Atopy is the most significant risk factor for the development of keratoconus, as vigorous and prolonged eye rubbing can lead to irreversible corneal thinning and scar formation [7]. Cataracts in patients with atopic dermatitis are either anterior or posterior subcapsular cataract [8], while glucocorticoid use is usually associated with posterior subcapsular cataract [9]. In this case series we report the novel observation of splinter-shaped cortical cataract in 16 eyes of 14 patients with keratoconus in the absence of other risk factors of cataract development from a single center in Riyadh, Saudi Arabia.

Case Report

This is a case series of 16 eyes of 14 patients diagnosed with keratoconus and found to have splinter cortical cataract. Patients were enrolled from the Ophthalmology outpatient clinic at a tertiary eye care hospital in Riyadh, Saudi Arabia from January 2017 to March 2022. Retrospective review of charts was carried out and demographic data, including age and gender, were recorded, as well as history of atopy, medical comorbidities, history of smoking, and medications use, including steroids. Patients were also asked about past or current history of eye rubbing, and to illustrate the significance of eye rubbing, certain variables were ascertained, including the duration of eye rubbing, gentle or vigorous in nature, and unilateral or bilateral. Complete ocular examination was performed, including uncorrected (UCVA) and best corrected visual acuity (BCVA), slit-lamp examination, Pentacam® tomography (Oculus Systems, Wetzlar, Germany), and all results were recorded. Slit-lamp photography of the lens was conducted for all patients.

A total of 16 eyes of 14 patients were included in this case series. Eleven patients (78.6%) were male and 3 patients (21.4%) were female. Patients had an average age of 26 years (range, 16–40). All eyes had splinter-shaped cortical cataract in the inferotemporal quadrant of the crystalline lens and not involving the visual axis. The location of the cataract corresponded to the keratoconus cone location in 12 out of 16 eyes (75%). This sign was first described by the principal investigator of this series (Dr. Omar Kirat). Two patients had bilateral splinter cortical cataract (14%) and 3 patients had visually significant corneal scar (21.4%). A history of vernal keratoconjunctivitis (VKC) was found in 62.5% of eyes (10 eyes) and all patients gave a positive history of frequent eye rubbing. Only 2 eyes of 2 patients had a history of using a short course of topical steroids. None of the patients had a history of systemic steroid use. Six eyes (37.5%) had positive vernal signs of slit-lamp examination, such as conjunctival papillae and pseudogerontoxon. Slit-lamp photographs of the lens changes are shown in Figure 1. Fundus examination was normal in all patients. Best corrected visual acuity (BCVA) by the logarithm of the minimum angle of resolution (LogMAR) was reported between 0 to 0.2 in 69% of eyes (11 eyes) and 4 eyes (25%) had BCVA of 0.3 to 0.6, and 1 eye (6%) had BCVA of 1.3. Thirteen eyes (81%) had clinically proven keratoconus, while 3 eyes (19%) were keratoconus suspects. Based on Krumeich classification of keratoconus [10], 8 out of 16 eyes (50%) had stage I keratoconus, 1 eye had stage II (6%), 3 eyes (19%) had stage III, and 4 eyes (25%) had stage IV keratoconus. The complete details of patients with their keratometry values are tabulated in Table 1.

Discussion

Keratoconus has been associated with multiple etiologies and risk factors in the literature, such as ethnic background, genetic and environmental factors, ultraviolet (UV) exposure, and, most importantly, eye rubbing [11]. Eye rubbing is a common habit among individuals, which can occur spontaneously or as a response to ocular irritation and fatigue or compulsive eye rubbing in individuals with mental illness [12]. Chronic abnormal eye rubbing is associated with keratoconus development [11], and repetitive and vigorous knuckle-grinding rubbing is associated with progression of keratoconus [13]. In this case series we report an intriguing observation of splinter-shaped cortical cataract in the inferotemporal quadrant of the crystalline lens in patients with habitual eye rubbing.

There are many proven consequences of eye rubbing on ocular structures in the literature [13–16]. An experimental study asked volunteers to rub their eyes for 60 seconds and tear samples were collected and tested, showing that multiple inflammatory markers were significantly raised after eye rubbing, including matrix metalloproteinase-13 and interleukin-6 and tumor necrosis factor-a [13]. These markers are believed to play a role in the development of keratoconus [17]. Increased corneal temperature and spikes in intraocular pressure (IOP) were also observed [18]. Yusuf and Salmon reported a case of iridoschisis and keratoconus in a patient with compulsive eye rubbing [15]. Panikkar et al reported a case of bilateral retinal detachment secondary to vigorous eye rubbing in an 18-year-old male with obsessive compulsive disorder [16].

To the best of our knowledge, there are no existing reports of splinter-shaped cataract formation secondary to frequent eye rubbing in keratoconus patients. In this case series of 16 eyes, we report the presence of splinter-shaped cortical cataract in the inferotemporal quadrant of the crystalline lens, and all eyes had a history of frequent eye rubbing. Stage I keratoconus was the most common (50%) among 16 eyes, followed by stage IV, then stage III (25% and 19%, respectively) and lastly stage II (6%), which may indicate that splinter-shaped cataract is not limited to a certain stage of keratoconus severity. The morphology of the cataract described in this case series is unlike the cataract frequently found in keratconic eyes. For example, atopy-related cataract is described as anterior subcapsular opacities [8,19], while steroid-induced cataract has a characteristic appearance of opacities confined in the posterior subcapsular area of the crystalline lens [9].

It is important to highlight that the clinical diagnosis of this sign can be easily missed because the opacities are usually found in the periphery of the crystalline lens, as shown in the clinical photographs; therefore, meticulous dilated-pupil examination of the crystalline lens is critical to making a diagnosis. Splinter-shaped cataract reported in this case series did not involve the visual axis; therefore, cataract removal was not warranted. All patients were observed with periodic IOP assessment. Most of the eyes reported in this series had unilateral cataract except for 2 patients who had bilateral cataract, and this could be attributed to many factors, including the pattern of eye rubbing and hand dominance. Similarly, Kymionis et al reported unilateral keratoconus in a patient with bilateral eye rubbing related to hand dominance [20].

The mechanism of cataract development with frequent eye rubbing is not completely understood. However, a few theories have been proposed, one of which is that repetitive mechanical rubbing of the cornea or iris against the crystalline lens could be responsible for cataract development. Furthermore, ocular rigidity is reduced in ectatic corneas [21,22], which might support the theory that mechanical rubbing, even in mild forms, in patients with keratoconus can play a role in cataract development due to greater corneal deformability.

This case series also illustrates that 75% of eyes had correspondence between the cataract and the inferotemporal cone location on topography. The inferotemporal location of the cataract could be related to the usual site of contact with the eye during rubbing by fingers or knuckles. Similarly, a study investigating the effect of eye rubbing on corneal epithelium showed significant thinning in the inferotemporal quadrant on anterior segment optical coherence tomography [23]. Other theories include inflammatory mechanism related to increased mediators secondary to eye rubbing [13,24], and intermittent elevation in IOP triggered by eye rubbing might play a role in cataract development [25]. Another possibility is that the lens undergoes ectasia similar to what happens to the cornea during eye rubbing.

The limitations of this case series include the lack of a control group, the lack of an objective and quantifiable measure of eye rubbing frequency and intensity due to recall bias, and the limited possibility to establish a cause-effect relationship. Furthermore, the results should be interpreted with caution due to the small sample size. However, we believe that by reporting this sign we can stimulate researchers and scientists to investigate the proposed hypotheses by experimental studies. Informed consent was obtained from all patients to publish clinical/topography/slit-lamp images. The study adhered to the Declaration of Helsinki and was approved by the Institutional Research Board (KKESH, RP 22043-R) at King Khaled Eye Specialist Hospital.

Conclusions

In conclusion, splinter-shaped cortical cataract could be a sign of frequent eye rubbing. Careful examination of the crystalline lens with dilated pupil might reveal peripheral cortical lens opacities in the inferotemporal quadrant, which can alert the physician that the patient has habitual eye rubbing and is at increased risk of keratoconus development or progression, which warrants patient counselling for behavioral change. Splinter-shaped cataract is visually insignificant and can be managed with observation alone with periodic IOP assessment.